Alkali fluosilicates

J. Reich 6 also patented a process based on the calcination of the alkali fluosilicate or fluoborate with an oxide of the alkaline earths. When the calcined mass is lixiviated with water, the alkali fluoride is obtained in soln. L. Schuch 6 made sodium fluoride by boiling finely powdered cryolite with a cone. soln. of sodium hydroxide—the alumina and silica pass into soln.—sodium fluoride crystallizes from the cooling soln. Sodium silicate can be used in place of the hydroxide. F. Jean made sodium fluoride by leaching a calcined mixture of fluorspar, limestone, Glauber s salt, and charcoal. 

Modern analytical instrumentation has been used in the last 23 years for determining commercially important characteristics of soluble silicates, and the nature of silicate species in silicate glasses and solutions. The classical wet methods for assay of silicate solutions are alkali titration and gravimetric determination of silica, which can also be determined, with lesser precision, by the alkali fluosilicate method. 

If combined with alkali fluosilicates, water glass solutions exhibit setting and hardening based on a chemical reaction between the dissolved alkali silicate and the fluosilicate (Odler and Heimicke, 1991) ... 

In alkali silicate binders the setting and hardening is based on a reaction between a water glass (a solution of an alkali silicate in water) and alkali fluosilicate (see also section 15.3). The reaction product is an amorphous form of Si02 with embedded ciystals of alkah fluoride. The amorphous Si02 remains preserved until about 550°C and converts gradually to quartz and tridimite at higher temperatures. At 750°C crystalline sodium disilicate starts to be formed. 

The elucidation of the factors determining the relative stability of alternative crystalline structures of a substance would be of the greatest significance in the development of the theory of the solid state. Why, for example, do some of the alkali halides crystallize with the sodium chloride structure and some with the cesium chloride structure Why does titanium dioxide under different conditions assume the different structures of rutile, brookite and anatase Why does aluminum fluosilicate, AljSiCV F2, crystallize with the structure of topaz and not with some other structure These questions are answered formally by the statement that in each case the structure with the minimum free energy is stable. This answer, however, is not satisfying what is desired in our atomistic and quantum theoretical era is the explanation of this minimum free energy in terms of atoms or ions and their properties. 

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. 

Occurrence.—Many silicates contain traces of lithium, usually associated with large proportions of sodium and potassium. Lithium compounds are mainly derived from lepidolite or lithia-mica, a double fluosilicate of aluminium and an alkali-metal, containing 0 8—2-7 per cent, of lithium and petalite, a double silicate of aluminium and lithium with an admixture of sodium, containing 2 per cent, of lithium. 

As alkali fluozirconates are soluble in water, and alkali Neonates are soluble in strong acid, fusion with fluosilicates or with alkali hydroxides are useful steps for getting Zr02 into aqueous solution. 

Gravimetric silica jfO.05% Fluosilicate reaction 0.3% Alkali Titration J O.1%... 

However, in the commercial world the ultimate in precision is often not needed to satisfy the situational analytical requirements. Because the gravimetric procedure involves many time consuming steps, the fluosilicate reaction is generally preferable as the usual silica wet chemical assay method. It is not as precise as a normal alkali titration because of the difficulty of observing the end point. 

Made and described BeF. Dissolved BeO in HF. Obtained an easily soluble substance which dries to a gummy mass and which loses H O at 100°, becoming milk white and foamy. Loses part of its HF on ignition. Yields double salts with alkalies of which the potassium salt is very insoluble. Obtained a beryllium fluosilicate by action of fluosilicic acid. 

Bergman, in his examination of volcanic minerals, noticed the gelatinisation of silica when some silicates (zeolites) are treated with acids. He showed that the waters of several springs contain dissolved silica. He obtained artificial quartz ciystals by letting powdered quartz stand in a corked bottle for two years with hydrofluoric acid (containing hydrofluosilicic acid), and he emphasised that the precipitate (potassium or sodium fluosilicate) formed from the solution by vegetable or mineral alkali (potash or soda) is a triple salt of a peculiar kind, composed of siliceous earth, fluor acid, and fixed alkali, which dissolves with difficulty in warm water , whilst the precipitate with ammonia is pure silica. ... 

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