Refractory metals zirconium

Refractory metals Zirconium Hafnium Titanium Kroll process, chlorination, and magnesium reduction Chlorine, chlorides, SiCli Wet scrubbers... 

Nitrogen and carbon are the most potent solutes to obtain high strength in refractory metals (55). Particulady effective ate carbides and carbonitrides of hafnium in tungsten, niobium, and tantalum alloys, and carbides of titanium and zirconium in molybdenum alloys. 

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. 

The manufacture of refractory metals such as titanium, zirconium, and hafnium by sodium reduction of their haHdes is a growing appHcation, except for titanium, which is produced principally via magnesium reduction (109—114). Typical overall haHde reactions are... 

Once initiated, zirconium and carbon powders react exothermically in a vacuum or inert atmosphere to form zirconium carbide. With the greater availabiHty of relatively pure metal powders, this technique is coming into common use for the production of several refractory carbides. Zirconium carbide is not a fixed stoichiometric compound, but a defect compound with a single-phase composition ranging from ZrCQ to ZrCQ at 2400°C. 

Borides are inert toward nonoxidizing acids however, a few, such as Be2B and MgB2, react with aqueous acids to form boron hydrides. Most borides dissolve in oxidizing acids such as nitric or hot sulfuric acid and they ate also readily attacked by hot alkaline salt melts or fused alkaU peroxides, forming the mote stable borates. In dry air, where a protective oxide film can be preserved, borides ate relatively resistant to oxidation. For example, the borides of vanadium, niobium, tantalum, molybdenum, and tungsten do not oxidize appreciably in air up to temperatures of 1000—1200°C. Zirconium and titanium borides ate fairly resistant up to 1400°C. Engineering and other properties of refractory metal borides have been summarized (1). 

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... 

A number of attempts to produce tire refractory metals, such as titanium and zirconium, by molten chloride electrolysis have not met widr success with two exceptions. The electrolysis of caesium salts such as Cs2ZrCl6 and CsTaCle, and of the fluorides Na2ZrF6 and NaTaFg have produced satisfactoty products on the laboratory scale (Flengas and Pint, 1969) but other systems have produced merely metallic dusts aird dendritic deposits. These observations suggest tlrat, as in tire case of metal deposition from aqueous electrolytes, e.g. Ag from Ag(CN)/ instead of from AgNOj, tire formation of stable metal complexes in tire liquid electrolyte is the key to success. 

CVD developed slowly in the next fifty years and was limited mostly to extraction and pyrometallurgy for the production of high-purity refractory metals such as tantalum, titanium, and zirconium. Several classical CVD reactionswere developedatthattimeincludingthecarbonyl cycle (the Mond process), the iodide decomposition (the de Boer-Van Arkelprocess)andthemagnesium-reduction reaction (the Kroll process). 

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-... 

Lubricants. Tellurides of titanium, zirconium, molybdenum, tungsten, and other refractory metals are heat- and vacuum-stable. This property makes them useful in solid self-lubricating composites in the electronics, instrumentation, and aerospace fields (see Lubrication and lubricants). Organic tellurides are antioxidants in lubricating oils and greases. 

Refractory metals such as titanium and zirconium can be won from their oxides by reduction with metals which have oxides with a high heat of formation. Of these, only calcium (or calcium hydride) is capable of producing refractory metals in purities approaching those required for metallurgical uses. 

Caution. Finely divided titanium, zirconium, and other refractory metals are often pyrophoric and should be handled with a minimum exposure to air. Weighings should be made in a closed container. 

Decontamination of equipment is identical to that described in the synthesis of calcium metal. A similar procedure can be used to produce powders of zirconium, chromium, vanadium, thorium, uranium, and other refractory metals from their oxides the reductant/metal oxide ratio, however, differs for each metal in order to avoid formation of oxygenated metal by-products and ensure maximum product purity. 

Nitric acid may also be used to treat surfaces of nickel and chrome alloys, in metal etching and in treatment of refractory metals such as zirconium. 

Refractory metals, such as tantalum and zirconium, can be deposited from their fluorides in a molten salt bath. In the case of zirconium, for example, the bath consists of ZrF or ZrF in a KF/NaF/LiF mixture. The alkali fluorides are employed to increase conductivity and decrease the melting point. Even so, these baths are operated at about 800 C. Good deposits have been reported as long as the right valency was chosen for each metal (3 for Mo and V, 4 for Nb and Zr, 5 for Ta). The bath must be operated in a pure argon atmosphere, and impurities must be strictly excluded. It siiould be obvious that the operation of such baths is expensive and control is difficult. Thus their use is limited either for research purposes or for highly specialized applications, where cost is of secondary importance. 

Use Source of zirconium oxide, metallic zirconium, and hafnium abrasive refractories enamels refractory porcelain catalyst silicone rubbers foundry cores. 

The hot-wire process was developed by Van Arkel and de Boer [V2], who used it to produce the first pure, massive specimens of many refractory metals, notably titanium, zirconium, hafnium, and thorium. An interesting account of early uses of this process is given in... 

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