Abstract: Quartz glass element, such as a diffusion tube useful in the production of semiconductor elements, capable of forming an outer layer of uniformly fine crystalline silica such as cristobalite or tridymite when heated to a temperature at which such crystalline silica forms containing crystallization promoting nuclei having a rate of diffusion in quartz glass less than that of sodium at elevated temperatures. Such nuclei are preferably present in the outer half of the element wall. When the quartz glass element is exposed to elevated temperatures, the nuclei promotes the formation of the outer layer of uniformly fine crystalline silica which imparts thermal dimensional stability for extended periods of use at elevated temperatures.

Abstract: A crucible of pure transparent silica glass or pure translucent or opaque silica glass for the production of monocrystals used in making semiconductor elements which includes a hollow cylindrical part and a welded-on head. The head end of the hollow cylindrical part is formed from a tube with a head margin portion constricted towards the tube axis which is formed by shaping one end of the tube. A plate is welded into the aperture formed by the constricted head margin portion and has an area equal to at least one-tenth and at most four-fifths of the total head area made up by the head margin portion and the head.

Abstract: Tubes of transparent, translucent or opaque fused silica are made by heating a hollow cylindrical blank in a drawing zone, drawing the blank from the zone while maintaining its interior under pressure and rotating same about its longitudinal axis, and calibrating the still-plastic tube immediately upon leaving the drawing zone in a calibration zone defined by two graphite plates. Apparatus for carrying out the method includes means for heating the blank to a drawing temperature in a drawing zone, means for drawing the blank from the zone, means for maintaining the interior of the blank under pressure and means for rotating the blank as it is drawn, and calibrating means for calibrating the still-plastic tube immediately upon leaving the drawing zone including two graphite plate means disposed on metal plates through which a coolant can flow.

Abstract: Quartz glass element, such as a diffusion tube useful in the production of semiconductor elements, capable of forming an outer layer of uniformly fine crystalline silica such as cristobalite or tridymite when heated to a temperature at which such crystalline silica forms containing crystallization promoting nuclei having a rate of diffusion in quartz glass less than that of sodium at elevated temperatures. Such nuclei are present in the outer half of the element wall and the maximum concentration of such nuclei is at the surface of the element and then diminishes inwardly. When the quartz glass element is exposed to elevated temperatures, the nuclei promotes the formation of the outer layer of uniformly fine crystalline silica which imparts thermal dimensional stability for extended periods of use at elevated temperatures.