Refractory metal compounds

The fundamentals of intermetallic oxidation will be briefly described followed by discussion of work on the Ni- and Fe aluminides, Ti aluminides, and refractory metal compounds. It will become clear that work is now focussed in two general areas (i) adding to the fundamental knowledge of oxidation mechanisms and (ii) developing approaches to allow intermetallics to reach the application stage e. g. coating, composite development, and life predictions. 

The attainment of stable solutions of some refractory metal compounds in molten solvents can present major problems. Thus, solutes can be lost through vaporization the volatility of TiCU, for example, has undoubtedly hindered the commercial exploitation of electrolytic routes for extracting titanium, since the tetrachloride is the feedstock of choice. The formation of insoluble cluster compounds and the disproportionation of dissolved species also present added complicationsTable 3 shows some of the systems in which these effects occur and the factors which control the stability of the solutions. 

Sadoway, D.R. (1990) The synthesis of refractory-metal compounds by electrochemical processing. In Non Aqueous Media in Refractory Metals Extraction, Processing, and Applications. The Minerals, Metals, and Materials Society, TMS Publishing, Warrendale, PA, pp. 213-220. 

Stohr, U. and Freyland, W. (1999) Electrochemical impedance investigations of redox mechanisms of refractory metal compounds in molten salts. I. Niobium chloride and oxychloride in CsCl-NaCI eutectic melt. FJectrochim. Acta, 44(13), 2199-2207. 

VA Gubanov, AL Ivanovsky, GP Shveikin, DE Elhs. Vacancies and the energy spectrum of refractory metal compounds TiC and TiO. J Phys Chem Solids 45 719, 1984. 

At elevated temperatures, CaH2 reacts with halogens, sulfur, phosphoms, alcohols, and ammonia. At high temperatures, it reacts with refractory metal oxides and haUdes. Calcium hydride is substantially inert to organic compounds that do not contain acidic hydrogens. 

Chlorination. In some instances, the extraction of a pure metal is more easily achieved from the chloride than from the oxide. Oxide ores and concentrates react at high temperature with chlorine gas to produce volatile chlorides of the metal. This reaction can be used for common nonferrous metals, but it is particularly useful for refractory metals like titanium (see Titanium and titanium alloys) and 2irconium (see Zirconium and zirconium compounds), and for reactive metals like aluminum. 

In direction evaporation, the evaporant is the refractory compound itself, whereas in reactive or activated reactive evaporation (ARE), a metal or a low valency metal compound is evaporated in the presence of a partial pressure of a reactive gas to form a compound deposit, eg, Ti is evaporated in the presence of N2 to form TiN, or Si or SiO is evaporated in the presence of O2 to form Si02. 

Next to Cr C2, TiC is the principal component for heat and oxidation-resistant cemented carbides. TiC-based boats, containing aluminum nitride, AIN, boron nitride, BN, and titanium boride, TiB2, have been found satisfactory for the evaporation of metals (see Boron compounds, refractory boron compounds Nitrides). 

Vanadium-Sodium Compounds Most Corrosive. Physical property data for vanadates, phase diagrams, laboratory experiments, and numerous field investigations have shown that the sodium vanadates are the lowest melting compounds and are the most corrosive to metals and refractories. These compounds are thought to form by either the vapor phase reaction of NaCI and V2O5 or by the combination of fine droplets of these materials upon the cooler parts of combustion equipment. 

Plutonium-noble metal compounds have both technological and theoretical importance. Modeling of nuclear fuel interactions with refractory containers and extension of alloy bonding theories to include actinides require accurate thermodynamic properties of these materials. Plutonium was shown to react with noble metals such as platinum, rhodium, iridium, ruthenium, and osmium to form highly stable intermetallics. 

The silicides of major industrial importance are the disilicides of the refractory metals molybdenum, tantalum, titanium, tungsten, vanadium, and zirconium.pl] These compounds are of great interest par-... 

The coating material, usually in the form of powder, is metered into a compressed-gas stream and fed into the heat source where it is heated to its melting point and proj ected onto the substrate. In the case of refractory metals and compounds which have high melting points, spraying is carried out in an inert atmosphere to avoid detrimental chemical reactions such as oxidation. 

Activated carbon has high specific surface area with respect to its volume, and thus has high adsorption capacity. Activated carbon adsorption is considered to be one of the most versatile treatment technologies and can remove classical pollutants such as COD, TOC, BOD, and nitrogen, as well as toxic pollutants such as phenol, refractory organic compounds, VOCs, and soluble heavy metals.38 Activated alumina and peat have also demonstrated similar abilities. 

BOD, inorganic salts, heavy metals pathogens, refractory organic compounds, plastics nitrate metals including iron, copper, manganese suspended solids... 

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