Types of Glass-to-Metal Hermetic Seals

When the glass and the metal being hermetically sealed have the same coefficient of thermal expansion, a “matched seal” derives its strength from bond between the glass and the metal’s oxide. This type of glass-to-metal hermetic seal is the weaker of the two types and is generally used for low-intensity applications such as in light bulb bases.

“Compression seals” occur when the glass and the metal have different coefficients of thermal expansion such that the metal compresses around the solidified glass as it cools. Compression seals can withstand very high pressure and are used in a variety of industrial applications.[2]