Silicon carbide nanofibers

SiC nanofibers were synthesized by Honda et cd. on Si substrates covered by Ni thin films using high-power microwave plasma CVD under hydrogen gas [117]. The resultant fibrous material was identified as (3-SiC with a high crystallinity. SiC nanofibers were also fabricated by these authors using the VLS mechanism, in which SiC is precipitated from supersaturated liquid Ni nanoballs. 

Huczko et al. synthesized P-SiC nanofibers via the dehalogenation of various alkyl- and acryl-halides with Si-containing compounds [118]. The combustion process resulted in SiC nanofibers and nanotubes 20-100 nm in diameter, with an aspect ratio higher than 1000. This method is simple and requires no catalyst or template. 

The synthesis of SiC nanofibers (5-20 nm in diameter) by using sol-gel and polymer blend techniques was achieved by Raman et cd. [119]. In this case, tetra-ethoxysUane and methyltriethoxysUane were used as a Si source, and polycarbonate as a carbon source. A polymer solution containing alkoxide, water, and a suitable solvent was stirred and freeze-dried to produce an intimate mixture of polycarbonate and sol-gel-derived sUica. The dried precursor was then pyrolyzed at 1400 °C in an argon atmosphere to obtain nanostructmed SiC. 

More recently, Hao et cd. investigated the influence of various metal catalysts on the morphologies of nanostructmed SiC produced by a sol-gel route, using lanthanum nitrate as an additive to prepare a xerogel [120]. The xerogel was converted, via a VLS mechanism, into bamboo-like SiC nanofibers with diameters of 40-100 nm and lengths of hundreds of micrometers. 

SiC nanofibers by melt-spinning of polymer blends have been prepared from PCS as a SiC ceramic precursor and a novolac-type phenol-formaldehyde resin [121]. These nanofibers were amorphous, about 100 nm in diameter, more than 100 (un long, and were rich in oxygen. 

---

Ceramic whiskers have been produced for many years, as reported by Gordon (1978), though their use in epoxies seems to be limited. However, aluminum borate whiskers have been combined with thermoset polymer matrices by Liang and coworkers (Liang and Hu 2004 Tang et al. 2007). Ceramic nanotubes have been produced by coating carbon nanotubes with silicon carbide (Morisada et al. 2007). Silicon carbide nanofibers, which can be about 40 nm in diameter with lengths of up to several hundred microns, have also been produced (Zhu et al. 2002 Bechelany et al. 2007). 

Figure 8.4 Relationship between soft segment crystallinity and the extent of non-covalent filler-matrix interactions in shape memory polyurethane (SMPU) composites filled with organoclay, carbon nanofIber (CNF), oxidized carbon nanofiber (ox-CNF), silicon carbide (SiC), and carbon black (CB). The ratio A/Ai. determined from fluorescence emission spectroscopy experiments, is a measure of the...

The rod-like nanoparticles that are commonly discussed in the scientific literature are carbon nanotubes. Carbon nanofibers (CNFs), which have a larger diameter, are also available. They are cheaper and are available in much larger quantities than carbon nanotubes. Ceramic nanotubes (e.g., zirconia, tungsten disulfide) or whiskers (e.g., silicon nitride, silicon carbide, alumina) can also be used. 

If the slip correction factors in Eq. (4) are close to 1 (Kn = 2Xjd < 1), it can be shown by substitution that the equivalent aerodynamic diameter is a function of 1)3/ and L / . Cheng et al. confirmed this experimentally with silicon carbide whiskers ranging from 50 nm to 1 qm in diameter and from less than 2 qm to more than 15 qm in length. Experiments were carried out for both a centrifuge and an inertial impactor [14], and a relatively narrow diameter distribution for classified nanofibers was achieved in each case. 

---