*Recent Advances in Applications of Ceramic Nanofibers DOI: http://dx.doi.org/10.5772/intechopen.97118*

*Nanofibers - Synthesis, Properties and Applications*

**60**

**Ceramic nanofiber composition**

TiO2

ZrO2

SiC SiC-Si

N3

4/graphite SiC/ZrC/SiZrOC nanofibers

SiC/C ZrC/SiC

SiO2 mullite SiO2/aluminoborosilicate nanofibrous

aerogels

electrospinning, calcination

thermal insulation materials

at 600, 800, 1000, and

1200°C

electrospinning, calcination

thermal insulation materials

between 900 and 1500°C

electrospinning, calcination

thermal insulation materials

at 900°C

electrospinning, calcination

EMI shielding

at 1300-1500°C

electrospinning, calcination

EMI shielding

at 1400°C

electrospinning, calcination

EMI shielding

at 1400 and 1500°C

electrospinning, calcination

EMI shielding

at 800, 1300, 1400, and

1500°C

**Processes**

**Potential**

**Important**

**Ref.**

[67]

**results**

calcination temperature dependent phase,

Pd on anatase TiO2 could be used to catalyze the Suzuki

coupling reactions and operated in a continuous flow fashion,

nitric acid treatment provided reactivation

flexible, hydrophobic, corrosion resistant, and thermally stable

[75]

nanofibers with excellent EMI shielding properties with an

effective absorption bandwidth of 4–18 GHz

nanofibers annealed at 1300°C in Ar showed a RLmin of −57.8 dB

[76]

at 14.6 GHz with EAB of 5.5 GHz,

nanofibers annealed at 1300°C in N2 exhibited a RLmin of

−32.3 dB with EAB of 6.4 GHz over the range of 11.3–17.7 GHz

[72]

reasonable electrical

conductivity microwave-absorbing

capability RLmin of about −40.38 dB at 14.1 GHz,

antioxidant properties at 600°C

lightweight and high EMI shielding efficiency,

[73]

an ultrathin paraffin matrix with 30 wt.% SiC/C nanofibers

exhibited superior EM wave absorption performance

(RL < −10 dB) over the range of 12.6 and 16.7 GHz

Flexible, lightweight nanofiber mats,

[74]

3-layer ZrC/SiC nanofiber mats with a thickness of 1.8 mm

showed EMI shielding effectiveness (SET) of 18.9 dB, further

improved to 20.1 dB at 600°C

ultra-softness, enhanced tensile strength,

[77]

ultra-low thermal conductivity of 0.0058 W m − 1 K − 1

diphasic nanofibers with average diameter of 216 ± 40 nm

flyweight densities of >0.15 mg cm − 3, zero Poisson's ratio,

rapid recovery from 80% strain, and temperature-invariant

superelasticity up to 1100°C, robust fire resistance and thermal

insulation performance

[79]

[78]

**applications**

catalytic system for Suzuki

cross-coupling reactions

**applied**

electrospinning, calcination

at 510, 550, and 800°C

electrospinning, calcination

EMI shielding

at 1350°C

**Table 1.**

*Ceramic nanofibers by electrospinning method and their applications.*

#### **3.1 Tissue engineering applications**

Tissue engineering scaffolds are often made of biodegradable polymeric materials. The biodegradable polymeric scaffolds are not widely used in regeneration of load-bearing bones due to their limited mechanical strength. There have been many efforts invested to enhance the mechanical properties of the scaffolds, i.e., CNFs, reinforced by hydroxyapatite (HA), have provided mechanical support and osteoconductivity to the growing cells in bone regeneration.

Wu et al. [36] electrospun a precursor mixture of Ca(NO3)2·4H2O and (C2H5O)3PO with a polymer additive, then applied thermal treatment at 600°C for 1 h and prepared HA (Ca10(PO4)6(OH)2) fibers. The pure fibers obtained were 10–30 μm in diameter and up to 10 mm in length. The HA grain size was ~1 μm [36]. Kim and Kim produced HA nanofibers and also their fluoridated forms for dental restoration applications to stimulate bone cell responses and provide protection against the formation of dental caries [44]. Xiaoshu and Shivkumar [35] electrospun nanofibers from polyvinyl alcohol (PVA) solution containing calcium phosphate-based sol and then calcined them at 600°C for 6 h to obtain an inorganic, fibrous network, which was suggested for use in the tissue engineering and drug delivery [35]. Franco et al. used phosphorus pentoxide (P2O5) and calcium nitrate tetrahydrate (Ca (NO3)2.4H2O) as precursors of phosphorus and calcium and polyvinylpyrrolidone (PVP) as the polymer to electrospin CNFs [43]. Wang et al. [45] electrospun pure titanium dioxide (TiO2) nanofiber meshes with different surface microroughness and nanofiber diameters and investigated the osteoblast differentiation on these meshes by analyzing the cell number, differentiation markers and local factor production for MG63 cells seeded on TiO2 meshes. Cells with similar morphology were observed to grow throughout the entire surfaces. While the cell number was found to be sensitive to surface microroughness, the cell differentiation and local factor production were observed to be regulated by both surface roughness and nanofiber diameter. These results indicated that the TiO2 nanofiber meshes could be used to create an osteogenic environment without using exogenous factors [45]. Aly et al. [46] developed wollastonite glass ceramic composites reinforced by electrospun TiO2 nanofibers for use in hard tissue engineering applications. The composite material exhibited greater densification and better mechanical characteristics in comparison to pure wollastonite. The composites having 0, 10, 20 and 30 wt.% metal oxide nanofibers were sintered at 900, 1100 and 1250°C. While the compressive strength, bulk density, and microhardness increased, the water adsorption capacity and porosity decreased with the increase in the TiO2 nanofiber content. When the wollastonite and wollastonite/TiO2 nanofibers were soaked in simulated body fluid, bone-like apatite was formed on their surface. The characteristics of wollastonite were improved with incorporation of TiO2 nanofibers while its in-vitro bioactivity was preserved. The developed composite was suggested for use as a bone substitute in high load bearing sites [46]. Nagarajan et al. [47] produced boron nitride-reinforced gelatin nanofibers as a new class of two-dimensional biocompatible nanomaterials, showing enhanced mechanical properties, stability to the glutaraldehyde cross-linking, high bioactivity in forming bone-like HA, and biodegradability. Depending on the analysis of osteoblast gene expression and the measurement of alkaline phosphatase activity, they were proven to be suitable for bone tissue engineering applications [47].

Apart from the use of CNFs in bone tissue engineering applications, Du et al. [42] recently fabricated highly aligned, zirconia-based, shape memory nanofiber yarns and springs by electrospinning for artificial muscle applications at elevated temperatures. The nanofiber yarns displayed a recoverable strain of up to ~5% and short recovery time (0.16 s) at actuation temperatures of 328–388°C. When heated

**63**

*Recent Advances in Applications of Ceramic Nanofibers DOI: http://dx.doi.org/10.5772/intechopen.97118*

and some other polymer-based artificial muscles [42].

and a low humidity dependence [31].

**3.2 Gas sensors**

performance.

by a Bunsen burner, the shape memory ceramic springs could lift up to 87 times their own weight with a stroke of ~3.9 mm. The ceramic yarns/springs exhibited an output stress of 14.5–22.6 MPa, a work density of ~15–20 kJ m−3, and a tensile strength of ~100–200 MPa, which were much higher than those of human muscles

Sensors, which are used to monitor and quantify volatiles related to environmental monitoring, analyze food quality, and diagnose illnesses, have attracted great interest in the recent years. Sensors designed are required to display high selectivity, low power consumption, fast response/recovery rate, low detection limit

The ceramic nanofibers have been extensively studied for gas sensing applica-

tions due to their advantages such as good directional carrier transport, high surface energy, large surface-to-volume ratio, high chemical stability, great sensing performance. Ceramics are inherently resistant to aggressive physical and corrosive chemical circumstances and they offer significantly minimized hysteresis with increased relaxation time, which improves the stability, performance, and response time of pressure sensors [87]. Many researchers showed the applicability of electrospun ceramic nanofibers in gas sensing applications for detection of many different gases such as acetone [34, 49, 88–97], ethanol [98–101], formaldehyde [102], ammonia [103–107], hydrogen sulfide [108], nitrogen dioxide [109–111], acetic acid [112], carbon monoxide [113, 114], hydrogen [115], and toluene [116]. The sensing properties of metal oxides depend on their shape, size, size distribution, surface area, structure, phase, the grain size, crystallinity, the presence of crystal lattice defects, the type of the charge carriers, and the oxidizing or reducing nature of the target gas [31, 117–120]. Besides, the composition of the sensor is another important factor. The most effective methods for improving response time and sensitivity are (i) doping with different metals such as Ce, Cu, Pr, La, Pd, Mn [91, 94, 106, 112, 114, 121], (ii) formation of composites by coupling of two or more oxide metals [118, 119, 122–124], and (iii) addition of graphene [125–127]. For gas sensors made up of ceramic nanofibers, the composition and the nanofiber configuration are other important characteristics that can be controlled to improve the sensor

Liu et al. [32] prepared polycrystalline CeO2 nanofibers by combination of electrospinning and calcination. The average diameter of the nanofibers was measured as 376 ± 55 nm. They displayed good morphological and structural stability at high temperatures (800–1000°C) and showed reversible, sensitive, and reproducible response when used for real-time oxygen (O2) and carbon monoxide (CO) monitoring at 800°C and 1000°C, respectively [32]. Tong et al. [49] prepared acetone sensors based on LnFeO3 (Ln = La, Nd, and Sm) nanofibers produced by electrospinning and investigated the effect of lanthanide on acetone sensing properties of the nanofibers at different temperatures and acetone concentrations. The results indicated that the lanthanides significantly affected the sensing properties of LnFeO3. When exposed to 100 ppm acetone at 140°C, the SmFeO3 sensor exhibited the largest sensing response (Response = 9.98). The response and recovery times for the SmFeO3 sensor were about 17 and 16 s, respectively [49]. Ma et al. [34]prepared hollow perovskite praseodymium ferrite (PrFeO3) nanofibers via electrospinning followed by calcina-

characteristics. They showed good selectivity, long-time stability at 180°C, and high response value. While the response time of the sensor to 10 ppm acetone was about 4 s, the recovery time was measured as 4 s. [34]. Teli and Nadathur [48] prepared

g−1) with mesoporous

tion. The samples had a large specific surface area (33.74 m2

by a Bunsen burner, the shape memory ceramic springs could lift up to 87 times their own weight with a stroke of ~3.9 mm. The ceramic yarns/springs exhibited an output stress of 14.5–22.6 MPa, a work density of ~15–20 kJ m−3, and a tensile strength of ~100–200 MPa, which were much higher than those of human muscles and some other polymer-based artificial muscles [42].
