Chemical hafnium oxide

Figure 4.3. Chemical sequence representing deposition of hafnium oxide sulfates and generalized formulation for HafSOx. ...

For practical purposes, then, the third transition series begins with hafnium, having the ground state outer electron configuration 6s25d2, and embraces the elements Ta, W, Re, Os, Ir, Pt, and Au, all of which have partially filled 5d shells in one or more chemically important oxidation states as well as (except Au) in the neutral atom. 

In 2005, De Laeter discussed the role of isotope reference materials for the analysis of non-traditionaT stable isotopes. At present, no isotopically certified reference materials exist for a large number of elements, including Cu, Zn, Mo and Cd, and it is important that this situation be rectified as soon as practicable. Before the isotopically certified reference materials become available for selected elements, suitable reference materials can be created as a standard if sufficient and reliable isotope data have been obtained by interlaboratory comparisons. For example, the Hf/ Hf isotope ratio was measured using hafnium oxide from Johnson Matthey Chemicals, JMC-475, for hafnium isotope ratio measurements with different multi-collector mass spectrometers (ICP-MS and TIMS) as summarized in Table 8.1. However, no isotope SRM is certified for the element Mo either. Mo isotope analysis is relevant, for example, for studying the isotope fractionation of molybdenum during chemical processes or the isotope variation of molybdenum in nature as the result of the predicted double (3 decay of Zr or 18.26-28 spectroscopically pure sample from Johnson Mattey Specpure is proposed as a laboratory standard reference material if sufficient and reliable isotope data are collected via an interlaboratory comparison. 

A stock solution of hafnium oxide dichloride octahydrate was prepared in the manner described previously (10). The stock solution was analyzed for hafnium gravimetrically, as the oxide, and for chloride by the modified Volhard method. Other stock solutions—i.e., NaCl, NaHC03, and HC1—were prepared from reagent grade chemicals and standardized by the usual methods. 

Lee, M., Zine, N., Baraket, A., Zabala, M., Campabadal, R, Caruso, R., Trivella, M.G., Jaffrezic-Renault, N., Errachid, A., 2012. A novel biosensor based on hafnium oxide application for early stage detection of human interleukin-10. Sensors and Actuators B Chemical 175 (0), 201-207. 

There are many compounds of various chemical classes that crystallize in this structural type fluorides of alkaline-earth elements, lead and cadmium high-temperature modifications of zirconium and hafnium oxides, solid solutions Mi xRxF2+x (M = Ca, Sr, Ba, Pb, Cd R = RE elements) [7,21, 31 and others] Bai ,.Bi ,.(0,F)2+6 [32], fluorite-Uke modifications of MOF (M = RE elements, Bi) and Mi xTex(0,F)2+ oxyfluoride phases [33,34], solid solutions in the BiOF-YOF system [24] etc. 

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. 

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). 

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). 

The Phalaborwa complex ia the northeastern Transvaal is a complex volcanic orebody. Different sections are mined to recover magnetite, apatite, a copper concentrate, vermicuhte, and baddeleyite, Hsted in order of aimual quantities mined. The baddeleyite is contained in the foskorite ore zone at a zirconium oxide concentration of 0.2%, and at a lesser concentration in the carbonatite orebody. Although baddeleyite is recovered from the process tailings to meet market demand, the maximum output could be limited by the requirements for the magnetite and apatite. The baddeleyite concentrate contains ca 96% zirconium oxide with a hafnium content of 2% Hf/Zr + Hf. A comminuted, chemically beneficiated concentrate containing ca 99% zirconium oxide is produced also. 

Chemical Resistance. Hafnium carbide oxidizes in air at 500°C. It is not as chemically resistant as TiC and is similar to ZrC in that respect. 

The silvery, shiny, ductile metal is passivated with an oxide layer. Chemically very similar to and always found with zirconium (like chemical twins, with almost identical ionic radii) the two are difficult to separate. Used in control rods in nuclear reactors (e.g. in nuclear submarines), as it absorbs electrons more effectively than any other element. Also used in special lamps and flash devices. Alloys with niobium and tantalum are used in the construction of chemical plants. Hafnium dioxide is a better insulator than Si02. Hafnium carbide (HfC) has the highest melting point of all solid substances (3890 °C record ). 

Hafnium is a ductile metal that looks and feels much hke stainless steel, but it is significantly heavier than steel. When freshly cut, metallic hafnium has a bright silvery shine. When the fresh surface is exposed to air, it rapidly forms a protective oxidized coating on its surface. Therefore, once oxidized, hafnium resists corrosion, as do most transition metals, when exposed to the air. Chemically and physically, hafnium is very similar to zirconium, which is located just above it in group 4 on the periodic table. In fact, they are so similar that it is almost impossible to secure a pure sample of either one without a small percentage of the other. Each will contain a small amount of the other metal after final refining. 

X-Ray diffraction studies have identified a distorted octahedral environment about zirconium in KZr2(P04)3, and the structures of zirconium phosphates have been discussed in terms of their utility as chemical sieves.Some preparative and structural aspects of the normal sulphates of zirconium and hafnium have been reviewed and X-ray studies have shown that the sulphates Zr20(S04)3,5H20 and Hf20(S04)3,5H20 are isostructural and are more accurately represented as M2(OH)2(S04)3,4H20. Other studies of zirconates and hafnates and related mixed oxide systems are summarized in Table 2. 

Many [M(dik)4] complexes are volatile, especially those that contain fluorinated diketonate ligands. Mass spectra and gas chromatographic behavior of several of these complexes have been studied (see Table 10). Isenhour and coworkers240 241 have employed fluorinated diketonates in mass spectrometric procedures for determination of Zr and Zr/Hf ratios in geological samples. The most intense peak in mass spectra of [M(dik)4] complexes is [M(dik)3]+. Sievers et al.242 have used gas chromatography of metal trifluoroacetylacetonates to separate Zr from Al, Cr and Rh. However, attempts to separate [Zr(tfacac)4] and [Hf(tfacac)4] by gas chromatography were unsuccessful. Zirconium and hafnium can be separated by solvent extraction procedures that employ fluorinated diketones.105 [M(dik)4] (M = Zr or Hf dik = acac, dpm, tfacac or hfacac) have been used as volatile source materials for chemical vapor deposition of thin films of the metal oxides.243,244... 

Element 104. (eka-hafnium) is predicted to resemble its homolc hafnium (element 72) in its chemical properties. It is expected to be predominantly tetra-positive, both in aqueous solution and in its solid compounds, although it should exhibit sohd halides and perhaps aqueous ions of the +2 and +3 oxidation state as well. 

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