碳化锆陶瓷有机前驱体的热解过程

Pyrolysis of an organic polymeric precursor of zirconium carbide ceramics

合成了碳化锆陶瓷有机前驱体,研究了其在热解过程中化学成分和物相组成变化,探讨了从有机高分子向无机陶瓷转化的机理,对碳热还原反应进行了热力学分析。结果表明,前驱体在600℃以下完成了有机结构的断裂、裂解碎片的重排与挥发,600℃以上裂解产物不再具备有机特征;随热解温度升高,无定型碳和单斜相ZrO2逐渐生成,大于1200℃时可检测到立方相ZrC,1400℃时单斜相ZrO2基本消失;1500℃时完成碳热还原反应,在远低于热力学反应温度的条件下生成了高度结晶的纳米尺寸的立方相碳化锆陶瓷。

To meet the requirement of rapid development in near spacecraft, continuous research efforts have been focused on the antioxidation materials which can be applied in very harsh environmental conditions. Carbon fiber reinforced SiC matrix(C/SiC) composites have overall advantages including lower density, good mechanical performance, and strong anti-oxidation capability, etc. Therefore, it can be used as various aerospace structural materials. However, C/SiCcomposites can only endure the short-time use(1 000 s) when the temperature is lower than 1 800℃, and longer-time use below 1 600℃ in oxidizing environment. In this case, ZrC has been considered as a good candidate, owing to its melting point of 3 540℃. Adding ZrC could increase the anti-oxidation capability of C/SiC composites, and besides, preceramic polymer processing is a good way to obtain ceramic matrix composites at a relatively low temperature. Various precursors of ceramic have been synthesized, but very little systematic work has been done regarding to the pyrolysis mechanism of polymeric precursor to zirconium carbide ceramics. In this work, pyrolysis process of an organic polymeric precursor of zirconium carbide(PZC) was investigated, the conversion mechanism of the precursor to ceramics was studied in detail as well. The methodology involved the microstructure analysis and phase composition of products by FT-IR, XRF, TG-DSC, MS-online, XRD and SEM. Furthermore, thermodynamics of carbothermal reduction reaction was calculated as well. The results showed that there was the decomposition of PZC with the temperature up to 600 ℃, including the release of small-molecule gases, such as water vapor, carbon monoxide, carbon dioxide, methane, acetone, and tetrahydrofuran, which were formed from the rearrangement of pyrolysis species. Then the solid inorganic products of amorphous-free carbon and m-ZrO2 were formed with the temperature range from 600 ℃ to 1 200 ℃. Cubic ZrC crystalline in nano size can be formed above 1 300℃, via the carbothermal reduction reaction between carbon and m-ZrO2, and this temperature was lower than the temperature from thermodynamic calculations. The ceramization of PZC could be completed with temperature at 1 500℃, and the yield of ceramic was 33.45%.