Metallic vapor processes

Reduction to Liquid Metal. Reduction to Hquid metal is the most common metal reduction process. It is preferred for metals of moderate melting point and low vapor pressure. Because most metallic compounds are fairly insoluble in molten metals, the separation of the Hquified metal from a sohd residue or from another Hquid phase of different density is usually complete and relatively simple. Because the product is in condensed form, the throughput per unit volume of reactor is high, and the number and si2e of the units is rninimi2ed. The common furnaces for production of Hquid metals are the blast furnace, the reverberatory furnace, the converter, the flash smelting furnace, and the electric-arc furnace (see Furnaces, electric). 

Condensation of metal vapors followed by deposition on cooler surfaces yields metal powders as does decomposition of metal hydrides. Vacuum treatment of metal hydrides gives powders of fine particle size. Reaction of a metal haHde and molten magnesium, known as the KroU process, is used for titanium and zirconium. This results in a sponge-like product. 

Indirect (French) Process. Ziac metal vapor for burning is produced ia several ways, one of which iavolves horizontal retorts. Siace all the vapor is burned ia a combustion chamber, the purity of the oxide depends on that of the ziac feed. Oxide of the highest purity requires special high grade ziac and less-pure products are made by blending ia Prime Western and even scrap ziac. 

In these processes, a special base coat is applied to the surface of the plastic product to be metallized. The product is then placed in a vacuum chamber in which a metallic vapor is created and deposited on the product. A protective clear top coat is then applied over the thin metal layer for abrasion and environmental resistance. The simplest vacuum metallizing processes use resistance heating to melt and vaporize the metal. 

Briquettes of CaO with 5-20% excess powdered A1 are heated under vacuum to 1170°C in a Ni-Cr steel (15/28) retort in which the Ca vapor, produced by reduction of solid CaO by A1 vapor, is condensed in a zone at 680-740 C. Any Mg impurity is condensed in a zone at 275-350°C a mixture of the two metals condenses in an intermediate zone. The A1 content of the product can be reduced by passing the metal vapor, before it condenses, through a vessel filled with solid CaO. The adaptation of the FeSi thermal reduction process for Mg production (see 7.2.3.2.1) to Ca manufacture has also been described but is not economically viable in comparison with the above process. The thermal reduction of CaO with carbon has been proposed as for Mg production, however, the reversibility of the equilibrium ... 

Vacuum metalizing is the process of coating a workpiece with metal by flash heating metal vapor in a high-vacuum chamber containing the workpiece. The vapor condenses on all exposed surfaces. 

Summary of experimental data Film boiling correlations have been quite successfully developed with ordinary liquids. Since the thermal properties of metal vapors are not markedly different from those of ordinary liquids, it can be expected that the accepted correlations are applicable to liquid metals with a possible change of proportionality constants. In addition, film boiling data for liquid metals generally show considerably higher heat transfer coefficients than is predicted by the available theoretical correlations for hc. Radiant heat contribution obviously contributes to some of the difference (Fig. 2.40). There is a third mode of heat transfer that does not exist with ordinary liquids, namely, heat transport by the combined process of chemical dimerization and mass diffusion (Eq. 2-162). 

Sample. This source places no restrictions on target material. Clusters of metals, produced. For example, polyethylene and alumina have been studied as well as refractory metals like tungsten and niobium. Molecular solids, liquids, and solutions could also be used. However the complexity of the vaporization process and plasma chemistry makes for even more complex mixtures in the gas phase. To date the transition metals(1-3) and early members of group 13 (IIIA) and 14 (IVA)( 11-16) have been the most actively studied. 

Entrainment Separators. In any process in which the product is volatilized, including both Gas Recycle and Liquid Recycle, ppm or ppb levels of metal catalyst may be entrained in the vapors leaving the separation system. Entrainment separators (Figure 2.9) are often included to recover the metal. Vaporous product effluent from a gas recycle reactor may be sent to a separator where it is passed through a demisting pad to return some aldehyde and condensation product and particularly to prevent potential carryover of catalyst. [6]... 

Vaporization processes that produce the high 5 Fe values of deep sea spherules are, of course, more complicated, because a large portion of the heating and vaporization occurs in the atmosphere, and is accompanied hy conversion of Fe metal to Fe oxides. 

Lastly, and ultimately the most important, is evaluation of the applicability of the metal vapor top contact process for insertion into fabrication lines for mass production. At this point, significant improvements are required, well beyond the present state-of-the art, in order to achieve large cost efficient, high yield, high throughput fabrication. Hopefully, in the next decade, many of these issues will be resolved by the integrated research results from workers worldwide. 

In the evaporation process, wastewaters from metal finishing processes are heated until water vapor is formed. The water vapor is continuously removed and condensed. In this manner,... 

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