Determination hafnium

Hafnium, determination of, in zirconium-hafnium solution, 3 69 extraction of, from cyrtolite and separation from zirconium, 3 67, 74... 

Of the remaining insoluble elements, recent evaluation of zirconium and hafriium concentrations derived from terrigenous sediment (McLennan, 2001b) show no significant differences with Taylor and McLennan s estimates, whose upper cmstal zirconium value derives from the Handbook of Geochemistry (Wedepohl, 1969-1978), with hafnium determined from an assumed Zr/Hf ratio of 33. These values lie within —20% of the surface-exposure averages (Table 2, Figure 3). 

A sample of a compound synthesized and purified in the laboratory contains 25.0 g hafnium and 31.5 g tellurium. The identical compound is discovered in a rock formation. A sample from the rock formation contains 0.125 g hafnium. Determine how much tellurium is in the sample from the rock formation. 

Analyses of alloys or ores for hafnium by plasma emission atomic absorption spectroscopy, optical emission spectroscopy (qv), mass spectrometry (qv), x-ray spectroscopy (see X-ray technology), and neutron activation are possible without prior separation of hafnium (19). Alternatively, the combined hafnium and zirconium content can be separated from the sample by fusing the sample with sodium hydroxide, separating silica if present, and precipitating with mandelic acid from a dilute hydrochloric acid solution (20). The precipitate is ignited to oxide which is analy2ed by x-ray or emission spectroscopy to determine the relative proportion of each oxide. 

Oxygen and nitrogen also are deterrnined by conductivity or chromatographic techniques following a hot vacuum extraction or inert-gas fusion of hafnium with a noble metal (25,26). Nitrogen also may be deterrnined by the Kjeldahl technique (19). Phosphoms is determined by phosphine evolution and flame-emission detection. Chloride is determined indirecdy by atomic absorption or x-ray spectroscopy, or at higher levels by a selective-ion electrode. Fluoride can be determined similarly (27,28). Uranium and U-235 have been determined by inductively coupled plasma mass spectroscopy (29). 

Zirconium is often deterniined gravimetrically. The most common procedure utilizes mandelic acid (81) which is fairly specific for zirconium plus hafnium. Other precipitants, including nine inorganic and 42 organic reagents, are Hsted in Reference 82. Volumetric procedures for zirconium, which also include hafnium as zirconium, are limited to either EDTA titrations (83) or indirect procedures (84). X-ray fluorescence spectroscopy gives quantitative results for zirconium, without including hafnium, for concentrations from 0.1 to 50% (85). Atomic absorption determines zirconium in aluminum in the presence of hafnium at concentrations of 0.1—3% (86). 

Glocker and Frohnmayer determined the characteristic constant c for nine elements (Reference 2, Table 4) ranging in atomic numbers from 42 (molybdenum) to 90 (thorium). They proved that identical results could be obtained with the sample in the primary (polychromatic) or in the diffracted (monochromatic) beam. The method was applied with good results to the determination of barium in glass of antimony in a silicate of hafnium in the mineral alvite and of molybdenum, antimony, barium, and lanthanum in a solution of their salts—for example, 5.45% barium was found on 90-minute exposure by the x-ray method for a glass that yielded 5.8% on being analyzed chemically. 

The crystal structures of Hf 2 (OH) 2 (S0O 3 (H2O) i, (14) and Ce2(0H)2(S0i,)3 (H20)it (14) also have been determined and found to be isomorphous to the zirconium compound. The cell constants for this series of four isomorphous compounds reflect the effect of the ionic radii on the dimensions of the unit cell. The values for these cell constants are in Table II. Thus, the cell constants for the zirconium and hafnium compounds are nearly identical and smaller than the cell constants for the cerium and plutonium compounds which are also nearly identical. This trend is exactly that followed by the ionic radii of these elements. 

The binary borohydride species Zr( III 11)4 and U(BH4)4 have been investigated by quantum mechanical techniques and, for the zirconium case, also by gas-phase electron diffraction. All confirm that these simple molecules have a staggered conformation of borohydride ligands.15 In a related study, the hafnium analog Hf(BH4)4 has also been analyzed and is essentially isostructural.16 These studies show the molecules to possess tetrahedral symmetry with all of the BH4 ligands triply (i.e., if) bridging. Photoelectron spectra [He(i)] of the half and bent metallocene complexes Zr(7]S-CsHs)(BH4)4, M(7]S-CsHs)2(BH4)2 (M = Zr, Hf), and Ta(7]S-CsHs)2(BH4) have been determined.17... 

Even though hafnium is not a scarce or rare element, it was not discovered until 1923 because of its close association with zirconium. Several scientists suspected that another element was mixed with zirconium but could not determine how to separate the two because zirconium ore contains about 50 times more zirconium than hafnium. Mendeleev predicted that there was an element with the atomic number of 72, but he predicted it would be found in titanium ore, not zirconium ore. 

The stepwise stability constants for zirconium and hafnium thiocyanato-complexes have been determined by solvent-extraction techniques. The values ) i = 12.1 2.2, = 215 11, P4. = 205 + 20 for zirconium, and Pi =... 

The X-ray determination of crystal structure of tetracyclopentadienyl-hafnium has established that the molecule should be represented as [(7r-Cp)2-Hf(Cp)2], and thus resembles the titanium rather than the zirconium analogue. Both [(7i-Cp)2Hf(Cp)2] and [(it-Cp)2Zr(Cp)] exchange nonequivalent cyclopentadienyl rings very easily such that, even at — 150°C, only one sharp line is observed in the H n.m.r. spectrum. ... 

Korte N, Kollenbach M, Donivan S. 1983. The determination of uranium, thorium, yttrium, zirconium and hafnium in zircon. Analyt Chim Acta 146 267-270. 

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... 

A somewhat surprising group of coordination compounds consists of the volatile heavy metal nitrates, such as those of copper, zinc, mercury, titanium, zirconium and hafnium. The structures of some of these, in the gaseous state, have been determined thus Cu(N03)2 contains two bidentate, almost planar, staggered nitrato groups. Some derivatives of metal nitrates have also been found to be volatile for example, Fe(N03)3 N204 and Al(N03)3 2MeCN.39... 

The best indicator for use in acidic media from 0.1 M HN03 up to pH 5.6 is xylenol orange (XO 44). Direct determinations can be made of cadmium and cobalt (at 60 °C), copper (in the presence of phen), lead and zinc, scandium, indium, yttrium and the lanthanons, zirconium, hafnium and thorium. Many other elements that block the indicator can be determined indirectly. Consecutive titrations such as Bi (at pH 2) and Pb (at pH 5.5) can be carried out in the same solution and the colour change for the latter is particularly sharp from an intense reddish violet to lemon yellow. The extensive literature on this indicator is reviewed in several places. 2>4>76.87... 

The adsorption of hafnium species on glass was found to increase with the solution pH and hafnium concentration. The effects on the adsorption of the solution preparation and age were studied and the equilibration time for the adsorption process was determined. The surface area of the glass sample was determined by the B.E.T. method using water vapor. The results are discussed in terms of the hydrolyzed hafnium(IV) species. At equilibrium, nearly monolayer coverage was obtained at pH > 4.5. Under these conditions hafnium is in the solution in its entirety in the form of neutral, soluble Hf(OHspecies. In the close packed adsorption layer the cross-sectional area of this species is 24 A which is nearly the same as for water on silica surfaces. 

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