GB1280735A - High pressure metal-vapour discharge tube - Google Patents

Abstract

1280735 Metal vapour lamps MATSUSHITA ELECTRONICS CORP 25 Aug 1970 [29 Aug 1969] 40870/70 Heading H1D A high pressure metal vapour discharge lamp comprises a sealed transparent polycrystalline high density ceramic tubular enclosure 1 (e.g. alumina, beryllia, magnesia) containing a rare gas (e.g. Xe), Hg, and one or more alkali metals (e.g. Na) to form a saturated vapour pressure, and metal layers 5 in contact with the outer wall at each end to conduct heat from the hotter to the cooler parts. The layer 5 is preferably a metal of high m.p., high thermal conductivity and low vapour pressure and may be Ti, Y, Rh, Ru, Mo, Nb, Ta, W, Pt, Ir, Re or Os and may be foil such as 0À02 mm. thick Ta, formed by chemical or vapour deposition, or by sputtering. Ceramic end discs 2 may be replaced by metal end caps. The metal layers preferably do not extend beyond 5 mm. from the front tip of electrodes 6. In sputtering, the central part of the tube is covered with an insulator such as porcelain supporting a W anode, and the end parts are wound with metal foil. For chemical deposition, the end parts may be heated to 600‹ to 700‹ C. and contacted with a mixed gas of molybdenum pentachloride and hydrogen. Ceramic cement seals the enclosure, discs 2 and leadin metal tubes 3. Discs 2 are preferably the same material as the enclosure, but may be other ceramics with high thermal expansion coefficient approximating that high m.p. tubes 3 of Nb, Ta or Mo for example. Alkali vapour pressures may be 300 to 1000 torr and the coolest and highest tube temperatures may be 650‹ to 800‹ C. and 1200‹ C. respectively (e.g. Fig. 2, not shown).