Hafnium manufacture

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. 

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... 

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. 

Hafnium carbide (HfC) This alloy has one of the highest melting points of any binary compound (3.890°C). It is extremely hard and resists corrosion while absorbing slow neutrons. Therefore, it is an ideal metal in the manufacture of control rods for nuclear reactors. 

Ammonium thiocyanate is used in the manufacture of herbicides, thiourea, and transparent artificial resins in matches as a stabilizing agent in photography in various rustproofing compositions as an adjuvant in textile dyeing and printing as a tracer in oil fields in the separation of hafnium from zirconium, and in titrimetric analyses. 

Normally, nitration of deactivated compounds (and therefore polynitration of toluene) is carried out using aggressive nitric acid - oleum mixtures. Dinitration of toluene with mixed acids produces a 4 1 ratio of 2,4- and 2,6-dinitrotoluenes, from which the former is isolated for manufacture of toluenediisocyanate (TDI) and toluenediamine, both of which are used in the manufacture of polyurethanes. Zirconium and hafnium derivatives catalyse nitration of o-nitrotoluene, but ratios of 2,4- 2,6-dinitrotoluene are modest (66 34).12 Dinitration of toluene using Claycop (copper nitrate on K10 clay), acetic anhydride and nitric acid in the presence of carbon tetrachloride produced dinitrotoluenes in a yield of 85% with a ratio of 2,4- 2,6-dinitrotoluene of 9 1.13 This method, however, requires a large excess of nitric acid, the use of an unacceptable solvent and long reaction times. The direct nitration of toluene to 2,4-dinitrotoluene using nitric acid over a zeolite P catalyst, with azeotropic removal of water, is reported to give a 2,4 2,6 ratio of 14, but full results are yet to be published.14... 

Zirconium carbide, ZrC, and hafnium carbide, HfC, can be manufactured in a similar way to titanium carbide. They are not very important in cemented carbide technology. The recent strong reduction in the price of HfC has enabled its application as a substitute for the dearer tantalum carbide. 

Complex FCC oxides of the fluorite type represent oxygen-conduction solid electrolytes (SOE s). They comprise a typical class of materials for the manufacture of sensors of oxygen activity in complex gas mixtures, oxygen pumps, electrolyzers and high-temperature fuel elements. These materials are based on doped oxides of cerium and thorium, zirconium and hafnium, and bismuth oxide. Materials based on zirconium oxide, for example, yttrium stabilized zirconia (YSZ) are the most known and studied among them. This fact is explained both by their processibility and a wide spectrum of practical applications and by the possibility to conduct studies on single crystals, which have the commercial name "fianites" and are used in jewelry. 

Manufacturing Chemists Ass n., Wash., D. C, Chemical Safety Data Sheet SZ)-92, Zirconium and Hafnium Powder, (adopted 1966). 

Hudswell, F. and Hutcheon, J. M. The Manufacture of Hafnium— free Zirconium. I.M.M. Symposium on the Extraction and Refining of the Rarer Metals, London, 1957. Paper 22. 

Because of its low neutron-capture cross-section and high resistance to corrosion, the manufacture of high-grade zirconium, free from hafnium, has been developed to a great extent in the U.S.A. for use in pressurized water reactors. 

The demand for hafnium metal is small. Figure 9.7 shows how it can be obtained in a high state of purity as a by-product from the manufacture of zirconium. The conversion of the pure by-product solution to oxide is via sulphite as in the case of zirconium, and similarly several alternative precipitants would each be satisfactory. The Van Arkel iodide decomposition process has been shown, in its cheapest form, i.e. based upon a carbide feed. Either of the two metal-producing stages shown for zirconium are equally applicable. 

The other big problem was the hafnium content of natural zirconium. In the actual tubes the hafnium content must be lower than 100 ppm, because hafnium absorbs neutrons 550 times more strongly than zirconium. Zircon sand, the most important ore, has a hafnium content of 1.5-2.596 (relative to zirconium). Thus it was necessary to find a separation method with which hafnium-free zirconium could be manufactured. The solution of this problem was liquid-liquid extraction. From an impure zirconium solution in hydrochloric acid, iron is first removed by solvent extraction. Then ammonium thiocyanate is added to the chloride solution containing Zr -i- Hf. Hafnium is extracted into an organic phase of methyl isobutyl ketone. The pure zirconium solution in the water phase is worked up for zirconium. Hafnium is recovered from the ketone solution by scrubbing with dilute sulfuric acid. 

The separation technique described and the Kroll process created the possibihty of manufacturing hafnium-free zirconium on an industrial scale for atomic energy... 

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