The metal materials which are similar to the thermal expansion coefficient of the glass are sealed and connected with the glass.
Such as sealing electrical connector. The electric connector is composed of a metal casing, a sealing glass and a metal pin. Case and pin of the metal material selection is to consider the metal mechanical strength, conductivity and other factors, and the selection of sealing glass is taken into account the insulation, air tightness, heat resistance and other factors. It is known that the glass is brittle, and its resistance to stress is not tensile (tensile). How to make the sealing glass in the compressive stress state? This should consider the sealing and cooling process of the sealing glass. Sealing glass after heating, melting, filling the space to the diaspora, and the metal surface (containing oxide layer, such as Fe3O4, FeO, Cr2O3) / produce chemical bonding action to form solid interface. But after the high temperature sealing sealing parts to be cooled to room temperature, in the process, especially when the temperature drops below the glass transition temperature (from elastic to just change the setting) below, will be in the sealing parts produced in the residual thermal stress. The nature of the residual stress and the degree of influence is crucial for sealing glass material; the design requirements through proper thermal expansion coefficient, the sealing glass substrate and glass metal interface on the compressive stress produced for sealing parts of interface, structural integrity and tightness.
The glass sealing can be carried out in a chain type sealing furnace, which comprises a few temperature zones, and the sealing element is subjected to the process of preheating, constant temperature and cooling. The key is to control the furnace atmosphere, usually with some kind of mixed gas (reducing atmosphere or neutral atmosphere), ensure the metal surface oxide layer is appropriate, do not produce nitriding or carburizing phenomenon, and ensure that the glass can't be reduced. The infiltration of the oxide layer on the surface of glass and metal, and the slow cooling of the seal are the key to ensure the sealing quality. Metal and glass sealing can be pre oxidation in the same sealing furnace in sequence, i.e. metal components without prior pre oxidation and glass slabs on the graphite fixture assembly, and then in the furnace in the low-temperature stage (before the glass does not melt into gas, metal oxide), then in the air under the protection of heating to the sealing temperature, sealing immediately.
Such as sealing glass and metal shell and the metal pin three of the thermal expansion coefficient is basically the same, sealing parts in thermal stress can be ignored, so as to realize the matching sealing, but still use the glass and metal oxide sealing principle.