Abstract: In order to connect a tube of a more common material, such as stainless steel, to a tube of a highly corrosion-resistant metal such as tantalum, where the two tubes cannot be welded together by fussion technology, a connection piece is made of two closely fitting layers of the two materials telescoped into each other, which are exposed to hot compressed noble gas, such as argon, in a pressure vessel, with precautions against oxidation from residual oxygen in the noble gas. Then the ends are machined to remove any hard soldered portion used to make a gas-tight seal of the blank before pressure treatment, after which a longer ring-shaped section of the stainless part of the connection piece is removed at one end and likewise a section of the tantalum part of the connection piece at the other end, so that the projecting ends can be welded to the pipes to be joined.

Abstract: For the production of a bubble-free vitreous material, and in particular bubble-free vitreous silica, bubbles-containing vitreous material is exposed in a furnace, at a temperature which reduces its viscosity to a value between 10.sup.13.5 and 10.sup.8 Pa.sec, to the omnidirectional pressure ranging from 100 to 3000 bars of a gas which is insoluble in the vitreous material for a period of not less than 10 minutes and is then cooled.

Abstract: Optical-grade zinc sulfide bodies produced by the CVD technique and subjected to an aftertreatment under a high gas pressure and at elevated temperature possess improved optical properties. They are suited for use as infrared windows.