Study On Preparation And Properties Of Bi-based Low Melting Point Glass

Based on the concept of environmental protection and the limitation of the application of lead-based glass in sealing glass,the lead-free bismuth-based low melting point glass is proposed to replace the traditional lead-based glass.The composition of Bi₂O₃-ZnO-B₂O₃-SiO₂-Al₂O₃-BaO glass was designed in this experiment,and the contents of Al2O3,ZnO and BaO were adjusted.The microstructure,characteristic temperature,sintering morphology and acid resistance of low melting point glass were measured by FTIR,NMR,Raman,XRD,DSC and high temperature microscopy,which provided theoretical support for the industrialized production and application of bismuth-based low melting point glass.The experimental results show that:?1?When Al₂O₃ content is less than or equal to 3 wt%,Al³⁺takes precedence over B³⁺in combination with free oxygen to form[AlO₄]tetrahedron because of its larger nuclear charge number,which enhances the network structure of glass and decreases the thermal expansion coefficient.When more than 3 wt%,[BO₄]decreased and[BO₃]increased correspondingly,the network structure of glass became loose and the thermal expansion coefficient increased.ZnAl₂O₄ crystal precipitates and the thermal expansion coefficient decreases when Al₂O₃ content is 7 wt%.The characteristic temperature Tg and Tf of glass decreased with the increase of Al₂O₃ content,and the service temperature range of glass is 550⁶40?.In summary,when the addition of Al₂O₃ content is 3 wt%,the glass has lower glass softening temperature,lower thermal expansion coefficient and better thermal stability.?2?When ZnO content is less than or equal to 12 wt%,[ZnO₄]tetrahedron was formed by the preferential combination of Zn²⁺and free oxygen,which enhanced the network structure,increases T_g and T_f,decreased thermal expansion coefficient.When more than 12 wt%,the content of free oxygen in glass decreased,and the zinc-oxygen polyhedron changes from[ZnO₄]to[ZnO₆],which destroyed the network.At the same time,the decrease of[BO₄]makes the glass network structure loosed,Tg and Tf decreased,and the thermal expansion coefficient increased.When ZnO content is 16wt%,the aggregation effect of[AlO₄]on the network skeleton is slightly stronger than that of[ZnO₆]and[AlO₆],which makes the thermal expansion coefficients of samples decrease slightly.The service temperature range of glass is 544⁶28?.In conclusion,when ZnO content is 12 wt%,the glass has the highest chemical stability and the maximum sintering temperature range.?3?When BaO content is less than 3 wt%,the addition of BaO provides more free oxygen,[AlO₆]transforms into[AlO₄],[BO₃]transforms into[BO₄],enhances the network structure and reduces the thermal expansion coefficient.When more than 3wt%,a large number of Ba²⁺as the outer body of the network enters into the gap of the glass network,which weakens the existing bridge oxygen vibration in the glass structure and increases the thermal expansion coefficient.The Al-O polyhedron in glass structure changes from[AlO₆],[AlO₅],[AlO₄]coexistence to[AlO₄].The results of high temperature microscopy show that the temperature range of glass is 546⁶39 C.When the heat treatment temperature is 580?and BaO content equal to or more than9 wt%,a small amount of BaAl₂Si₂O₈ precipitated.When the heat treatment temperature was 600?and BaO content equal to or more than 6 wt%,BaAl₂Si₂O₈were precipitated.The amount of crystallization increases with the increase of BaO content and temperature.In conclusion,when BaO content is 3 wt%,glass has the best chemical stability and lower thermal expansion coefficient.