DECREASE OF SILICON DEFECTS IN OXYNITRIDE GLASS

Mg-Si-Al-O-N oxynitride glass fiber with an average elastic modulus of 115 GPa and tensile strength of 4500 MPa was prepared by melting the mixtures of SiO2, MgO, Al2O3 and Si3N4 powders at 1720 degrees C and r efined at 1600 degrees C in molybdenum crucible in flowing nitrogen ga s. The high tensile strength was achieved by decreasing silicon partic les which were internal defects of the oxynitride glass. The glass of 3 mm thick had transmittance of more than 90%. The silicon particles w ere generated in the glass by decomposition of SiO2 above 1720 degrees C under strong reducing conditions, which caused coloration of the gl ass and low fiber strength. Refining of the glass at 1600 degrees C de creased the silicon particles. The reaction between =Si-N=, =Si-O- in the glass matrix and molybdenum formed molybdenum silicides with the e volution of nitrogen and oxygen gases. Silicon particles were oxidized by oxygen evolved.