Microstructural Changes of Amorphous Si-N-C Fine Powders at High Temperatures

Abstract

Microstructural changes of amorphous Si-N-C fine powders were studied by X-ray diffraction, transmission electron microscopy, IR spectroscopy and chemical analysis. The samples examined had varying contents of Si, N and C (C5: Si-35.8N-4.8C, C8: Si-32.8N-8.1C, C17: Si-29.0N-17.3C, C20: Si-24.2N-19.7C), and were prepared by pyrolysis of hexamethyldisilazane ((Me3Si)2NH, Me=CH3). These samples were heat-treated in an argon atmosphere at 1743 and 1803K for periods of up to 64.8ks. X-ray diffraction showed that the crystallized phase consisted mainly of α-Si3N4 and β-SiC. In the C5 and C8 powders, the size of crystallized β-SiC was 20-100nm under all heat treatment conditions, and β-SiC in C17 and C20 powders grew 50-1500nm and 20-200nm in size respectively, after heat treatment at 1803K for 64.8ks. The morphology of α-Si3N4 in C5 and C8 powders was rod-shaped, and the size of the α-Si3N4 was larger than that of β-SiC. On the other hand, the fine-grained and the thin-plated α-Si3N4 were observed in all of the samples heat-treated for 64.8ks at 1803K. We believe that the formation of fine-grained and thin-plated α-Si3N4 relate to the development of mechanical properties of Si3N4-SiC composites.