Study on some thermo-physical properties in Li 2O–ZnO–SiO 2 glass-ceramics

Abstract

Lithium zinc silicate (LZS) glasses containing Li 2O–ZnO–SiO 2–Na 2O–B 2O 3–P 2O 5 were prepared by conventional melt and quench technique and subsequently converted to glass-ceramics by controlled nucleation and crystallization. Both these parameters were determined by differential thermal analysis (DTA) studies. The effect of ZnO/(ZnO+SiO 2) ratio on various thermo-physical properties was investigated by changing the ratio from 0.1 to 0.31. A number of crystalline phases have been identified by X-ray diffraction studies on the glass-ceramics including cristobalite (SiO 2), lithium zinc silicate (Li 3Zn 0.5SiO 4) and lithium silicate (Li 2SiO 3). Density ( ρ) was found to increase from 2.62 to 2.82 g cm −3 while microhardness (Vicker's hardness number, VHN) decreased from 6.56 to 5.79 GPa with increase in ZnO/(ZnO+SiO 2) ratio in the glass-ceramics. Average thermal expansion coefficient (TEC) in the temperature range 30–450 °C increased from 125×10 −7 to 185×10 −7/°C. The increase in expansion coefficient and decrease in microhardness are thought to be due to the formation of different phases which in turn influence the rigidity/bonding in the glass-ceramics. The material has been used for the fabrication of hermetic seal with copper. A study on the microstructure close to the interface of the glass-ceramics to metal is also carried out. The seal withstands a vacuum of ∼10 −6 Torr at helium leak rate of 3×10 −10 Torr l/s.