Crystallization, thermal expansion and hardness of Y2O3–Al2O3–SiO2 glasses

Abstract The effect of crystallization of y-Y2Si2O7 (Y-c and Y2S-c2)/Y4.67(SiO4)3O (Y2S-c1) single crystal or simultaneously y-Y2Si2O7, Al6Si2O13 and SiO2 crystals (YMS-c) on the hardness and thermal expansion coefficient (TEC) of Y2O3–Al2O3–SiO2 (YAS) glass is studied. Crystallization activation energy is 591, 650 and 282 kJ/mol for Y, Y2S and YMS glasses, crystallization mechanisms of glasses Y and Y2S (Tc1) are surface crystallization and one-dimensional crystal growth, while YMS glass is two- and one-dimensional growth of crystals. The volume fraction of crystalline phases in Y-c (91.45%), Y2S-c1 (83.00%) and -c2 (92.55%) glass ceramics are larger than that of YMS-c (71.11%), precipitated y-Y2Si2O7 single crystal decrease the TEC ( × 10−6 °C−1/30–1000 °C) of Y and Y2S parent glasses to 3.95 (Y-c) and 5.09 (Y2S-c2) while Y4.67(SiO4)3O single crystal increase the TEC of Y2S-c1 to 7.15, YMS-c has the smallest TEC (3.34) among studied glass ceramics, the enhancing effect of Y4.67(SiO4)3O on the hardness of Y2S glass is more than that of y-Y2Si2O7. Y and YMS glasses could be used as coating, sealing and jointing materials for SiC ceramics used in the high temperature fields.