Hoechst Ceramtec Aktiengesellschaft

Reinhold Gradl

Heinrich Groh

Klaus Popp

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

Process for vacuum-tight sealing of a ceramic tube

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%.

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Rueckersdorf, Germany

Reinhold Gradl