CRYSTALLIZATION AND PROPERTIES OF A SI-Y-AL-O-N GLASS-CERAMIC

Glasses have been prepared in the Si-Y-Al-O-N system by melting mixtur es of silica, alumina, yttria, and silicon nitride. One particular gla ss containing 17 equiv% N has been investigated to observe the crystal lization at temperatures in the range 1050-degrees-1300-degrees-C. The major crystalline phase observed is Y2Si2O7, existing as the alpha fo rm below 1200-degrees-C and the beta form above this temperature. Prop erties of the glass-ceramic, including thermal expansion coefficient, hardness, electrical resistivity, and creep have been assessed.