High-temperature vacuum

These provide thin films of a soHd, or a combination of soHds, interposed between two moving surfaces to reduce friction and wear. They are coming into more general use for high temperatures, vacuum, nuclear radiation, aerospace, and other environments that prohibit use of oils and greases. 

The first commercial use of tantalum was as filaments ia iacandescent lamps but it was soon displaced by tungsten. Tantalum is used ia chemical iadustry equipment for reaction vessels and heat exchangers ia corrosive environments. It is usually the metal of choice for heating elements and shields ia high temperature vacuum sintering furnaces. In 1994, over 72% of the tantalum produced ia the world went iato the manufacturiag of over 10 x 10 soHd tantalum capacitors for use ia the most demanding electronic appHcations. 

Typical equipment made from tantalum includes heat exchangers, reaction vessels liners, thermowells, and heating elements or heat shields for high temperature vacuum sintering furnaces. Tantalum fabricated parts are found in the manufacturing of pharmaceuticals, explosives, insecticides, dyes, acidic baskets for silver cyanide barrel platers, and in hydrochloric and hydrobromic acid condensers. 

Aluminothermal Method. Calcium metal is produced by high temperature vacuum reduction of calcium oxide in the aluminothermal process. This process, in which aluminum [7429-90-5] metal serves as the reducing agent, was commercialized in the 1940s. The reactions, which are thermodynamically unfavorable at temperatures below 2000°C, have been summarized as ... 

Having established the feasibility of niobium metal production by the carbothermic reduction of niobium pentoxide under temperature and pressure conditions readily attainable in the laboratory and in industry, the principles of efficient process execution may now be examined. In a high-temperature vacuum furnace operation, the quantity of gas that is to be pumped off can influence the choice of the vacuum process. When the reduction of niobium pentoxide with either carbon or niobium carbide is attempted according to the following overall equations ... 

It is produced by the reduction of barium oxide (BaO), using aluminum or sihcon in a high-temperature vacuum. It is also commercially produced by the electrolysis of molten barium chloride (BaCy at about 950°C, wherein the barium metal is collected at the cathode and chlorine gas is emitted at the anode. 

J.W. Patten, M Permanent High Temperature Vacuum Tubing Joints , Boeing Co, AD-695-493, 1969, 15 pp 7)Gunther Coho, Edit, Expls Pyrots 3 (4), 1970 (Abstract)... 

Coils should be considered only if jacketing alone does not provide a sufficient heat transfer area, if jacket pressure exceeds 150 psig, or if high-temperature vacuum processing is required. The coil offers the advantage of a higher overall film coefficient because of thinner walls with the latter conditions, but the wall resistance may not be significant compared to that on the process side (e.g., with a viscous liquid). 

On using various CNM purification methods (acid washing, ultrasonication, high temperature vacuum annealing) we managed to remove almost all the catalyst impurities and soot inclusions. 

A well defined amount of water, depending on the cation, is kept after vacuum drying (10 5 torr) at room temperature (fig. 1). This residual water (1 to 2 H2O/SO3 ) is desorbed after heating above the glass transition of the Nafion matrix. During rehydration of the high temperature vacuum dried sample the initial isotherm sorption curve is reobtained only above a well defined relative water pressure (fig. 2). 

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