Carbon reduction reaction in the Y2O3-SiO2 glass system at high temperature

In order to assess the role of carbon with respect to the grain boundary ch emistry Of Si3N4-based ceramics model experiments were performed. Y2O3-SiO2 glass systems with various amount of carbon (from 1 to 30 wt.%) were prepa red by high-temperature treatment in a graphite furnace. High carbon activi ty of the furnace atmosphere was observed. EDX analysis proved the formatio n of SiC by the carbothermal reduction Of SiO2 either in the melt or in the solid state. The melting temperature of the Y2O3-SiO2 system is strongly d ependent on the amount of reduced SiO2. XRD analysis of the products docume nted the presence Of Y2Si2O7, Y2SiO5 and Y2O3 crystalline phases in that or der with an increasing amount of free C in the starting mixture. The reduct ion of Y2O3 was not confirmed. (C) 2001 Elsevier Science Ltd. All rights re served.