**3. Results and discussion**

### **3.1 Open-circuit potential measurements**

Open-circuit potential, Eoc, changes were measured against a standard saturated calomel electrode placed in the same compartment. The recycled aluminum alloy was immersed in the culinary media exposing a circular area of about 3.46 cm<sup>2</sup> . A copper wire was soldered at the rear of the electrode which was housed in a glass tube to protect it from the test culinary media. Results of the open circuit

**41**

**Figure 1.**

*Electrochemical Impedance Spectroscopy (EIS) Characterization of Kitchen Utensils Used…*

potential (Eoc) are shown in **Figure 1**. In the curve (**Figure 1**), a rapid increase of the open circuit potential was observed followed by a decrease of the value in the two culinary media. Open-circuit potential was studied for 15 min of cooking in the various culinary media. From the curve, a rapid increase of the open-circuit potentials followed by a decreasing of the value in the two culinary media (salt

vary toward higher values during the first 150 seconds of cooking but after that, an almost decrease of the potential is observed. In this case, we can observe the aluminum passivation tendency which could have many forms: passivation caused by hydroxides which are absorbed at the metal surface, that caused by absorption of

A comparison of the behavior of recycled alloy in the media (broken rice and salt water) indicated that significantly higher corrosion potential was recorded in the salt water compared to broken rice media. This could be explained by their negative effect susceptible of influencing the passivation during the first minutes of cooking. According to literatures, the presence of chloride ions in study media could compete with media hydroxides ions when absorbed at the surface, allowing a localized corrosion and then a deterioration of the passive film [13]. In order to understand more about the existing behavior for metal/media in the cooking media, a series of curves was set out by electrochemical impedance spectroscopy in the

Behavior to corrosion from recycled alloy in the two cooking media simulating a similar process to Burkina Faso cooking habit was studied by electrochemical impedance spectroscopy at 100°C and different cooking times. The frequency ranged from 100 KHz to 100 mHz, and the amplitude was set at 10 mV. Nyquist and Bode plots were used in broken rice media and that of salt water titrated at 3 g.L<sup>−</sup><sup>1</sup> and up to boiling temperature after various cooking times in an open-circuit. Data

the existing components of the two cooking media or their combination.

**3.2 Electrochemical impedance spectroscopy (EIS) measurements**

*Open-circuit potential for recycled aluminum alloy in salt water and broken rice.*

context of comparative study in the different media.

and broken rice) were observed. It can be noticed that these curves

*DOI: http://dx.doi.org/10.5772/intechopen.90877*

water at 3 g.L<sup>−</sup><sup>1</sup>

*Electrochemical Impedance Spectroscopy (EIS) Characterization of Kitchen Utensils Used… DOI: http://dx.doi.org/10.5772/intechopen.90877*

potential (Eoc) are shown in **Figure 1**. In the curve (**Figure 1**), a rapid increase of the open circuit potential was observed followed by a decrease of the value in the two culinary media. Open-circuit potential was studied for 15 min of cooking in the various culinary media. From the curve, a rapid increase of the open-circuit potentials followed by a decreasing of the value in the two culinary media (salt water at 3 g.L<sup>−</sup><sup>1</sup> and broken rice) were observed. It can be noticed that these curves vary toward higher values during the first 150 seconds of cooking but after that, an almost decrease of the potential is observed. In this case, we can observe the aluminum passivation tendency which could have many forms: passivation caused by hydroxides which are absorbed at the metal surface, that caused by absorption of the existing components of the two cooking media or their combination.

A comparison of the behavior of recycled alloy in the media (broken rice and salt water) indicated that significantly higher corrosion potential was recorded in the salt water compared to broken rice media. This could be explained by their negative effect susceptible of influencing the passivation during the first minutes of cooking. According to literatures, the presence of chloride ions in study media could compete with media hydroxides ions when absorbed at the surface, allowing a localized corrosion and then a deterioration of the passive film [13]. In order to understand more about the existing behavior for metal/media in the cooking media, a series of curves was set out by electrochemical impedance spectroscopy in the context of comparative study in the different media.

#### **3.2 Electrochemical impedance spectroscopy (EIS) measurements**

Behavior to corrosion from recycled alloy in the two cooking media simulating a similar process to Burkina Faso cooking habit was studied by electrochemical impedance spectroscopy at 100°C and different cooking times. The frequency ranged from 100 KHz to 100 mHz, and the amplitude was set at 10 mV. Nyquist and Bode plots were used in broken rice media and that of salt water titrated at 3 g.L<sup>−</sup><sup>1</sup> and up to boiling temperature after various cooking times in an open-circuit. Data

**Figure 1.** *Open-circuit potential for recycled aluminum alloy in salt water and broken rice.*

*Electrochemical Impedance Spectroscopy*

Ascorbic acid 2%

Complete distilled water (ml)

Al concentration (mg/L)

*Composition of standard scale.*

(ml)

**Table 2.**

**Control sample**

protective coatings. Within short testing times, EIS measurements provide reliable data, allowing for the prediction of the long-term performance of the coatings. The result of EIS is the impedance of the electrochemical system as a function of frequency. EIS is a versatile testing procedure and can be performed under different conditions of stress, depending on the performance of the tested coatings. Electrochemical impedance spectroscopy (EIS) is a powerful technique that utilizes a small amplitude, alternating current (AC) signal to probe the impedance characteristics of a cell. The AC signal is scanned over a wide range of frequencies to generate an impedance spectrum for the electrochemical cell under test. EIS differs from direct current (DC) techniques in that it allows the study of capacitive, induc-

Volume of S0 (ml) 0 0.08 1.6 3.2 4 5 6.25 6.5 7.5 9 10 12.5 Distilled water 10 10 10 10 10 10 10 10 10 10 10 10 EBT (ml) 5 5 5 5 5 5 5 5 5 5 5 5 Buffer pH = 6 (ml) 15 15 15 15 15 15 15 15 15 15 15 15

**S2 S3 S4 S5 S6 S7 S8 S9 S10 S11 S12**

1 1 1 1 1 1 1 1 1 1 1 1

50 50 50 50 50 50 50 50 50 50 50 50

0 0.016 0.032 0.64 0.8 0.1 1.25 1.3 1.5 1.8 2 2.5

The electrochemical measurements were conducted in the Analytical Chemistry and Interfacial Chemistry (CHANI) of the University of Brussels (ULB). The EIS measurements were determined in a three electrodes electrochemical cell containing the culinary media. There are three electrodes – the reference electrode, the auxiliary electrode, and the working electrode. A saturated calomel electrode (SCE) was used as the reference electrode, a platinum metal gate as the auxiliary electrode, and a recycled aluminum alloy as working electrode (WE) made in the laboratory. The EIS measurements were performed with employed Princeton Applied Research potentiostat (model PGSTAT 50). A microcomputer was used for data acquisition.

Open-circuit potential, Eoc, changes were measured against a standard saturated calomel electrode placed in the same compartment. The recycled aluminum alloy was immersed in the culinary media exposing a circular area of about 3.46 cm<sup>2</sup>

A copper wire was soldered at the rear of the electrode which was housed in a glass tube to protect it from the test culinary media. Results of the open circuit

.

tive, and diffusion processes taking place in the electrochemical cell.

The measurements were carried out after 60 minutes of cooking.

**2.6 Electrochemical measurements**

**3. Results and discussion**

**3.1 Open-circuit potential measurements**

**40**

acquisition and analysis were performed with microcomputer. The spectra were interpreted using the ZSimpWin program. These measures were performed in five replicates to ensure the results reproducibility.

## **3.3 Effect of cooking times**

Measuring electrochemical impedance consists in studying the response of the electrochemical system, due to disturbance which is most often a low amplitude double signal. The strength of this technique is to differentiate the reaction phenomena from their relaxation times. Only quick processes are characterized in high frequencies; when the applied frequency decreases, appears the contribution of slower steps as transport phenomena or solution diffusion. To evaluate the behavior of the passive layer in various culinary media, the sample of aluminum alloy was immersed continuously for 60 minutes (00, 15, 30, and 60 minutes) for broken rice and salt water. During these cooking times, only measurements of impedances have been regularly performed since they do not disturb the system. Nyquist graph (**Figures 2** and **3**) illustrates the experimental impedance diagrams to corrosion potential obtained from the aluminum alloy in the studied culinary media. Indeed, **Figure 3** shows a progressive decrease in the size of the impedance spectrum in a more or less flattened half circle shape, characterizing the formation of the protective layer (alumina Al2O3). This leads to a decrease of the total recycled aluminum resistance with regards to the cooking time. In contrast to the salt water media, the broken rice media (**Figure 2**) show an increase in the spectra size, confirming the sample resistance of the media [14]. We find a phase difference with respect to axis of real (**Figures 2** and **3**), which may be explained by the surface none-homogeneity. However, for a better correlation between the experimental data and simulation, we introduced into the procedure for calculating a constant phase element and the surface none-homogeneity is realized through this constant phase element as follows (Eq. 1) [15–18].

Despite a constant phase element being utilized for data fitting instead of an ideal capacitor, since n values obtained from data fitting were in the range from 0.85 to 0.95, the value obtained from data fitting was taken as the capacitance (Eq. (1)).

$$Z\_{\rm CPE} = \mathbb{C} \left[ \left( \text{j}\alpha \right) \right]^{\cdot \cdot \mathbb{n}} \tag{1}$$

*ZCPE* = the impedance of the CPE;

CPE: constant phase element.

*C* = the capacitance associated to an ideal capacitor;

*j* = the complex imaginary number;

*ω* = the angular frequency and

$$\mathbf{-1} \text{ (n/ 1)}$$

When n = 1, CPE is an ideal capacitor (Eq. (2)) [19, 20].

$$Z\_{dc} = \mathbb{C}\left[\left(\text{jo}\right)\right]^{-1} \tag{2}$$

**43**

**Figure 3.**

**Figure 2.**

*Electrochemical Impedance Spectroscopy (EIS) Characterization of Kitchen Utensils Used…*

*DOI: http://dx.doi.org/10.5772/intechopen.90877*

*Nyquist plots for recycled aluminum alloy tested in broken rice media.*

*Nyquist plots for recycled aluminum alloy tested in salt water media.*

*Zdc* = double layer capacitance.

A true capacitive behavior is rarely obtained. The n values close to 1 represent the deviation from the ideal capacitive behavior [21].

The best simulation is obtained from the use of equivalent circuit proposed for metal/electrolyte interface and illustrated in **Figure 4**. This equivalent circuit was

*Electrochemical Impedance Spectroscopy (EIS) Characterization of Kitchen Utensils Used… DOI: http://dx.doi.org/10.5772/intechopen.90877*

**Figure 2.** *Nyquist plots for recycled aluminum alloy tested in broken rice media.*

**Figure 3.** *Nyquist plots for recycled aluminum alloy tested in salt water media.*

*Electrochemical Impedance Spectroscopy*

**3.3 Effect of cooking times**

follows (Eq. 1) [15–18].

*ZCPE* = the impedance of the CPE; CPE: constant phase element.

*j* = the complex imaginary number; *ω* = the angular frequency and

*Zdc* = double layer capacitance.

‐1 〈 n 〈 1

the deviation from the ideal capacitive behavior [21].

*C* = the capacitance associated to an ideal capacitor;

When n = 1, CPE is an ideal capacitor (Eq. (2)) [19, 20].

*Zdc* = C

[(jω)]

A true capacitive behavior is rarely obtained. The n values close to 1 represent

The best simulation is obtained from the use of equivalent circuit proposed for metal/electrolyte interface and illustrated in **Figure 4**. This equivalent circuit was

replicates to ensure the results reproducibility.

acquisition and analysis were performed with microcomputer. The spectra were interpreted using the ZSimpWin program. These measures were performed in five

Measuring electrochemical impedance consists in studying the response of the electrochemical system, due to disturbance which is most often a low amplitude double signal. The strength of this technique is to differentiate the reaction phenomena from their relaxation times. Only quick processes are characterized in high frequencies; when the applied frequency decreases, appears the contribution of slower steps as transport phenomena or solution diffusion. To evaluate the behavior of the passive layer in various culinary media, the sample of aluminum alloy was immersed continuously for 60 minutes (00, 15, 30, and 60 minutes) for broken rice and salt water. During these cooking times, only measurements of impedances have been regularly performed since they do not disturb the system. Nyquist graph (**Figures 2** and **3**) illustrates the experimental impedance diagrams to corrosion potential obtained from the aluminum alloy in the studied culinary media. Indeed, **Figure 3** shows a progressive decrease in the size of the impedance spectrum in a more or less flattened half circle shape, characterizing the formation of the protective layer (alumina Al2O3). This leads to a decrease of the total recycled aluminum resistance with regards to the cooking time. In contrast to the salt water media, the broken rice media (**Figure 2**) show an increase in the spectra size, confirming the sample resistance of the media [14]. We find a phase difference with respect to axis of real (**Figures 2** and **3**), which may be explained by the surface none-homogeneity. However, for a better correlation between the experimental data and simulation, we introduced into the procedure for calculating a constant phase element and the surface none-homogeneity is realized through this constant phase element as

Despite a constant phase element being utilized for data fitting instead of an ideal capacitor, since n values obtained from data fitting were in the range from 0.85 to 0.95, the value obtained from data fitting was taken as the capacitance (Eq. (1)).

*Z*CPE = C [(jω)]

‐<sup>n</sup> (1)

−1 (2)

**42**

#### **Figure 4.**

*Equivalent circuit to aluminum alloy in the cooking food of Burkina Faso.*


*R, solution resistor; R1, polarization resistance; R2, oxide pore resistance; Q, constant phase; C, coating capacitance.*

#### **Table 3.**

*Electrical parameters of equivalent circuit obtained by fitting the experimental results of EIS tests.*

proposed by Zhang et al. [9] to describe the bi-layer oxide film formed on aluminum and aluminum corrosion aqueous media.

This circuit is valid for all determinations. In the equivalent circuit, R is the salt water and the broken rice resistance, R1 is the resistance to polarization, C is the corresponding capacity to the dense oxide layer, R2 is the resistance in porous oxide position, and Q is the corresponding component of the constant phase to porous oxide positions. The results of the parameters in the equivalent circuit are shown in **Table 3**.

For the recycled aluminum alloy, different resistivity profiles in both media, regardless of the cooking time are observed as the impedance diagrams vary with the immersion time (**Figures 5** and **6**). It shows that parameters in the salt water media decrease in contrast to those in broken rice media for different cooking times up to 60 minutes. This behavior may be associated with physicochemical variations which occurred in the oxide film (alumina) during cooking in the salt water media (penetration of the electrolyte into the oxide layer and hydration of alumina) containing chloride ions. Comparison of the curves (**Figures 5** and **6**) clearly shows that resistivities in the layer alumina developed on the alloy recycled aluminum are higher in the broken rice media than those in the salt water. This could be explained by the presence of a more homogeneous and dense layer for the recycled aluminum in the media and also that of chloride ions in the salt water. Because, the behavior of interface/media is completely different with the latter. The overall behavior is reflected in the impedance diagram by a decrease in

**45**

**Figure 6.**

**Figure 5.**

*Electrochemical Impedance Spectroscopy (EIS) Characterization of Kitchen Utensils Used…*

*DOI: http://dx.doi.org/10.5772/intechopen.90877*

*Bode plots spectra for recycled aluminum alloy tested in broken rice media.*

*Bode plots spectra for recycled aluminum alloy tested in salt water media.*

*Electrochemical Impedance Spectroscopy (EIS) Characterization of Kitchen Utensils Used… DOI: http://dx.doi.org/10.5772/intechopen.90877*

**Figure 5.** *Bode plots spectra for recycled aluminum alloy tested in broken rice media.*

**Figure 6.** *Bode plots spectra for recycled aluminum alloy tested in salt water media.*

*Electrochemical Impedance Spectroscopy*

proposed by Zhang et al. [9] to describe the bi-layer oxide film formed on alumi-

*Electrical parameters of equivalent circuit obtained by fitting the experimental results of EIS tests.*

This circuit is valid for all determinations. In the equivalent circuit, R is the salt water and the broken rice resistance, R1 is the resistance to polarization, C is the corresponding capacity to the dense oxide layer, R2 is the resistance in porous oxide position, and Q is the corresponding component of the constant phase to porous oxide positions. The results of the parameters in the equivalent circuit are

**Media Times R C R1 Q n R2**

*Equivalent circuit to aluminum alloy in the cooking food of Burkina Faso.*

Broken rice 0 0.697 0.0017 0.3480 0.0048 0.73 75.4

Salt water 0 6.70.10-11 1.41.10-5 0.4474 0.0426 0.80 330.9

*R, solution resistor; R1, polarization resistance; R2, oxide pore resistance; Q, constant phase; C, coating capacitance.*

**(min) kΩ·cm2 F·cm<sup>−</sup><sup>2</sup> kΩ·cm2 S sn·cm<sup>−</sup><sup>2</sup> kΩ·cm2**

15 1.81.10-8 1.72.10-5 0.4830 0.0053 0.78 196.8 30 3.21.10-8 1.53.10-5 0.5364 0.0060 0.76 223.8 60 1.96.10-6 9.14.10-6 0.3061 0.0015 0.87 259.2

15 2.30.10-7 2.04.10-5 0.5586 0.0080 0.74 155.9 30 2.40.10-8 1.53.10-5 0.5366 0.0060 0.76 222.3 60 2.89.10-7 1.58.10-5 0.6573 0.0105 0.66 152.8

For the recycled aluminum alloy, different resistivity profiles in both media, regardless of the cooking time are observed as the impedance diagrams vary with the immersion time (**Figures 5** and **6**). It shows that parameters in the salt water media decrease in contrast to those in broken rice media for different cooking times up to 60 minutes. This behavior may be associated with physicochemical variations which occurred in the oxide film (alumina) during cooking in the salt water media (penetration of the electrolyte into the oxide layer and hydration of alumina) containing chloride ions. Comparison of the curves (**Figures 5** and **6**) clearly shows that resistivities in the layer alumina developed on the alloy recycled aluminum are higher in the broken rice media than those in the salt water. This could be explained by the presence of a more homogeneous and dense layer for the recycled aluminum in the media and also that of chloride ions in the salt water. Because, the behavior of interface/media is completely different with the latter. The overall behavior is reflected in the impedance diagram by a decrease in

num and aluminum corrosion aqueous media.

shown in **Table 3**.

**Table 3.**

**Figure 4.**

**44**

size of the capacitive phenomenon. This can be explained by the weakening and destruction of a film which is likely to be developed on the surface of the studied alloy allowing disappearance of the distribution phenomenon and the decrease of the resistance. These differences may be explained by the oxide layer composition developed on the alloy which is influenced by the chemical composition of material solid media and by the chemical composition of the intermetallic particles [22–24].

In conclusion, resistivity profiles obtained for recycled aluminum alloy showed that the oxide layer developed is less protective in the salt water media than the broken rice. This result would be bound to the zinc presence which would return this less resistant system [25–27]. The negative effect of chlorides in the salt water media are presented in **Table 3**. This result was translated by the decrease in the polarization resistance. There also appeared an increase in the capacity associated with the polarization resistance. This increase may reflect the dissolution of the recycled alloy in the salt water media. The polarization resistance stands for the sum of the dense oxide layer resistance and that of the two cooking media (salt water and broken rice) [28]. In this case, R2 is much larger than R1, therefore, it can be considered as the polarization resistance. **Table 3** illustrated the simulation parameters. It shows that the polarization resistance increases gradually with the increased cooking time up to 60 minutes for media broken rice while for the salt water media, a decrease is observed followed by a slight increase. Highest values of the polarization resistance in broken rice media as compared to the salt water can be explained partly by the chemical composition of the recycled alloy capable of modifying the physical and chemical properties of the oxide layer into more or less noble depending on the studied media, and second, by the resistance of the charge transfer (R) which is not identical for both media. **Figure 7** indicated a clear difference between the polarization resistance values from the two cooking media.

Observation **Figure 7** curves show that the sample from the broken rice media is less corroded than that from the salt water media. This confirmed the destructive effect of the salt water media on our sample [29, 30].

**47**

lar toxicological danger.

**4. Conclusions**

*Electrochemical Impedance Spectroscopy (EIS) Characterization of Kitchen Utensils Used…*

**Sample Times (min) WS WR** D 25°C 100°C 25°C 100°C

ddl 3 3 Probability <0.0001 <0.0001 Manning HS HS *Results are means of 3 replications; HS = high significant. Test Ryan-Einot-Gabriel-Welsch (REGWQ ), the difference* 

*Aluminum content measured in various cooking media of sample D after different contact times at room* 

1440 5,84i 5.24j

15 57.85h 52.39g 30 62.78e 56.82d 60 70.78a 64.24a

Aluminum content released after 30 and 60 minutes in various cooking media is

The same absorbance measured 30 and 60 minutes of cooking duration in the media WS (titrated at 3 g.L-1 of salt) has given more important result in the other media (WR) of study. The high quantity of aluminum in this media has been probably linked to the presence of chloride ion and also to environmental pH. This result is according to the study conducted by Bommersbach and Duggan [31, 32]. Similar increase of aluminum loss with the increase of alcohol-free drinks acidity package in the aluminum bottle. These contents are very comparable with those got using tape water, concentrated tomato, and media WR in the same conditions. Other minerals in the tape water added to chloride ion have a significant influence on aluminum leaching with local kitchen utensils. For media WR important contents of aluminum had been lost in the cooking media after 30–60 minutes in the four local kitchen utensils. These results are similar to those decrypted by some authors [33, 34], in cooking breaking rice (WR) found to be not aggressive operation for sample containing more silicon. Studies showed that concentrated tomatoes caused more effect on cooking utensils [35]. Acidity of this product is so probability equivalent to those of fresh tomatoes, that is surely again a consequence of their origin and mode of production. Contributions of water at room temperature and tomato are so low that aluminum quantities swallowed and are relatively independent form the proportion of rice water. But, toxicity norm by some authors [26, 36] do state of acceptable daily dose to 1 mg by kilogram of body weight for human. This dose is a maximal tolerable quantity by human organism above which aluminum became toxic for him [22, 37]. This simplified outcome showed that we are far from the critical threshold for which human health is in danger. From this study, we can conclude that kitchen cooking utensils in Burkina Faso have not involved in particu-

This study contributed to the characterization by electrochemical impedance spectroscopy of the local kitchen utensils used for cooking. From this study, we

*DOI: http://dx.doi.org/10.5772/intechopen.90877*

**3.4 Influence of media, WS, and WR**

*temperature (25°C) and at boiling temperature.*

*is not significant between values added by the same letter in the same line.*

given in **Table 4**.

**Table 4.**

**Figure 7.** *Polarization resistance according to cooking times.*

*Electrochemical Impedance Spectroscopy (EIS) Characterization of Kitchen Utensils Used… DOI: http://dx.doi.org/10.5772/intechopen.90877*


*Results are means of 3 replications; HS = high significant. Test Ryan-Einot-Gabriel-Welsch (REGWQ ), the difference is not significant between values added by the same letter in the same line.*

#### **Table 4.**

*Electrochemical Impedance Spectroscopy*

particles [22–24].

size of the capacitive phenomenon. This can be explained by the weakening and destruction of a film which is likely to be developed on the surface of the studied alloy allowing disappearance of the distribution phenomenon and the decrease of the resistance. These differences may be explained by the oxide layer composition developed on the alloy which is influenced by the chemical composition of material solid media and by the chemical composition of the intermetallic

In conclusion, resistivity profiles obtained for recycled aluminum alloy showed that the oxide layer developed is less protective in the salt water media than the broken rice. This result would be bound to the zinc presence which would return this less resistant system [25–27]. The negative effect of chlorides in the salt water media are presented in **Table 3**. This result was translated by the decrease in the polarization resistance. There also appeared an increase in the capacity associated with the polarization resistance. This increase may reflect the dissolution of the recycled alloy in the salt water media. The polarization resistance stands for the sum of the dense oxide layer resistance and that of the two cooking media (salt water and broken rice) [28]. In this case, R2 is much larger than R1, therefore, it can be considered as the polarization resistance. **Table 3** illustrated the simulation parameters. It shows that the polarization resistance increases gradually with the increased cooking time up to 60 minutes for media broken rice while for the salt water media, a decrease is observed followed by a slight increase. Highest values of the polarization resistance in broken rice media as compared to the salt water can be explained partly by the chemical composition of the recycled alloy capable of modifying the physical and chemical properties of the oxide layer into more or less noble depending on the studied media, and second, by the resistance of the charge transfer (R) which is not identical for both media. **Figure 7** indicated a clear difference between

Observation **Figure 7** curves show that the sample from the broken rice media is less corroded than that from the salt water media. This confirmed the destructive

the polarization resistance values from the two cooking media.

effect of the salt water media on our sample [29, 30].

**46**

**Figure 7.**

*Polarization resistance according to cooking times.*

*Aluminum content measured in various cooking media of sample D after different contact times at room temperature (25°C) and at boiling temperature.*
