Hafnium source materials

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... 

An altered zircon, cyrtolite, which is a hydrated zirconium silicate in which part of the zirconium is replaced by hafnium, and divalent and trivalent metals, is used as the raw material. This ore, although not very abundant, is used as the source material rather than the zircon or baddeleyite (1) because of its higher hafnium content (5 to 9 per cent compared to 2 per cent or less for the normal ores), and (2) because it is easily susceptible to acid attack. Ordinarily silicates are not easily attacked by acid treatment and must be handled by some fusion method. However, Urbain reported successful extraction by sulfuric acid at 65° of malacon, an altered zircon, and other investigators have noted that cyrtolite also yields to sulfuric acid treatment. 

Apart from the reactions described above for the formation of thin films of metals and compounds by the use of a solid source of the material, a very important industrial application of vapour phase transport involves the preparation of gas mixtures at room temperature which are then submitted to thermal decomposition in a high temperature furnace to produce a thin film at this temperature. Many of the molecular species and reactions which were considered earlier are used in this procedure, and so the conclusions which were drawn regarding choice and optimal performance apply again. For example, instead of using a solid source to prepare refractory compounds, as in the case of silicon carbide discussed above, a similar reaction has been used to prepare titanium boride coatings on silicon carbide and hafnium diboride coatings on carbon by means of a gaseous input to the deposition furnace (Choy and Derby, 1993) (Shinavski and Diefendorf, 1993). 

For heterometallic materials, lanthanum hafnium oxide thin films continue to attract attention, with FIf(N(Me)(Et))4 serving as the Hf source, and either La(C5FI4Et)3 49 or La(C5I I4 Pr)350 serving as the La source. 

The presence of hafnium in zirconium does not significantly influence mechanical properties other than the thermal neutron cross-section. Moreover, hafniiun is a valuable metal for many applications. The source of hafnium comes as the byproduct in the production of zirconium. The nonnudear grades of zirconium alloys are also low in hafnium content. Consequently, the coimterparts of nuclear and normuclear grades of zirconium alloys are interchangeable in mechanical properties. However, specification requirements for nuclear materials are more extensive than those for nonnuclear materials. Only requirements for nonnuclear materials are given in Table 22.3 and Table 22.4. It can be seen that Zr 705 is the... 

The neutron absorption of hafnium leads to the formation of hafnium isotopes, themselves absorbers (Fig. 15.7) and then to isotopes of heavier elements Ta, and W (up to a few percent Lu is produced in very small amounts). Among these, Ta is the main source of the radiotoxicity of the material, but with a 115-day period, making it a shortlived waste. 

There exist a number of laser-induced techniques for ionizing these neutrals, such as resonance-enhanced multiphoton ionization (in ion source I or II, Figures lA and IB), laser-induced vacuum UV ionization (e.g. by 118 nm from a 3x355 nm/ Nd YAG laser), electron attachment (in ion source I) and electron ionization (in ion source II). Electrons may be supplied by laser-induced photoelectron emission from metal surfaces, preferably from thin wires made out of material having a low work function (e.g. hafnium). Ions formed in source I have to drift into the ion optics of the mass spectrometer (together with the neutral molecular beam) and can be extracted by a pulsed electric field while ionization in source II may be performed within a static electric field with instantaneous ion extraction. 

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