Effect of ZnO, La2O3, and YF3 on Crystallization and Rehological Behavior of Y2O3-Al2O3-SiO2 Glass

The effect of substitution La2O3 and YF3 as network modifiers respectively for Y2O3, and ZnO as intermediate oxide for Al2O3 on crystallization and viscous behavior of Y2O3-Al2O3-SiO2 glass was studied. La2O3 and YF3 substitution for Y2O3 decreases the melting temperature of studied glass from 1 402 to 1 346 and 1 379 & DEG;C, and the activation energy of viscous flow decreases from 340 to 250 and 265 kJ/mol. Meanwhile, ZnO substitution for Al2O3 decreases the melting temperature to 1379 & DEG;C while increases the activation energy of viscous flow to 542 kJ/mol, due to their different role in glass structure. Substitution ZnO for Al2O3 refines and homogenizes the crystals size and lowers crystallinity because the nucleation and crystal growth are depressed by higher activation energy of crystallization and change of crystallization mechanism from bulk crystallization to surface crystallization. Replacement of Y2O3 by La2O3 and YF3 respectively also decreases the crystallinity of Y2O3-Al2O3-SiO2 glass ceramic due to competitive and hindering effect on the rearranged atoms, structural units and groups required by precipitated two crystals. Besides, y-Y2Si2O7, precipitation of Y-4.67(SiO4)(3)O, ZnAl2O4, and Y3Si3O10F were observed respectively due to incorporation of La2O3, ZnO, and YF3.