Effect of Crystallization Rate on Sealing Behaviour of BaO-Al2O3-B2O3-SiO2-La2O3-TiO2 Glass System

Glasses with nominal composition (mol%) 34BaO-10Al(2)O(3)-17B(2)O(3)-34SiO(2)-(5-x)La2O3-xTiO(2) (x = 0, 1, 2, 3, 4) were prepared by melt quenching technique. Activation energy of crystallization (E-a) was calculated by Kissinger's model considering the shift in peak crystallization temperature (T-c) at three different heating rates (10 degrees, 15 degrees and 20 degrees C. min(-1)) in differential thermal analysis. Among the glasses studied, composition with x = 1 had the maximum E-a as a result of its slower crystallization rate. Thermal expansion coefficients of as prepared bulk glasses matched with that of Crofer 22APU alloy. Sandwich type seals were made with two Crofer plates at 990 degrees C and their vacuum integrity was tested at room temperature. Cross-sectional interface of the seals was studied under scanning electron microscope with energy dispersive X-ray analysis. Very different morphology at metal to glass-ceramics interface was observed with varying TiO2 concentration. Microstructure at the interface of the seal with x = 1 glass had less porosity and less chromium enrichment at the interface than the other compositions which was probably due to slower rate of crystallization during the heat treatment.