Vacuum performance of glass

    The sources of gas inside the glass material mainly include the following parts: the gas adsorbed on the glass surface (mainly water vapor and carbon dioxide); the water adsorbed by the glass during long-term storage is complicated on the basis of the hydrolysis of alkaline silicate in the glass. Chemical reactions, when the glass bulb is evacuated or heated to degas, the products of these chemical reactions are one of the gas sources;

    In the process of glass melting, the molten glass interacts with the surrounding gas to dissolve the gas (mainly carbon monoxide, nitrogen and oxygen) remaining in the glass. Therefore, when the glass that has not been degassed is working under vacuum, a large amount of gas is emitted, especially when the temperature is raised.

    When the temperature rises, the first thing that is released is the water vapor and carbon dioxide adsorbed on the glass surface. The gas output increases as the temperature rises, and the gas output reaches the maximum; then, the gas output decreases due to the decrease of the water vapor and carbon dioxide adsorption layer on the glass surface. When the temperature is higher than 450°C, the gas adsorbed on the glass surface is basically released, and the gas output is reduced to a minimum.

    If the temperature continues to rise, the gas dissolved in the glass will continue to be released, and the glass will decompose to produce gas at high temperatures, causing the gas output to continue to rise.

    Therefore, glass parts used in electric vacuum devices must be degassed in advance or during device production. For closed electric vacuum devices, the effect of glass helium infiltration on the device must also be considered during long-term operation.

(huiputech)