Thermal behavior of GeO2 doped PbO–B2O3–ZnO–Bi2O3 glasses

PbO–B2O3–ZnO–Bi2O3 glass is a representative system for vacuum and electronic sealing. Effects of GeO2 on thermal properties of the glass have been investigated in this paper. Activation energy for crystallization, glass structure, the type of crystals were characterized by differential scanning calorimetry, infrared spectroscopy, X-ray diffraction and optical microscopy. Results indicate that the addition of GeO2 (0.4–2 wt.%) to PbO–B2O3–ZnO–Bi2O3 glass can suppress crystallization of the glass and decrease the sealing temperature. With the increase of GeO2 content, germanate crystals were revealed, resulting in a slight increase of sealing temperature. When the content of GeO2 is 0.7 wt.%, the glass possesses the highest stability and lowest sealing temperature (400 °C), which is desirable for low-temperature sealing. The coefficient of thermal expansion of PbO–B2O3–ZnO–Bi2O3 glass was measured by dilatometry. The result shows that the coefficient of thermal expansion of the glass increases with the content of GeO2. The adjustability of the coefficient of thermal expansion would expand the applications of PbO–B2O3–ZnO–Bi2O3 glass. A flexural strength of 28.3 MPa was obtained at the GeO2 content of 0.7 wt.%, showing good mechanical property for sealing process.