前驱体转化低铝含量非晶Si-Al-C-N的高温析晶行为

将不同铝含量的聚铝硅氮烷前驱体在氮气保护下1200℃裂解,再在1400-1800℃高温处理,制备出非晶Si-Al-C-N.采用红外光谱、X射线衍射,拉曼光谱和透射电子显微镜分别表征前驱体的结构、Si-Al-C-N的析晶特性、自由碳的微观结构,研究了铝含量、析晶温度和保温时间对非晶Si-Al-C-N析晶性能的影响.结果表...

High-temperature Crystallization Behaviors of Amorphous Si-Al-C-N with Low Aluminum Content

Amorphous Si-AI-C-N ceramics with varied aluminum contents,which were derived from polyaluminasilazanes at 1200℃,were heat-treated at 1400-1800℃.The structures of precursors and the crystallization behaviors,free-carbon and microstructure of Si-AI-C-N were characterized by Infrared spectrometry,X-ray diffraction,Raman spectra and transmission electron microscopy.The effects of aluminum contents,crystallization temperatures and times on crystallization properties of amorphous Si-AI-C-N were investigated.The results show that amorphous 5i-AI-C-N ceramics are amorphous at 1400℃,but include free-carbon.Nano-scaleβ-Si₃N₄ andα-Si₃N₄ nuclei are precipitated at 1500℃. Theα-Si₃N₄ nucleus transforms intoβ-Si₃N₄ after treated at 1600℃,at the same time,a minute quantity ofα-SiC and 2H-SiC/AIN solid solution nuclei precipitated.At 1700℃a large number of 2H-SiC/AIN solid solution crystals and a fewα/β-SiC crystals precipitated besidesβ-Si₃N₄,and theβ-Si₃N₄ phase in the Si-AI-C-N ceramic with lowest aluminum content disappears.At 1800℃onlyβ-SiC and 2H-SiC/AIN solid solution crystal are observed.But phase separation takes place at this temperature, leading to the formation of AIN-rich and SiC-rich solid solution region,respectively.With increasing aluminum content,crystallization ability of amorphous Si-AI-C-N ceramics and quantities of grain increase. Nano-scale crystals precipitate from the amorphous Si-AI-C-N at 1500℃,but even until 1800℃the precipitated crystals are still nano-scale crystals.The high-temperature crystallization process of amorphous Si-AI-C-N with high covalence is a process controlled by thermodynamics.