Glass-to-metal seals are a very important element of the construction of vacuum tubes, electric discharge tubes, incandescent light bulbs, glass encapsulated semiconductor diodes, reed switches, pressure tight glass windows in metal cases, and metal or ceramic packages of electronic components.
Properly done, such a seal is hermetic. To achieve such a seal, two properties must hold:
- The molten glass must be capable of wetting the metal, in order to form a tight bond, and
- The thermal expansion of the glass and metal must be closely matched so that the seal remains solid as the assembly cools.
When one material goes through a hole in the other, such as a metal wire through a glass bulb, and the inner material's coefficient of thermal expansion is higher than that of the outer, it will shrink more as it cools, cracking the seal. If the inner material's coefficient of expansion is slightly less, the seal will tighten as it cools, which is often beneficial. Since most metals expand much more with heat than most glasses, this is not easy to arrange.
Read more about Glass-to-metal Seal: Glass-to-metal Bonds, Mercury Seal, Platinum Wire Seal, Dumet Wire Seal, Copper Tube Seal, Copper Disc Seal, Matched Seal, Molybdenum Foil Seal, Compression Seal, Design Aspects
Other articles related to "seal":
... Also the mechanical design of a glass-to-metal seal has an important influence on the reliability of the seal ... In practical glass-to-metal seals cracks usually start at the edge of the interface between glass and metal either inside or outside the glass container ... reach the surface on the same side where it started and the seal will not leak despite the crack ...
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