Fused salts continued

More than one boride phase can be formed with most metals, and in many cases a continuous series of solid solutions may be formed. Several methods have been used for the relatively large-scale preparation of metal borides. One that is commonly used is carbon reduction of boric oxide and the appropriate metal oxide at temperatures up to 2000 °C. Fused salt electrolysis of borax or boric oxide and a metal oxide at 700 1000 °C have also been used. Small-scale methods available include direct reaction of the elements at temperatures above 1000 °C and the reaction of elemental boron with metal oxides at temperatures approaching 2000 °C. One commercial use of borides is in titanium boride-aluminum nitride crucibles or boats for evaporation of aluminum by resistance heating in the aluminizing process, and for rare earth hexaborides as electronic cathodes. Borides have also been used in sliding electrical contacts and as cathodes in HaU cells for aluminum processing. 

Another possibility lies in the use of equipment being developed by Manowitz and co-workers (H2). The equipment, called a continuous calciner, converts aqueous slurries to compact fused salts. One source of fission products of high specific activity would be the Mn02 scavenge cake used in separations processes, to remove most of the fission products in a head-end treatment prior to a solvent extraction process. Mn02 may be dissolved in fused caustic in a continuous calciner to form a highly concentrated radiation source. 

Heat cleaning n. (1) A batch or continuous process in which sizing on glass fibers is vaporized off. (2) Cleaning residual polymer from small extruder screws, dies or other small parts by immersing them in fused salts such as sodium nitrate. 

If low impurity levels are required, the method of preparing the fluoride for the electrolytic method is not as critical as for the Ca reduction method - at least with respect to the O content of CeFs. In the electrolytic method Ce02 or Ce203 is added to the fluoride flux, and it is the oxide which is reduced to the metal. For the Ca reduction method the O content of the fluoride is quite critical since any oxide present in the fluoride will end up in the metal. Furthermore, as noted by Carlson et al. (1960) the fluoride flux may serve to extract some of the impurities. These authors found that the levels of C, N, O, F, Mg and Ni in a Y-Mg alloy are reduced by extraction with a fused salt. Similarly, in the electrolytic preparation one might expect that the long contact time of the metal with the fluoride flux may decrease the level of some impurities in the metal. This behavior of the fluoride flux, however, may lead to difficulties if the flux is contaminated from the previous runs, since continued use would saturate the flux with certain impurities, and they would no longer be extracted, and even might be introduced into the next metal sample. 

Ervin, Jr., G. Ueltz, H.F.G. (1958) Apparatus for continuous production of refractory metal by electrolysis of fused salts. US Patent 2,837,478. 

The two types of high temperature fuel cell are quite different from each other (Table 6). The molten carbonate fuel cell, which operates at 650°C, has a metal anode (nickel), a conducting oxide cathode (e.g. lithiated NiO) and a mixed Li2C03/K2C03 fused salt electrolyte. Sulphur attack of the anode, to form liquid nickel sulphide, is a severe problem and it is necessary to remove H2S from the fuel gas to <1 ppm or better. However, CO is not a poison. Other materials science problems include anode sintering and degradation, corrosion of cell components and evaporation of the electrolyte. Work continues on this fuel cell in U.S.A. and there is some optimism that the problem will be solved within 10 years. 

Lamaze AP, Paillere P (1990) Fused salts for continuous production of multivalent metal from halide. European patent n°394154A... 

Heat in a porcelain dish, set over a small flame, 12 g of KSCN just to fusion (m.p,172°C). While continuing to heat gently, sift on the fused salt, in small portions, 10 g of chrome alum, stirring well after each addition. Eventually the red-violet mixture is almost solidified. Allow to cool in a desiccator. Then quickly scrape the solid from the dish into 60-70 cm C2H5OH in a mortar and crush and triturate with the solvent. Filter the insoluble K2SO4 and quickly concentrate the filtrate on a boiling water bath, until a crystalline crust is formed. Dry in a vacuum desiccator over cone. H2SO4. Calculate % yield. 

Chemical reaction This involves the formation of distinct compounds by reaction between the solid metal and the fused metal or salt. If such compounds form an adherent, continuous layer at the interface they tend to inhibit continuation of the reaction. If, however, they are non-adherent or soluble in the molten phase, no protection will be offered. In some instances, the compounds form in the matrix of the alloy, for example as grain-boundary intermetallic compound, and result in harmful liquid metal embrittlement (LME) although no corrosion loss can be observed. 

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