Study On The Sealing Properties Of Bi₂O₃-ZnO-B₂O₃ Low-melting Glass

Sealing glasses are widely used in the field of microelectronics, Electro Vacuum and astronavigation, glass-metal sealing which use sealing glass is the most popular application.Nowadays main development orientations of sealing glasses are three points: lead-free glasses, lower sealing temperature, sealing glasses crystallization. The paper focuses on studying the performance of the lead-free and low melting Bi2O3-ZnO-B2O3 system and the seal of the glasses and metal.Thermal expansion device, differential thermal analysis, Rheotronic III paralleled plate rheometry, the infrared spectrometer and Raman spectrometer are used to study the performance of the sealing glasses. The sealing performance of the sealing glasses and 439L stainless steel is studied by the means of the Keyence VHX-600K digital microscope, high temperature microscope, electron probe X-ray analyzer, X-ray diffraction, scanning electron microscope.The results suggest that as the content of Bi2O3 (37.1-42.2mol%) increases, the linear expansion coefficient of the low melting Bi2O3-ZnO-B2O3 glasses has a slight increasing trend, glass transition temperature (Tg) and softening temperature (Ts) decreases a little, the viscosity of the Bi2O3-ZnO-B2O3 glasses in the same temperature(400～460℃) decreases a little. Structures of Bi2O3-ZnO-B2O3 glasses consist mainly of [BO3], [BiO3] and [BiO6] units. As the content of Bi2O3 increases, the number of [BO3], [BiO3] and [BiO6] units increases, while [BO4] units decreases, glass network structure converts to sheet structure which leads to more loose glass structure.Bi2O3-ZnO-B2O3 glasses powder are squashed and then heated in the paper. They would experience four stages:sintering densification, smooth surface outline, smooth whole outline and expansion, wetting stainless steel and flatting. As the content of Bi2O3 (37.1-42.2mol%) increases, samples undergo the process of sintering, expansion, smoothing, softening, collapse. Interface reaction between glasses and 439L stainless steel is mainly Fe-Cr-Bi reaction, we suggest that Bi diffusion is the key of transition layer growth. After heated in 530℃for half an hour, glass sample (37.1 mol% Bi2O3) and glass sample (39.8 mol% Bi2O3) can separate out spherical Bi6B10O24 crystal particle. The diameter of spherical crystal particle in glass sample (37.1 mol% Bi2O3) is about 0.5um, and the amount is relatively less. The diameter of spherical crystal particle in glass sample (39.8 mol% Bi2O3) is about 0.1-0.3um and the amount is relatively more. After heated in 530℃for half an hour, glass sample (41.0 mol% Bi2O3) can separate out acicular Bi24B2O39 crystal particle. When the temperature goes up to certain extent and sealing temperature and time of the heat preservation remain unchanged, if the roughness (Rz) slightly increases, the wetting angle of glass sample (41.0 mol% Bi2O3) and 439L stainless steel can slightly decrease. After sealing process the glass sample (41.0 mol% Bi2O3) can separate out crystal particle when sealing temperature goes up to about 460℃.