In hydrofluoric acid

Colorless crystals of iron(II) fluoride tetrahydrate [13940-89-1Fep2 4H2O, can be obtained by dissolving metallic iron or the anhydrous salt in hydrofluoric acid. The crystals of Fep2 4H2O are sparingly soluble in water and decompose to Fe202 when heated in air. 

Titanium trifluoride is prepared by dissolving titanium metal in hydrofluoric acid (1,2) or by passing anhydrous hydrogen fluoride over titanium trihydrate at 700°C or over heated titanium powder (3). Reaction of titanium trichloride and anhydrous hydrogen fluoride at room temperature yields a cmde product that can be purified by sublimation under high vacuum at 930—950°C. 

Fluorocarbons are made commercially also by the electrolysis of hydrocarbons in anhydrous hydrogen fluoride (Simons process) (14). Nickel anodes and nickel or steel cathodes are used. Special porous anodes improve the yields. This method is limited to starting materials that are appreciably soluble in hydrogen fluoride, and is most useflil for manufacturing perfluoroalkyl carboxyflc and sulfonic acids, and tertiary amines. For volatile materials with tittle solubility in hydrofluoric acid, a complementary method that uses porous carbon anodes and HF 2KF electrolyte (Phillips process) is useflil (14). 

Hafnium is readily soluble in hydrofluoric acid and is slowly attacked by concentrated sulfuric acid. Hafnium is unaffected by nitric acid in all concentrations. It is resistant to dilute solutions of hydrochloric acid and sulfuric acid. Hafnium is attacked by all mineral acids if traces of fluorides are present. Hafnium is very resistant to attack by alkaUes. 

Niobic Acid. Niobic acid, Nb20 XH2O, includes all hydrated forms of niobium pentoxide, where the degree of hydration depends on the method of preparation, age, etc. It is a white insoluble precipitate formed by acid hydrolysis of niobates that are prepared by alkaH pyrosulfate, carbonate, or hydroxide fusion base hydrolysis of niobium fluoride solutions or aqueous hydrolysis of chlorides or bromides. When it is formed in the presence of tannin, a volurninous red complex forms. Freshly precipitated niobic acid usually is coUoidal and is peptized by water washing, thus it is difficult to free from traces of electrolyte. Its properties vary with age and reactivity is noticeably diminished on standing for even a few days. It is soluble in concentrated hydrochloric and sulfuric acids but is reprecipitated on dilution and boiling and can be complexed when it is freshly made with oxaHc or tartaric acid. It is soluble in hydrofluoric acid of any concentration. 

Potassium Heptafluorotantalate. Potassium heptafluoiotantalate [16924-00-8], K TaF, ciystallizes in colodess, rhombic needles. It hydroly2es in Foiling water containing no excess of hydrofluoric acid. The solubility of potassium heptafluorotantalate in hydrofluoric acid decreases from 60 g/100 mL at 100°C to 0.5 g/100 mL at room temperature. The different solubility characteristics of K TaF and K NbOF are the fundamental basis of the Matignac process (16). A phase diagram exists for the system K TaF —NaCl—NaF—KCl (68). Potassium heptafluorotantalate has an LD q value of 2500 mg/kg. The recommended TWA maximum work lace exposure for K TaF in air is 2.5 mg /m (fluoride base) (69). 

In a detailed study the dissolution kinetics of shock-modified rutile in hydrofluoric acid were carefully studied by Casey and co-workers [88C01], Based on the defect studies of the previous sections in which quantitative measures of point and line defects were obtained, dissolution rates were measured on the as-shocked as well as on shocked and subsequently annealed powders. At each of the annealing temperatures of 200, 245, 330, 475, 675, 850, and 1000 °C, the defects were characterized. It was observed that the dissolution rates varied by only a factor of 2 in the most extreme case. Such a small effect was surprising given the very large dislocation densities in the samples. It was concluded that the dissolution rates were not controlled by the dislocations as had been previously proposed. 

Compared with reactions in other strong acids used in hydrogenations, such as hydrochloric, sulfuric, and trifluoroacetic acid, reactions in hydrofluoric acid are faster and proceed more selectively under milder conditions [2]... 

If the hydrogenation is carried out in hydrochloric instead of sulfuric acid, chloroaniline is formed (20), while in hydrofluoric acid, fluoroaniline is produced (37). 

Neither titanium nor zirconium is recommended for use in hydrofluoric acid. 

Tantalum-Tungsten Braun, Sedlatschek and Kieffer examined tantalum-tungsten alloys in 50% potassium hydroxide up to 80°C and in 20% hydrochloric acid at 20°C. In the alkaline solution the corrosion rate was a maximum when the tantalum was over 60 at.%. In hydrofluoric acid the alloy system exhibited the relatively low corrosion rates associated with tungsten until the tantalum concentration exceeded 80 at.%. 

Fused silica is a general classification within which is a range of varieties and types with differences in purity, transmission and grade. This glass may be used up to 900°C in continuous service it resists attack by a great many chemical reagents, rapid attack occurring only in hydrofluoric acid and concentrated alkali solutions. 

Howell and Moss [289] confirmed, by 19F NMR spectroscopy, that NbOF52 complex is present in hydrofluoric acid solutions of up to 30%. Increase in HF concentration leads to the formation of NbF6 complex ions. 

Tsikaeva et al. investigated the Raman and IR absorption spectra of solutions containing tantalum in hydrofluoric acid with no additional cations [290, 291]. 

Preparation of the solutions was similar to that of niobium-containing solutions, i.e. by dissolving tantalum metal powder in hydrofluoric acid, HF, at a concentration of about 40% weight. 

Anhydrous AgF is best made by fluorination of finely divided silver at room temperature alternatively it can be made by dissolving silver(II) oxide in hydrofluoric acid and crystallizing ... 

A further method for the determination of caesium isotopes in saline waters [60] is based on the high selectivity of ammonium cobalt ferrocyanide for caesium. The sample (100-500 ml) is made 1 M in hydrochloric acid and 0.5 M in hydrofluoric acid, then stirred for 5-10 min with 100 mg of the ferrocyanide. When the material has settled, it is collected on a filter (pore size 0.45 im), washed with water, drained dried under an infrared lamp, covered with plastic film and / -counted for 137caesium. If 131caesium is also present, the y-spectrometric method of Yamamoto [61] must be used. Caesium can be determined at levels down to 10 pCi/1. 

C. P. Fitzsimmons, C. B. Knkbnde.d Precision Enthalpy of Solution Calorimeterfor Slow Rates of Solution. The Enthalpy of Solution of Vitreous Silica in Hydrofluoric Acid. J. Chem. Thermodynamics 1970, 2, 265-273. 

A basic step in hydrofluoric acid manufacture is the reaction of sulfuric acid with fluorspar (calcium fluoride) to produce hydrogen fluoride and calcium sulfate. Spent alumina is also generated by the defluorination of some hydrofluoric acid alkylation products over alumina. It is disposed of or sent to the alumina supplier for recovery. Other solid residuals from hydrofluoric acid alkylation include any porous materials that may have come in contact with the hydrofluoric acid. 

Fluorine - the atomic number is 9 and the chemical symbol is F. The name derives from the Latin fluere for flow or flux since fluorspar (CaFj) was used as a flux in metallurgy because of its low melting point. It was discovered in hydrofluoric acid by the Swedish pharmacist and chemist Carl-Wilhelm Scheele in 1771 but it was not isolated until 1886 by the French pharmacist and chemist Ferdinand-Frederic-Henri Moisson. 

Ferris, L.M. Solubility of uranyl fluoride in hydrofluoric acid-nitric acid solutions at 25°, J. Am. Chem. Soc., 87(23) 5377-5379, 1965. 

As observed, aromatic hydrocarbons gave products of protonation on dissolution in hydrofluoric acid. Oxidation into aromatic cation-radicals did not take place (Kon and Blois 1958). Trifluoro-acetic acid is able to transform aromatics into cation-radicals. This acid is considered a middle-powered one-electron oxidant (Eberson and Radnor 1991). Its oxidative ability can be enhanced in the presence of lead tetraacetate. This mixture, however, should be used carefully to avoid oxidation deeper than the one-electron removal. Thus, oxidation of 1,2-phenylenediamine by the system Pb(OCOCH3)4 -I- CE3COOH -P CH2CI2 leads to the formation of either primary or secondary cation-radicals. The primary product is the cation radical of initial phenylenediamine, whereas the secondary product is the cation radical of dihydrophenazine (Omelka et al. 2001). Sulfuric acid is also used as an one-electron oxidant, especially for aromatic hydrocarbons. In this case, generation of cation radicals proceeds simultaneously with the hydrocarbon protonation and sulfonation (Weissmann et al. 1957). 

Also, cobalt(II) fluoride can he prepared as a tetrahydrate, C0F2 4H2O hy dissolving cobalt(ll) hydroxide in hydrofluoric acid. The tetrahydrate is then dehydrated to anhydrous fluoride. Elemental fluorine combines with cohalt at 450°C forming mixtures of cobalt(II) and cobalt(III) fluorides. 

Also, it is produced when nitrogeneous compounds are electrolyzed in hydrofluoric acid. 

Occurs as a close-packed hexagonal alpha-form and a hody-centered cubic beta modification melting point 2,233°C vaporizes at 4,602°C electrical resistivity 35.5 microhm-cm at 20°C magnetic susceptibility 0.42xlCL6 emu/g at 25°C thermal neutron absorption cross section 105 barns/atom work function 3.5 eV modulus of elasticity 20x10 psi tensile strength 58,000 psi at 25°C insoluble in water, dilute mineral acids and nitric acid at all concentrations soluble in hydrofluoric acid, concentrated sulfuric acid and aqua regia. 

White crystalline solid, when heated at 1,500°C, it transforms into a tetragonal modification with shrinkage tetragonal form converts to a cubic polymorph with fluorite structure when heated at 2,700°C density 9.68 g/cm melts at 2,774°C insoluble in water dissolves slowly in hydrofluoric acid at ordinary temperatures. 

White cubic crystals refractive index 1.3915 density 2.635 g/cm melts at 845°C vaporizes at 1,676°C very shghtly soluble in water 0.27 g/lOOg at 18°C soluble in hydrofluoric acid insoluble in alcohol. 

Grayish, soft metal with a white luster on polished surfaces ductile and very malleable at room temperature also highly ductile at cryogenic temperatures body-centered cubic crystals density 8.66 g/cm at 20°C melts at 2,468+10°C vaporizes at 5,127°C electrical resistivity 13.2 microhm-cm at 20°C becomes superconducting at 9.15K thermal neutron-capture cross section 1.1 barns insoluble in water insoluble in hydrochloric acid, nitric acid and aquaregia soluble in hydrofluoric acid soluble in fused alkah hydroxide. 

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