Lithium Zinc Silicate Glass Ceramic: A material for Hermetic (vacuum) Seal Applications

摘要

We report here the preparation and characterization of lithium zinc silicate (LZS) glass ceramic, particularly with low zinc content, for application of hermetic sealing to copper metal. The base glass of nominal composition (in weight %) of the constituents SiO_2:74.4, Li_2O :12.65, Al_2O_3:3.8, K_2O:2.95, P_2O_5:3.15, ZnO :1.85 and B_2O_3:1.2 was prepared by melt quench technique and subsequently converted to glass-ceramic by controlled crystallization at temperatures 780°C and 580°C based on differential thermal analysis (DTA) studies. The effect of dwell time at the crystallisation temperatures on average thermal expansion coefficient (TEC) was studied. Depending on the process parameters, TEC in the range 30-500°C, varied from 115x10~(-7)/°C to 178x10~(-7)/°C and found to be suitable for hermetic sealing with copper, stainless steel and inconel alloys. A four stage temperature schedule involving melting, nucleation, crystallization and annealing was evolved for fabrication of glass ceramic to metal (GCM) seal. The hermetic glass ceramic to metal seal with copper housing of dimension of 17.5 mm ID x 25.0 mm OD was successfully fabricated and found to withstand a vacuum of 10~(-6) ton with helium leak rate of less than 10~(-9) torr litre /sec.