Subject hafnium

After extraction, the loaded solvent contains 6 g T1 zirconium as zirconium oxide with 0.2% hafnium oxide. The raffinate is left with 0.2 to 0.3 g l l of the oxides of zirconium and hafnium of this, 70-90% is hafnium oxide. This raffinate can act as a feed solution for the recovery of pure hafnium oxide. The loaded extractant, on the other hand, is subjected to a scrubbing operation with pure zirconium sulfate solution to eliminate any co-extracted hafnium. This scrubbing operation is essentially a displacement reaction ... 

Recent Group IV chemistry has seen an upsurge in the number of amide derived species, and this has included fluoride derivatives. None of these compounds are of oxidation state -(-III or less, which are the subject of this review, but refer to titanium, zirconium or hafnium where the metal is the +IV state [1,9-12] and, consequently, not covered here. 

The zirconium and hafnium complexes of trifluoroacetyl-acetone are white crystalline solids, insoluble in water but soluble in benzene, cyclohexane, and carbon tetrachloride. The hafnium complex melts at 128 to 129° and the zirconium complex at 130 to 131°. The complexes have been subjected to gas-phase chromatography and may be sublimed at 115° at a pressure of 0.05 mm. The proton magnetic resonance spectra of the compounds dissolved in carbon tetrachloride show single peaks in the methyl and methylene regions. The peaks appear at 2.20 and 6.00 p.p.m. (5) relative to tetramethylsilane (internal reference) for the zirconium complex and at 2.20 and 5.97 p.p.m. for the hafnium complex. 

Product 5 was subjected to X-ray diffraction analysis (Fig. 2 and Table 2) [6]. The structure was found to be an octahedrally coordinated metal dichloro complex with the two bidentate ligands occupying the equatorial positions. The observed stereochemistry can be considered to be caused by the trans-effect of the tmen group [3], which activates the two chloro atoms of the hafnium tetrachloride in equatorial position and makes them susceptible to the nucleophilic attack by the silyl dianion. 

Zero-valent zirconium and hafnium compounds remain relatively rare, owing to the strong thermodynamic driving force for the second and third row metals to attain a higher oxidation state. Despite this obstacle, examples of formally zero-valent compounds have been reported and characterized. The majority of these are arene complexes, whose syntheses and resulting chemistry have been reviewed.1,2 In addition to arene compounds, formally zero-valent butadiene complexes have also been described and are the subject of a rather comprehensive review.3 The focus of this section will be on compounds that have not been covered. 

As expected, the strong-field 7r-acidic ligand, carbon monoxide, has also been used to isolate zero-valent zirconium and hafnium complexes. This area has been a subject of relatively long-standing interest and has been reviewed.7 Chemistry outside of this review will be the focus of this section. 

Allenes have also been used to stabilize low-valent zirconium and hafnium compounds. This chemistry has been the subject of a recent review.74... 

Zirconium and hafnium alkyne complexes display a wealth of reactivity. A comprehensive presentation of this chemistry has been the subject of several recent reviews.105-107 Reactivity beyond the scope of these reviews will be the focus here. 

Many other organic ligands have been studied for use as analytical reagents for zirconium and hafnium, but will not be treated here. This subject is adequately reviewed in the monograph by Elinson and Petrov 162). 

Recent studies with modern analytical techniques have shown much lower values for human body fluids. The mean zirconium concentration in whole human blood was found to be 9.6 5.8 pg L in the UK Master Mix (a collection of blood samples from humans in the UK), and 19.7 8 pg L for the mean value of individual blood samples (98 subjects). These values are in fair agreement with an estimate of 5.0 pg L in Italian blood samples. Here, the Zr concentration was derived on the basis of the measured concentration of hafnium, under the assumption of a Zr/Hf ratio of about 40, as found in soils and rocks. Morita etal. (1994), using ICP-MS, found a mean human serum Zr concentration of... 

Metallic materials with the exception of noble metals are also thermodynamically not stable in the acidic environment under the PEFC operating conditions and therefore subject to corrosion. Nevertheless, many different metals such as stainless steels, aluminum, aluminum composites, copper, nickel and nickel alloys, titanium alloys and even highly corrosion resistant materials used in chemical industry such as tantalum, hafnium, niobium or zirconium have been investigated with respect to applicability in PEFC with respect to corrosion resistance [68—71]. 

It is possible to separate zirconium and halfnium by cation-exchange, but they must both be first absorbed upon the resin and then subjected to elution analysis down a column of resin. This process was first described briefly by Street and Seaborg in 1948. They absorbed zirconium and hafnium from the oxychloride solution upon the cation-exchange resin... 

Ring opening of oxiranes is catalyzed by zirconium or hafnium complexes in the presence of nucleophiles. Cp2ZrCl2 was used as a catalyst for ring opening of substituted epoxides with alcohols under mild conditions. The corresponding alkoxyalcohols were obtained in good yields. As shown in Equation 38, when trans-stilbene oxide was subjected to the reaction in methanol, a mixture of anti-and syn isomers were obtained [43]. 

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