Powder industrial processes

R. M. German and R. G. lacocca, "Powder Metallurgy Processing and AppHcations for IntermetaUics," Mdvances in Powder Metallurgy (N Particulate Materials, Vol. 6, Metal Powder Industries federation, Princeton, N.J., 1993. 

Sodium Tetrahydroborate, Na[BH ]. This air-stable white powder, commonly referred to as sodium borohydride, is the most widely commercialized boron hydride material. It is used in a variety of industrial processes including bleaching of paper pulp and clays, preparation and purification of organic chemicals and pharmaceuticals, textile dye reduction, recovery of valuable metals, wastewater treatment, and production of dithionite compounds. Sodium borohydride is produced in the United States by Morton International, Inc., the Alfa Division of Johnson Matthey, Inc., and Covan Limited, with Morton International supplying about 75% of market. More than six million pounds of this material suppHed as powder, pellets, and aqueous solution, were produced in 1990. 

Thermal insulation is available over a wide range of temperatures, from near absolute zero (-273 C) ( 59.4°F) to perhaps 3,(1()0°C (5,432°F). Applications include residential and commercial buildings, high- or low-temperature industrial processes, ground and air vehicles, and shipping containers. The materials and systems in use can be broadly characterized as air-filled fibrous or porous, cellular solids, closed-cell polymer foams containing a gas other than air, evacuated powder-filled panels, or reflective foil systems. 

In the second part of the 20th century, the tantalum capacitor industry became a major consumer of tantalum powder. Electrochemically produced tantalum powder, which is characterized by an inconsistent dendrite structure, does not meet the requirements of the tantalum capacitor industry and thus has never been used for this purpose. This is the reason that current production of tantalum powder is performed by sodium reduction of potassium fluorotantalate from molten systems that also contain alkali metal halides. The development of electronics that require smaller sizes and higher capacitances drove the tantalum powder industry to the production of purer and finer powder providing a higher specific charge — CV per gram. This trend initiated the vigorous and rapid development of a sodium reduction process. 

Modem requirements of the capacitor industry initiate further development of tantalum powder production processes. The tendency is to produce powder of higher purity with a higher specific charge and at lower cost. Further development of the processes can be successfully achieved based on current achievements in the chemistry of tantalum and niobium fluoride compounds. 

This method involves the removal of mbber particles from tire tread by abrasion and is confined to the preparation of tire buffings, which is obtained as a by-product of retreading. It is a normal practice in industries to reuse tire buffings to make low-technical products by the revulcanization of the powder or by using the powder-sintering process. 

The main requirements for a coating are that it is easy to apply (i.e., low viscosity) and dries to a non-tacky finish within a reasonable time. Originally, this equated to the solution and evaporation of the solvent. However, because of environmental concerns, formulations have tended to shift the concentration of solvents from 80% to less than 20% (known as high solids coatings). Many industrial processes use polymer powders (of approximately 40 pm diameter),... 

There are a large number of industrial processes which employ cavitation as an energy source for the generation of fine emulsions and dispersions. One of the earliest devices which was developed for this purpose was the so-called liquid whistle (see Chapter 7) and this continues to be used widely. Typical examples of the uses of such whistles include the preparation of emulsion bases for soups, sauces or gravies which consist of a premix of water, milk powder, edible oil and fat together with flour or starch... 

Generally, alkoxide-derived monodisperse oxide particles have been produced by batch processes on a beaker scale. However, on an industrial scale, the batch process is not suitable. Therefore, a continuous process is required for mass production. The stirred tank reactors (46) used in industrial process usually lead to the formation of spherical, oxide powders with a broad particle size distribution, because the residence time distribution in reactor is broad. It is necessary to design a novel apparatus for a continuous production system of monodispersed, spherical oxide particles. So far, the continuous production system of monodisperse particles by the forced hydrolysis... 

In industrial processes, Ti02 powder is mainly produced by sulfate or chloride (vapor) method. In the laboratory, titanium alkoxide is frequently used as the starting material. 

A considerable amount of subsequent research and process development has been carried out to produce silicon carbide with a reduced level of excess carbon via processes that allow more facile cross-linking.2 -32 Several hundred papers and patents on this topic exist in the literature, and only a few examples will be mentioned here. One process development involves the slurry spinning of fibers in place of melt spinning.33 In this process, silicon carbide powder, made by a conventional industrial process, is dispersed in a solution of carbosilanes in toluene. The syrupy paste is spun into fibers and then pyrolyzed to silicon carbide. These fibers are reported to be stable at 1,500 °C for 120 hours. 

It has been shown earlier that the fluidisation properties of a powder in air at ambient conditions may be predicted by establishing in which Geldart group it lies. Table 8 shows that most fluidised bed industrial processes are operated at temperatures and pressures well above ambient. It is important to note that at operating temperatures and pressures... 

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