As carbon fiber reinforced silicon carbide composites combine the excellent mechanical properties of carbon fiber with good oxidation resistance of silicon carbide, considering material properties and economic cost, so much attention has been focused on short fiber reinforced ceramic matrix. but short carbon fiber is difficult to uniformly dispersed in the silicon carbide matrix, so how to disperse short carbon fibers in the matrix has become the key to prepare composite materials. In this article, through three processing methods to improve the dispersion, the three method are surface treatment of short carbon fibers, changing the mixed material ball milling time and adding a certain amount of SiC whisker. Results showed that the three processing methods all can improve the dispersion of short carbon fibers in silicon carbide matrix, but the dispersion effect also are different and the mechanism are different.the composites with better dispersion can achieved when carbon fibers which oxidized in concentrated nitric acid (68%) for 90minutes,and ball milling time was 48h and the concentration of SiC whisker was 5%.

Optical fiber preform is the core in the industry of optical fiber manufacturing, and vapor deposition is used in general internationally of which the raw material is expensive and the craft is complex. To reduce the cost of optical fiber,we selected tetraethoxysilane (TEOS) and H2O as raw material, ethanol as solvent, hydrochloric acid (HCl) and ammonia water as catalyst,in the condition of using different anti-cracking agent, including formamide (CH3NO), oxalic acid (C2H2O4), polyethyleneglycol 2000 (HO(C2H4O)nH), N, N-dimethyl formamide(C3H7NO) and glycerol(C3H8O3), to prepare SiO2 dry gel by sol-gel method in this paper. This paper mainly researched on the effect of anti-cracking agent on the cracking property of SiO2 dry gel. The XRD analysis indicated that the samples’ microstructures were amorphous. All kinds of anti-cracking agent were worked, but the effect on anti-cracking was different,and the dry gel which was added C3HNO was smooth and optimum, which were confirmed by the results of SEM. The analysis of the transmittance showed that the transmittance of dry gel with C3H8O3 was more than 92 percent.