Zirconium producers

Additions of selected alloying elements raise the recrystaUization temperature, extending to higher temperature regimes the tensile properties of the cold-worked molybdenum metal. The simultaneous additions of 0.5% titanium and 0.1% zirconium produce the TZM aUoy, which has a corresponding... 

About 90% of all the zirconium produced in the United States is used in the nuclear electrical power industry. Since it does not readily absorb neutrons, it is a desired metal in the manufacture of nuclear reactors and their fuel tubes, but it must be free of its twin hafnium for these purposes. Zirconium is also used as an alloy with steel to make surgical instruments. 

The most important application of zirconium is in the formulation of the base metal in an alloy of 98% zirconium. 1.5% tin, 0.35% lron-chromium-mckel. and 0.15% oxygen, This alloy is widely used in water-cooled nuclear reactors because of its excellent corrosion resistance up to about 350 in H 0, and its low neutron cross section. Currendy, about 90% of the zirconium produced is used for this application. The excellent corrosion resistance of zirconium to both strong acids and alkalis, particularly its resistance to strong caustic solutions at all concentrations and temperatures, is attracting increasing attention for application in chemical processing equipment, See also Nuclear Power Technology. 

ZrSi04) and baddeleyite, or zirconia or zirconium oxide (Zr02). The amount of zirconium produced in the United States is not reported. That information is regarded as a trade secret. As of 2008, the largest suppliers of zirconium minerals in the world are Australia and South Africa. These two countries produce about 72 percent of the world s zirconium. 

About 95 percent of all zirconium produced is converted into a compound before being used. The two most common compounds made are zircon (zirconium silicate) and zirconia (zirconium oxide). 

U.S. production in these years was around 150,000 short tons. Thus, Australia and the United States are the principal zirconium-producing nations. Most of their production was from dredging of black sands on beaches and in stream beds, where zircon has been concentrated hydraulically along with other relatively dense minerals such as rutile (TiOj), ilmenite (FeTiOs), and monazite (Chap. 6). 

Note that the initial addition of zirconium produces the greatest increase in burn rate (i.e., adding the first 5% zirconium produces about 50% of the total increase in burn rate). 

Because of its neuronic, mechanical, and physical properties, hafnium is an excellent control material for water-cooled, water-moderated reactors. It is found together with zirconium, and the process that produces pure zirconium produces hafnium as a by-product. Hafnium is resistant to corrosion by high-temperature water, has adequate mechanical strength, and can be readily fabricated. Hafnium consists of four isotopes, each of which has appreciable neutron absorption cross sections. The capture of neutrons by the isotope hafnium-177 leads to the formation of hafnium-178 the latter forms hafnium-179, which leads to hafnium-180. The first three have large resonance-capture cross sections, and hafnium-180 has a moderately large cross section. Thus, the element hafnium in its natural form has a long, useful lifetime as a neutron absorber. Because of the limited availability and high cost of hafnium, its use as a control material in civilian power reactors has been restricted. 

An example of the high purity of the zirconium produced by the iodide decomposition route is as follows... 

The trimethylphosphine adduct 83 of borabenzene was treated with a series of alcohols to give boracyclohexadienes 84, which upon deprotonation give the alkoxyboratabenzene Hgands 85 coordination with zirconium produces the metallocenes 86a—d (Scheme 26) (1999JA1288). These compounds are of interest for their abihty to react with excess methylaluminox-ane under 1 atm of ethylene to give aUcene mixtures. The structure of metallocene 86c was determined crystaUographically. 

Metallocenes, especially zirconocenes but also titanocenes, hafnocenes, and other transition metal complexes treated with MAO are highly active for the polymerization of olefins, diolefins, and styrene. The polymerization activity, which is up to 100 times higher than for classical Ziegler catalysts, as well as the possibility to easily tailor the microstructure of the polymer chain and to obtain polymers with special properties have motivated research groups worldwide to produce thousands of patents and publications in the last 20 years. An overview can be found in selected review articles and books [55-68]. A metallocene/MAO catalyst containing 1 g zirconium produced 40 x 10 g polyethylene in 1 h at 95°C and 8 bar ethene pressure (Table 1). 

It was originally separated from zirconium by repeated recrystallization of the double ammonium or potassium fluorides by von Hevesey and Jantzen. Metallic hafnium was first prepared by van Arkel and deBoer by passing the vapor of the tetraiodide over a heated tungsten filament. Almost all hafnium metal now produced is made by reducing the tetrachloride with magnesium or with sodium (Kroll Process). 

Hexafluorozirconic acid [12021 -95-3]], H2ZrP, is formed by dissolving freshly prepared oxide, fluoride, or carbonate of zirconium in aqueous HP. This acid is produced commercially in a concentration range of 10 to 47%. The acid can be stored at ambient temperatures in polyethylene or Teflon containers... 

Fluorozirconate Crystallization. Repeated dissolution and fractional crystallization of potassium hexafluorozirconate was the method first used to separate hafnium and zirconium (15), potassium fluorohafnate solubility being higher. This process is used in the Prinieprovsky Chemical Plant in Dnieprodzerzhinsk, Ukraine, to produce hafnium-free zirconium. Hafnium-enriched (about 6%) zirconium hydrous oxide is precipitated from the first-stage mother Hquors, and redissolved in acid to feed ion-exchange columns to obtain pure hafnium (10). 

Electrolysis. Electro winning of hafnium, zirconium, and titanium has been proposed as an alternative to the KroU process. Electrolysis of an all chloride hafnium salt system is inefficient because of the stabiHty of lower chlorides in these melts. The presence of fluoride salts in the melt increases the StabiHty of in solution and results in much better current efficiencies. Hafnium is produced by this procedure in Erance (17). 

Total hafnium available worldwide from nuclear zirconium production is estimated to be 130 metric tons annually. The annual usage, in all forms, is about 85 t. The balance is held in inventory in stable intermediate form such as oxide by the producers Teledyne Wah. Chang (Albany, Oregon) and Western Zirconium in the United States Ce2us in France Prinieprovsky Chemical Plant in Ukraine and Chepetsky Mechanical Plant in Russia (crystal bar). 

Another important class of titanates that can be produced by hydrothermal synthesis processes are those in the lead zirconate—lead titanate (PZT) family. These piezoelectric materials are widely used in manufacture of ultrasonic transducers, sensors, and minia ture actuators. The electrical properties of these materials are derived from the formation of a homogeneous soHd solution of the oxide end members. The process consists of preparing a coprecipitated titanium—zirconium hydroxide gel. The gel reacts with lead oxide in water to form crystalline PZT particles having an average size of about 1 ]lni (Eig. 3b). A process has been developed at BatteUe (Columbus, Ohio) to the pilot-scale level (5-kg/h). 

The abihty of magnesium metal to reduce oxides of other metals can be exploited to produce metals such as zirconium, titanium [7440-32-6] and uranium [7440-61-1] (see ZiRCONiUMAND ZIRCONIUM COMPOUNDS Titaniumand titanium alloys Uraniumand uranium compounds). These reactions are... 

Eabrication techniques must take into account the metallurgical properties of the metals to be joined and the possibiUty of undesirable diffusion at the interface during hot forming, heat treating, and welding. Compatible alloys, ie, those that do not form intermetaUic compounds upon alloying, eg, nickel and nickel alloys (qv), copper and copper alloys (qv), and stainless steel alloys clad to steel, may be treated by the traditional techniques developed for clads produced by other processes. On the other hand, incompatible combinations, eg, titanium, zirconium, or aluminum to steel, require special techniques designed to limit the production at the interface of undesirable intermetaUics which would jeopardize bond ductihty. 

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. 

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