Copper Disc Seal
In the copper disc seal, as proposed by W.G. Houskeeper, the end of a glass tube is closed by a round copper disc. An additional ring of glass on the opposite side of the disc increases the possible thickness of the disc to more than 0.3 mm. Best mechanical strength is obtained if both sides of the disc are fused to the same type of glass tube and both tubes are under vacuum. The disc seal is of special practical interest because it is a simple method to make a seal to low expansion borosilicate glass without the need of special tools or materials. The keys to success are proper borating, heating of the joint to a temperature as close to the melting point of the copper as possible and to slow down the cooling, at least by packing the assembly into glass wool while it is still red hot.
Read more about this topic: Glass-to-metal Seal
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