The Synthesis Of Bismuth And Phosphorus Lead-free Low Temperature Melting Glass Powder And Its Application In Silver Paste

Vacuum glass has a wide range of application prospects in the fields of construction,doors and windows of vehicles and ships,curtain walls and household appliances because of excellent thermal insulation effect.Traditional vacuum glass was sealed with organic polymer materials such as polycarbonate,polyvinyl butyral or soft solder,but these materials were prone to aging or corrosion and cannot guarantee long-term vacuum air tightness.High sealing temperature will reduce the mechanical properties of vacuum glass when using high temperature molting glass solder for sealing.But the low temperature melting glass solder usually contains lead and causes environmental pollution.Therefore,it has become an important research direction to study lead-free low temperature melting glass for low temperature sealing to prepare vacuum tempered glass that meets high air tightness and safety performance.In this work,two types of lead-free low temperature melting glass of bismuth and phosphorous series were mainly studied.Combined with infrared absorption spectroscopy and Raman scattering spectroscopy,the influence of the composition content of lead-free low temperature melting glasses on the glass network structure was deeply analyzed.The internal relationship between the composition changes of the bismuth series ternary Bi-B-Zn lead-free low temperature melting glass and the phosphorus series ternary P-V-Zn lead-free low temperature melting glass on the glass network structure and characteristic temperatures were established.Bismuth series lead-free low temperature melting glass network structures mainly has[Bi O₃],[Bi O₆]and[BO₃],[BO₄]units,the boron-oxygen structure transforms to the plane triangle structurre and the non-bridging oxygen content in[Bi O₆]structure increase with the increase of the Bi₂O₃ component content.The deterioration of the glass-forming performance and the decrease of glass transition temperature,and the decrease of the crystallization temperature were attributed to the weakening of the glass network structure.The change of Zn O content has a little effect on the glass structure.Phosphorus lead-free low temperature melting glass mainly contains[PO₄],[VO₂]and[VO₃]groups.The layered structure is connected by P-O-P,P-O-V and other bridge oxygen bonds,and there also have chain（VO₃）_n structures and VO₄^3-structures.Phosphorus series lead-free low temperature melting glass has better glass forming performance with the increase of V₂O₅ component content.The crystallization temperature increased and glass transition temperature decreased as V₂O₅ content increased.The glass transition temperature of the Bi-B-Zn and the P-V-Zn lead-free low temperature melting glass were as low as 325.7℃and 387℃,repectively.Combining the low temperature melting characteristics of the bismuth series ternary Bi-B-Zn lead-free low temperature melting glass,the lead-free low temperature sintered glass paste was prepared.The high strength connection of the soda lime tempered glass was realized on the basis of ensuring the high strength characteristics of the tempered glass.The maximum room temperature shear strength of the connection can reach 35.14±1.89 MPa.After the joining temperature exceeded 450℃,the Bi₄B₂O₉ phase precipitated in the weld structure and grew along the densely packed plane（113）.The shear fracture of tempered glass connector has large roughness,and a small amount of Bi-B-Zn lead-free low temperature melting glass solder remained.The precipitated crystalline phase hindered the crack propagation and prolonged the crack propagation path.A large number of fine Bi₄B₂O₉ phases precipitated at the interface,and there was mutual diffusion of Bi element and Si element formed a good diffusion connection,which increased the room temperature shear strengths of the tempered glass assemblies.The lead-free low-temperature melting Bi-B-Zn glass powder was used as the binder phase and applied to the silver paste to prepare the lead-free low-temperature sintered silver paste.The effects of the sintering temperature,lead-free low temperature melting glass content,and the particle size and morphology of the silver powder on the welded joints of tempred glass assemblies were investigated.Under the promoting sintering of lead-free low temperature melting glass,the microstructure of the thick silver film densified,and the least porosity of the surface microstructure of the thick silver film was 1.16%.Combined with the fracture morphology,the corresponding fracture modes under different conditions were summarized.The rapid reaction of tin-based solder and silver to produce Ag₃Sn while exposing lead-free low temperature melting glass was the inherent reason for the“dewetting”phenomenon.The wettability of the thick silver film surface corresponding to the molten tin-based solder under different conditions was analyzed.When the sintering temperature was 470℃,the zero-crossing time was0.93s,and the maximum resultant force was 0.76 m N.The wettability of the thick film surface was the best,and the wettability of the molten tin-based solder on the surface of the thick silver film became worse with the increasd of the lead-free low temperature melting glass content.Small-sized silver particles helped shorten the zero-crossing time and increased the maximum resultant value,and improved the wettability of the molten tin-based solder on the surface of the thick silver film.Finally,the lead-free low temperature sintered silver paste was used to metalize the surface of the tempered glass and then combined with soft soldering process to prepare successfully a vacuum tempered glass with low gas leakage rate and good heat insulation performance.