Preparation And Characterization Of Lead-free Glass For Low Temperature Sealing

Sealing glass is widely used in vacuum microelectronic technology,aerospace and automotive industries due to its excellent and unique properties such as good heat resistance,high chemical stability and high mechanical strength.Since the appearance of the sealing glass,highly toxic heavy metal oxides containing lead,cadmium,thallium have been added into the composition of glass.Although this kind of glass can meet the requirements for practical use,their harm to the environment and human health is inevitable.Therefore,the development of lead-free sealing glass is arising a hot topic in sealant materials fields.This paper has investigated lead-free phosphate sealing glass with low melting temperature.The glass was prepared by the melt-quenching method,and full characterization were carried out by the DSC,XRD,FTIR and XPS,to discuss the relationship between the composition,structure and properties of proposed glasses.The point-by-point method was used to obtain the glass forming region of ternary system P₂O₅-SnF₂-WO₃,the final samples exhibited low characteristic temperature,high coefficient of thermal expansion and poor chemical stability.The effect of NH₄H₂PO₄ content,the ratio of SnO/SnF₂ and B₂O₃ content on glass structure and properties have been discussed,respectively.The results are as follows:from the investigation of ternary system SnF₂-P₂O₅,the decomposition product of the NH₄H₂PO₄ is found to not be comprised of pure P₂O₅ under the low temperature condition,one-step experiment was conducted to find that the NH₃ replaces O^2-in the glass structure,and the new P-N bond has good water resistance.The O/P ratio increases as the SnO concentration increases,and the glass structure was converted from long to short chains,the measured non-bridged oxygen content increased sharply,and the decreasing content of P-O-P bonds with poor water resistance ability has significantly improved the water durability of glass;on the other hand,because the melting point of SnF₂ is lower than that of SnO,and the decrease in SnF₂ content results the reduce in P-F and Sn-F bonds,which increases the characterization temperature of glass.The prime addition of B₂O₃ allows an increase on glass characterization temperature;the glass network changes as the increasing concentration of B₂O₃,which results the characterization temperature decreases first then increases.At the end of this paper,the chemical states,bond type and relative proportion of the main elements in the glass have been studied,a three-dimensional ball and stick model was established;the sealing performance of the glass was also measured,the sealing temperature of this glass is around 305°C and exhibits good water resistance,this glass has the potential to be used as low temperature sealing material.