Aluminum niobium

Niobium is a soft grayish-silvery metal that resembles fresh-cut steel. It is usually found in minerals with other related metals. It neither tarnishes nor oxidizes in air at room temperature because of a thin coating of niobium oxide. It does readily oxidize at high temperatures (above 200°C), particularly with oxygen and halogens (group 17). When alloyed with tin and aluminum, niobium has the property of superconductivity at 9.25 Kelvin degrees. 

Titanium-aluminum-niobium alloys have been developed for biocompatible, high-strength surgical implants (Semlitsch et al. 1985), while metal-resin composites containing niobium as filler have potential use as restorative materials in dentistry (Misra and Bowen 1977). The metal possesses superior superconductive properties in strong magnetic fields, which may be... 

THE ELECTRODEPOSITION OF ALUMINUM-NIOBIUM ALLOYS FROM CHLOROALUMINATE ELECTROLYTES... 

Alloy Inconel X750 contains additions of aluminum, niobium and titanium which form an intermetallic compound, NislAl, Ti) to make it age hardenable and provide high strength. It is extremely resistant to SCC in chloride environment. It is used in gas turbines, vacuum envelopes, extrusion dies and springs. 

Valve metals Metals that can be oxidized to form dense, coherent oxide layers on the surface. Examples Aluminum niobium titanium. 

Material Aluminum Aluminum Aluminum Aluminum Niobium... 

In a generalized sense, acids are electron pair acceptors. They include both protic (Bronsted) acids and Lewis acids such as AlCb and BF3 that have an electron-deficient central metal atom. Consequently, there is a priori no difference between Bronsted (protic) and Lewis acids. In extending the concept of superacidity to Lewis acid halides, those stronger than anhydrous aluminum chloride (the most commonly used Friedel-Crafts acid) are considered super Lewis acids. These superacidic Lewis acids include such higher-valence fluorides as antimony, arsenic, tantalum, niobium, and bismuth pentafluorides. Superacidity encompasses both very strong Bronsted and Lewis acids and their conjugate acid systems. 

Low Expansion Alloys. Binary Fe—Ni alloys as well as several alloys of the type Fe—Ni—X, where X = Cr or Co, are utilized for their low thermal expansion coefficients over a limited temperature range. Other elements also may be added to provide altered mechanical or physical properties. Common trade names include Invar (64%Fe—36%Ni), F.linvar (52%Fe—36%Ni—12%Cr) and super Invar (63%Fe—32%Ni—5%Co). These alloys, which have many commercial appHcations, are typically used at low (25—500°C) temperatures. Exceptions are automotive pistons and components of gas turbines. These alloys are useful to about 650°C while retaining low coefficients of thermal expansion. Alloys 903, 907, and 909, based on 42%Fe—38%Ni—13%Co and having varying amounts of niobium, titanium, and aluminum, are examples of such alloys (2). 

Some metals used as metallic coatings are considered nontoxic, such as aluminum, magnesium, iron, tin, indium, molybdenum, tungsten, titanium, tantalum, niobium, bismuth, and the precious metals such as gold, platinum, rhodium, and palladium. However, some of the most important poUutants are metallic contaminants of these metals. Metals that can be bioconcentrated to harmful levels, especially in predators at the top of the food chain, such as mercury, cadmium, and lead are especially problematic. Other metals such as silver, copper, nickel, zinc, and chromium in the hexavalent oxidation state are highly toxic to aquatic Hfe (37,57—60). 

The reaction of chlorine gas with a mixture of ore and carbon at 500—1000°C yields volatile chlorides of niobium and other metals. These can be separated by fractional condensation (21—23). This method, used on columbites, is less suited to the chlorination of pyrochlore because of the formation of nonvolatile alkaU and alkaline-earth chlorides which remain in the reaction 2one as a residue. The chlorination of ferroniobium, however, is used commercially. The product mixture of niobium pentachloride, iron chlorides, and chlorides of other impurities is passed through a heated column of sodium chloride pellets at 400°C to remove iron and aluminum by formation of a low melting eutectic compound which drains from the bottom of the column. The niobium pentachloride passes through the column and is selectively condensed the more volatile chlorides pass through the condenser in the off-gas. The niobium pentachloride then can be processed further. 

Niobium pentoxide also is reduced to metal commercially by the aluminothermic process. The finely ground powder is mixed with atomized aluminum and an accelerator compound which gives extra heat during reaction, then is ignited. The reaction is completed quickly and, after cooling, the slag is broken loose to free the metal derby which is purified by electron-beam melting. 

Phosgene can be employed in a variety of metal-recovery operations, eg, in the recovery of platinum, uranium, plutonium, and niobium (69—73). Phosgene has been proposed for the manufacture of aluminum chloride, beryllium chloride, and boron trichloride (74—76). Phosgene has been patented as a stabilizer, either by itself or in combination with thionyl chloride, for Hquid SO2 (77). 

Ammonia and alcohol may be used instead of sodium alkoxides to manufacture alkoxides of titanium and other metals such as tirconium, hafnium, germanium, niobium, tantalum, aluminum, and tin. 

Sihca is reduced to siUcon at 1300—1400°C by hydrogen, carbon, and a variety of metallic elements. Gaseous siUcon monoxide is also formed. At pressures of >40 MPa (400 atm), in the presence of aluminum and aluminum haUdes, siUca can be converted to silane in high yields by reaction with hydrogen (15). SiUcon itself is not hydrogenated under these conditions. The formation of siUcon by reduction of siUca with carbon is important in the technical preparation of the element and its alloys and in the preparation of siUcon carbide in the electric furnace. Reduction with lithium and sodium occurs at 200—250°C, with the formation of metal oxide and siUcate. At 800—900°C, siUca is reduced by calcium, magnesium, and aluminum. Other metals reported to reduce siUca to the element include manganese, iron, niobium, uranium, lanthanum, cerium, and neodymium (16). 

The elements that decrease the extent of the austenite field include chromium, siUcon, molybdenum, tungsten, vanadium, tin, niobium, phosphoms, aluminum, and titanium. These are known as ferrite stabilizers. 

The fluorine concentration in hydrofluorides of tantalum and niobium is an extremely important issue. Fluorine that separates into the gaseous phase interacts with the construction elements of the furnaces, leading to additional contamination of the final product by silicon, aluminum, etc. Thus, it is recommended to perform diying in crucibles made of Teflon or polypropylene with appropriate temperature limitations. Use of crucibles made of carbon-glass ensures high quality and a broad working temperature range, at least up to 300-350°C. 

Several methods are described for the production of tantalum and niobium metal. Metals can be obtained by reduction of pentachlorides with magnesium, sodium, hydrogen or by thermal decomposition in vacuum [24,28]. Oxides can be reduced using carbon, aluminum, calcium, magnesium [28, 537, 538] or alkali and rare earth metals [539]. 

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