Abstract: Cylindrical tubes of translucent alumina ceramic, which have metallic current bushings at the ends, are sealed vacuum-tight. For this purpose, a metallizing paste which contains(a) at least one finely dispersed metal powder composed of tungsten, molybdenum, niobium or tantalum,(b) a liquid organic binder and(c) a pulverulent calcium-magnesium silicate having a melting point in the range of 1200.degree.-1500.degree. C.,is applied to the ends of the tube, the paste is burned in on the alumina ceramic and a thin metal layer is thus produced, a further layer of nickel or copper is deposited chemically or by electroplating on the metal layer remaining after the burning-in, metallic current bushings are inserted into the tube in the region of the tube ends, and the ends are sealed in the metallized areas by means of a brazing solder having a melting point between 950.degree. and 1200.degree. C., for example a Cu/Ag alloy, if necessary with the use of disk-shaped gasket elements.

Abstract: An improved process for producing polycrystalline, translucent sintered aluminum oxide tubes for use as high pressure gas discharge lamps is provided, in which an aluminum oxide powder mixture is dispersed and foamed prior to plasticizing. Into the dried powder plasticizing components based on PVA or low viscosity, weakly swelling methylcellulose adhesives in the form of a paste are mixed and the powder mixture subsequently cold formed to tubular form by extrusion. The application of these measures results not only in an especially low surface roughness with an average value of 0.2 micron, but also in a mechanical strength of at least 320 N/mm.sup.2 and an in-line light transmission of more than 64%.

Abstract: An improved process for producing polycrystalline, translucent sintered aluminum oxide tubes for use as high pressure gas discharge lamps is provided, in which an aluminum oxide powder mixture is dispersed and foamed prior to plasticizing. Into the dried powder plasticizing components based on PVA or low viscosity, weakly swelling methylcellulose adhesives in the form of a paste are mixed and the powder mixture subsequently cold formed to tubular form by extrusion. The application of these measures results not only in an especially low surface roughness with an average value of 0.2 micron, but also in a mechanical strength of at least 320 N/mm.sup.2 and an in-line light transmission of more than 64%.