Influence of compositions on sealing temperature and properties of lead borate non-crystallizing sealing glasses

Lead borate sealing glasses, composed of 30–75PbO, 20–65B2O3, 0–10ZnO, 1–5Bi2O3 and 0–4GeO2 in mole percent, were prepared by conventional melting-quenching method. Influence of PbO/B2O3 ratios and the content of oxide additives on sealing temperature, thermal expansion properties, thermal stabilities and mechanical properties of lead borate glass were investigated by IR, DSC, thermal expansion and mechanical measurement. Results indicate that the ratio of PbO/B2O3, both as the main glass formers, had crucial influence on network structure of lead borate glass. An appropriate proportion of PbO/B2O3, ZnO and GeO2 are beneficial to lower sealing temperature and stabilize the glass against devitrification. When 1 mol% GeO2 is introduced, the glass possesses the highest stability and lowest sealing temperature (400 °C), which is desirable for low-temperature sealing. Bi2O3 has little effects on the melting temperature and sealing temperature, while it helps to improve mechanical properties of lead borate glasses. Only the introduction of GeO2 causes a little tendency for crystallization. The modified Johnson–Mehl–Avrami (JMA) equation was used to describe the crystallization kinetics of GeO2 doped lead borate glasses. The precipitation of crystals before melting is a block for the decrease of sealing temperature. Furthermore the adjustability of the coefficient of thermal expansion caused by the additives would expand applications of lead borate glass.