Contribution of di- and trivalent oxides to crystal phase formations and properties of yttrium aluminosilicate glass-ceramics

Abstract

The crystallization behaviour, phase composition, microhardness and chemical durability of some silicate glasses and glass-ceramics based on LiAlSi2O6-YAlSiO5 system were investigated. The effects of partial replacements of LiAlSi2O6 mostly with LiFeSi2O6 and complete replacement of YAlSiO5 with CaMgSi2O6 were considered. In some cases small amount of Cr2O3 was introduced as nucleating agent or Fe2O3 was partially replaced with chromium or indium oxides. The main crystalline phases formed after controlled heat-treatments of the glasses were yttrium-containing ?-spodumene solid solution (ss) - Li(Al,Y)Si2O6, together with varieties of pyroxene-ss including lithium iron pyroxene-ss - LiFeSi2O6-CaMgSi2O6, augite - Ca(Mg,Fe)Si2O6, chromoaugitess, Li-aegirine - LiFeSi2O6, diopside - CaMgSi2O6 and lithium indium silicate - LiInSi2O6 phases. The Vickers? microhardness values of the studied glasses (ranged from 4610 to 6185MPa) were greatly affected by the modifications of the glass compositions. On the other hand, the glass-ceramics? microhardness (7245- 8175MPa) was markedly improved depending on the microstructure and the nature of crystalline phases formed. The glass-ceramics have chemical stability better than those for the corresponding glasses.