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有机聚合物先驱体由于其分子可设计性好、成型方便、低温裂解转化为陶瓷的特点,在陶瓷纤维和纤维增韧陶瓷基复合材料的制备中表现出极大的优势。针对先驱体转化法体积收缩大、孔隙率高的不足,在先驱体中引入适当的活性填料是解决其不足的有效方法。以聚碳硅烷(PCS)为 SiC 陶瓷的先驱体,以金属(Al、Cr、Mo、Ta、Ti、W、Zr)、非金属(B、Si)及其化合物(CrSi_2、TiH_2、TiB_2)微粉为活性填料,对活性填料控制的 PCS 裂解陶瓷的陶瓷产率、线收缩率、密度、力学性能、产物结构等进行了系统的研究。对活性填料控制的 PCS 先驱体裂解陶瓷的尺寸变化进行了模型分析。从理论上揭示了活性填料的临界体积分数与活性填料反应的产率、反应前后的密度比之间的相关性。通过对 PCS/Al/SiC/N_2裂解体系反应热力学参数的计算,从理论上预测可能发生的反应与不可能发生反应。将热分析反应动力学方法应用到活性填料 Al 控制的 PCS 先驱体的裂解中。分别研究了 N_2中纯 PCS、纯 Al、Al/SiC、PCS/Al/SiC 体系各阶段的表观活化能及其裂解-反应机理函数以 X 射线衍射,电子显微镜元素线扫描等方法对 PCS/Al/SiCN_2体系的裂解-反应机理进行研究。在含活性填料的先驱体转化法制备纤维复合材料的致密化-密度增长模型中,引入体积收缩率的参数,对先驱体转化法纤维复合材料的密度增长模型进行了修正。将活性填料 Al 应用到单向 M40JB 纤维和吉林碳纤维增强 SiC 陶瓷基复合材料及反坦克导弹陶瓷喷管的制备工艺中,并对裂解产物进行了表征,获得很好的效果。这一结果对促进先驱体转化法陶瓷构件在武器装备中的应用具有重要意义。
Organic polymer precursors have shown great advantages in the preparation of ceramic fibers and fiber toughened ceramic matrix composites because of their good molecular design, easy forming and low temperature pyrolysis. In view of the large volume shrinkage and high porosity of the precursor conversion method, it is an effective way to solve the problem by introducing appropriate active filler into the precursor. In this paper, polycarbosilane (PCS) was used as a precursor of SiC ceramics. The microstructure and properties of PCS were investigated by means of metal powders (Al, Cr, Mo, Ta, Ti, W, Zr), nonmetal (B, Si) and their compounds (CrSi_2, TiH_2 and TiB_2) As active filler, systematically studied the ceramic yield, linear shrinkage, density, mechanical properties and product structure of PCS cracked ceramics controlled by active filler. The model analysis of the size change of active filler-controlled PCS precursor pyrolytic ceramics was carried out. The correlation between the critical volume fraction of active filler and the reaction yield of active filler and the density ratio before and after reaction were revealed theoretically. By calculating the reaction thermodynamic parameters of the PCS / Al / SiC / N2 cleavage system, it is theoretically possible to predict possible reaction and impossible reaction. The thermal analysis reaction kinetics method was applied to the cleavage of PCS precursors controlled by the activated filler Al. The activation energy and the mechanism of cleavage-reaction of each phase of pure PCS, pure Al, Al / SiC and PCS / Al / SiC in N_2 were studied respectively by X-ray diffraction and electron microscopy. Al / SiCN_2 system cleavage - reaction mechanism. In the model of densification - density growth of fiber composites prepared by precursor conversion with active filler, the volume shrinkage parameter was introduced to modify the density growth model of the fiber composite by the precursor conversion method. The active filler Al was applied to the preparation process of unidirectional M40JB fiber and Jilin carbon fiber reinforced SiC ceramic matrix composite and antitank missile ceramic nozzle, and the cracking products were characterized and achieved good results. This result is of great significance to promote the application of precursor transformation ceramic components in weaponry.