Quartz to metal seal

Seals for electrical devices (e.g. infra-red lamps) comprising a member of fused silica or quartz and a sealed in lead-in conductor are adapted for use at elevated temperatures by constructing the outer lead 8 (Fig. 3), of oxidation resisting material, e.g. platinum and filling the cavity 9 (which is caused by the difference in the coefficient of expansion of the quartz and metal) with a low melting point lead-borate glass which forms a liquid seal at elevated temperatures and is held in the cavity by capillary action. The outer lead 8 is attached to an intermediate foliated portion 6 (preferably of molybdenum) which may be integral with the molybdenum inner lead 7. The glass 10 is introduced into the cavity 9 by slipping a bead of glass 11 (Fig. 2) of the low-melting point glass over the outer lead 8 of the otherwise completed lamp in an upright position. Heat is applied to the surface of the seal portion 4 by a small oxyhydrogen flame, the bead melts and is drawn down into the capillary space 9. The glass composition is in parts by weight, preferred range in brackets: 0-10 (2-5) SiO2; 65-85 (70-80) PbO2; 10-20 (12-15) B2O3; 0-7 (1-5 Tl2O3; 0-5 (1-2) ZnO; 0-2 (0.25-1) CaO; 0-2 (0.25-1) K2O; 0-2 (0-0.5) Na2O; 0-2 (0-0.5) Li2O; 0-7 (1-4)F2.