Oxides, reduction of refractory metal

Oxalates, determination of, in rare earth oxalates, 2 60 Oxalato salts, tri-, 1 35 Oxides, reduction of refractory metal, to metal powders with calcium, 6 47... 

Hydrogen Reduction of Refractory Metal Oxides in Thermal Plasma and Plasma Metallurgy of Tungsten and Molybdenum... 

The complexing role of fluoride ions in the reduction of refractory metals is now well known for the metal recovery [12]. The technology of extracting tantalum in molten salts is based on the formation of K2TaF7, obtained by reaction of HF on the oxide Ta205 extracted from raw materials [14] before the reduction of this compound by sodium in the liquid phase ... 

The Kroll process for tire reduction of tire halides of refractory metals by magnesium is exemplified by the reduction of zirconium tetrachloride to produce an impure metal which is subsequently refined with the van Arkel process to produce metal of nuclear reactor grade. After the chlorination of the impure oxide in the presence of carbon... 

Reduction of a Metal Oxide wear eye protection ). Assemble the apparatus shown in Fig. 44 and check its tightness. Put 40-50 pieces of granulated zinc into a 250-ml flask. Pour anhydrous calcium chloride into U-shaped tube. Put 0.3 g of copper oxide into the wide part of a refractory tube, and a piece of copper gauze or foil (why ) into the gas-discharge tube out of which hydrogen will flow. Pour 100-150 ml of a 20% sulphuric acid solution into the flask. Again check... 

Metals are important resources and have a wide range of applications. Metals are often extracted from ores. Once the ore is mined, the metals must be extracted, usually by chemical or electrolytic reduction. Pyrometallurgy uses high temperatures to convert ore into raw metals, while hydrometalluigy employs aqueous chemistry for the same purpose. The methods used depend on the metal and their contaminants. Most metals are obtained by hydrometallurgical processes such as aqueous acids or alkalis are predominantly used to dissolve the metal oxides, sulfides, or silicates. Electrowinning and solvent extraction are frequently used to recover and concentrate the metals. A limited number of high-temperature molten salts have also been used for the recovery of refractory metals, such as titanium and aluminum, from their ores... 

Another technique that involves creation of an intimate mixture of metal and refractory oxide consists of dry reduction of a metal oxide and refractory precursors. A classic example is the Fe/K/Al203 catalyst used in the manufacture of ammonia and alternatively, of hydrocarbon fuels . The active species is metallic iron, enhanced... 

Resistant to acid and basic fluxes if diese do not oxidize. Some sur ce contamination when metals are fused in vessels made of this material Formation of SIC above 1400 C on contact with silica-containing materials Vessels for silicate melts, sinter processes, production of refractory metals and reduction of metal oxides... 

Another example of H2 plasma reduction of oxides of refractory metals is the production of Mo ... 

The X-ray phase analysis confirmed that the synthesis products are TiC, ZrC, NbC and TaC carbides, which do not contain free carbon. Fineness of the carbides is determined by the grain size of the metal powder. The synthesis time depends on the diffusion rate of carbon into the volume of the grain or the crystallite. We used oxides of refractory metals as the starting materials for production of fine (1-5 pm) carbides. In this case the mass of the metallic calcium was increased taking into account its consumption for the calcium thermal reduction of the oxides. The presence of a higher amount of the calcium oxide in the salt melt did not incur large difficulties in the synthesis of the carbides and their washing with water to remove salts, because the calcium oxide easily dissolves in acidified water. This method of the carbide synthesis has been covered by a Russian Federation patent [6]. 

One of the advantages of pure chloride media is their low cost which makes them economically attractive. Unfortunately, in these media, the chemistry of refractory metal ions is very complicated, due to their high degree of oxidation (5 for Ta and Nb, 4 for Hf, 6 for W...) In some cases, each subhalide can intervene in the overall process for example, Boiko et al have observed on a chronopotentiogram of a solution of niobium ions in molten NaCl-KCl (Fig.l) five steps of reduction of Nb to Nb [8] subsequent to the successive formation of subhalides on the electrode where the coating occurs, chemical reactions such as disproportionation, adsorption or precipitation reactions may occur during the reduction process and act to the formation of powdery coatings. 

High density tungsten alloy machine chips are recovered by oxidation at about 850°C, foUowed by reduction in hydrogen at 700—900°C. Typically, the resultant powders are about 3-p.m grain size and resinter readily. There can be some pickup of refractory materials used in furnace constmction, which must be controUed. This process is important commercially. Eor materials that may be contaminated with other metals or impurities, the preferred recovery process is the wet chemical conversion process used for recovery of tungsten from ores and process wastes. Materials can always be considered for use as additions in alloy steel melting. 

Stable oxides, such as those of clrromium, vanadium and titanium cannot be reduced to the metal by carbon and tire production of these metals, which have melting points above 2000 K, would lead to a refractoty solid containing carbon. The co-reduction of the oxides widr iron oxide leads to the formation of lower melting products, the feno-alloys, and tlris process is successfully used in industrial production. Since these metals form such stable oxides and carbides, tire process based on carbon reduction in a blast furnace would appear to be unsatisfactory, unless a product samrated with carbon is acceptable. This could not be decarburized by oxygen blowing without significairt re-oxidation of the refractory metal. 

The high temperatures of coal char oxidation lead to a partial vaporization of the mineral or ash inclusions. Compounds of the alkali metals, the alkaline earth metals, silicon, and iron are volatilized during char combustion. The volatilization of silicon, magnesium, calcium, and iron can be greatly enhanced by reduction of their refractory oxides to more volatile forms (e.g., metal suboxides or elemental metals) in the locally reducing environment of the coal particle. The volatilized suboxides and elemental metals are then reoxidized in the boundary layer around the burning particle, where they subsequently nucleate to form a submicron aerosol. 

The carbothermic reduction processes outlined so far apply to relatively unstable oxides of those metals which do not react with the carbon used as the reductant to form stable carbides. There are several metal oxides which are intermediate in stability. These oxides are less stable than carbon monoxide at temperatures above 1000 °C, but the metals form stable carbides. Examples are metals such as vanadium, chromium, niobium, and tantalum. Carbothermic reduction becomes complicated in such cases and was not preferred as a method of metal production earlier. However, the scenario changed when vacuum began to be used along with high temperatures for metal reduction. Carbothermic reduction under pyrovacuum conditions (high temperature and vacuum) emerged as a very useful commercial process for the production of the refractory metals, as for example, niobium and tantalum, and to a very limited extent, of vanadium. 

The aluminum reduction of a refractory metal oxide invariably yields a metal product containing significant amounts of residual aluminum and oxygen, represented usually as a metal-aluminum-oxygen alloy. When the metal contains aluminum in addition to oxygen, a number of reactions can occur during pyrovacuum treatments. These are ... 

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