Effect of Heat Treatment on the Microstructure of Amorphous Si-N-C Fine Powders

Crystallization processes of four kinds of amorphous Si-N-C fine powders were studied by X-ray diffraction, IR spectroscopy, transmission electron microscopy, analytical electron microscopy and chemical analysis. The samples examined had varying contents of Si, N and C (Si : 53-58 mass%, N : 24-36 mass%, C : 5-20 mass%), and were prepared by pyrolysis of hexamethyldisilazane ((Me_3Si)_2NH, Me=CH_3). These samples were heat-treated in an argon atmosphere at a temperature between 1713-1803K for periods of up to 21.6ks. All of the fine powders examined were nearly spherical and were 100-500nm in size before heat treatment. The first sign of crystallization of the powders was observed after 21.6ks heat treatment at 1713K. X-ray diffraction showed that the crystallized phase consisted mainly of β-SiC and α-Si_3N_4 . The formation of β-SiC occurred during the early stage of heat treatment. The formation of α-Si_3N_4 then followed. After heat treatment for 21.6ks at 1743K, more than 80% of crystallinity was observed in all of the samples examined. The quantity of α-Si_3N_4 and β-SiC in the samples was related to the carbon content in the powders. The crystallized β-SiC was between 20-100nm in size. On the other hand, the size of α-Si_3N_4 was consistently larger than that of β-SiC and depended on the nitrogen content in the powders