材料期刊网

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。结果表明:
具有不同铝含量的非晶Si--Al--C--N在1400℃处理后仍为非晶状态, 但发生组份偏析形成自由碳; 在1500℃出现纳米级β--Si3N4和α--Si3N4晶体; 在1600℃α--Si3N4转变为β--Si3N4,并析出微量α--SiC和2H--SiC/AlN固溶体型晶核; 在1700℃除β--Si3N4外,还析出大量2H--SiC/AlN固溶体和部分α/β--SiC晶体,铝含量最低的Si--Al--C--N陶瓷中的β--Si3N4消失; 在1800℃,只含有β--SiC和2H--SiC/AlN固溶体晶体, 但是发生了相分离并分别形成富AlN和富SiC固溶体区。铝含量的增加有利于晶体析出和晶体数量的增加。非晶SiAlCN在1500℃开始析出纳米晶,在1800℃处理后析出的晶体仍为纳米晶。高共价键非晶SiAlCN的高温析晶过程, 是一个主要由热力学控制的过程。

Amorphous Si–Al–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–Al–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–Al–C–N were investigated. The results show that amorphous Si–Al–C–N ceramics are amorphous at 1400 %, but include free-carbon. Nano–scale β–Si3N4 and α–Si3N4 nuclei are precipitated at 1500 %. The α–Si3N4 nucleus transforms into β–Si3N4 after treated at 1600 %, at the same time, a minute quantity of α–SiC and 2H–SiC/AlN solid solution nuclei precipitated. At 1700 % a large number of 2H–SiC/AlN solid solution crystals and a few α/β–SiC crystals precipitated besides β–Si3N4, and the β–Si3N4 phase in the Si–Al–C–N ceramic with lowest aluminum content disappears. At 1800 % only β–SiC and 2H–SiC/AlN solid solution crystal are observed. But phase separation takes place at this temperature, leading to the formation of AlN–rich and SiC–rich solid solution region, respectively. With increasing aluminum content, crystallization ability of amorphous Si–Al–C–N ceramics and quantities of grain increase. Nano-scale crystals precipitate from the amorphous Si–Al–C–N at 1500 %, but even until 1800 % the precipitated crystals are still nano–scale crystals. The high-temperature crystallization process of amorphous Si–Al–C–N with high covalence is a process controlled by thermodynamics.