Hydrofluoric acid treatment

The residue consists of the impurities, and the loss in weight of the crucible gives the amount of pure silica present, provided that the contaminants are in the same form before and after the hydrofluoric acid treatment and are not volatilised in the operation. Although silicon is not the only element that forms a volatile fluoride, it is by far the most abundant and most often encountered element consequently the volatilisation method of separation is generally satisfactory. 

The stimulation treatments were performed using retarded hydrofluoric acid. A typical retarded hydrofluoric acid treatment consisted of ... 

Gas production from sixteen wells was also analyzed. Twelve retarded hydrofluoric acid treatments did not include the clay stabilization polymer. The overall gas production increase was 116% compared to an overall increase of 200% obtained from four wells for which the clay stabilization polymer was included in the well treatment. With the exception of the use of the clay stabilizer, the sixteen well treatment designs were identical. 

A white solid, possibly polonium tetrafluoride, is obtained by treating polonium hydroxide or tetrachloride with dilute aqueous hydrofluoric acid treatment of this solid, in suspension in dilute hydrofluoric acid, with sulfur dioxide yields a bluish grey product (possibly PoF2) which rapidly reverts to the original white solid on standing, presumably owing to radio-lytic oxidation 12). The solubility of polonium(IV) in aqueous hydrofluoric acid increases rapidly with acid concentration, indicating complex ion formation (/ft), p. 48). 

Choice of a dissolution method also depends on the range of substances to be analyzed, but in some specific instances the chemical form of the element is of even more importance. For example, particles formed at high temperature usually contain refractory oxides and silicates which may require fusion with either an acidic or basic flux, or hydrofluoric acid treatment to remove silica, or a combination of these techniques. 

Gonzalez-Munoz, M.P., Navarro, R., Saucedo, I., et al. 2006. Hydrofluoric acid treatment for improved performance of a nanofiltration membrane. Destination 191 273-278. 

Lead oxide Lead oxide is an important constituent of glasses. Other constituents, especially zinc oxide, barium oxide, and calcium oxide, influence the determination of lead oxide in various glasses. Separation of lead oxide using electrolysis to form lead dioxide on the anode and subsequent EDTA titration is a popular method, applied to 50-100 mg of PbO after nitric acid-hydrofluoric acid treatment of the glass in a platinum dish. 

A polymer gel based on an (inverse) opal was applied in order to obtain shorter switching times, which are also desirable for electrochemical color display purposes [346]. Hence, an all-color display was developed that, dependent on the applied potential, could reversibly switch between blue, green, red, and black. Here, crosslinked polyferrocenylsilane gels were partly swollen with glutaronitrile electrolyte. The degree of swelling was controlled electrochemically. Subsequently, the distance between the voids formed by the silica beads, which were etched by hydrofluoric acid treatment, could be altered. It should be mentioned that there are also other concepts for electrically switchable photonic crystals that are not directly connected to electrochemically induced solvation [347-349]. 

All silicon compounds on oxidation yield silica or silicates these are difficult to detect but silica (given by silicates after acid treatment) is insoluble in all acids except hydrofluoric acid. 

Precautions in Handling. Ammonium bifluoride, like all soluble fluorides, is toxic if taken internally. Hydrofluoric acid bums may occur if the material comes in contact with moist skin. Ammonium bifluoride solutions should be thoroughly washed from the skin with mildly alkaline soap as soon as possible however, if contact has been prolonged, the affected areas should be soaked with 0.13% solution of Zephiran chloride, or 0.2% Hyamine 1622 (Lonza, Inc.) or calcium gluconate, the treatment recommended for hydrofluoric acid bums. If any of these solutions come in contact with the eyes, they should be washed with water for at least 10 min and a physician should be consulted. 

Acid Treatment. The treatment of petroleum products with acids has been in use for a considerable time in the petroleum industry. Various acids such as hydrofluoric acid, hydrochloric acid, nitric acid, and phosphoric acid have been used in addition to the most commonly used sulfuric acid, but in most instances there is Httie advantage in using any acid other than sulfuric. 

When sihca volatilizes, vapors condense on cooler areas to form a white bloom that can be removed by heat or dilute hydrofluoric acid. Because dilute hydrofluoric acid also attacks the substrate, a mild, careful treatment is required. To minimize volatilization, the temperature should be as low as possible. 

Zirconium is readily attacked by acidic solutions containing fluorides. As Httle as 3 ppm flouride ion in 50% boiling sulfuric acid corrodes zirconium at 1.25 mm/yr. Solutions of ammonium hydrogen fluoride or potassium hydrogen fluoride have been used for pickling and electropolishing zirconium. Commercial pickling is conducted with nitric—hydrofluoric acid mixtures (see Metal surface treatments). 

Arsenates are oxidizing agents and are reduced by concentrated hydrochloric acid or sulfur dioxide. Treatment of a solution of orthoarsenate with silver nitrate in neutral solution results in the formation of a chocolate-brown precipitate of silver orthoarsenate, Ag AsO, which may be used as a test to distinguish arsenates from phosphates. With hydrofluoric acid, orthoarsenate solutions yield hexafluoroarsenates, eg, potassium hexafluoroarsenate [17029-22-0] (KAsFg)2 H2O. Arsenates of calcium or lead are used as insecticides sodium arsenate is used in printing inks and as a mordant. 

Treatment of chloroform, obtained by reacting methanol and chlorine, with the hydrofluoric acid yields monochlorodifluoromethane, also used as a refrigerant, which is a gas boiling at -40.8 C. 

Trimethylbenzylammonium hydroxide has been converted to benzyl fluoride in 22-60% yield by treatment with 20% hydrofluoric acid followed by vacuum distillation [71, 72]... 

The Dow No. 7 treatment, popular in the USA, also falls within this class. The process differs from other chromate treatments in that the activator, magnesium fluoride, is formed on the metal surface by immersion in 20% hydrofluoric acid solution, the parts then being immersed in a 10-15% alkali dichromate solution with or without sufficient alkaline earth fluoride to saturate it. A slow action occurs on the surface and the fluoride film is replaced by a chromate or mixed chromate/fluoride film. 

First, handling of highly concentrated acids, including hydrofluoric acid, especially at elevated temperatures, is very dangerous and requires use of special equipment and appropriate training of personnel. Second, the required amount of fluorine (or HF) is well above the amount needed based on the interaction stoichiometry. This results in large amounts of liquid waste, the treatment of which is very expensive. 

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