## 3 Results and Discussions  
### Characterization of Combustion Synthesized (CSed) Silicon carbide Nanowchiskers (SiC NWs)  
Figure 1 shows the XRD patterns of the CSed SiC samples, indicating that the sample without added W particles exhibits the presence of residual C and Si elements. However, when W was introduced as catalyst, no residual C and Si were observed, and all the main peaks agree well with the standard JCPDS 65-0360, which was identified to be cubic \(\beta\)-SiC (space group F-43m (216), with the lattice constant a = 4.358 A). The strong intensity and narrow width of the \(\beta\)-SiC peaks also demonstrate a highly crystalline structure. Other weak peaks in W-catalyzed samples are demonstrated to be Si\({}_{3}\)N\({}_{4}\) (JCPDS 09-0250) and Si\({}_{2}\)W (JCPDS 44-1055) phases. The melting point of the by-product Si\({}_{2}\)W was up to 2423 K, according to the Si-W phase diagram [24], the high melting point of Si\({}_{2}\)W and Si\({}_{3}\)N\({}_{4}\) by products is positive for the high temperature application of SiC NWs. XRD results indicate that the W catalyst is able to hinder the formation of C and Si residues. As we know, residual C and Si elements generally result in poor mechanical properties of bulk ceramics at high temperatures [1].  
Figure 2a shows the CSed SC sample prepared without W catalyst. Clearly, the sample exhibits a graded structure, that is the core is fluffer than the surface. Moreover, the surface products are somewhat dense (compared with the fluffy core). Figure 2b shows the typical SEM morphology of the SC sample, exhibiting the presence of numerous coarse or spherical residual particles in the SiC NWs, and according to the XRD results shown in Figure 1, these particles are considered to be C and Si particles. In contrast, the W-catalyzed CSed W-SC sample was fluffy from surface to the core, and a little bit green colored, which is similar to another report [25], as shown in Figure 3a. The diameter of the entire product was about 7 cm, which revealed the possibility of large-scale fabrication of CSed W-SC samples. Figure 3b,c display the typical SEM images of the fluffy W-SC sample products, revealing that all products are NW structured, and the CSed W-SC is about several hundred micrometers long,  
Figure 1: X-ray diffraction (XRD) patterns of the combustion synthesized (CSed) silicon carbide nanowchiskers (SiC NWs).  
with diameters less than 1 \(\mu\)m. Tiny amounts of coarse particles may be attributed to the by-products corresponding to Si\({}_{2}\)W and Si\({}_{3}\)N\({}_{4}\) phases.  
Results of TEM provide further insight into the W-catalyzed CSed SiC NWs. Figure 4a shows an individual SiC NW with a diameter of about 20 nm. Moreover, dense stacking faults can be observed  
Figure 3: (**a**) Fluffy and green colored W-catalyzed CSed SiC NWs; (**b**,**c**) typical SEM images of the W-catalyzed CSed SiC NWs.  
Figure 2: CSed SiC NWs without W as the catalyst: (**a**) sample morphology and (**b**) typical scanning electron microscope (SEM) images revealing the existence of residual particles in the NWs.  
in the whisker, which can be further demonstrated in the atomic structure shown in Figure 4b. The d spacing measured along the growth direction was calculated to be 0.252 nm, indicating the (111) growth direction of the CSed SiC NWs.