PHASE-EQUILIBRIA AND PROPERTIES OF GLASSES IN THE AL2O3-YB2O3-SIO2 SYSTEM

The phase diagram and properties of glasses of the Al2O3-Yb2O3-SiO2 system were studied by X-ray diffraction, differential thermal analysis, scanning electron microscopy and infrared absorption spectroscopy. The lowest solidus temperature in this system was 1500-degrees-C. The glass-forming region was determined by quenching specimens after melting in an infrared image furnace. The glass transition temperature,the onset and peak temperatures for crystallization were investigated as a function of composition and found to increase with increase in SiO2 concentration. The activation energy for crystal growth in glasses tended to attain a maximum at the eutectic composition. It is suggested that Yb ion is mainly a network modifier in glasses. The solidus temeperature of this system was compared with those of the systems containing other rare-earth oxides.