Al、O含量对SiAlCO纤维高温转化为Si(Al)C纤维过程的影响

Effects of Al and O Content on Transformation from SiAlCO to Si(Al)C Fibers after High Temperature Treatment

采用不同Al含量的聚铝碳硅烷（PACS）为先驱体,通过不同的PACS纤维不熔化方法调节O引入量,制备了具有不同Al和O含量的连续Si Al CO纤维。研究了Si Al CO纤维经高温处理转变为Si（Al）C纤维过程中,Al、O含量对Si CxOy相分解、β-Si C结晶生长和微观形貌的影响。结果表明：纤维中Si CxOy相的分解温度区间为1300～1700℃,与Al、O含量基本无关;提高Al含量可减少纤维在高温下表面形成粗大Si C结晶颗粒和相互连通的气孔,并且对1700℃以上β-Si C结晶生长的抑制作用增强,有利于烧结致密化;利用纤维中O元素,以放出CO或CO2方式脱除富余C,但O含量过高导致气体逸出时产生较大孔洞,不利于烧结致密化。当Al和O含量分别约为0.6wt%和9wt%时,Si Al CO纤维经高温处理后能得到具有较大β-Si C晶粒尺寸的致密化Si（Al）C纤维。

Continuous Si Al CO fibers were prepared by polymer-derived method using polyaluminocarbosilane（PACS） with various Al contents as precursor. The O content of the fibers was controlled by different curing methods. The effects of the Al and O content on Si CxOy decomposition, β-Si C grain growth, and fiber morphological evolution in the heat-treatment process were investigated. The results reveal that Si CxOydecompostion initiates at 1300℃ and completes at 1700℃ for all kinds of fibers, which is irrelevant to Al and O contents. Al in the fibers is beneficial to reduction of both coarse Si C crystallites and interconnected pores on the surface, and increases suppressing effects on the growth of β-Si C under the tempertature above 1700℃, resulting in densification. Excessive carbon is eliminated as CO and CO2 by oxygen from Si Al CO fibers during annealing process. However, excessive oxygen creates big pores in fibers, harmful to densification. A densified Si（Al）C fiber with a decently large crystallite size of β-Si C can be achieved with an optimal Al and O content of 0.6wt% and 9wt%, respectively.