Preparation And Properties Of Phosphate Sealing Glasses

Vacuum plate glass is a new energy-efficient, transparent and heat insulation material produced in recent years. It has a great potential in insulation cabinets, doors and windows of buildings and other fields. Vacuum plate glass is formed by adhering two glass plates with sealing solder in a vacuum furnace. The sealing solder with low melting point, suitable thermal expansion coefficient is an important material for preparing the vacuum glass. Phosphate sealing glasses have a low sealing temperature and wide range of thermal expansion coefficient, which can meet requirements of the low-temperature sealing and comply with lead-free sealing solder trends.The?Na₂O-CaO-SiO₂?-P₂O₅ system was selected as the base to determine the best lead-free low-temperature sealing glass for uses in vacuum plate glass. The effects of the contents of the P₂O₅ and SiO₂, the additions of B₂O₃, ZnO, Fe₂O₃ and ZrOCl₂ on structure and properties of the glass samples have been studied.The density of the glass samples increases with increasing the molar content of P₂O₅. Further reducing the amount of SiO₂, the chemical stability of glass got improved but is still poor. With increasing the B₂O₃/ZnO molar ratio, the density and thermal expansion coefficient decrease, while the glass transition temperature and the expansion softening temperature increase. When the ratio of B₂O₃/ZnO is 1/3, the best chemical stability is obtained but still not satisfied. Characteristic temperatures of the melting and flowing of the glass powders increase with the increasing ratio of B₂O₃/ZnO. The sealing temperature of these glass is higher than 600 oC. They can not be used for sealing flat glass.Replacing B₂O₃ with Fe₂O₃, the density and chemical stability increase, while the thermal expansion coefficient decreases. The glass transition temperature and the expansion softening temperature reach minimum values, 402 oC and 450 oC respectively, when the amount of Fe₂O₃ is 5mol%. Characteristic temperatures of these glass powders decrease with increasing Fe₂O₃. Their using temperature can be lower than 500 oC.Replacing ZnO with Fe₂O₃, the density, chemical stability, glass transition temperature and expansion softening temperature increase. The optimized glass composition is 10?R2O+RO?-24.4?Al2O3+SiO₂+ZnO?-54?P₂O₅+B₂O₃?-11.6Fe₂O₃. The glass has the density 2.93g/cm3, weight loss of 0.69%, thermal expansion coefficient of 8.61×10-6/oC, expansion softening temperature 465 oC and sealing temperature range of 395oC⁴90oC.By adding 2mol% of ZrOCl₂ into the aboved optimized glass, the weight loss of the glass particles in boiling water is only 0.22%. The obtain glass has the density 2.96g/cm3, thermal expansion coefficient 8.56×10-6/oC, expansion softening temperature 459 oC and sealing temperature range of 390oC⁴83oC.The results show that adding B₂O₃ and ZnO makes the sealing properties of the glass poor, whereas Fe₂O₃ and ZrOCl₂ can improve the sealing properties of the glass.