**Structural and Electrochemical Properties of Cementitious and Hybrid Materials Based on Nacrite**

Nouha Jaafar, Hafsia Ben Rhaiem and Abdesslem Ben Haj Amara

Additional information is available at the end of the chapter

http://dx.doi.org/10.5772/61594

## **Abstract**

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This chapter gives possible valorization of a well-crystallized Tunisian nacrite as an interesting clay mineral belonging to the kaolin group: The first part of the chapter aims to produce a new synthetic material labeled ''metanacrite". Metanacrite is a supplementary cementitious material originated by heating a raw Tunisian nacrite at 823 K. The structure of the amorphous synthetic product was corroborated by X-ray diffraction (XRD) and infrared spectroscopy (IR). The decomposition of the silicate framework was confirmed by transmission electron microscope (TEM). The obtained metanacrite was also examined by electrochemical impedance spectroscopy (EIS). Accordingly, a semiconductor behavior of the novel synthetic material is evidenced. The second part of this chapter deals with the intercalation of lithium chloride salt between the planar layers of this Tunisian nacrite. The intercalation leads to a stable hybrid material that after calcination under inert atmosphere at 723–873 K induces an amorphous hybrid. The structural identification of the obtained nacrite–LiCl hybrid was determined by means of XRD, IR, TGA, and EIS. Finally, the resulting amorphous hybrid shows a superionic behavior with high ionic conductivity up to 10–2 S.m–1, good electrochemical stability, and can be used as an innovative solid electrolyte in lithium batteries and other electrochemical devices.

**Keywords:** Nacrite, Clay Mineral, Metanacrite, Hybrid, Lithium-Ion Battery

## **1. Introduction**

Clay minerals are abundant in soil and important to a wide variety of disciplines such as environmental chemistry, astrophysics, geology, and the ceramics industry [1]. One of the most

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used clay minerals is **kaolin,** which is a 1:1 dioctahedral layered aluminosilicate produced of advanced weathering processes [2]. Kaolin clays include kaolin-group minerals, of which the most common are kaolinite, dickite, nacrite, and halloysite [3]. Kaolin is white or near white color with pseudo-hexagonal crystal along with plates, some larger books, and vermicular stacks [4]. The structural formula of kaolin is [Al2Si2O5(OH)4] per half unit cell with Si/Al ratio ∼. 1One layer of the mineral consists of an alumina octahedral sheet and a silica tetrahedral sheet that share a common plane of oxygen atoms and repeating layers of the mineral are hydrogen bonded together [2,5]. Quantitative estimates indicate that the cohesive energy between kaolinite layers is primarily electrostatic [6]. There is also a certain degree of van der Waals attraction between the hydroxyl groups of the gibbsite sheet and the oxygen atoms of the adjoining silica sheet [7, 8].

Consequently, wide applications based on virgin as well as treated (heat treatment, function‐ alization, etc.) kaolinite were developed:


In this regard, Tunisian nacrite has been employed as a natural clay mineral in the development of new materials with high functionalities and unique properties. Therefore, the first part of this study herein describes the structural and electrochemical characteristics of a novel material, commonly named "*metanacrite*". This chapter allows us to achieve better applicability of the calcined nacrite, as a supplementary cementitious material (SCM) that can be used to replace part of the clinker in a cement or cement in a concrete mixture. The second part of this work deals with the control of the evolution of the nacrite structure during the intercalation process and the study of the structural and electrochemical properties of the novel synthesized material labeled "*nacrite*–*LiCl nanohybrid*".

## **2. Tunisian nacrite: Starting clay mineral**

used clay minerals is **kaolin,** which is a 1:1 dioctahedral layered aluminosilicate produced of advanced weathering processes [2]. Kaolin clays include kaolin-group minerals, of which the most common are kaolinite, dickite, nacrite, and halloysite [3]. Kaolin is white or near white color with pseudo-hexagonal crystal along with plates, some larger books, and vermicular stacks [4]. The structural formula of kaolin is [Al2Si2O5(OH)4] per half unit cell with Si/Al ratio ∼. 1One layer of the mineral consists of an alumina octahedral sheet and a silica tetrahedral sheet that share a common plane of oxygen atoms and repeating layers of the mineral are hydrogen bonded together [2,5]. Quantitative estimates indicate that the cohesive energy between kaolinite layers is primarily electrostatic [6]. There is also a certain degree of van der Waals attraction between the hydroxyl groups of the gibbsite sheet and the oxygen atoms of

Consequently, wide applications based on virgin as well as treated (heat treatment, function‐

**1.** Clay minerals in soil play an important role in the environment by acting as a natural scavenger of pollutants from water through adsorption mechanism [9]. For example, China clay can confiscate cadmium from hazardous waste [10]. Use of kaolinite for the

**2.** Conversion of kaolin to metakaolin by firing above the dehydroxylation temperature activates the clay and improves its properties [12]. The heating process drives off water from the mineral (Al2O3⋅2SiO2⋅2H2O), the main constituent of kaolin clay, and collapses the material structure, resulting in an amorphous aluminosilicate (Al2O3⋅2SiO2), meta‐ kaolin. Metakaolin (MK) had 99.9% particles <16 μm with a mean particle size of about 3 μm (www.metakaolin.com). Therefore, there is an ongoing interest to apply metakaolin in the construction industry as a raw material for the production of white cement clinker and as an artificial pozzolanic additive for concrete to produce blended cement [4]. The use of by-products like metakaolin in cement and concrete has gained significant impor‐ tance because of the requirements of environmental protection and sustainable construc‐

**3.** The ability to modify clay minerals by insertion of inorganic and/or organic guest species into the interlamellar region opens up a range of potential uses for these materials. The resultant hybrid materials combine the features of the clay and the guest species. These complexes have the potential to be used as adsorbents, as catalyst support, and in

In this regard, Tunisian nacrite has been employed as a natural clay mineral in the development of new materials with high functionalities and unique properties. Therefore, the first part of this study herein describes the structural and electrochemical characteristics of a novel material, commonly named "*metanacrite*". This chapter allows us to achieve better applicability of the calcined nacrite, as a supplementary cementitious material (SCM) that can be used to replace part of the clinker in a cement or cement in a concrete mixture. The second part of this work deals with the control of the evolution of the nacrite structure during the intercalation process and the study of the structural and electrochemical properties of the novel synthesized

removal of copper, nickel, cobalt, and manganese is also studied [11].

the adjoining silica sheet [7, 8].

tion in the future [13].

material labeled "*nacrite*–*LiCl nanohybrid*".

chromatographic columns and ion exchangers [14].

alization, etc.) kaolinite were developed:

130 Clays, Clay Minerals and Ceramic Materials Based on Clay Minerals

Well-crystallized Tunisian nacrite from North Tunisia (Jbel Slata, Kef) was used in this work as a starting clay mineral economically viable and technically efficient [15]. This layered aluminosilicate material contributes large particle size and high chemical stability and has been previously characterized in the work of Ben Haj Amara and co-workers [15–21]. Bailey [22] described nacrite by a 2M stacking mode which crystallized in the monoclinic lattice with a Cc space group. The structural parameters of nacrite are *a* = 0.8906 nm, *b* = 0.5146 nm, *c* = 1.5669 nm, and *β* = 113.58° with a main basal distance *d*002 = *c* sin *β*/2 = 0.72 nm [15, 19].

## **3. Dehydroxylation of nacrite: Metanacrite**

Recently, several studies focused on the physicochemical characteristics of *metakaolin* (MK) materials derived from dehydroxylation of *kaolin* at 823 K. This phenomenon is accompanied by loss of water and decomposition into a disordered metastate [23], which undergoes massive structural changes of the octahedral layer: aluminium changes its coordination from six to four and five [24–26]. In Tunisia, particular attention is given to the exploitation of clays which are abundant in the country and may present potential pozzolanic activity, if they are appropri‐ ately calcined at relatively low temperatures [27, 28].

## **3.1. Calcination procedure**

The sample of about 20 g was heat treated in the "Nabertherm GmbH" laboratory furnace. The optimal calcination parameters, for which complete dehydroxylation of the material was achieved, are temperature of 823 K and heating time of 120 min. The dehydroxylation process may be presented by the following simple equation [29]:

$$\begin{aligned} Al\_2O\_3.2SiO\_2.2H\_2O &\to Al\_2O\_3.2SiO\_2 + 2H\_2O.\\ \text{nacrite} & \quad \text{metanacrite} \quad \text{water} \end{aligned}$$

### **3.2. Structural Properties of Tunisian Metanacrite**

### *3.2.1. X-Ray Diffraction*

The experimental X-ray diffraction patterns of both nacrite and metanacrite are reported in Figures 1(a) and 1(b), respectively. Results show a broad characteristic reflection extending from approximately 17 to 39° 2*θ* attributed to the overlapping of the 00*l* reflections of the wellcrystallized natural nacrite [15–21]. The XRD analysis illustrates then the amorphous structure of the obtained metanacrite synthetic phase [29].

(c) *3.2.2. IR Spectroscopy* 

By comparing the IR spectra of metanacrite and nacrite recorded in Figure 1(c), it is possible to follow the modifications of the stretching and deformation vibrations obtained after heating nacrite above 823 K: they shift from their positions in the spectrum of untreated nacrite, and their shapes change. Indeed, *at high frequencies*, it should be mentioned that no bands were detected in the infrared spectrum of metanacrite, indicating the disappearance of the OH lattice stretching band since it is located in the envelope of water band corresponding to natural nacrite at 3714 and 3647 cm<sup>−</sup>1 [15, 17–21]. Figure 1(c) reveals that, *at low frequencies*, the Si–O stretching vibrations υ(Si–O) located at 1073 cm<sup>−</sup>1 and the Si–O **Figure 1.** (a) Experimental X-ray pattern of nacrite raw-clay material [29]. (b) Experimental X-ray pattern of metana‐ crite synthetic material [29]. (c)Infrared spectra in the 4000–400 cm–1 region for nacrite and metanacrite samples [29].

deformation vibrations located at 459 cm<sup>−</sup>1 are commonly present with a slight change in their shape and intensity, while the Al–O deformation vibrations are shifted to high frequencies from 524 to 813 cm<sup>−</sup>1 and the Al–OH deformation vibrations placed at 753, 800, and 911 cm<sup>−</sup>1 in the spectrum of nacrite are omitted in the spectrum of metanacrite. All these changes in the infrared spectrum between metanacrite and nacrite imply that the starting aluminosilicate loses water during calcinations. The layered structure is then destroyed and

**Figure 1c.** Infrared spectra in the 4000–400 cm・1 region for nacrite and metanacrite samples [29].

The morphology, size, and composition of the synthesized sample were characterized via local chemical microanalysis performed using energy dispersive X-ray spectroscopy (EDXS) coupled to the transmission electron microscope (TEM). Figure 2 provides the TEM observations micrographs of Tunisian metanacrite. At first glance, the studied sample exhibits a disordered granular structure with various shapes and sizes. We note the presence of defects, mostly dislocations, which are generated by the distortion around the particle. The contributions of defects, grain size, distribution, and morphology confirm that the amorphous behavior dominates the whole structural composition of metanacrite synthetic material.

transformed into a disordered metanacrite phase possessing amorphous structure very different from the nacrite matrix [29].

*3.2.3. TEM and EDXS* 

### *3.2.2. IR Spectroscopy*

By comparing the IR spectra of metanacrite and nacrite recorded in Figure 1(c), it is possible to follow the modifications of the stretching and deformation vibrations obtained after heating nacrite above 823 K: they shift from their positions in the spectrum of untreated nacrite, and their shapes change. Indeed, *at high frequencies*, it should be mentioned that no bands were detected in the infrared spectrum of metanacrite, indicating the disappearance of the OH lattice stretching band since it is located in the envelope of water band corresponding to natural nacrite at 3714 and 3647 cm−1 [15, 17–21]. Figure 1(c) reveals that, *at low frequencies*, the Si–O stretching vibrations υ(Si–O) located at 1073 cm−1 and the Si–O deformation vibrations located at 459 cm−1 are commonly present with a slight change in their shape and intensity, while the Al–O deformation vibrations are shifted to high frequencies from 524 to 813 cm−1 and the Al– OH deformation vibrations placed at 753, 800, and 911 cm−1 in the spectrum of nacrite are omitted in the spectrum of metanacrite. All these changes in the infrared spectrum between metanacrite and nacrite imply that the starting aluminosilicate loses water during calcinations. The layered structure is then destroyed and transformed into a disordered metanacrite phase possessing amorphous structure very different from the nacrite matrix [29].

## *3.2.3. TEM and EDXS*

**10 20 30 40 50**

(a)

 **(C u-k <sup>1</sup> )**)

**1 0 2 0 3 0 4 0 5 0**

 **(C u-k <sup>1</sup> )**)

**°** *2* 

**(c)** raw nacrite

(b)

synthetic metanacrite

**4000 3500 3000 2500 2000 1500 1000 500**

(c) *3.2.2. IR Spectroscopy*  By comparing the IR spectra of metanacrite and nacrite recorded in Figure 1(c), it is possible to follow the modifications of the stretching and deformation vibrations obtained after heating nacrite above 823 K: they shift from their positions in the spectrum of untreated nacrite, and their shapes change. Indeed, *at high frequencies*, it should be mentioned that no bands were detected in the infrared spectrum of metanacrite, indicating the disappearance of the OH lattice stretching band since it is located in the envelope of water band corresponding to natural nacrite at 3714 and 3647 cm<sup>−</sup>1 [15, 17–21]. Figure 1(c) reveals that, *at low frequencies*, the Si–O stretching vibrations υ(Si–O) located at 1073 cm<sup>−</sup>1 and the Si–O deformation vibrations located at 459 cm<sup>−</sup>1 are commonly present with a slight change in their shape and intensity, while the Al–O deformation vibrations are shifted to high frequencies from 524 to 813 cm<sup>−</sup>1 and the Al–OH deformation vibrations placed at 753, 800, and 911 cm<sup>−</sup>1 in the spectrum of nacrite are omitted in the spectrum of metanacrite. All these changes in the infrared spectrum between metanacrite and nacrite imply that the starting aluminosilicate loses water during calcinations. The layered structure is then destroyed and

**Figure 1.** (a) Experimental X-ray pattern of nacrite raw-clay material [29]. (b) Experimental X-ray pattern of metana‐ crite synthetic material [29]. (c)Infrared spectra in the 4000–400 cm–1 region for nacrite and metanacrite samples [29].

**Figure 1c.** Infrared spectra in the 4000–400 cm・1 region for nacrite and metanacrite samples [29].

The morphology, size, and composition of the synthesized sample were characterized via local chemical microanalysis performed using energy dispersive X-ray spectroscopy (EDXS) coupled to the transmission electron microscope (TEM). Figure 2 provides the TEM observations micrographs of Tunisian metanacrite. At first glance, the studied sample exhibits a disordered granular structure with various shapes and sizes. We note the presence of defects, mostly dislocations, which are generated by the distortion around the particle. The contributions of defects, grain size, distribution, and morphology confirm that the amorphous behavior dominates the whole structural composition of metanacrite synthetic material.

**wavenumber (cm-1)**

*<sup>008</sup> <sup>006</sup>*

synthetic m etanacrite

**753800**

**911**

**813**

**1036**

**1073**

**1128**

**466 524**

**459**

**°** *2* 

**Intensity (a.u)**

132 Clays, Clay Minerals and Ceramic Materials Based on Clay Minerals

**Intensity (a.u)**

natural nacrite **(a )**

*004*

d *<sup>002</sup>*=7.2Å

**(b )**

**3647**

**3714**

transformed into a disordered metanacrite phase possessing amorphous structure very different from the nacrite matrix [29].

*3.2.3. TEM and EDXS* 

**Absorbance (a.u)**

The morphology, size, and composition of the synthesized sample were characterized via local chemical microanalysis performed using energy dispersive X-ray spectroscopy (EDXS) coupled to the transmission electron microscope (TEM). Figure 2 provides the TEM observa‐ tions micrographs of Tunisian metanacrite. At first glance, the studied sample exhibits a disordered granular structure with various shapes and sizes. We note the presence of defects, mostly dislocations, which are generated by the distortion around the particle. The contribu‐ tions of defects, grain size, distribution, and morphology confirm that the amorphous behavior dominates the whole structural composition of metanacrite synthetic material. Such defects seem to be produced during the heating of the starting nacrite clay material and play an important role in the second part of this paper. The larger the number of defects and disorder, the higher the mobility of the free charge carriers, which results in an improvement of the conduction behavior. In order to obtain more detailed information about the microstructure and the chemical composition of metanacrite, we performed *TEM* coupled with *EDXS* analysis. The obtained spectra show the presence of Si and Al atoms with a major proportion, consti‐ tuting the fundamental elements of the metanacrite phase, with a minor contribution of Fe and Cu atoms corresponding to the presence of a trace amount of impurities in the metanacrite material. However, the presence of Ni atoms belongs to the membrane on which the sample is placed. The preliminary physicochemical analysis of metanacrite reveals that the sample is mainly in high amorphous aluminosilicate phase with a disordered polymerized silicon/ aluminum framework which allows its applicability as a new synthetic source of pozzolan for producing composite building materials [29].

#### **3.3. Electrochemical properties of Tunisian Metanacrite**

In order to investigate the role of the microstructure of the resultant amorphous synthetic material in the transport properties, we carried out electrochemical impedance spectroscopy (EIS). The impedance measurements were taken in an open circuit in the frequency range from 10 Hz to 13 MHz, with an applied potential of 50 mV at different temperatures. The metanacrite sample was ground to fine powder and pressed into a pellet. Platinum electrodes were deposited by sputtering on both parallel faces of the pellet to form a symmetrical cell. The cell was then placed inside a programmable oven coupled with a temperature controller [29, 30].

**Figure 2.** TEM micrographs of metanacrite synthetic material [29]. **Figure 2.** TEM micrographs of metanacrite synthetic material [29].

symmetrical cell. The cell was then placed inside a programmable oven coupled with a temperature controller [29, 30].

Such defects seem to be produced during the heating of the starting nacrite clay material and play an important role in the second part of this paper. The larger the number of defects and disorder, the higher the mobility of the free charge carriers, which results in an improvement of the conduction behavior. In order to obtain more detailed information about the microstructure and the chemical composition of metanacrite, we performed *TEM* coupled with *EDXS* analysis. The obtained spectra show the presence of Si and Al atoms with a major proportion, constituting the fundamental elements of the metanacrite phase, with a minor contribution of Fe and Cu atoms corresponding to the presence of a trace amount of impurities in the metanacrite material. However, the presence of Ni atoms belongs to the membrane on which the sample is placed. The preliminary physicochemical analysis of metanacrite reveals that the sample is mainly in high amorphous aluminosilicate phase with a disordered polymerized silicon/aluminum framework which allows its applicability as a

In order to investigate the role of the microstructure of the resultant amorphous synthetic material in the transport properties, we carried out electrochemical impedance spectroscopy (EIS). The impedance measurements were taken in an open circuit in the frequency range from 10 Hz to 13 MHz, with an applied potential of 50 mV at different temperatures. The metanacrite sample was ground to fine powder and pressed into a pellet. Platinum electrodes were deposited by sputtering on both parallel faces of the pellet to form a

**Figure 2.** TEM micrographs of metanacrite synthetic material [29].

**Figure 3.** Nyquist diagram of metanacrite at the temperature range from 298 to 873 K [29].

### *3.3.1. Impedance Analysis*

(EIS). The impedance measurements were taken in an open circuit in the frequency range from 10 Hz to 13 MHz, with an applied potential of 50 mV at different temperatures. The metanacrite sample was ground to fine powder and pressed into a pellet. Platinum electrodes were deposited by sputtering on both parallel faces of the pellet to form a symmetrical cell. The cell was then placed inside a programmable oven coupled with a temperature controller [29, 30].

134 Clays, Clay Minerals and Ceramic Materials Based on Clay Minerals

**Figure 2.** TEM micrographs of metanacrite synthetic material [29].

**Figure 2.** TEM micrographs of metanacrite synthetic material [29].

In this section, we will discover the influence of the heat treatment of metanacrite from room temperature to 873 K on the enhancement of the electrical conductivity. Accordingly, the complex impedance plots of metanacrite in the temperature range 298–873 K are displayed in Figure 3. *3.3.1. Impedance Analysis*  In this section, we will discover the influence of the heat treatment of metanacrite from room temperature to 873 K on the enhancement of the electrical conductivity. Accordingly, the complex impedance plots of metanacrite in the temperature range 298–873 K are displayed in Figure 3.

new synthetic source of pozzolan for producing composite building materials [29].

**3.3. Electrochemical properties of Tunisian Metanacrite** 

**Figure 3.** Nyquist diagram of metanacrite at the temperature range from 298 to 873 K [29].

The Nyquist plots describe the transport properties which are strongly affected by the microstructure. From Figure 3, two domains are identified: the first one is observed at low temperature (298–673 K) describing the insulator behavior and the second one is detected at high temperature (673–873K) for which a significant increase in conductivity is observed. The increase of the electrical conductivity may be attributed to an increase of the disorder degree as well as defects density in the sample [29]. *3.3.2. Electrical conductivity*  Different models have been proposed to describe and draw the ac conduction model corresponding to metanacrite such as quantum mechanical tunneling (Q.M.T.) [31,32], nonoverlapping small-polaron tunneling (N.S.P.T), overlapping large-polaron tunneling (O.L.P.T.), and the correlated barrier hopping (C.B.H.) [31–36]. All these models were deemed to The Nyquist plots describe the transport properties which are strongly affected by the microstructure. From Figure 3, two domains are identified: the first one is observed at low temperature (298–673 K) describing the insulator behavior and the second one is detected at high temperature (673–873K) for which a significant increase in conductivity is observed. The increase of the electrical conductivity may be attributed to an increase of the disorder degree as well as defects density in the sample [29].

### *3.3.2. Electrical conductivity*

Different models have been proposed to describe and draw the ac conduction model corre‐ sponding to metanacrite such as quantum mechanical tunneling (Q.M.T.) [31,32], nonoverlapping small-polaron tunneling (N.S.P.T), overlapping large-polaron tunneling (O.L.P.T.), and the correlated barrier hopping (C.B.H.) [31–36]. All these models were deemed to be in disagreement with our results. Therefore, the experimental data will be discussed in the frame of the C.B.H. model. Thus, the conduction occurs via the hopping carriers over a potential barrier between two different valence states. The ac conductivity and frequency exponent expressions due to the C.B.H. model are given by the following equations:

$$s\_{ac} \left(\mathfrak{op}\right) = \left(\frac{1}{24}\right) \mathfrak{n}^3 \mathfrak{s}^i \mathbf{N}^2 \mathfrak{s}\_0 \mathfrak{op} \mathbf{R}^6 \tag{1}$$

$$s = 1 - \left\{\frac{6kT}{\mathcal{W}\_M + \ \kappa\_B T \ln\left(1/\mathfrak{o}\sigma\_0\right)}\right\} \tag{2}$$

where *σac* is the ac conductivity, *ε*0 is the free-space dielectric permittivity, is the dielectric constant, *N* is the density of states at Fermi level, *Rω* is the hopping length at frequency **ω**, *WM* is the maximum barrier height, *τ*0 the atomic vibration period, *s* is the frequency exponent, and *kB* is the Boltzmann constant. be in disagreement with our results. Therefore, the experimental data will be discussed in the frame of the C.B.H. model. Thus, the conduction occurs via the hopping carriers over a potential barrier between two different valence states. The ac conductivity and frequency exponent expressions due to the C.B.H. model are given by the following equations: ������ � � � ��� �������� � �� � **(1)** ����� ��� �� � ��� �� �� ����� � **(2)**

Equation (2) predicts that *s* decreases with increasing temperature. Therefore, the C.B.H. is the involved conduction mechanism for the investigated metanacrite sample [37, 38]. where ��� is the ac conductivity, �� is the free-space dielectric permittivity, �� is the dielectric constant, � is the density of states at Fermi level, �� is the hopping length at frequency �, �� is the maximum barrier height, �� the atomic vibration period, � is the frequency exponent, and �� is the Boltzmann constant. Equation (2) predicts that � decreases with increasing temperature. Therefore, the C.B.H. is the involved conduction mechanism for the investigated metanacrite sample [37, 38].

**Figure 4.** Temperature dependence of frequency exponent(s) for metanacrite sample [29].

Concerning the ac conductivity of metanacrite, it is found to obey the universal Arrhenius power law [39]: ������� Concerning the ac conductivity of metanacrite, it is found to obey the universal Arrhenius power law [39]:

**Figure 4.** Temperature dependence of frequency exponent(s) for metanacrite sample [29].

$$
\sigma\_{\omega} = \sigma\_i \exp\left(\frac{-E\_{\omega(\mathbf{a})}}{k\_3 \cdot \mathbf{T}}\right) \tag{3}
$$

between the localized states. Consequently, the activation energy decreases with increasing frequency. Moreover, at high frequency, the ac activation energies are found to be lower than those found at low frequency regions [29]. Therefore, at high frequencies the mobility of charge carriers over short distances needs lower energy than that necessary for mobility over longer distances at low frequencies. The ac conductivity increases as a function of frequency at a fixed temperature (773 K) from 3.40⋅10−6 S⋅m−1 at � =100 Hz to 1.27⋅ 10−2 S⋅m−1 at � = 10 MHz [29]. Besides the ac conductivity increases as a function of temperature at a fixed frequency (� = 10 MHz), it increases from 1.27 ⋅10−2 S⋅m−1 at � = 773K to 1.98 ⋅10−2 S⋅m−1 at � = 873 K. The small values of the ac activation energy ������ and the increase of ac conductivity ��� with the increase of frequency confirm the dominant hopping conduction mechanism. The conductivity is thermally activated; therefore, the electrical conduction follows a process in which the electron or hole hops from one localized site to another. The electron resides where *σ*<sup>0</sup> is the pre-exponential factor, *kB* is the Boltzmann constant, *T* is the temperature, and *E*a(ac) is the activation energy that controls the jump of charge carriers from one site to another neighboring site. The (ac) values have been calculated at four fixed frequencies [29]. Indeed, the activation energy varies between 0.24 ± 0.01 eV (at low frequencies) and 0.17 ± 0.01 eV (at high frequencies). These results are specific to the temperature range 773–873 K. Thus, the increase of the applied frequency enhances the electronic jumps between the localized states.

at one site; when it is thermally activated, it migrates to another site. Moreover, we demonstrated in the first part of this chapter that the defects constitute the active sites in the conduction process. Therefore, the electron or hole tends to associate with local defects, so the activation energy for charge transport may also include the energy of freeing the hole

As mentioned above, the ac conductivity increases with increasing both temperature and frequency. Simultaneously, the dc conductivity increases with increasing temperature (Figure

1,14 1,16 1,18 1,20 1,22 1,24 1,26 1,28 1,30

1000/T (K-1)

**Figure 5.** Evolution of the *dc* conductivity of metanacrite between 773 K and 873K [29]. where σ� is the pre-exponential factor, ������ is the activation energy, *T* is the temperature, and �� is the Boltzmann constant. As a consequence of the increased dc conductivity with

From these results, we deduce a correlation between the electrochemical impedance spectroscopy and the structural properties of amorphous Tunisian metanacrite synthetic material.

E**a**(dc)= 0.24 ± 0.01 eV

from its position next to the defect [40]. Otherwise, the electronic conduction takes place by hopping between two charge-defect states over the barrier separating them.

5). Indeed, the dc conductivity (�dc) fits the well-known Arrhenius relation [39]. We found ������ = 0.24 ± 0.01 eV ( Figure 5):

�� � � **(4)**


temperature for small activation energies, we conclude that the amorphous metanacrite sample behaves like a semiconductor material [29].

log (dc.T) [S.m-1.K]

� **exp** ��������

**4. Functionalization of Nacrite: Nacrite–LiCl Nanohybrid** 

 ��� � ��

� **(1)**

� **(2)**

Consequently, the activation energy decreases with increasing frequency. Moreover, at high frequency, the ac activation energies are found to be lower than those found at low frequency regions [29]. Therefore, at high frequencies the mobility of charge carriers over short distances needs lower energy than that necessary for mobility over longer distances at low frequencies. 760 780 800 820 840 860 880 0,35 0,40 0,45 **Exponent frequency s**

be in disagreement with our results. Therefore, the experimental data will be discussed in the frame of the C.B.H. model. Thus, the conduction occurs via the hopping carriers over a potential barrier between two different valence states. The ac conductivity and frequency exponent expressions due to the C.B.H. model are given by the following equations:

��� �������� � ��

�� � ��� �� �� �����

where ��� is the ac conductivity, �� is the free-space dielectric permittivity, �� is the dielectric constant, � is the density of states at Fermi level, �� is the hopping length at frequency

Equation (2) predicts that � decreases with increasing temperature. Therefore, the C.B.H. is the involved conduction mechanism for the investigated metanacrite sample [37, 38].

������ � � �

�, �� is the maximum barrier height, �� the atomic vibration period, � is the frequency exponent, and �� is the Boltzmann constant.

0,50

0,65 0,70 0,75 ����� ���

( ) 32 6

<sup>0</sup> ( )

where *σac* is the ac conductivity, *ε*0 is the free-space dielectric permittivity, is the dielectric constant, *N* is the density of states at Fermi level, *Rω* is the hopping length at frequency **ω**, *WM* is the maximum barrier height, *τ*0 the atomic vibration period, *s* is the frequency

potential barrier between two different valence states. The ac conductivity and frequency exponent expressions due to the C.B.H. model are given by the following equations:

Equation (2) predicts that *s* decreases with increasing temperature. Therefore, the C.B.H. is

760 780 800 820 840 860 880

**Figure 4.** Temperature dependence of frequency exponent(s) for metanacrite sample [29].

Concerning the ac conductivity of metanacrite, it is found to obey the universal Arrhenius

where �� is the pre-exponential factor, �� is the Boltzmann constant, *T* is the temperature, and ������ is the activation energy that controls the jump of charge carriers from one site to another neighboring site. The (ac) values have been calculated at four fixed frequencies [29]. Indeed, the activation energy varies between 0.24 ± 0.01 eV (at low frequencies) and 0.17 ± 0.01 eV (at high frequencies). These results are specific to the temperature range 773–873 K. Thus, the increase of the applied frequency enhances the electronic jumps between the localized states. Consequently, the activation energy decreases with increasing frequency. Moreover, at high frequency, the ac activation energies are found to be lower than those found at low frequency regions [29]. Therefore, at high frequencies the mobility of charge carriers over short distances needs lower energy than that necessary for mobility

ç ÷ è ø *a ac B E*

The ac conductivity increases as a function of frequency at a fixed temperature (773 K) from 3.40⋅10−6 S⋅m−1 at � =100 Hz to 1.27⋅ 10−2 S⋅m−1 at � = 10 MHz [29]. Besides the ac conductivity increases as a function of temperature at a fixed frequency (� = 10 MHz), it increases from 1.27 ⋅10−2 S⋅m−1 at � = 773K to 1.98 ⋅10−2 S⋅m−1 at � = 873 K. The small values of

where *σ*<sup>0</sup> is the pre-exponential factor, *kB* is the Boltzmann constant, *T* is the temperature, and *E*a(ac) is the activation energy that controls the jump of charge carriers from one site to another neighboring site. The (ac) values have been calculated at four fixed frequencies [29]. Indeed, the activation energy varies between 0.24 ± 0.01 eV (at low frequencies) and 0.17 ± 0.01 eV (at high frequencies). These results are specific to the temperature range 773–873 K. Thus, the increase of the applied frequency enhances the electronic jumps between the localized states.

at one site; when it is thermally activated, it migrates to another site. Moreover, we demonstrated in the first part of this chapter that the defects constitute the active sites in the conduction process. Therefore, the electron or hole tends to associate with local defects, so the activation energy for charge transport may also include the energy of freeing the hole

As mentioned above, the ac conductivity increases with increasing both temperature and frequency. Simultaneously, the dc conductivity increases with increasing temperature (Figure

1,14 1,16 1,18 1,20 1,22 1,24 1,26 1,28 1,30

1000/T (K-1 )

**Figure 5.** Evolution of the *dc* conductivity of metanacrite between 773 K and 873K [29]. where σ� is the pre-exponential factor, ������ is the activation energy, *T* is the temperature, and �� is the Boltzmann constant. As a consequence of the increased dc conductivity with

From these results, we deduce a correlation between the electrochemical impedance spectroscopy and the structural properties of amorphous Tunisian metanacrite synthetic material.

E**a**(dc)= 0.24 ± 0.01 eV

�������

( )

�� � � **(3)**

(3)

 ��� � �� **exp** �

<sup>0</sup>exp æ ö - <sup>=</sup> ç ÷

*k T ac*

**Figure 4.** Temperature dependence of frequency exponent(s) for metanacrite sample [29].

the ac activation energy ������ and the increase of ac conductivity ��� with the increase of frequency confirm the dominant hopping conduction mechanism.

from its position next to the defect [40]. Otherwise, the electronic conduction takes place by hopping between two charge-defect states over the barrier separating them.

**Temperature (K)**

Equation (2) predicts that � decreases with increasing temperature. Therefore, the C.B.H. is the involved conduction mechanism for the investigated metanacrite sample [37, 38].

the involved conduction mechanism for the investigated metanacrite sample [37, 38].

����� ���

1

��� �������� � ��

�� � ��� �� �� �����

 e *N R* e w

ì ü ï ï = - í ý <sup>+</sup> ï ï î þ *kT*

*W k T ln M B*

1 ' 24 æ ö <sup>=</sup> ç ÷ è ø

<sup>6</sup> <sup>1</sup>

������ � � �

*sacω* w

136 Clays, Clay Minerals and Ceramic Materials Based on Clay Minerals

*s*

�, �� is the maximum barrier height, �� the atomic vibration period, � is the frequency exponent, and �� is the Boltzmann constant.

exponent, and *kB* is the Boltzmann constant.

0,35 0,40 0,45 0,50 0,55 0,60 0,65 0,70 0,75

5). Indeed, the dc conductivity (�dc) fits the well-known Arrhenius relation [39]. We found ������ = 0.24 ± 0.01 eV ( Figure 5):

�� � � **(4)**


temperature for small activation energies, we conclude that the amorphous metanacrite sample behaves like a semiconductor material [29].

log (dc.T) [S.m-1.K]

� **exp** �

**4. Functionalization of Nacrite: Nacrite–LiCl Nanohybrid** 

�������

**Exponent frequency s**

Concerning the ac conductivity of metanacrite, it is found to obey the universal Arrhenius power law [39]:

power law [39]:

over longer distances at low frequencies.

 ��� � ��

0

wt

� **(1)**

� **(2)**

(1)

(2)

 ��� � ��

� **exp** ��������

**4. Functionalization of Nacrite: Nacrite–LiCl Nanohybrid** 

be in disagreement with our results. Therefore, the experimental data will be discussed in the frame of the C.B.H. model. Thus, the conduction occurs via the hopping carriers over a The ac conductivity increases as a function of frequency at a fixed temperature (773 K) from 3.40⋅10−6 S⋅m−1 at *f* =100 Hz to 1.27⋅ 10−2 S⋅m−1 at *f* = 10 MHz [29]. Besides the ac conductivity increases as a function of temperature at a fixed frequency (*f* = 10 MHz), it increases from 1.27 ⋅10−2 S⋅m−1 at *T* = 773K to 1.98 ⋅10−2 S⋅m−1 at *T* = 873 K. The small values of the ac activation energy *E*a(ac) and the increase of ac conductivity *σac* with the increase of frequency confirm the dominant hopping conduction mechanism. **Temperature (K) Figure 4.** Temperature dependence of frequency exponent(s) for metanacrite sample [29]. Concerning the ac conductivity of metanacrite, it is found to obey the universal Arrhenius power law [39]: ��� � �� **exp** � ������� �� � � **(3)**

where ��� is the ac conductivity, �� is the free-space dielectric permittivity, �� is the dielectric constant, � is the density of states at Fermi level, �� is the hopping length at frequency The conductivity is thermally activated; therefore, the electrical conduction follows a process in which the electron or hole hops from one localized site to another. The electron resides at one site; when it is thermally activated, it migrates to another site. Moreover, we demonstrated in the first part of this chapter that the defects constitute the active sites in the conduction process. Therefore, the electron or hole tends to associate with local defects, so the activation energy for charge transport may also include the energy of freeing the hole from its position next to the defect [40]. Otherwise, the electronic conduction takes place by hopping between two charge-defect states over the barrier separating them. where �� is the pre-exponential factor, �� is the Boltzmann constant, *T* is the temperature, and ������ is the activation energy that controls the jump of charge carriers from one site to another neighboring site. The (ac) values have been calculated at four fixed frequencies [29]. Indeed, the activation energy varies between 0.24 ± 0.01 eV (at low frequencies) and 0.17 ± 0.01 eV (at high frequencies). These results are specific to the temperature range 773–873 K. Thus, the increase of the applied frequency enhances the electronic jumps between the localized states. Consequently, the activation energy decreases with increasing frequency. Moreover, at high frequency, the ac activation energies are found to be lower than those found at low frequency regions [29]. Therefore, at high frequencies the mobility of charge carriers over short distances needs lower energy than that necessary for mobility over longer distances at low frequencies. The ac conductivity increases as a function of frequency at a fixed temperature (773 K) from 3.40⋅10−6 S⋅m−1 at � =100 Hz to 1.27⋅ 10−2 S⋅m−1 at � = 10 MHz [29]. Besides the ac conductivity increases as a function of temperature at a fixed frequency (� = 10 MHz), it increases from 1.27 ⋅10−2 S⋅m−1 at � = 773K to 1.98 ⋅10−2 S⋅m−1 at � = 873 K. The small values of the ac activation energy ������ and the increase of ac conductivity ��� with the increase of frequency confirm the dominant hopping conduction mechanism. The conductivity is thermally activated; therefore, the electrical conduction follows a process in which the electron or hole hops from one localized site to another. The electron resides

> As mentioned above, the ac conductivity increases with increasing both temperature and frequency. Simultaneously, the dc conductivity increases with increasing temperature (Figure 5). Indeed, the dc conductivity (*σ*dc) fits the well-known Arrhenius relation [39]. We found *E*a(dc) = 0.24 ± 0.01 eV (Figure 5): at one site; when it is thermally activated, it migrates to another site. Moreover, we demonstrated in the first part of this chapter that the defects constitute the active sites in the conduction process. Therefore, the electron or hole tends to associate with local defects, so the activation energy for charge transport may also include the energy of freeing the hole from its position next to the defect [40]. Otherwise, the electronic conduction takes place by hopping between two charge-defect states over the barrier separating them. As mentioned above, the ac conductivity increases with increasing both temperature and frequency. Simultaneously, the dc conductivity increases with increasing temperature (Figure 5). Indeed, the dc conductivity (�dc) fits the well-known Arrhenius relation [39]. We found ������ = 0.24 ± 0.01 eV ( Figure 5):

$$
\sigma\_{de} = \frac{\sigma\_0}{T} \exp\left(\frac{-E\_{adc}}{k\_\text{g} \ T}\right) \tag{4}
$$

where σ� is the pre-exponential factor, ������ is the activation energy, *T* is the temperature, and �� is the Boltzmann constant. As a consequence of the increased dc conductivity with

From these results, we deduce a correlation between the electrochemical impedance spectroscopy and the structural properties of amorphous Tunisian metanacrite synthetic material.

The conductivity is thermally activated; therefore, the electrical conduction follows a process in which the electron or hole hops from one localized site to another. The electron resides **Figure 5.** Evolution of the *dc* conductivity of metanacrite between 773 K and 873K [29]. **Figure 5.** Evolution of the *dc* conductivity of metanacrite between 773 K and 873K [29].

temperature for small activation energies, we conclude that the amorphous metanacrite sample behaves like a semiconductor material [29].

where *σ*0 is the pre-exponential factor, *E*a(ac) is the activation energy, *T* is the temperature, and *kB* is the Boltzmann constant. As a consequence of the increased dc conductivity with temper‐ ature for small activation energies, we conclude that the amorphous metanacrite sample behaves like a semiconductor material [29].

From these results, we deduce a correlation between the electrochemical impedance spectro‐ scopy and the structural properties of amorphous Tunisian metanacrite synthetic material.

## **4. Functionalization of Nacrite: Nacrite–LiCl Nanohybrid**

Intercalation of kaolin nanoclay minerals with inorganic and organic compounds has wide potential for scientific and industrial applications [41]. Indeed, intercalation is eventually accompanied by substantial modifications of the kaolin surface due to the expansion of the interlamellar space [42,43]. The resulting hybrid materials have attracted much interest from researchers, since they frequently show unexpected and remarkable improvements in the rheological, mechanical, thermal, optical, and electrical properties compared to the unmodi‐ fied aluminosilicate clay mineral.

However, due to the hydrogen-bonding between the layers of kaolinite, only a limited number of small and highly polar organic compounds such as dimethyl-sulfoxide, deuterated dimeth‐ yl-sulfoxide [44], formamide [45], N-methylformamide (NMF), dimethylformamide, acet‐ amide, pyridine N-oxide, potassium acetate, and methanol can directly be intercalated [46, 47]. Thus, these kaolinite intercalation compounds were used as precursors, because interca‐ lation reactions of kaolinite have been extended by a guest displacement method in which a new guest can be intercalated by displacing previously intercalated species [48]. Additionally, three intercalation modes of alkali halides into the kaolin subgroup can be distinguished [49]: Mode A includes those species that are directly intercalated [50, 51]. Mode B includes those species which can enter the interlayer space by means of an "entraining agent" such as hydrazine or ammonium acetates [52]. Mode C includes those species which can only be intercalated into the interlayer space by the displacement of a previously intercalated com‐ pound such as dimethylsulfoxide "DMSO" [52].

In the case of Tunisian nacrite-polytype, the intercalation process of several inorganic salts and dipolar organic molecules are well documented and numerous publications are available [16, 21, 49, 53, 54]. In this study, we focus eventually on the intercalation of LiCl alkali halide in the interlayer space of nacrite. Mode B has been adopted, firstly, due to hydrogen bonds between the oxygen atoms on the surface of the tetrahedral sheet of one layer and adjacent hydroxyl groups on the surface of the octahedral sheet of the next layer [55]. Secondly, this process ensures the fast intercalation of the alkali halide without destruction of the kaolinite framework and complications of the kaolinite/alkali halide interactions compared to Mode A. Finally, the protocol of synthesis followed in Mode B is much easier in comparison to that in Mode C. For these reasons, potassium acetate "KAc" was selected as a precursor for the expansion of nacrite [15, 49, 52]. The resulting KAc complex is characterized by a basal distance equal to 1.4 nm; it is then washed with water and air dried leading to a stable hydrate (0.84 nm), which constituted the starting material for the next step of the synthesis of the new hybrid material [15, 17, 20, 49].

## **4.1. The Intercalation Process of Lithium Chloride Alkali Halide in the Interlamellar Space of Nacrite**

The inorganic salt employed during the course of this work was imposed by the literature data [52, 56], since the intercalation of lithium chloride alkali halide into kaolinite, in the previous cases, has failed due to the hygroscopic properties of the salt–clay mixture [57]. Thus, this research has been the first to intercalate LiCl in the interlamellar space of nacrite. Experiments based on the use of water as a solvent induces an unaccomplished intercalation of Li+ cations. For this reason, different organic solvents (acetone, methanol, ethanol, glycerol, and ethylene glycol) were tried until an intercalation of 0.82 g of LiCl was reached in the presence of 20 ml of acetone at room temperature [49]. Indeed, acetone is considered as the best solvent for nacrite intercalation after 3 days of mechanical shaking under a magnetic stirrer. The final hybrid product was obtained and labeled: nacrite–LiCl [49].

## **4.2. Structural Characterization of Nacrite–LiCl Nanohybrid Material**

The intercalation process is characterized via X-ray diffraction analysis, thermogravimetric analysis, infrared spectroscopy, and electrochemical impedance spectroscopy. In the following sections, the structural properties of nacrite–LiCl hybrid will be detailed starting with X-ray diffraction analysis.

### *4.2.1. X-ray Measurements*

where *σ*0 is the pre-exponential factor, *E*a(ac) is the activation energy, *T* is the temperature, and *kB* is the Boltzmann constant. As a consequence of the increased dc conductivity with temper‐ ature for small activation energies, we conclude that the amorphous metanacrite sample

From these results, we deduce a correlation between the electrochemical impedance spectro‐ scopy and the structural properties of amorphous Tunisian metanacrite synthetic material.

Intercalation of kaolin nanoclay minerals with inorganic and organic compounds has wide potential for scientific and industrial applications [41]. Indeed, intercalation is eventually accompanied by substantial modifications of the kaolin surface due to the expansion of the interlamellar space [42,43]. The resulting hybrid materials have attracted much interest from researchers, since they frequently show unexpected and remarkable improvements in the rheological, mechanical, thermal, optical, and electrical properties compared to the unmodi‐

However, due to the hydrogen-bonding between the layers of kaolinite, only a limited number of small and highly polar organic compounds such as dimethyl-sulfoxide, deuterated dimeth‐ yl-sulfoxide [44], formamide [45], N-methylformamide (NMF), dimethylformamide, acet‐ amide, pyridine N-oxide, potassium acetate, and methanol can directly be intercalated [46, 47]. Thus, these kaolinite intercalation compounds were used as precursors, because interca‐ lation reactions of kaolinite have been extended by a guest displacement method in which a new guest can be intercalated by displacing previously intercalated species [48]. Additionally, three intercalation modes of alkali halides into the kaolin subgroup can be distinguished [49]: Mode A includes those species that are directly intercalated [50, 51]. Mode B includes those species which can enter the interlayer space by means of an "entraining agent" such as hydrazine or ammonium acetates [52]. Mode C includes those species which can only be intercalated into the interlayer space by the displacement of a previously intercalated com‐

In the case of Tunisian nacrite-polytype, the intercalation process of several inorganic salts and dipolar organic molecules are well documented and numerous publications are available [16, 21, 49, 53, 54]. In this study, we focus eventually on the intercalation of LiCl alkali halide in the interlayer space of nacrite. Mode B has been adopted, firstly, due to hydrogen bonds between the oxygen atoms on the surface of the tetrahedral sheet of one layer and adjacent hydroxyl groups on the surface of the octahedral sheet of the next layer [55]. Secondly, this process ensures the fast intercalation of the alkali halide without destruction of the kaolinite framework and complications of the kaolinite/alkali halide interactions compared to Mode A. Finally, the protocol of synthesis followed in Mode B is much easier in comparison to that in Mode C. For these reasons, potassium acetate "KAc" was selected as a precursor for the expansion of nacrite [15, 49, 52]. The resulting KAc complex is characterized by a basal distance equal to 1.4 nm; it is then washed with water and air dried leading to a stable hydrate (0.84

**4. Functionalization of Nacrite: Nacrite–LiCl Nanohybrid**

behaves like a semiconductor material [29].

138 Clays, Clay Minerals and Ceramic Materials Based on Clay Minerals

fied aluminosilicate clay mineral.

pound such as dimethylsulfoxide "DMSO" [52].

## *4.2.1.1. Qualitative XRD Analysis*

By examining the *00l* reflections of the XRD pattern related to the stable nacrite–LiCl hybrid, Figure 6, we note a main reflection situated at 7.724°2*θ*, with *d*002= 1.143± 0.002 nm basal spacing value attributed to an expansion of the interlamellar space of nacrite by ~0.423 nm along the *c\** axis. This result is probably due to the insertion of lithium chloride salt accompanied by one water sheet into the nacrite matrix [49]. The exploitation of the CV coefficient and the ration‐ ality series confirm the homogenous sample character [49].

However, the high *FWHM* value at around 0.846˚2*θ* of the first reflection is interpreted as a contradictory result. This is traduced by the fact that the *FWHM* could be notably affected by stress, strain, and interstratifications [49]. The extent of intercalation was determined using integrated areas of the reflections [58]:

$$\text{Interrelation ratio} = \left[\frac{\text{I}\_{02}\text{ hybrid}}{\text{I}\_{02}\text{ hybrid} + \text{I}\_{02}\text{ancrite}}\right] \times 100\% \tag{5}$$

where I002hybrid and I002nacrite represent the main basal peak intensity of the hybrid and of the unexpanded nacrite component (*d*<sup>002</sup> ~ 0.72 nm), respectively. The intercalation ratio value is equal to 86% for nacrite–LiCl and remained unchanged even for long time reaction.

*4.2.1. X-ray Measurements 4.2.1.1. Qualitative XRD Analysis* 

unmodified aluminosilicate clay mineral.

intercalated compound such as dimethylsulfoxide "DMSO" [52].

**4.2. Structural Characterization of Nacrite**–**LiCl Nanohybrid Material** 

**4.1. The Intercalation Process of Lithium Chloride Alkali Halide in the Interlamellar Space of Nacrite** 

following sections, the structural properties of nacrite–LiCl hybrid will be detailed starting with X-ray diffraction analysis.

Intercalation of kaolin nanoclay minerals with inorganic and organic compounds has wide potential for scientific and industrial applications [41]. Indeed, intercalation is eventually accompanied by substantial modifications of the kaolin surface due to the expansion of the interlamellar space [42,43]. The resulting hybrid materials have attracted much interest from researchers, since they frequently show unexpected and remarkable improvements in the rheological, mechanical, thermal, optical, and electrical properties compared to the

However, due to the hydrogen-bonding between the layers of kaolinite, only a limited number of small and highly polar organic compounds such as dimethyl-sulfoxide, deuterated dimethyl-sulfoxide [44], formamide [45], N-methylformamide (NMF), dimethylformamide, acetamide, pyridine N-oxide, potassium acetate, and methanol can directly be intercalated [46, 47]. Thus, these kaolinite intercalation compounds were used as precursors, because intercalation reactions of kaolinite have been extended by a guest displacement method in which a new guest can be intercalated by displacing previously intercalated species [48]. Additionally, three intercalation modes of alkali halides into the kaolin subgroup can be distinguished [49]: Mode A includes those species that are directly intercalated [50, 51]. Mode B includes those species which can enter the interlayer space by means of an "entraining agent" such as hydrazine or ammonium acetates [52]. Mode C includes those species which can only be intercalated into the interlayer space by the displacement of a previously

In the case of Tunisian nacrite-polytype, the intercalation process of several inorganic salts and dipolar organic molecules are well documented and numerous publications are available [16, 21, 49, 53, 54]. In this study, we focus eventually on the intercalation of LiCl alkali halide in the interlayer space of nacrite. Mode B has been adopted, firstly, due to hydrogen bonds between the oxygen atoms on the surface of the tetrahedral sheet of one layer and adjacent hydroxyl groups on the surface of the octahedral sheet of the next layer [55]. Secondly, this process ensures the fast intercalation of the alkali halide without destruction of the kaolinite framework and complications of the kaolinite/alkali halide interactions compared to Mode A. Finally, the protocol of synthesis followed in Mode B is much easier in comparison to that in Mode C. For these reasons, potassium acetate "KAc" was selected as a precursor for the expansion of nacrite [15, 49, 52]. The resulting KAc complex is characterized by a basal distance equal to 1.4 nm; it is then washed with water and air dried

The inorganic salt employed during the course of this work was imposed by the literature data [52, 56], since the intercalation of lithium chloride alkali halide into kaolinite, in the previous cases, has failed due to the hygroscopic properties of the salt–clay mixture [57]. Thus, this research has been the first to intercalate LiCl in the interlamellar space of nacrite. Experiments based on the use of water as a solvent induces an unaccomplished intercalation of Li+ cations. For this reason, different organic solvents (acetone, methanol, ethanol, glycerol, and ethylene glycol) were tried until an intercalation of 0.82 g of LiCl was reached in the presence of 20 ml of acetone at room temperature [49]. Indeed, acetone is considered as the best solvent for nacrite intercalation after 3 days of mechanical shaking under a magnetic stirrer. The final hybrid product was obtained and labeled: nacrite–LiCl [49].

The intercalation process is characterized via X-ray diffraction analysis, thermogravimetric analysis, infrared spectroscopy, and electrochemical impedance spectroscopy. In the

By examining the *00l* reflections of the XRD pattern related to the stable nacrite–LiCl hybrid, Figure 6, we note a main reflection situated at 7.724°2*θ*, with *d*002= 1.143± 0.002 nm basal spacing value attributed to an expansion of the interlamellar space of nacrite by ~0.423 nm along the *c\** axis. This result is probably due to the insertion of lithium chloride salt accompanied by one water sheet into the nacrite matrix [49]. The exploitation of the CV coefficient and the rationality series confirm the homogenous sample character [49].

However, the high *FWHM* value at around 0.8462*θ* of the first reflection is interpreted as a contradictory result. This is traduced by the fact that the *FWHM* could be notably affected

**Figure 6.** Experimental XRD pattern of the nacrite–LiCl hybrid [49].

leading to a stable hydrate (0.84 nm), which constituted the starting material for the next step of the synthesis of the new hybrid material [15, 17, 20, 49].

**Figure 6.** Experimental XRD pattern of the nacrite–LiCl hybrid [49].

#### *4.2.1.2. Quantitative XRD Analysis* by stress, strain, and interstratifications [49]. The extent of intercalation was determined using integrated areas of the reflections [58]:

Simulations of the *00l* reflections seem to be a dominant path to gain an accurate picture about the fine structure of the nacrite–LiCl hybrid including the number and positions of the intercalated species in the interlayer space of nacrite. For that, an XRD-modeling computer program designed to carry out intensity calculations was used: The quantitative XRD analysis is based essentially on comparison between the experimental XRD pattern with the theoretical one [49]. Intercalation ratio = [ ������������ ����������������������������� ]� ���� **(5)** where I���hybrid and I���nacrite represent the main basal peak intensity of the hybrid and of the unexpanded nacrite component (*d*002 ~ 0.72 nm), respectively. The intercalation ratio value is equal to 86% for nacrite–LiCl and remained unchanged even for long time reaction.

However, the tiny atomic scattering factor of Li+ (2) prevents the location of this cation with good preciseness in the interlamellar space of nacrite. So, we dressed a series of models with different positions of Li+ cation [49]. It was therefore interesting to handle the unweighted R*<sup>p</sup>* factor of each model as an indication of the effectiveness of fit [59]:

$$R\_p = \sqrt{\frac{\sum \left[ I \left( 2\theta\_i \right) obs - I \left( 2\theta\_i \right) calc}{\sqrt{I \left( 2\theta\_i \right) obs}} \right]^2} \tag{6}$$

where, *I*(2*θi*)*obs* and *I*(2*θi*)*calc* represent measured and calculated intensities, respectively, at the 2*θ<sup>i</sup>* position, the subscript **i** running over all points in the refined angular range. R*p* is mainly influenced by the most intense diffraction maxima, such as the *00l* reflections, which contains essential information on the proportions of the different layer types and layer thickness [49].

The best model belongs to the smallest R*p* factor (6.20%) [49]. This model suggests the pres‐ ence of a hydrated salt and is in agreement with the qualitative analysis. It allows then a more accurate determination of the structural parameters of the stable nacrite–LiCl hybrid per half unit-cell: The *z* coordinates of intercalated Li+ and Cl– cations, taken from the oxygen surface oxygen along the normal to the layer, are respectively, 0.96 ± 0.01 nm and 0.64 ± 0.01 nm along c\* axis. Finally, one intercalated water molecule situated at *z = 0.*79 ± 0.01 nm is sandwiched between the cation and the anion [49].

To summarize, the intercalated species stand vertically in the interlayer space of nacrite, where the cations are located close to the ditrigonal holes of the tetrahedral layers and the anions are located close to the inner-surface hydroxyls ofthe octahedral layer ofthe subsequent sheet[49]. Moreover, the quantitative study of the nacrite–LiCl hybrid clearly showed an interstratified stacking characterized by a segregation tendency consisting of a total demixion of two types of layers: Layer A related to a minor fraction (14%) of the unexpanded 0.72 nm clay and Layer B attributed to a major fraction (86%) of the intercalated nacrite {*WA =* 0.86, *WB =* 0.14*, PAA =* 1, *PAB =* 0, *PBA=* 0, *PBB =* 1}[49]. The structural formula of the studied hybrid at room temperature was then determined as {(1–*α*)[Si2Al2O5(OH)4LiCl.H2O] + *α*[Si2Al2O5(OH)4]} per half unit cell, where "*α*" is equal to 0.14 and corresponds to the unexpanded nacrite fraction [49].

#### **Figure 6.** Experimental XRD pattern of the nacrite–LiCl hybrid [49]. **4.3. IR Spectroscopy**

*4.2.1.2. Quantitative XRD Analysis*

However, the tiny atomic scattering factor of Li+

**Figure 6.** Experimental XRD pattern of the nacrite–LiCl hybrid [49].

unmodified aluminosilicate clay mineral.

intercalated compound such as dimethylsulfoxide "DMSO" [52].

**4.2. Structural Characterization of Nacrite**–**LiCl Nanohybrid Material** 

*4.2.1. X-ray Measurements 4.2.1.1. Qualitative XRD Analysis* 

140 Clays, Clay Minerals and Ceramic Materials Based on Clay Minerals

**Intensity (a.u)**

d002=1.143 nm

0.72 nm

*004*

*p*

*R*

factor of each model as an indication of the effectiveness of fit [59]:

one [49].

the 2*θ<sup>i</sup>*

different positions of Li+

Simulations of the *00l* reflections seem to be a dominant path to gain an accurate picture about the fine structure of the nacrite–LiCl hybrid including the number and positions of the intercalated species in the interlayer space of nacrite. For that, an XRD-modeling computer program designed to carry out intensity calculations was used: The quantitative XRD analysis is based essentially on comparison between the experimental XRD pattern with the theoretical

value is equal to 86% for nacrite–LiCl and remained unchanged even for long time reaction.

**10 20 30 40 50**

*008*

0.36 nm

*°2* **(Cu-k )**

*006*

good preciseness in the interlamellar space of nacrite. So, we dressed a series of models with

( ) ( )

*i i*

*I obs I calc*

2 2

é ù - ë û <sup>=</sup> é ù ë û

q

( )

q

*i*

where, *I*(2*θi*)*obs* and *I*(2*θi*)*calc* represent measured and calculated intensities, respectively, at

 position, the subscript **i** running over all points in the refined angular range. R*p* is mainly influenced by the most intense diffraction maxima, such as the *00l* reflections, which contains essential information on the proportions of the different layer types and layer thickness [49]. The best model belongs to the smallest R*p* factor (6.20%) [49]. This model suggests the pres‐ ence of a hydrated salt and is in agreement with the qualitative analysis. It allows then a more

*I obs*

2

2

 q

cation [49]. It was therefore interesting to handle the unweighted R*<sup>p</sup>*

2

<sup>å</sup> (6)

(2) prevents the location of this cation with

����������������������������� ]� ���� **(5)**

*0012*

Intercalation ratio = [ ������������

*nacrite-LiCl hybrid*

*0010*

by stress, strain, and interstratifications [49]. The extent of intercalation was determined using integrated areas of the reflections [58]:

Intercalation of kaolin nanoclay minerals with inorganic and organic compounds has wide potential for scientific and industrial applications [41]. Indeed, intercalation is eventually accompanied by substantial modifications of the kaolin surface due to the expansion of the interlamellar space [42,43]. The resulting hybrid materials have attracted much interest from researchers, since they frequently show unexpected and remarkable improvements in the rheological, mechanical, thermal, optical, and electrical properties compared to the

However, due to the hydrogen-bonding between the layers of kaolinite, only a limited number of small and highly polar organic compounds such as dimethyl-sulfoxide, deuterated dimethyl-sulfoxide [44], formamide [45], N-methylformamide (NMF), dimethylformamide, acetamide, pyridine N-oxide, potassium acetate, and methanol can directly be intercalated [46, 47]. Thus, these kaolinite intercalation compounds were used as precursors, because intercalation reactions of kaolinite have been extended by a guest displacement method in which a new guest can be intercalated by displacing previously intercalated species [48]. Additionally, three intercalation modes of alkali halides into the kaolin subgroup can be distinguished [49]: Mode A includes those species that are directly intercalated [50, 51]. Mode B includes those species which can enter the interlayer space by means of an "entraining agent" such as hydrazine or ammonium acetates [52]. Mode C includes those species which can only be intercalated into the interlayer space by the displacement of a previously

In the case of Tunisian nacrite-polytype, the intercalation process of several inorganic salts and dipolar organic molecules are well documented and numerous publications are available [16, 21, 49, 53, 54]. In this study, we focus eventually on the intercalation of LiCl alkali halide in the interlayer space of nacrite. Mode B has been adopted, firstly, due to hydrogen bonds between the oxygen atoms on the surface of the tetrahedral sheet of one layer and adjacent hydroxyl groups on the surface of the octahedral sheet of the next layer [55]. Secondly, this process ensures the fast intercalation of the alkali halide without destruction of the kaolinite framework and complications of the kaolinite/alkali halide interactions compared to Mode A. Finally, the protocol of synthesis followed in Mode B is much easier in comparison to that in Mode C. For these reasons, potassium acetate "KAc" was selected as a precursor for the expansion of nacrite [15, 49, 52]. The resulting KAc complex is characterized by a basal distance equal to 1.4 nm; it is then washed with water and air dried

The inorganic salt employed during the course of this work was imposed by the literature data [52, 56], since the intercalation of lithium chloride alkali halide into kaolinite, in the previous cases, has failed due to the hygroscopic properties of the salt–clay mixture [57]. Thus, this research has been the first to intercalate LiCl in the interlamellar space of nacrite. Experiments based on the use of water as a solvent induces an unaccomplished intercalation of Li+ cations. For this reason, different organic solvents (acetone, methanol, ethanol, glycerol, and ethylene glycol) were tried until an intercalation of 0.82 g of LiCl was reached in the presence of 20 ml of acetone at room temperature [49]. Indeed, acetone is considered as the best solvent for nacrite intercalation after 3 days of mechanical shaking under a magnetic stirrer. The final hybrid product was obtained and labeled: nacrite–LiCl [49].

The intercalation process is characterized via X-ray diffraction analysis, thermogravimetric analysis, infrared spectroscopy, and electrochemical impedance spectroscopy. In the

By examining the *00l* reflections of the XRD pattern related to the stable nacrite–LiCl hybrid, Figure 6, we note a main reflection situated at 7.724°2*θ*, with *d*002= 1.143± 0.002 nm basal spacing value attributed to an expansion of the interlamellar space of nacrite by ~0.423 nm along the *c\** axis. This result is probably due to the insertion of lithium chloride salt accompanied by one water sheet into the nacrite matrix [49]. The exploitation of the CV coefficient and the rationality series confirm the homogenous sample character [49].

leading to a stable hydrate (0.84 nm), which constituted the starting material for the next step of the synthesis of the new hybrid material [15, 17, 20, 49].

**4.1. The Intercalation Process of Lithium Chloride Alkali Halide in the Interlamellar Space of Nacrite** 

following sections, the structural properties of nacrite–LiCl hybrid will be detailed starting with X-ray diffraction analysis.

However, the high *FWHM* value at around 0.8462*θ* of the first reflection is interpreted as a contradictory result. This is traduced by the fact that the *FWHM* could be notably affected where I���hybrid and I���nacrite represent the main basal peak intensity of the hybrid and of the unexpanded nacrite component (*d*002 ~ 0.72 nm), respectively. The intercalation ratio By comparing the spectrum of nacrite intercalated with lithium chloride to the spectrum of the untreated nacrite, it is possible to follow the modification of the stretching and deformation vibrations: they shift from their positions and their shapes change. These effects are a conse‐ quence of several factors, such as the intercalated entities, the degree of intercalation, and the degree of hydration [60].

These modifications are manifested in the recorded spectrum of the nacrite–LiCl hybrid [49].

Finally, IR spectroscopy proved that the intercalating species overcome the strong interactions between the nacrite-like layers and form hydrogen bonds with components of the TO layer [49]:


These results are in concordance with those suggested by [50, 51, 60–62].

## **4.4. Thermal Analysis: Decomposition Process of the Nacrite–LiCl Nanohybrid During Heat Treatment**

Thermogravimetric analysis of the nacrite–LiCl hybrid reveals that the sample gradually loses weight from room temperature to 800˚C (Scheme 1) [49]:

**1.** The first remarkable weight loss was observed between 298 and 423 K and is mostly attributed to the drying process by which the water molecules that are confined to the clay mineral pores are released.

**2.** The second weight loss (3.62%) occurred between 673 and 773 K and belongs to the removal of the intercalated water molecule. This temperature range is also characterized by the beginning of the dehydroxylation of the hybrid at around 723 K. The chemical decomposition reaction of the hybrid per half unit cell can be expressed as follows:

$$\begin{aligned} & \left\{ (1-a) \left[ \mathrm{Si}\_2 \mathrm{Al}\_2 \mathrm{O}\_5 \mathrm{(OH)} \right]\_4 \mathrm{LiCl} \right\} + a \left[ \mathrm{Si}\_2 \mathrm{Al}\_2 \mathrm{O}\_5 \mathrm{(OH)} \right]\_4 \mathrm{J} \\ & \rightarrow \left\{ (1-a) \left[ \mathrm{Si}\_2 \mathrm{Al}\_2 \mathrm{O}\_7 \mathrm{LiCl} \right] \right. + a \left[ \mathrm{Si}\_2 \mathrm{Al}\_2 \mathrm{O}\_7 \right] \mathrm{J} + \left\{ 2 \left( 1-a \right) \mathrm{H}\_2 \mathrm{O} \right. + 2a \mathrm{H}\_2 \mathrm{O} \right\}. \end{aligned}$$

The product formed at the commencement of the dehydroxylation of the hybrid is called "metanacrite–LiCl hybrid": { Si2Al2O7.(1-α)LiCl }, (*α* = 0.14), and is amorphous.

**3.** The third weight loss was centered on 873 K (9.23%) and was due to the removal of two structural water {2(1-α) H2O + 2α H2O} = {2 H2O} during the calcination process. This step was ultimately accompanied by the evolution of the hydrogen halide which results from the following thermal hydrolysis [63, 64]:

$$2SiO\_2Al\_2O\_3 + \ (1-\alpha)\ LiCl \rightarrow 2SiO\_2Al\_2O\_3 \cdot \frac{(1-\alpha)}{2}$$

$$Li\_2O + \ (1-\alpha)\ HCl \rightarrow \frac{(1-\alpha)}{2}H\_2O.$$

On the clay surface, a liberated water molecule associates with Cl– to form volatile HCl. The volatilization of HCl is responsible for a great amount of thermal mass loss of the examined hybrid. This phenomenon causes the trapping of the alkali metal oxide Li2O within the metanacrite matrix. The amorphous hybrid phase formed during this step has the following chemical formula: {Si2Al2O7. (1−*α*) / 2Li2O}. Knowing that (1−*α*) / 2 coefficient is equal to 0.43 ~ 0.5, we can simplify this chemical formula and express our "metanacrite–Li2O hybrid" by the following formula {Si2Al2O7. 1 / 2Li2O} [49].

#### **4.5. Electrochemical Characterization of Nacrite–LiCl Nanohybrid Material**

Over the past three decades, much attention has been paid to solid electrolytes instead of liquid electrolytes because of their potential use in the electrochemical power sources (batteries, lithium ion cells, lithium batteries, fuel cells, electrochemical sensors, etc.) [65]. The advantages of solid electrolytes include longer life, high energy density, and no possibility of leak, etc. They are suitable in compact power batteries used in pace-makers, mobile telephones, and laptops [66]. In order to improve the bulk properties of solid electrolytes, a good number of researchers are interested in the synthesis and characterization of lithium-ion conductors based on different classes of materials such as ceramics, polymers, glasses, and so on [65, 30]. They are motivated by the small ionic radius of Li+ cation, its low weight, ease of motion, and its appliance in high energy density batteries [67–71]. Therefore, we are proposing to innovate a new class of conductors based on nacrite-polytype clay [30].

**Scheme 1.** Schematic representation of the thermal transformations of heat-treated nacrite–LiCl hybrid from room temperature to 873K [30]. **4.5. Electrochemical Characterization of Nacrite**–**LiCl Nanohybrid Material Scheme 1.** Schematic representation of the thermal transformations of heat-treated nacrite–LiCl hybrid from room temperature to 873K [30]. **4.5. Electrochemical Characterization of Nacrite**–**LiCl Nanohybrid Material Scheme 1.** Schematic representation of the thermal transformations of heat-treated nacrite–LiCl hybrid from room tem‐ perature to 873K [30].

#### *4.5.1. Impedance Analysis* Over the past three decades, much attention has been paid to solid electrolytes instead of liquid electrolytes because of their potential use in the electrochemical power sources (batteries, lithium ion cells, lithium batteries, fuel cells, electrochemical sensors, etc.) [65]. The advantages of solid electrolytes include longer life, high energy density, and no Over the past three decades, much attention has been paid to solid electrolytes instead of liquid electrolytes because of their potential use in the electrochemical power sources (batteries, lithium ion cells, lithium batteries, fuel cells, electrochemical sensors, etc.) [65]. The advantages of solid electrolytes include longer life, high energy density, and no

**2.** The second weight loss (3.62%) occurred between 673 and 773 K and belongs to the removal of the intercalated water molecule. This temperature range is also characterized by the beginning of the dehydroxylation of the hybrid at around 723 K. The chemical decomposition reaction of the hybrid per half unit cell can be expressed as follows:

( ) ( )

 

2 27 2 27 2 2

*Si Al O LiCl Si Al O HO HO*

{( )[ ] [ ] { 2 }.}

The product formed at the commencement of the dehydroxylation of the hybrid is called

**3.** The third weight loss was centered on 873 K (9.23%) and was due to the removal of two structural water {2(1-α) H2O + 2α H2O} = {2 H2O} during the calcination process. This step was ultimately accompanied by the evolution of the hydrogen halide which results from

2 25 2 25 4 4


1 . 21 [ ] [ ]}

 

"metanacrite–LiCl hybrid": { Si2Al2O7.(1-α)LiCl }, (*α* = 0.14), and is amorphous.

( )

2 2

**4.5. Electrochemical Characterization of Nacrite–LiCl Nanohybrid Material**

*Li O HCl H O*


2 23 2 23

(1 ) 1 .

*SiO Al O LiCl SiO Al O*

(1 ) 2. 1 2. .


2

On the clay surface, a liberated water molecule associates with Cl– to form volatile HCl. The volatilization of HCl is responsible for a great amount of thermal mass loss of the examined hybrid. This phenomenon causes the trapping of the alkali metal oxide Li2O within the metanacrite matrix. The amorphous hybrid phase formed during this step has the following chemical formula: {Si2Al2O7. (1−*α*) / 2Li2O}. Knowing that (1−*α*) / 2 coefficient is equal to 0.43 ~ 0.5, we can simplify this chemical formula and express our "metanacrite–Li2O hybrid" by

Over the past three decades, much attention has been paid to solid electrolytes instead of liquid electrolytes because of their potential use in the electrochemical power sources (batteries, lithium ion cells, lithium batteries, fuel cells, electrochemical sensors, etc.) [65]. The advantages of solid electrolytes include longer life, high energy density, and no possibility of leak, etc. They are suitable in compact power batteries used in pace-makers, mobile telephones, and laptops [66]. In order to improve the bulk properties of solid electrolytes, a good number of researchers are interested in the synthesis and characterization of lithium-ion conductors based on different classes of materials such as ceramics, polymers, glasses, and so on [65, 30]. They

appliance in high energy density batteries [67–71]. Therefore, we are proposing to innovate a

*α*

( )

*Si Al O OH LiCl Si Al O OH*

{( )1 .

142 Clays, Clay Minerals and Ceramic Materials Based on Clay Minerals

the following thermal hydrolysis [63, 64]:

the following formula {Si2Al2O7. 1 / 2Li2O} [49].

are motivated by the small ionic radius of Li+

new class of conductors based on nacrite-polytype clay [30].


( )

2

*α*

cation, its low weight, ease of motion, and its

With the ((−*Z*'')) versus *Z*' representations (Figure 7), we observed the existence of semicircles in the complex plane from 548 K to 873 K. At high temperature, these semi-arcs shift toward higher frequencies with a significant reduction of their size. We point out that nacrite–LiCl hybrid becomes more conductive at high temperature. We think that this phenomenon is attributed to the existence of a deformation (destruction) of some physical characteristics of the host clay material framework and to some chemical characteristics of LiCl alkali halide [30]. possibility of leak, etc. They are suitable in compact power batteries used in pace-makers, mobile telephones, and laptops [66]. In order to improve the bulk properties of solid electrolytes, a good number of researchers are interested in the synthesis and characterization of lithium-ion conductors based on different classes of materials such as ceramics, polymers, glasses, and so on [65, 30]. They are motivated by the small ionic radius of Li+ cation, its low weight, ease of motion, and its appliance in high energy density batteries [67– 71]. Therefore, we are proposing to innovate a new class of conductors based on nacrite-polytype clay [30]. *4.5.1. Impedance Analysis*  With the (����) versus �� representations (Figure 7), we observed the existence of semicircles in the complex plane from 548 K to 873 K. At high temperature, these semi-arcs shift toward higher frequencies with a significant reduction of their size. We point out that nacrite–LiCl hybrid becomes more conductive at high temperature. We think that this phenomenon is attributed to the existence of a deformation (destruction) of some physical characteristics of the host clay material framework and to some chemical characteristics of LiCl alkali halide [30]. electrolytes, a good number of researchers are interested in the synthesis and characterization of lithium-ion conductors based on different classes of materials such as ceramics, polymers, glasses, and so on [65, 30]. They are motivated by the small ionic radius of Li+ cation, its low weight, ease of motion, and its appliance in high energy density batteries [67– 71]. Therefore, we are proposing to innovate a new class of conductors based on nacrite-polytype clay [30]. *4.5.1. Impedance Analysis*  With the (����) versus �� representations (Figure 7), we observed the existence of semicircles in the complex plane from 548 K to 873 K. At high temperature, these semi-arcs shift toward higher frequencies with a significant reduction of their size. We point out that nacrite–LiCl hybrid becomes more conductive at high temperature. We think that this phenomenon is attributed to the existence of a deformation (destruction) of some physical characteristics of the host clay material framework and to some chemical characteristics of LiCl alkali halide [30].

process. The *ac* conductivity measurements at high frequencies (1 MHz) show that σac increases from 1.22.

appears to be rather less mobile than the cation due to its great ionic radius equal to 0.181 nm [66].

by the amorphicity of the metanacrite framework through which mobile lithium ions may migrate.

process. The *ac* conductivity measurements at high frequencies (1 MHz) show that σac increases from 1.22.

appears to be rather less mobile than the cation due to its great ionic radius equal to 0.181 nm [66].

by the amorphicity of the metanacrite framework through which mobile lithium ions may migrate.

10−6 S.m−1) at 523 K to the (0.11.

10−6 S.m−1) at 523 K to the (0.11.

from the slope of log(���*.T*) versus(1000 /*T*) and was found to be 0.84 eV and 0.82 eV, respectively, below and above 673 K [30]. The obtained values suggest an ionic conduction

from the slope of log(���*.T*) versus(1000 /*T*) and was found to be 0.84 eV and 0.82 eV, respectively, below and above 673 K [30]. The obtained values suggest an ionic conduction

related to the increase of the number of free ions in the hybrid matrix in terms of temperature [30]. The *E*a(ac) , calculated in agreement with (Eq.(3)), corresponds to the free energy barrier that an ion has to overcome for a successful jump from one site to another. These values designate that the ionic transport mechanism can be interpreted by the thermally

According to these experimental results, we deduce that the disordered hybrid bears easier motion than the ordered one [30]. We conclude that contribution of disorder and defects in

Furthermore, Li+ is known as an excellent current carrying ion in superionic solids motivated by its small ionic radius of 0.076 nm, lower weight, and ease of motion [66], but Cl− anion

To conclude, Li+ is the common current carrier via hopping from one site to the next for both "metanacrite–LiCl hybrid" and "metanacrite–Li2O hybrid". Since the "metanacrite–Li2O hybrid" phase is more amorphous than the "metanacrite–LiCl hybrid" phase, therefore it produces greater ionic conductivity. This shows that the conductivity was preferably affected

possibility of leak, etc. They are suitable in compact power batteries used in pace-makers, mobile telephones, and laptops [66]. In order to improve the bulk properties of solid

related to the increase of the number of free ions in the hybrid matrix in terms of temperature [30]. The *E*a(ac) , calculated in agreement with (Eq.(3)), corresponds to the free energy barrier that an ion has to overcome for a successful jump from one site to another. These values designate that the ionic transport mechanism can be interpreted by the thermally

According to these experimental results, we deduce that the disordered hybrid bears easier motion than the ordered one [30]. We conclude that contribution of disorder and defects in

Furthermore, Li+ is known as an excellent current carrying ion in superionic solids motivated by its small ionic radius of 0.076 nm, lower weight, and ease of motion [66], but Cl− anion

To conclude, Li+ is the common current carrier via hopping from one site to the next for both "metanacrite–LiCl hybrid" and "metanacrite–Li2O hybrid". Since the "metanacrite–Li2O hybrid" phase is more amorphous than the "metanacrite–LiCl hybrid" phase, therefore it produces greater ionic conductivity. This shows that the conductivity was preferably affected

� Li2O hybrid's high conductivity ( ��� ~ 10−2 S.m−1) makes it an excellent candidate as electrolyte solid for lithium-ion batteries. Furthermore, this amorphous-type Li-ion conductor offers several advantages such as low cost and ease of handling. Its use instead of the conventional superionic conductors can drastically improve the safety aspects of

� Li2O hybrid's high conductivity ( ��� ~ 10−2 S.m−1) makes it an excellent candidate as electrolyte solid for lithium-ion batteries. Furthermore, this amorphous-type Li-ion conductor offers several advantages such as low cost and ease of handling. Its use instead of the conventional superionic conductors can drastically improve the safety aspects of

the hybrid framework are responsible for the motion of charge carriers; this result is in agreement with the previous publication of Kumar and Yashonath [66, 30].

the hybrid framework are responsible for the motion of charge carriers; this result is in agreement with the previous publication of Kumar and Yashonath [66, 30].

10−2 S.m−1) at 873 K. An Arrhenius behavior was observed for the hybrid. The *E*a(dc) was determined

10−2 S.m−1) at 873 K. An Arrhenius behavior was observed for the hybrid. The *E*a(dc) was determined

10−2 S.m−1 at 873 K. This remarkable increase is also

10−2 S.m−1 at 873 K. This remarkable increase is also

10−4 S.m−1 at 523 K to 0.13.

10−4 S.m−1 at 523 K to 0.13.

**Figure 7.** Nyquist diagram of nacrite–LiCl hybrid at a temperature range from 473 to 873 K [30]. **Figure 7.** Nyquist diagram of nacrite–LiCl hybrid at a temperature range from 473 to 873 K [30]. **Figure 7.** Nyquist diagram of nacrite–LiCl hybrid at a temperature range from 473 to 873 K [30].

*4.5.2. Electrical Conductivity* 

*4.5.2. Electrical Conductivity* 

activated hopping process [72].

activated hopping process [72].

Si2Al2O7. �

lithium batteries [30].

lithium batteries [30].

Si2Al2O7. �

The ��� of nacrite–LiCl hybrid increases from (4.02.

The ��� of nacrite–LiCl hybrid increases from (4.02.

## *4.5.2. Electrical Conductivity*

The *σdc* of nacrite–LiCl hybrid increases from (4.02. 10−6 S.m−1) at 523 K to the (0.11. 10−2 S.m−1) at 873 K. An Arrhenius behavior was observed for the hybrid. The *E*a(dc) was determined from the slope of log (*σdc*.*T*) versus(1000 /*T*) and was found to be 0.84 eV and 0.82 eV, respectively, below and above 673 K [30]. The obtained values suggest an ionic conduction process. The *ac* conductivity measurements at high frequencies (1 MHz) show that σac increases from 1.22. 10−4 S.m−1 at 523 K to 0.13. 10−2 S.m−1 at 873 K. This remarkable increase is also related to the increase of the number of free ions in the hybrid matrix in terms of temperature [30]. The *E*a(ac), calculated in agreement with (Eq.(3)), corresponds to the free energy barrier that an ion has to overcome for a successful jump from one site to another. These values designate that the ionic transport mechanism can be interpreted by the thermally activated hopping process [72].

According to these experimental results, we deduce that the disordered hybrid bears easier motion than the ordered one [30]. We conclude that contribution of disorder and defects in the hybrid framework are responsible for the motion of charge carriers; this result is in agreement with the previous publication of Kumar and Yashonath [66, 30].

Furthermore, Li+ is known as an excellent current carrying ion in superionic solids motivated byits smallionic radiusof 0.076nm,lowerweight, andeaseofmotion[66],butCl<sup>−</sup> anionappears to be rather less mobile than the cation due to its great ionic radius equal to 0.181 nm [66].

To conclude, Li+ is the common current carrier via hopping from one site to the next for both "metanacrite–LiCl hybrid" and "metanacrite–Li2O hybrid". Since the "metanacrite–Li2O hybrid" phase is more amorphous than the "metanacrite–LiCl hybrid" phase, therefore it produces greater ionic conductivity. This shows that the conductivity was preferably affected by the amorphicity of the metanacrite framework through which mobile lithium ions may migrate.

*Si* <sup>2</sup>*Al* <sup>2</sup>*O*<sup>7</sup> <sup>⋅</sup> <sup>1</sup> <sup>2</sup> ⋅ *L i* <sup>2</sup>*O* hybrid's high conductivity (*σac*~ 10−2 S.m−1) makes it an excellent candidate as electrolyte solid for lithium-ion batteries. Furthermore, this amorphous-type Li-ion conductor offers several advantages such as low cost and ease of handling. Its use instead of the conventional superionic conductors can drastically improve the safety aspects of lithium batteries [30].

## **5. Concluding Remarks**

The structural and electrical properties of metanacrite synthesized from Tunisian nacrite were investigated in the first part of this work. The amorphous character of metanacrite was identified using XRD, IR, TEM, and EDXS analysis. Results of the electrochemical impedance spectroscopy show that the amorphous sample behaves like a semiconductor material. The present work gives possible valorization of Tunisian metanacrite as an interesting precursor to produce a new class of cementitious materials [29]. In the second part, structural experiments have been conducted in order to characterize the salt intercalation process between the nacrite layers. The stable intercalated material has been characterized by XRD, TG, and IR analyses. The XRD pattern showed basal spacing at 1.143± 0.002 nm with integral series of 00*l*reflections, indicating an ordered structure of parallel 1:1 layers. The quantitative XRD analysis showed that best agreement between the observed and simulated patterns (R*p* = 6.20%) was obtained with one Cl<sup>−</sup> ion at *z* = 0.64 ± 0.01 nm, one Li+ ion at *z* = 0.96 ± 0.01 nm and one H2O at *z* = 0.79 ± 0.01 nm in the interlamellar space of nacrite (per half-unit cell). The Li+ cation was located near the oxygen atom plane while the Cl<sup>−</sup> anion was near the hydroxyl groups of the adjacent layer. The TG analysis of the hybrid produced showed a loss of water between 723 and 873 K, the weight loss (1 molecule per half unit cell) corresponding to the interlamellar water, in agreement with that showed by XRD. The positions of the H2O molecules, Li+ and Cl<sup>−</sup> , suggest an interaction between Li+ and the basal oxygen on one side and Cl<sup>−</sup> and the surface hydroxyls on the other side. The H2O can establish binding either with Li+ cation or Cl<sup>−</sup> ions [49]. The investigation of the *ac* and *dc* conductivity of nacrite–LiCl hybrid suggests that the suppression in the degree of crystallinity of the elaborated hybrid improves dramatically the ionic con‐ duction, which is about ten orders of magnitude larger than the low temperature conductivity value. The activation energies for conduction measured at different temperatures indicate that the conduction mechanism is driven by hopping of Li+ ions from one site to the neighboring one [30].

Finally, Tunisian nacrite is a candidate for the production of metanacrite as a supplementary cementitious material and as a host material of nanohybrid owing to its high crystallinity and unique structure. Further studies are in progress to point out the use of nacrite to synthesize other materials for a wide range of applications.

## **Author details**

*4.5.2. Electrical Conductivity*

10−4 S.m−1 at 523 K to 0.13.

1.22.

Furthermore, Li+

migrate.

batteries [30].

<sup>2</sup> ⋅ *L i*

**5. Concluding Remarks**

*Si* <sup>2</sup>*Al* <sup>2</sup>*O*<sup>7</sup> <sup>⋅</sup> <sup>1</sup>

The *σdc* of nacrite–LiCl hybrid increases from (4.02.

144 Clays, Clay Minerals and Ceramic Materials Based on Clay Minerals

with the previous publication of Kumar and Yashonath [66, 30].

at 873 K. An Arrhenius behavior was observed for the hybrid. The *E*a(dc) was determined from the slope of log (*σdc*.*T*) versus(1000 /*T*) and was found to be 0.84 eV and 0.82 eV, respectively, below and above 673 K [30]. The obtained values suggest an ionic conduction process. The *ac* conductivity measurements at high frequencies (1 MHz) show that σac increases from

increase of the number of free ions in the hybrid matrix in terms of temperature [30]. The *E*a(ac), calculated in agreement with (Eq.(3)), corresponds to the free energy barrier that an ion has to overcome for a successful jump from one site to another. These values designate that the ionic transport mechanism can be interpreted by the thermally activated hopping process [72].

According to these experimental results, we deduce that the disordered hybrid bears easier motion than the ordered one [30]. We conclude that contribution of disorder and defects in the hybrid framework are responsible for the motion of charge carriers; this result is in agreement

byits smallionic radiusof 0.076nm,lowerweight, andeaseofmotion[66],butCl<sup>−</sup> anionappears to be rather less mobile than the cation due to its great ionic radius equal to 0.181 nm [66].

To conclude, Li+ is the common current carrier via hopping from one site to the next for both "metanacrite–LiCl hybrid" and "metanacrite–Li2O hybrid". Since the "metanacrite–Li2O hybrid" phase is more amorphous than the "metanacrite–LiCl hybrid" phase, therefore it produces greater ionic conductivity. This shows that the conductivity was preferably affected by the amorphicity of the metanacrite framework through which mobile lithium ions may

as electrolyte solid for lithium-ion batteries. Furthermore, this amorphous-type Li-ion conductor offers several advantages such as low cost and ease of handling. Its use instead of the conventional superionic conductors can drastically improve the safety aspects of lithium

The structural and electrical properties of metanacrite synthesized from Tunisian nacrite were investigated in the first part of this work. The amorphous character of metanacrite was identified using XRD, IR, TEM, and EDXS analysis. Results of the electrochemical impedance spectroscopy show that the amorphous sample behaves like a semiconductor material. The present work gives possible valorization of Tunisian metanacrite as an interesting precursor to produce a new class of cementitious materials [29]. In the second part, structural experiments have been conducted in order to characterize the salt intercalation process between the nacrite

is known as an excellent current carrying ion in superionic solids motivated

<sup>2</sup>*O* hybrid's high conductivity (*σac*~ 10−2 S.m−1) makes it an excellent candidate

10−6 S.m−1) at 523 K to the (0.11.

10−2 S.m−1 at 873 K. This remarkable increase is also related to the

10−2 S.m−1)

Nouha Jaafar\* , Hafsia Ben Rhaiem and Abdesslem Ben Haj Amara

\*Address all correspondence to: nouhajaafar@yahoo.fr

Laboratory of Physics of Lamellar Hybrid Materials and Nanomaterials, Department of Physics, Faculty of Sciences, Bizerte, University of Carthage, Tunis, Tunisia

## **References**


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[15] Ben Haj Amara A. X-ray diffraction, infrared and TGA/DTG analysis of hydrated na‐

[16] Ben Haj Amara A, Ben Brahim J, Besson G, Pons CH. Study of intercalated nacrite with dimethylsufoxide and n-methylacetamide. Clay Miner 1995;30:295–306.

[17] Ben Haj Amara A, Ben Brahim J, Ben Ayed N, Ben Rhaiem H. Occurence of nacrite in

[18] Ben Haj Amara A, Ben Brahim J, Plançon A, Ben Rhaiem H, Besson G. Etude Struc‐

[19] Ben Haj Amara A, Plançon A, Ben Brahim J, Ben Rhaiem H. XRD Study of the stack‐ ing mode in natural and hydrated nacrite. Mater Sci Forum 1998a;278–81:809–13.

[20] Ben Haj Amara A, Ben Brahim J, Plançon A, Ben Rhaiem H. X-Ray Diffraction study of the stacking modes of hydrated and dehydrated nacrite. J Appl Crystallograph

[21] Ben Haj Amara A, Ben Rhaiem H, Plançon, A. Structural evolution of nacrite as a function of the nature of the intercalated organic molecules. J Appl Crystallograph

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**Chapter 6**

## **Clay/Biopolymer Composite and Electrorheological Properties**

## Mehmet Cabuk

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relaxation parameters of some Ag+

chim Acta 2004;49:3595–602.

2013;111:108 –13.

Additional information is available at the end of the chapter

http://dx.doi.org/10.5772/62270

#### **Abstract**

The combination of clays with polymers having different characteristics opens a way to new composite materials showing novel properties. Electrorheological (ER) fluids show phase transition from a liquid to a solid-like state between the electrodes of a rheometer due to the interactions of polarized particles. Composite systems comprising biodegrada‐ ble chitosan (CS) and natural bentonite (BNT) are important in ER applications. In this study, BNT/CS composites were synthesized by the in situ method. The structure and morphology of the synthesized composites were characterized using X-ray diffraction (XRD), thermo-gravimetric analysis (TGA), and scanning electron microscopy (SEM) techniques. Thermal stability was observed to increase with the presence of BNT clay. Conductivity of the composites was found the suitable range for ER measurements. Ac‐ cording to ER results, BNT/CS composites were found to be sensitive to external electric field strength, exhibiting a typical shear thinning non-Newtonian viscoelastic behavior.

**Keywords:** Bentonite, clay/biopolymer composite, electrorheology, viscoelastic material

## **1. Introduction**

The combination of clays with polymers having different characteristics opens a way to new composite materials showing novel properties [1]. The clay component of the composites provides a potential for high carrier mobility; band gap tunability; a range of electric, magnetic, and dielectric properties; and thermal/mechanical stabilities. On the other hand, polymer component of the composites offers structural flexibility, convenient processing, and tunable electrical and electronic properties. A major attraction of such research activities is to combine these desired advanced properties in the organic/inorganic hybrid materials, which can even be improved in comparison with the intrinsic properties of each component. Various polymer/ clay composites can be synthesized via different preparation methods, including polymer

© 2016 The Author(s). Licensee InTech. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

intercalation into the layers of clays, in which clay minerals are offered various advantages such as high thermal stability, enhanced reinforcement, small particle size, layer expanding capabilities, and insolubility [2].

Bentonite (BNT) clays are largely composed of the mineral montmorillonite. It is constructed from octahedral alumina sheets sandwiched between two tetrahedral silicate sheets, which exhibit a net negative charge on the surface and can adsorb positive charges. BNT dispersions are widely used in industrial processes because of their exceptional rheological behavior. Compatibility with various polymers is accomplished by modifying the layers of BNT with surfactants via an ion-exchange reaction. When the BNT clay is exchanged with Na+ ion, it possesses an excellent swelling behavior in water, and interlayer spacing becomes large enough for the penetration of polymer chains [3].

## **2. Electrorheological fluids**

Electrorheological (ER) fluids are heterogeneous colloidal suspensions whose properties strongly depend on an externally applied electric field [4]. Commonly, these kinds of fluids are suspensions containing polarizable solid particles (dispersed phase) and non-conducting oils (continuous phase). When an electric field is imposed, suspended particles in the suspen‐ sion are polarized due to the mismatches of electrical conductivity and dielectric permittivity between the dispersed particles and the continuous phase. The ER fluid shows phase transition from a liquid to a solid-like state between the electrodes of a rheometer due to the interactions of polarized particles (Scheme 1). This solid-like fibrillation of particles is due to the electric field–induced increase in the apparent viscosity of suspensions [5].

**Sheme 1.** ER response of clay/biopolymer composite particles dispersed in silicone oil.

According to chemical contents of ER suspensions, dispersed phase can be composed of organic (i.e. polymer) or inorganic (i.e. clay) particles [6]. Composite systems comprising natural materials such as chitosan (CS) and BNT are important in ER applications. In addition, the synthesis and ER properties of composites containing different clay groups (montmoril‐ lonite, silica, etc.) were reported in the literature [7, 8].

#### **2.1. Synthesis of bentonite/chitosan composites**

intercalation into the layers of clays, in which clay minerals are offered various advantages such as high thermal stability, enhanced reinforcement, small particle size, layer expanding

Bentonite (BNT) clays are largely composed of the mineral montmorillonite. It is constructed from octahedral alumina sheets sandwiched between two tetrahedral silicate sheets, which exhibit a net negative charge on the surface and can adsorb positive charges. BNT dispersions are widely used in industrial processes because of their exceptional rheological behavior. Compatibility with various polymers is accomplished by modifying the layers of BNT with surfactants via an ion-exchange reaction. When the BNT clay is exchanged with Na+

possesses an excellent swelling behavior in water, and interlayer spacing becomes large

Electrorheological (ER) fluids are heterogeneous colloidal suspensions whose properties strongly depend on an externally applied electric field [4]. Commonly, these kinds of fluids are suspensions containing polarizable solid particles (dispersed phase) and non-conducting oils (continuous phase). When an electric field is imposed, suspended particles in the suspen‐ sion are polarized due to the mismatches of electrical conductivity and dielectric permittivity between the dispersed particles and the continuous phase. The ER fluid shows phase transition from a liquid to a solid-like state between the electrodes of a rheometer due to the interactions of polarized particles (Scheme 1). This solid-like fibrillation of particles is due to the electric

ion, it

capabilities, and insolubility [2].

**2. Electrorheological fluids**

enough for the penetration of polymer chains [3].

152 Clays, Clay Minerals and Ceramic Materials Based on Clay Minerals

field–induced increase in the apparent viscosity of suspensions [5].

**Sheme 1.** ER response of clay/biopolymer composite particles dispersed in silicone oil.

lonite, silica, etc.) were reported in the literature [7, 8].

According to chemical contents of ER suspensions, dispersed phase can be composed of organic (i.e. polymer) or inorganic (i.e. clay) particles [6]. Composite systems comprising natural materials such as chitosan (CS) and BNT are important in ER applications. In addition, the synthesis and ER properties of composites containing different clay groups (montmoril‐ This study was aimed at synthesizing BNT/CS composites by the intercalation method [9]. A definite amount of BNT [SiO2 (54.82%), Al2O3 (20.27%), Fe2O3 (9.08%), MgO (3.02%), CaO (2.10%), Na2O (1.31%), TiO2 (0.78%), and K2O (0.06%)] was dispersed in 1 wt.% acetic acid and stirred for 2 h with the presence of 0.1 g cetyltrimethylammonium bromide (CTAB) cationic surfactant. Then, a definite amount of CS [medium molecular weight (i.e. *M*¯ *w* = 190,000–300,000 g mol−1) with 75–85% deacetylation degree) that was dissolved in 1 wt.% acetic acid was added into the aqueous dispersions. The mixture was stirred for 12 h for the intercalation of CS chains between BNT layers. Then, the dispersion was transferred into a flask containing 0.5 M NaOH(aq) and stirred for 2 h for neutralization. It is known that CS is soluble in weak acids and insoluble in alkaline medium. The crude BNT/CS composite particles were recovered from NaOH(aq) solution and washed with distilled water until the particles were neutral. Finally, the BNT/CS composites obtained were dried in a vacuum oven at 60°C for 2 days. By this method, three different biodegradable BNT/CS composites were synthesized and coded as BNT/ CS(1%), BNT/CS(5%), and BNT/CS(25%).

#### **2.2. Electrorheological measurements**

Silicone oil (SO) was used in a continuous phase (*ρ* = 0.965 g/cm3 , *η* = 1 Pa s, *ε* = 2.61 at 25°C). The sample suspensions were prepared in SO at a series of concentrations (*c* = 5–25 wt.%), dispersing definite amount of dispersed phase in calculated amount of continuous phase (SO) according to formula (1):

$$\mathcal{L} = \left(\frac{m\_{\text{dispersed phase}}}{m\_{\text{dispersed phase}} + m\_{\text{continuous phase}}}\right) \times 100\tag{1}$$

ER properties of the suspensions were determined with a Termo-Haake RS600 parallel plate torque electrorheometer (Germany). The gap between the parallel plates was 1.0 mm, and the diameters of the upper and lower plates were 35 mm. The voltage used in these experiments was supplied by a 0–12.5 kV (with 0.5 kV increments) direct current electric field generator (Fug Electronics, HCL 14, Germany), which enabled the creation of resistivity during the experiments.

## **3. Results and discussion**

#### **3.1. Characterization results**

Average particle sizes, densities, and conductivities of the samples were given in Table 1. The diffraction pattern of BNT indicated the crystalline nature, whereas CS showed the amorphous nature. The XRD pattern of pure BNT has sharp peaks around 2θ = 8°, 18°, 21°, 26°, and 28° that are typical of BNT [10]. The XRD pattern of BNT/CS composites has peaks with relatively lower intensities than that of BNT. This indicates that the amorphous structure of CS covers the crystalline structure of BNT, which confirms the more amorphous nature of the composites. According to the TGA curves of the samples in contrast to pure CS, the residual amounts of the composites increased with increasing BNT content as follows: (89%)BNT > (86%)BNT/CS(1%) > (81%)BNT/CS(5%) > (57%)BNT/CS(25%) > (30%)CS. This tendency can be attributed to high thermal stability of the BNT component. These thermal stability results of BNT/CS composites are very suitable for potential and industrial applications as new ER materials [11]. According to the SEM results, CS chains not only intercalated inside the interlayer spaces of BNT but also settled on the surface of BNT layers (flocculated) [12]. The flocculated formation of the composites could be due to the hydroxylated edge–edge interaction of the silicate layers between the silicate hydroxylated edge groups and the CS chains.


**Table 1.** Some physical properties of the samples.

### **3.2. Electrorheological properties**

The electric field viscosities of BNT/CS/SO suspensions increased with increasing electric field strength and reached to 470, 980, 550, and 515 Pa s under *E* = 1 kV/mm, respectively (Fig. 1). BNT/SO ER fluid exhibited to enhance ER effect with applied electric field to improve the particles' polarization ability and a typical shear thinning non-Newtonian viscoelastic behavior [13]. When *E* was applied to the ER suspension, the magnitude of the polarization forces between particles increased and the particles rapidly formed fibrillar structure perpen‐ dicular to the electrodes, which resulted in enhanced electric field–induced viscosity.

For the composites, the highest electric field viscosity (980 Pa s) was obtained for BNT/CS(1%)/ SO suspension under *E* = 1 kV/mm, whereas the lowest electric field viscosity (515 Pa s) was obtained for BNT/CS(25%)/SO suspension under the same field strength. This result may be attributed to a decrease in the mutual action between the particles due to increasing particle size or BNT content, which reduces the possibility of the formation of strong chains between the upper and lower electrodes. Shear stress is one of the critical design parameters in ER phenomenon. The change of electric field–induced shear stress (τ*E*) of the suspensions increased with the increasing electric field strength as follows: (190 Pa)BNT/CS(1%) > (118 Pa)BNT/ CS(5%) > (95 Pa)BNT/CS(25%) > (88 Pa)BNT under *E* = 1 kV/mm.

lower intensities than that of BNT. This indicates that the amorphous structure of CS covers the crystalline structure of BNT, which confirms the more amorphous nature of the composites. According to the TGA curves of the samples in contrast to pure CS, the residual amounts of the composites increased with increasing BNT content as follows: (89%)BNT > (86%)BNT/CS(1%) > (81%)BNT/CS(5%) > (57%)BNT/CS(25%) > (30%)CS. This tendency can be attributed to high thermal stability of the BNT component. These thermal stability results of BNT/CS composites are very suitable for potential and industrial applications as new ER materials [11]. According to the SEM results, CS chains not only intercalated inside the interlayer spaces of BNT but also settled on the surface of BNT layers (flocculated) [12]. The flocculated formation of the composites could be due to the hydroxylated edge–edge interaction of the silicate layers between the

**Density**

**(g cm−3) Average particle size ((m)**

silicate hydroxylated edge groups and the CS chains.

**(S cm−1) × 10<sup>5</sup>**

CS 5.88 1.035 65 BNT 1.51 1.245 11 BNT/CS(1%) 1.01 1.158 14 BNT/CS(5%) 1.71 1.122 23 BNT/CS(25%) 3.45 1.116 51

The electric field viscosities of BNT/CS/SO suspensions increased with increasing electric field strength and reached to 470, 980, 550, and 515 Pa s under *E* = 1 kV/mm, respectively (Fig. 1). BNT/SO ER fluid exhibited to enhance ER effect with applied electric field to improve the particles' polarization ability and a typical shear thinning non-Newtonian viscoelastic behavior [13]. When *E* was applied to the ER suspension, the magnitude of the polarization forces between particles increased and the particles rapidly formed fibrillar structure perpen‐

For the composites, the highest electric field viscosity (980 Pa s) was obtained for BNT/CS(1%)/ SO suspension under *E* = 1 kV/mm, whereas the lowest electric field viscosity (515 Pa s) was obtained for BNT/CS(25%)/SO suspension under the same field strength. This result may be attributed to a decrease in the mutual action between the particles due to increasing particle size or BNT content, which reduces the possibility of the formation of strong chains between the upper and lower electrodes. Shear stress is one of the critical design parameters in ER phenomenon. The change of electric field–induced shear stress (τ*E*) of the suspensions increased with the increasing electric field strength as follows: (190 Pa)BNT/CS(1%) > (118 Pa)BNT/

dicular to the electrodes, which resulted in enhanced electric field–induced viscosity.

**Samples Conductivity**

154 Clays, Clay Minerals and Ceramic Materials Based on Clay Minerals

**Table 1.** Some physical properties of the samples.

CS(5%) > (95 Pa)BNT/CS(25%) > (88 Pa)BNT under *E* = 1 kV/mm.

**3.2. Electrorheological properties**

**Figure 1.** Effect of electric field strength on viscosity, K1: BNT/CS(1%), K5 : BNT/CS(5%), and K25 : BNT/CS(25%), (T = 25°C, *c* = 25 wt.%, and *γ*˙ = 0.2 s−1).

**Figure 2.** Change in G′ and G″ with frequency, K1: BNT/CS(1%), K5 : BNT/CS(5%), and K25 : BNT/CS(25%), (*c* = 25 wt. %, T = 25°C, τ = 10 Pa, and *E* = 1 kV/mm).

The external frequency is an essential factor for characterizing the dynamic viscoelastic properties of ER fluids. Storage modulus (G′) and loss modulus (G″) values of CS/SO, BNT/SO and BNT/CS/SO suspensions slightly increased with increasing frequency (Fig. 2). These variations in G′ and G″ correspond to energy change occurring during dynamic shear process and are strongly dependent on the interactions between CS chains and BNT layer interphases in the suspension [14].

The G′ values of the prepared suspensions are higher than G″ values. According to this result, strong interactions were developed between CS and BNT interphases, which enhance the elastic properties of these composites.

In conclusion, characterization results confirmed the introduction of the CS side chains into the BNT layers. ER activities of the suspensions increased with increasing electric field strength, dispersing particle concentration, and decreasing shear rate. Viscoelastic properties of the suspensions enhanced due to the interactions between BNT and CS. BNT-based ER fluids with improved ER and viscoelastic behaviors could be a good candidate as a smart material for ER applications.

## **Author details**

## Mehmet Cabuk\*

Address all correspondence to: mehmetcabuk@sdu.edu.tr; mhmtcbk@gmail.com

Department of Chemistry, Faculty of Arts and Sciences, Süleyman Demirel University, Isparta, Turkey

## **References**


[5] Wu S. & Shen J. (1996) Electrorheological properties of chitin suspensions, *Journal of Applied Polymer Science,* 60, 2159–2164.

The external frequency is an essential factor for characterizing the dynamic viscoelastic properties of ER fluids. Storage modulus (G′) and loss modulus (G″) values of CS/SO, BNT/SO and BNT/CS/SO suspensions slightly increased with increasing frequency (Fig. 2). These variations in G′ and G″ correspond to energy change occurring during dynamic shear process and are strongly dependent on the interactions between CS chains and BNT layer

The G′ values of the prepared suspensions are higher than G″ values. According to this result, strong interactions were developed between CS and BNT interphases, which enhance the

In conclusion, characterization results confirmed the introduction of the CS side chains into the BNT layers. ER activities of the suspensions increased with increasing electric field strength, dispersing particle concentration, and decreasing shear rate. Viscoelastic properties of the suspensions enhanced due to the interactions between BNT and CS. BNT-based ER fluids with improved ER and viscoelastic behaviors could be a good candidate as a smart material

Address all correspondence to: mehmetcabuk@sdu.edu.tr; mhmtcbk@gmail.com

*Journal of Fuel Chemistry and Technology,* 37, 489–495.

*Materials Chemistry and Physics*, 130 (3), 956–961.

*Identification.* Mineralogical Society, London.

Department of Chemistry, Faculty of Arts and Sciences, Süleyman Demirel University,

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156 Clays, Clay Minerals and Ceramic Materials Based on Clay Minerals

elastic properties of these composites.

for ER applications.

**Author details**

Mehmet Cabuk\*

Isparta, Turkey

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