HFS element

Si 10 most abundant elements Rb 11-20th most abundant elements cr 21-40th most abundant elements Hf elements in trace abundance... 

Fogler HF. Elements of chemical reaction engineering. Upper Saddle River Prentice Hall International 2004. 

The second type of the HF modules has also been developed by Schlosser group [25,38 0,92,104]. This module enables a cross flow of the liquid membrane phase or its pulsation perpendicular to fibers, as shown in Figure 13.13. The planar HF elements can be assembled for contacting four or more phases. 

Sr, Eu) with the less mobile HFS elerhehts (Y, Hf, Zr, Ti, Nb, Ta). On the one hand the LIL element concentrations may be a function of the behaviour of a fluid phase, whilst the HFS element concentrations are controlled by the chemistry of the source and the crystal/melr processes which have taken place during the evolution of the rock. Partition coefficients for the HFS elements in the major rock-forming minerals in a range of melt compositions are summarized in Tables 4.1 to 4.3. 

A discrimination diagram based upon the immobile HFS elements Th-Hf—Ta was proposed by Wood (1980). In order to expand and centre the fields of basalt types, concentrations are plotted (in ppm) as Th, Hf/3 and Ta. The elements Th, Hf and Ta are present in very low concentrations in basalts and cannot be accurately determined by XRF analysis and so must be determined by INAA. In cases where reliable Hf and Ta analyses are not given but Zr and Nb concentrations have be ... 

Veining of subcontinental mantle by LIL- and hfs- element enriched fluid... 

Fig. 4. Equipment flow sheet of elemental fluorine production and liquefaction plant, 9 t/d capacity. Step 1 purging residual F2 at rates indicated all but a trace of residual F2 is removed in 15min N2 purge is maintained for 1 h to remove last traces. Step 2 HF removal at rates indicated all but a trace of HF is...

High Purity Aluminum Trifluoride. High purity anhydrous aluminum triduoride that is free from oxide impurities can be prepared by reaction of gaseous anhydrous HF and AlCl at 100°C, gradually raising the temperature to 400°C. It can also be prepared by the action of elemental fluorine on metal/metal oxide and subsequent sublimation (12) or the decomposition of ammonium duoroaluminate at 700°C. 

Titanium tetrafluoride may be prepared by the action of elemental fluorine on titanium metal at 250°C (5) or on Ti02 at 350°C. The most economical and convenient method is the action of Hquid anhydrous HF on commercially available titanium tetrachloride in Teflon or Kynar containers. Polyethylene reacts with TiCl and turns dark upon prolonged exposure. The excess of HF used is boiled off to remove residual chloride present in the intermediates. 

Replacement of Hydrogen. Three methods of substitution of a hydrogen atom by fluorine are (/) reaction of a G—H bond with elemental fluorine (direct fluorination, (2) reaction of a G—H bond with a high valence state metal fluoride like Agp2 or GoF, and (J) electrochemical fluorination in which the reaction occurs at the anode of a cell containing a source of fluoride, usually HF. 

Hafnium [7440-58-6] Hf, is in Group 4 (IVB) of the Periodic Table as are the lighter elements zirconium and titanium. Hafnium is a heavy gray-white metallic element never found free in nature. It is always found associated with the more plentiful zirconium. The two elements are almost identical in chemical behavior. This close similarity in chemical properties is related to the configuration of the valence electrons, and for zirconium and... 

Hafnium Sulfides. Several sulfides of hafnium have been prepared, including Hf2S, HfS, and HfS2, by the reaction of the mixed elements at... 

Fig. 14. Stress—rupture properties of NiAl alloys and composites compared with superaHoy Renit 80 (77). The Heusler precipitates (ppts) = 50 Ni—25 Al—25X (at. %), where X = a Group 4 (IVB) or Group 5 (VB) element such as Hf. To convert MPa to psi, multiply by 145.

Silicon carbide has very high thermal conductivity and can withstand thermal shock cycling without damage. It also is an electrical conductor and is used for electrical heating elements. Other carbides have relatively poor oxidation resistance. Under neutral or reducing conditions, several carbides have potential usehilness as technical ceramics in aerospace appHcation, eg, the carbides (qv) of B, Nb, Hf, Ta, Zr, Ti, V, Mo, and Cr. Ba, Be, Ca, and Sr carbides are hydrolyzed by water vapor. 

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