液态聚碳硅烷的结构及固化行为对其陶瓷化的影响

Effect of Structure and Curing Behavior of Liquid Polycarbosilane on Ceramicization

液态聚碳硅烷作为一种新型陶瓷先驱体,可通过先驱体浸渍裂解工艺(PIP)制备陶瓷基复合材料(CMC),也可通过包覆有机纤维来提高柔性绝热层的耐烧蚀性能。文中通过红外光谱和核磁共振表征了3种液态聚碳硅烷先驱体VHPCS,VHPCS-S和AHPCS的结构组成,在150℃前的固化反应主要通过C═C键以多种方式进行,与AHPCS相比,VHPCS和VHPCS-S中双键与硅氢键的摩尔比提高了约18.2%;采用非等温差示扫描量热分析(DSC)法研究了3种先驱体及其在交联剂过氧化二异丙苯体系时的固化反应动力学,发现固化反应温度和表观活化能均有所降低,先驱体可以在低温下实现快速交联反应;利用同步热分析和X射线衍射分析了先驱体的陶瓷化过程及裂解产物的结晶行为,VHPCS-S在1200℃时的陶瓷产率高于其余2种先驱体VHPCS与AHPCS。对于DCP/VHPCS-S交联体系,在150℃固化后陶瓷产率达到89.82%。此外,DCP的加入可以有效抑制β-SiC结晶。

Liquid polycarbosilane,as a new precursor of ceramics,can be used to prepare ceramic matrix composites(CMC)by precursor infiltration and pyrolysis(PIP)process,and to improve the ablative resistance of flexible insulation layer by coating organic fibers.The structures of three liquid polycarbosilane precursors(VHPCS,VHPCs-S and AHPCS)were characterized by IR and NMR.The curing reaction before 150℃was mainly carried out by various ways of C═C bond.Compared with the AHPCS,the mole ratio of double bond to hydrogen silicon bond in the VHPCS and VHPCS-S is increased by about 18.2%.The curing kinetics of three precursors in the system of dicumyl peroxide(DCP)was studied by non-isothermal DSC.The curing temperature and apparent activation energy of the precursors are decreased,and the precursors could achieve rapid crosslinking reaction at low temperature.The ceramization process of precursor and crystallization behavior of its pyrolysis products were analyzed by STA and XRD.The ceramic yield of VHPCS-S at 1200℃is higher than that of the other two precursors(VHPCS and AHPCS).For the DCP/VHPCS-S crosslinking system,the ceramic yield reaches 89.82%after curing at 150℃.In addition,the addition of DCP can effectively inhibitβ-SiC crystallization.