Research On Corrosion And Preparation Of Carbon/Carbon Composites Surface Silicon-based Materials

SiC coatings of a variety of morphologies were prepared on C/C composites heating surface by CVD method. The microscopic morphology and crystal structure of as-prepared coatings were characterized by XRD,SEM, TEM,IR,Raman analyses.The growth mechanism of SiC whisker under the conditions of without catalyst were investigated. The impact of the CVD process parameters on the morphology of the SiC coatings prepared on C/C composites heating surface were explored.The resistance to chemical corrosion of SiC coatings with a variety of morphologies were investigated, the corrosion mechanism of SiC coatings in different corrosive medias were analyzed. The main contents and conclusion are listed as follows:(1) Under the conditions of without catalyst, using the MTS-H2system in situ growth of SiCw coating on C/C composites heating surface, preparation process of high length-diameter ratio SiCw was studied. The results showed that deposition temperature1100℃, Carrier gas and diluent gas were H2, flow rate of carrier gas and dilution gas for100ml/min and500ml/min, respectively; deposition time for7h, a diameter of about50-100nm(3-SiC whiskers can be prepared.(2) Under the conditions of without catalyst, SiC whisker is solid, bamboo-like, the trunk was straight and branching growth.The growth mechanism of the SiC whisker was the gas (V)-solid (S) mechanism.(3) Effects of deposition press and deposition location on CVD-SiC coating morphology were investigated.The study found that change deposition location also changed growth morphology of CVD-SiC. With the increase of the inlet distance, the CVD-SiC morphology from a smaller grain size of the cellular dendrite structure into equiaxed spherical particles, and then into a short rod-like whiskers until last into a loose structure, small diameter, and the intertwining of aggregation growth. As the system pressure increased from0.4～12Kpa, CVD-SiC morphology also showed a similar law.(4) The resistance corrosion capacity of C/C composites heating coated by CVD-SiC has been improved in HCl、 HF、HNO3.After corrosion100h in HCl、HF at95℃, and in HCl the total weight loss greater than in HF. However, after corrosion100h in HNO3, the total weight increased. As SiC morphological changed, the corrosion resistance to three kinds of corrosive medium also changed. The corrosion resistance ability of granular SiC coating was the best, followed by short rod-like whiskers, and tiny granular coating was the worst.