Characterization of oxycarbide glasses prepared by melt solidification

Oxycarbide glasses in the Y-Si-Al-O-C system were successfully prepared at 1500°C by melt solidification techniques while glasses prepared at 1600 & 1700°C foamed resulting in a spongy material. For a fixed cation composition (16.5Y: 56Si: 27.5Al in eq.%) varying O:C ratios corresponding to carbon contents of 1, 2, 2.5, 5 and 10 eq.% were chosen to determine the solubility limit of carbon in this system. Properties such as density, microhardness, elastic modulus and glass } transition temperature were measured for glasses made at 1500°C and found to increase up to 2 eq.% addition of carbon. X-ray diffraction analysis carried out on all these glasses revealed the existence of SiC peaks except for the 1 and 2 eq.% carbon containing composition. 2 eq.% carbon appears to be the solid solubility limit for carbon in these yttrium alumino-silicate liquids at J 1500°C. The devitrification studies carried out using differential thermal analysis (DTA) and tube furnace heat treatment indicated heterogeneous nucleation mechanism with yttrium disilicate and mullite being the predominant phases formed.