GB821772A - Improvements in or relating to window seals for electrical devices - Google Patents

Abstract

821,772. Waveguide windows. GENERAL ELECTRIC CO. Ltd. Dec. 20, 1957 [Dec. 28, 1956], No. 39559/56. Class 40 (8). [Also in Group XXXVI] A method of making a window seal comprises arranging a refractory metal cup 2, having in its base a central aperture 5 with tapered edges, between inner and outer vitreous quartz cups 1 and 3, one of which has a tubular stem 4 extending from its skirt, heating the rims of the quartz cups to seal them together (an inert gas such as nitrogen being passed into the assembly through the stem 4 to prevent oxidation) and subsequently evacuating the assembly and heating by oxy-hydrogen blowlamps to cause the quartz to collapse on to the metal, first across the aperture and then around the rest of the cup. The ends of the quartz skirts are then cut away to leave the metal skirts projecting (Fig. 3) so that they may be sealed into a device such as a waveguide, a metal ring being interposed if required. To prevent the skirts of the quartz cups adhering to the end of the metal cup skirt molybdenum foils 6 may be interposed. The refractory metal for the cup is molybdenum, but tantalum or indium are given as possible alternatives. Before assembly the cup is etched in an aqueous solution of sulphuric and nitric acids to reduce its wall thickness and produce a feather edge around the sealing aperture in the base. Suitable heating and annealing treatments are described. Specification 821,771 is referred to.