Research On Production Of High-containing C/C Composites By Mean Of Sol-gel Method

C/C composite, which is a material of carbon fiber reinforced carbon matrix composite and has anti-high temperature, low density, high specific strength, high specific stiffness and excellent thermal shock resistance and other characteristics, is an excellent high-temperature ablation resistant material. However, at the environment of high temperature and high pressure gas flow, C/C composite can be ablated and oxidized quickly, which has extremely limited its application. At present, doping refractory compounds is a good mean to improve the anti-ablation of C/C composites above 3000℃.In this paper, we doped Zirconium compounds into low density C/C composite by method of sol-gel, in order to produce high Zirconium-containing C/C composites. Mainly studied the macrostructure and anti-ablation of the C/C composite made by mean of sol-gel. During the selection process of sol-gel, we found that Zirconium acetate mixed with jellies made by ourselves, had a low viscosity, and could fast gel at low temperature, which was suitable for low density C/C composite to be doped with Zirconium compounds. TG-DSC curves of zirconium acetate gel showed that zirconium acetate gel mainly weight loss occurred below 400℃, and the cure toned down after 400℃; FTIR spectra of the zirconium acetate gel showed that organic compounds had decompounded completely at 800℃, and ZrO2 was appeared at this temperature. Through high temperature treatment of zirconium acetate gel, we found that ZrO2 begin to convert to ZrC at 1600℃, and completely become cubic phase ZrC at 2600℃; with the increase of treatment temperature, the size and crystalline also increased.The zirconium acetate sol was used to impregnate the C/C composites which had different densities of 1.39 and 1.59 g/cm3, and the weights were apparently increased, reaching 1.88 and 1.86g/cm3 separately, and the contents of Zr (ZrO2) reached 24% and 14% finally, which demonstrate that sol-gel method was a quick and effective method in doping Zirconium compounds into low density C/C composite. With the use of back scattered electron, we had studied the distribution of zirconium in the C/C composites, finding that a zirconium coating layer was formed on the surface of the material, and in the internal of material, the distribution of zirconium was mainly depended on the distribution of boles with in the material itself. With the test of universal tensile machine to a certain density C/C composites with different Zirconium-content, we studied the mechanical properties of materials, and found that as zirconium content increased, the mechanical properties of materials were significantly declined, which were mainly due to the reaction between carbon fibers and ZrO2. At high temperature (1600℃above), ZrO2 can react with carbon in the matrix and fibers, turn to be ZrC, resulting in the mechanical properties of a substantial depreciation. After the testing of wind tunnel ablation on the Zr-containing C/C composites, a uniform ZrO2 film was found on the surface of material, which can cut off osculation of oxygen and C/C composites, and reduce the ablation rate of materials.