预氧化聚铝碳硅烷纤维的热分解动力学及其机理

利用热重分析仪(TGA)对预氧化聚铝碳硅烷(PACS)纤维进行了热动力学研究, 用改良的Coats-Redfern法计算了动力学参数, 用Doyle法计算了理论失重值, 并根据FT-IR, XRD和SEM对其热分解的机理进行了分析. 结果表明, 在热分解反应的主要阶段, 预氧化纤维的反应活化能低于PACS纤维, 氧的引入有利于纤维的热分解; 快速升温有利于预氧化PACS纤维的热分解. 在初始分解阶段, 主要为低分子量的PACS和H₂O的逸出, 同时≡Si—H键之间以及≡Si—H与≡Si—CH₃键发生了脱氢、脱CH₄反应, 从而导致交联程度的增加; 随热分解温度进一步的提高, 分子的有机侧基急剧热解, 分解产物从有机物转变为存在部分微晶的无机结构; 热分解温度继续提高, 纤维结构进一步完善, 1300 ℃左右, β-SiC晶粒大小约为2～4 nm左右, 纤维具有较好的性能.

Kinetics and Mechanism of Thermal Decomposition of Cured Polya-luminocarbosilane Fiber

The thermal decomposition of cured polyaluminocarbosilane (PACS) fiber was studied by using a thermogravimetric analyzer (TGA) under non-isothermal condition. The improved Coats-Redfern method was used to determine the kinetic parameters and Doyle method was used to calculate the decomposition data. The mechanism of thermal decomposition was studied by using FT-IR, XRD and SEM. It was found that the active energy of the cured PACS fiber is lower than that of the PACS fiber in the main stage of thermal decomposition. Introducing oxygen and increasing the heating rate were found to promote the thermal decomposition. The thermal decomposition of the cured PACS fiber occurred via dehydrogenation and dehydrocarbonation condensation with the evolution of low molecular species and water during the initial stage of heating. The fiber was converted into an inorganic structure through the decomposition of the side chains of the polymer at elevated temperatures. When the temperature was further increased, SiC nanocrystals were formed and the fiber was transformed to inorganic compound completely. At 1300 ℃, the SiC fiber exhibited a good property with the crystal size of β-SiC being 2～4 nm.