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Abstract

A fusion glass of the series SiO.sub.2 --Al.sub.2 O.sub.3 --Na.sub.2 O--PbO--Fe.sub.3 O.sub.4 consists essentially of 43.0-46.2% by weight of SiO.sub.2 ; 1.0-2.0% by weight of Al.sub.2 O.sub.3 ; 6.2-16.0% by weight of Na.sub.2 O; 33.0-46.1% by weight of PbO; 2.0-4.5% by weight of Fe.sub.3 O.sub.4 ; and a maximum of 0.2% by weight of Sb.sub.2 O.sub.3, all calculated as percent by weight of oxide. These heat-absorbing fusion glasses having a low softening point can be used especially for the hermetic encapsulation of electrotechnical components, especially of conductor contacts operated magnetically as well as nonmagnetically, having coefficients of thermal expansion in the temperature range of 20.degree.-300.degree. C. of about 8.4-12.2.times.10.sup.-6 /.degree.C. and maximum heat absorption at about 1 to 1.5 .mu.m. These glasses have softening temperatures (ST) of about 537.degree. to 601.degree. C., processing temperatures (PT) of about 763.degree. to 879.degree. C., and a lower tendency toward varporization during the fusion process. The fusion stresses between the metallic conductor and the glass, existing after the fusion process and occurring upon rapid cooling in air and after a 5.degree. C./min cooling step, are characterized by a maximum tensile stress corresponding to an optical path difference of .ltoreq.400 nm/cm, at a specific birefringence of about (2.7.+-.0.1).times.10.sup.-6 mm.sup.2 /N.

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