Hydrofluosilicic acid

Chemical Designations - Synonyms Fluorosilicic acid, Hexafluosilicic acid, Hydrofluosilicic acid. Hydrogen hexafluorosUicate, Sand acid, Silicofluoric acid Chemical Formula HjSiF -HjO. Observable Characteristics - Physical State (asshipped) Liquid Color Transparent, straw colored, colorless Odor Acrid, sharp. 

Virtually every alloy system has its specific environment conditions which will produce stress-corrosion cracking, and the time of exposure required to produce failure will vary from minutes to years. Typical examples include cracking of cold-formed brass in ammonia environments, cracking of austenitic stainless steels in the presence of chlorides, cracking of Monel in hydrofluosilicic acid, and caustic embrittlement cracking of steel in caustic solutions. 

Betts An electrolytic process for refining lead and recovering silver and gold from it. The electrolyte is a solution of lead fluosilicate and hydrofluosilicic acid. The other metals collect as a slime on the anode and are retained there. Developed by A.G. Betts in 1901, first operated at Trail, British Columbia, in 1903, and now widely used in locations having cheap electric power. 

Reaction with hydrofluosilicic acid followed by crystallization yields blue crystals of hydrated cupric fluosilicate, CuSiF6 4H20. 

Hydrofluosilicic Acid. See Fluorosilicic Acid in Vol 6 of Encycl, p F141-R... 

Precipitated silicas having properties matching those from the conventional sodium silicate route are said to be possible (79). The hydrofluosilicic acid that is generated can be recycled in the system, or can be used to manufacture sodium silicofluoride or ammonium fluoride. 

CuSiFg, 4H20 mw 277.72 blue, hygroscopic, poisonous crysts sp gr 2.158, mp — decompd sol in w, si sol in ale. Can be prepd by interaction of Cu hydroxide and hydrofluosilicic acid. Used for creating grape vines for "white disease" and for dyeing and hardening white maible (Ref 1)... 

Can be prepd by treating Mg hydroxide or carbonate with hydrofluosilicic acid. Used in ceramics, concrete hardening, waterproofing mothproofing... 

According to E. Fremy s Recherches sur les fluorures (1856), the acid furnished by the action of sulphuric acid on fluorspar always contains water, sulphuric acid, sulphurous acid, hydrofluosilicic acid, and other impurities. After many fruitless attempts to puiify and dehydrate the crude material so obtained, he sought other means of preparation, and found that anhydrous hydrofluoric acid could be satisfactorily obtained by heating well-dried potassium hydrogen fluoride in a platinum retort attached to a platinum receiver which was cooled by immersion in a freezing mixture. The first portions of the acid which distilled over contained a little moisture. H. Moissan thus describes the operation ... 

The properties of hydrofluoric acid.—Hydrogen fluoride is soluble in water between 0° and 19 4° in all proportions. The aq. soln. forms hydrofluoric acid the more cone, solutions fume strongly in air. The specific gravity of aq. soln. increases with increasing concentration of hydrogen fluoride up to a maximum 1 262 with soln. containing 75 93 per cent, of HF, and then decreases to unity as the concentration increases. The numbers in Table I are calculated from those of J. L. C. Eckelt,8 and of E. G. Hill and A. P. Sirkar. The table shows that the sp. gr. of a 63 per cent. soln. is 1 246 at 0°. Table II is due to C. Winteler. The contamination of the soln. with hydrofluosilicic acid greatly increases the density. 

G. S. Serullas treated potassium chlorate with an excess of hydrofluosilicic acid the clear liquid was decanted from the sparingly soluble potassium fluosilicate, the soln. evaporated below 30°, and filtered through glass powder J. J. Berzelius evaporated the acid liquid mixed with finely divided silica below 30° in air, or over cone, sulphuric acid and potassium hydroxide in vacuo. The excess of hydrofluoric acid was volatilized as silicon fluoride, and the clear liquid was then filtered from the excess of silica. R. Bottger treated sodium chlorate with oxalic acid whereby sparingly soluble sodium oxalate was formed J. L. Wheeler, and T. B. Munroe treated sodium chlorate with hydrofluosilicic acid and M. Brandau treated potassium chlorate with aluminium sulphate and sulphuric acid and precipitated the alum so formed with alcohol. Chloric acid is formed in many reactions with hypochlorous and chlorous acid for example, it is formed when an aq. soln. of chlorine or hypochlorous or chlorous acid decomposes in light. It is also formed when an aq. soln. of chlorine dioxide stands in darkness or in light. A mixture of alkali chlorate and chlorite is formed when an aq. soln. of an alkali hydroxide is treated with chlorine dioxide. 

Tungsto-vanadosilicates.—These complexes are analogous to the molybdo-vanadosilicates, and are prepared as yellowish-red to red crystals by the action of vanadates on the silico-tungstates, or by the action of hydrofluosilicic acid on the tungsto-vanadates. The following series has been recognised —... 

Hypovanadic oxide, V02, and vanadium pentoxide, V205, both dissolve in hydrofluosilicic acid to yield a vanadyl fluosilicate and a vanadium fluosilicate, both of doubtful composition.14... 

Cobalt Fluosilicate, CoSiF6.6H20, results when cobalt carbonate is dissolved in aqueous hydrofluosilicic acid and the solution allowed to evaporate.1 It crystallises out in red rhombohedra. 

IV.27 HEXAFLUOROSILICATES (SILICOFLUORIDES), [SiF6]2 Solubility Most metallic hexafluorosilicates (with the exception of the barium and potassium salts which are sparingly soluble), are soluble in water. A solution of the acid (hydrofluosilicic acid H2[SiF6]) is one of the products of the action of water upon silicon tetrailuoride, and is also formed by dissolving silica in hydrofluoric acid. 

Fluorosilicic (or Hydrofluosilicic) Acid, (Silicofluoric Acid), H2SiF6 mw 144.11 colorless, transparent, filming, corrosive, poisonous liquid attacks glass stoneware kept in wax, wood, or special plastic con-... 

Ammonium trithionate, (NH4)2S306.—An aqueous solution of potassium trithionate reacts with hydrofluosilicic acid and ammonia to form the trithionate, which is precipitated from its aqueous solution by alcohol as a very deliquescent, unstable salt.15 It is also formed, along with the tetrathionate, by the action of sulphur dioxide on ammonium thiosulphate 16... 

Auric cyanide, Au(CN)a.—Potassium auricyanide is transformed by strong acids such as hydrofluosilicic acid into auric cyanide. The reaction is more complex than is indicated by the equation... 

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