Uses of Hafnium

Refining. KroU-process hafnium sponge and electrowon hafnium do not meet the performance requirements for the two principal uses of hafnium metal. Eurther purification is accompHshed by the van Arkel-de Boer, ie, iodide bar, process (18) and by electron beam melting. 

Hf complexes seem to be good candidates in several catalytic reactions. However, information and data are needed to develop the use of hafnium surface complexes in catalysis. 

Use of hafnium instead of europium in atomic submarines for neutron absorption. 

The discovery of the element hafnium provides a further example of a missed opportunity to turn scientific achievement into practical application. Hafnium was discovered at Niels Bohr s institute in Copenhagen in 1923 and quickly turned out to be fairly abundant and of potential industrial interest. However, no Danish chemical company seems to have taken an interest in the discovery. The two discoverers, Hevesy and Dirk Coster, sold the patent rights to the Philips firm in the Netherlands. Philips at once took out several patents on the use of hafnium compounds and developed methods for applying the metal in electrodes, filaments and fireproof enamels. ... 

Hafnium is obtained as a by-product of the production of hafnium-free nuclear-grade 2irconium (see Nuclear reactors Zirconiumand zirconium compounds). Hafnium s primary use is as a minor strengthening agent in high temperature nickel-base superakoys. Additionally, hafnium is used as a neutron-absorber material, primarily in the form of control rods in nuclear reactors. 

Decomposition of Zircon. Zircon sand is inert and refractory. Therefore the first extractive step is to convert the zirconium and hafnium portions into active forms amenable to the subsequent processing scheme. For the production of hafnium, this is done in the United States by carbochlorination as shown in Figure 1. In the Ukraine, fluorosiUcate fusion is used. Caustic fusion is the usual starting procedure for the production of aqueous zirconium chemicals, which usually does not involve hafnium separation. Other methods of decomposing zircon such as plasma dissociation or lime fusions are used for production of some grades of zirconium oxide. 

Hafnium metal is analy2ed for impurities using analytical techniques used for 2irconium (19,21,22). Carbon and sulfur in hafnium are measured by combustion, followed by chromatographic or in measurement of the carbon and sulfur oxides (19). Chromatographic measurement of Hberated hydrogen follows the hot vacuum extraction or fusion of hafnium with a transition metal in an inert atmosphere (23,24). 

Fluorosilicate Fusion. The fusion reaction of milled zircon with potassium hydrogen fluoride was used to prepare potassium hexafluorozirconate [16923-95-8] for studies leading to the first separation of hafnium and zirconium (30). Similar reactions using potassium hexafluorosihcate have been used (31,32) commercially in the United States and the former USSR ... 

In the initial thiocyanate-complex Hquid—Hquid extraction process (42,43), the thiocyanate complexes of hafnium and zirconium were extracted with ether from a dilute sulfuric acid solution of zirconium and hafnium to obtain hafnium. This process was modified in 1949—1950 by an Oak Ridge team and is stiH used in the United States. A solution of thiocyanic acid in methyl isobutyl ketone (MIBK) is used to extract hafnium preferentially from a concentrated zirconium—hafnium oxide chloride solution which also contains thiocyanic acid. The separated metals are recovered by precipitation as basic zirconium sulfate and hydrous hafnium oxide, respectively, and calcined to the oxide (44,45). This process is used by Teledyne Wah Chang Albany Corporation and Western Zirconium Division of Westinghouse, and was used by Carbomndum Metals Company, Reactive Metals Inc., AMAX Specialty Metals, Toyo Zirconium in Japan, and Pechiney Ugine Kuhlmann in France. 

Pure zirconium tetrachloride is obtained by the fractional distillation of the anhydrous tetrachlorides in a high pressure system (58). Commercial operation of the fractional distillation process in a batch mode was proposed by Ishizuka Research Institute (59). The mixed tetrachlorides are heated above 437°C, the triple point of zirconium tetrachloride. AH of the hafnium tetrachloride and some of the zirconium tetrachloride are distiUed, leaving pure zirconium tetrachloride. The innovative aspect of this operation is the use of a double-sheU reactor. The autogenous pressure of 3—4.5 MPa (30—45 atm) inside the heated reactor is balanced by the nitrogen pressure contained in the cold outer reactor (60). However, previous evaluation in the former USSR of the binary distiUation process (61) has cast doubt on the feasibHity of also producing zirconium-free hafnium tetrachloride by this method because of the limited range of operating temperature imposed by the smaH difference in temperature between the triple point, 433°C, and critical temperature, 453°C, a hafnium tetrachloride. 

Zirconium metal is marketed in three forms zirconium-containing silicon—manganese, kon, ferrosiUcon, or magnesium master alloys commercially pure zirconium metal and hafnium-free pure zirconium metal. The use of zkcon for the production of zirconium metal of all three types is ca 5—8% of the total U.S. zkcon consumption. 

Assay of beryUium metal and beryUium compounds is usuaUy accompHshed by titration. The sample is dissolved in sulfuric acid. Solution pH is adjusted to 8.5 using sodium hydroxide. The beryUium hydroxide precipitate is redissolved by addition of excess sodium fluoride. Liberated hydroxide is titrated with sulfuric acid. The beryUium content of the sample is calculated from the titration volume. Standards containing known beryUium concentrations must be analyzed along with the samples, as complexation of beryUium by fluoride is not quantitative. Titration rate and hold times ate critical therefore use of an automatic titrator is recommended. Other fluotide-complexing elements such as aluminum, sUicon, zirconium, hafnium, uranium, thorium, and rate earth elements must be absent, or must be corrected for if present in smaU amounts. Copper-beryUium and nickel—beryUium aUoys can be analyzed by titration if the beryUium is first separated from copper, nickel, and cobalt by ammonium hydroxide precipitation (15,16). 

Hafnium Carbide. The need of pure zirconium [7440-67-7] for nuclear reactors prompted the large-scale separation of hafnium [7440-58-6] from zirconium. This in turn made sufficient quantities of hafnium dioxide [12055-23-17, Hf02, or Hf metal sponge available for production of HfC for use in cemented carbides (see Hafniumand hafnium compounds). 

One must consider, too, the cost of the materials themselves. Some of the metals used in conventional nickel alloys - such as hafnium - are hideously expensive (at UK 100,000 tonne or US 150,000 tonne ) and extremely scarce and the use of greater and greater quantities of exotic materials in an attempt to improve the creep properties will drive the cost of blades up. But expensive though it is, the cost of the... 

Thenoyltrifluoroacetone(TTA), C4H3S,CO,CH2,COCF3. This is a crystalline solid, m.p. 43 °C it is, of course, a /1-diketone, and the trifluoromethyl group increases the acidity of the enol form so that extractions at low pH values are feasible. The reactivity of TTA is similar to that of acetylacetone it is generally used as a 0.1-0.5 M solution in benzene or toluene. The difference in extraction behaviour of hafnium and zirconium, and also among lanthanides and actinides, is especially noteworthy. 

The extraction of metals by liquid amines has been widely investigated and depends on the formation of anionic complexes of the metals in aqueous solution. Such applications are illustrated by the use of Amberlite LA.l for extraction of zirconium and hafnium from hydrochloric acid solutions, and the use of liquid amines for extraction of uranium from sulphuric acid solutions.42,43... 

Fig. 9-3. Comparison of 50-kv, 40-ma (dotted line) spectra with 100-kv, 20-ma (solid line) spectra of hafnium and tantalum, showing efficient excitation of the K spectra at the higher voltage. The higher voltage is particularly useful in connection with analyses of niobium-tantalum mixtures and zirconium-hafnium mixtures which are difficult at the lower voltage because of the interference of the K lines of the lighter elements with the L spectra of the heavier elements. (Courtesy of M. L. Salmon, Fluo-X-Spec Analytical Laboratory, Denver, Colo.)...

In this table, the free energy of formation, AGf of the chloride of these metals is listed for four different temperatures. As can be seen, the values are more negative than that of hydrogen chloride. These metals can be used to reduce the halides of titanium, zirconium, or hafnium, whereas hydrogen, as mentioned above, cannot do so readily. In order to be useful in CVD, the by-product chloride must be volatile at the deposition temperature. This may rule out the use of sodium or potassium, which evaporate above 1400°C. 

Also increasingly common, as CVD precursors, are many halogen-acetylacetonate complexes, such as trifluoro-acetylacetonate thorium, Th(C5H4F302)4, used in the deposition of thoriated tungsten for thermionic emitters, the trifluoro-acetylacetonates of hafnium and zirconium and the hexafluoro-acetylacetonates of calcium, copper, magnesium, palladium, strontium, and yttrium. 

Atomic layer deposition of hafnium silicate thin films using... 

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