先驱体法制备的含铝SiC纤维的组成和结构研究

先驱体聚铝碳硅烷经熔融纺丝、空气预氧化处理、1300℃烧成可制得SiC(OAl)纤维(称为KD-A), 该纤?维再经1800℃烧结转变为SiC(Al)纤维(称 为KD-SA). 采用了元素分析、AES、SEM、XRD、RMS以及²⁹Si、¹³C、²⁷Al魔角自?旋固体核磁共振等测试方法对纤维的组成和结构进行了研究. 元素分析结果表?明KD-A的化学组成为SiC_1/31O_0.25Al_0.018, KD-SA为SiC_1.03O_0.013Al_0.024. AES表明, KD-A和KD-SA的表面和内部组成 不同. SEM表明KD-A、KD-SA表面光滑平坦, ?没出现孔洞、裂纹、沟槽等表面缺陷. XRD、RMS以及²⁹Si、¹³C、²⁷Al核磁共振的分析结果表明: KD-A包含较多的不定形游离C, O以不?定形SiC_xO_y复合相的形式存在, Al与复合相中的O相连存在于复合相中, 复合相在纤维中是连续相, 少量 的β-SiC微晶分散在其中, 是非晶SiC纤维; KD-SA含有大量的β-SiC晶粒, 少量的α-SiC和Al₂O₃, 是近化学计量比的多晶SiC纤维.

Composition and Structure of Polymer-derived Aluminium-containing SiC Fibers

A ceramic fiber with the SiC(OAl) composition, named KD-A, was prepared by the melt-spinning of precursor polyaluminocarbosilane, air-curing, and pyrolizing at 1300℃. The KD-A fiber was converted into SiC(Al) fiber, named KD-SA, by sintering at 1800℃. The composition and structure of the two kinds of fibers were characterized by chemical element analysis, AES, SEM, XRD, RMS, and ²⁹Si, ¹³C, ²⁷Al MAS NMR. The compositions of KD-A and KD-SA fibers are in the formula SiC_1.31O_0.25Al_0.018 and SiC_1.03O_0.013Al_0.024, respectively. The compositions of KD-A and KD-SA fibers on the surface are different from that of inside of the fibers. The surfaces of KD-A and KD-SA fibers are smooth and even, and there are no hole, crack and groove. KD-A fiber contains free carbon, small amount of β-SiC micro-crystal and aluminium embedded in an intergranular phase SiC_xO_y, which is ascribed to a non-crystalline SiC fiber. KD-SA fiber containsa large number of β-SiC, a small amount of α-SiC and Al₂O₃, which is ascribed to a crystalline SiC fiber with a nearly stoichiometric composition.