Sodium aluminium fluoride

The electrolytic production of aluminium is more complex. Hall and Heroult developed the current process independently in 1886. In this process, alumina, AI2O3, is dissolved in molten sodium aluminium fluoride (Na3AlF6) and electrolysed (Figure 9.22). Originally, the aluminium oxide was derived directly from the mineral bauxite, and the sodium aluminium fluoride was used in the form of the naturally occurring mineral cryolite. These days, synthetic cryolite is used, and the aluminium oxide is produced from a wider variety of mineral sources, consisting of aluminium oxide-hydroxides. 

The sodium beryllium fluoride product is soluble in water and can be leached out, together with some aluminium, excess sodium silicofluoride, and small amounts of other impurities. Unfortunately a high proportion of the valuable fluorine is lost as the gaseous and highly toxic silicon tetra-fluoride, or as undissolved sodium aluminium fluoride. However, the escape of volatile silicon tetrafluoride can be prevented if a small amount of sodium fluoride is present with the sodium silicofluoride, owing to the reaction... 

Cryolite. Natural sodium aluminium fluoride, NajAlF m.p. 980 C sp. gr. 2.95. Because of its low m.p. and its fluxing action, it is used in the manufacture of enamels and glass and in the ceramic coatings of welding rods. Opal glass is often made from batches containing about 10% cryolite a similar preparation is sometimes used in white cover-coat enamels. 

The material that is removed during the etching process results in the formation of a muddy residue on the bottom of the etching pot. This mud contains silver, silver fluoride, silicon fluoride, lithium fluoride, lithium aluminium fluoride, lithium sodium aluminium fluoride amongst others as shown by XRD analysis. These crystalline materials are from the residual silver nuclei, i.e. those that induced the crystallisation of the glass, but also insoluble reaction products of the HF attack on the glass and the lithium metasilicate. If only pure lithium metasilicate would have been dissolved only XRD peaks for lithium fluoride would have been found. 

In fluoride glasses, calcium fluoride is an essential constituent, but generally cryolite, NajAlFg, is also added as a flux to lower the temperature of fusion. Aluminium orthophosphate is also generally added to the fusion mixture for various reasons. Of course, the various elements may be added in different ways. Thus, calcium orthophosphate, aluminium fluoride and sodium carbonate are often used in the preparation of fluoride glasses. 

As the cement ages, absorption of water and loss of aluminium ions ceases (after 7 days). Other species - sodium and fluoride ions and silicic acid - continue to be eluted. The release of fluoride is important, for the glass polyalkenoate cement can be seen as a device for its sustained release. 

Aluminium borohydride Aluminium chloride Aluminium chlorate Ammonium tetrachloroaluminate Aluminium fluoride Aluminium trihydroxide Aluminium ammonium sulphate Aluminium potassium sulphate Aluminium nitride Aluminium nitrate Sodium aluminate Aluminium sodium aluminate Aluminium phosphate Aluminium phosphide Aluminium borate Aluminium oxychloride Aluminium fluorosilicate Aluminium magnesium silicate Aluminium sulphate... 

CsCl HgCl2=3 1, 2 1, 1 1, 2 3, 1 2, and 1 5 and five caesium antimonious fluorides where CsF SbF3=l 1, 3 4, 4 7, 1 2, and 1 3. According to I. Remsen s rale (1889) When a halide of any element combines with a halide of an alkali metal to form a double salt, the number of molecules of the alkali salt which are added to one molecule of the other halide is never greater, and is generally less than the number of halogen atoms contained in the latter—for instance, in the double fluoride of sodium and aluminium, where the negative halide has three fluorine atoms, no more than three molecules of sodium fluoride will be found united with one of aluminium fluoride. 

Flash inhibitor Potassium sulfate, potassium nitrate, potassium aluminium fluoride and sodium cryolite Reduce muzzle flash... 

A special flux consisting of the halides of alkali metals with the addition of sodium and aluminium fluorides was employed both to protect the aluminium melt from oxidation and to pre-heat the specimen to the required temperature. First, the flux was melted in a 26 mm inner diameter alumina crucible. Melting started at about 350°C. The height of the flux column was around 15 mm. Aluminium pieces were then melted under the flux layer. The amount of aluminium taken was equivalent to a volume of... 

Silicon tetrafluoride is thus a volatile compound because the molecule is shielded in the gas phase, that is to say that the charge has already reached the coordination number in contrast, for example, with sodium fluoride, where this is only i against 6, magnesium fluoride and aluminium fluoride where this ratio amounts respectively to 2 and 3 to 6. 

Eor example, to calculate the concentration of aluminium in solution, an ion for which no selective electrode exists, this analyte is transformed into insoluble aluminium fluoride AIE3 by adding sodium fluoride. The end point of this reaction is determined by the presence of an excess of sodium fluoride ions in solution, easily detected by a fluoride selective electrode. 

Some fluorine compounds enter into the atmosphere in the form of solid particles, such as cryolite, fluoroapatite, aluminium fluoride and sodium fluoride. 

Glass-ionomer cements have a degree of natural bioactivity. They release certain key ions into surrounding aqueous media, not only fluoride, but also sodium, aluminium, phosphate and silicate [103]. Under mildly acidic conditions, they release aU of these ions in larger quantities than in neutral conditions, and also release calcium (or strontium), ionic species which are insoluble in neutral solutions but which... 

In aqueous solution, resin-modified glass-ionomers have been found to release not only fluoride but also other ions [58,59], Under neutral conditions, ions released were sodium, aluminium, phosphorus (as some sort of phosphate) and silicon (as silicate). Under acidic conditions, in addition to these ions, either calcium or strontium was released as well [58,59], Acidic conditions also caused much higher concentrations of all ions to be released [59], This behaviour is similar to that of conventional glass-ionomers, though levels of phosphorus were much lower for resin-modified glass-ionomers for reasons that are not clear [59],... 

Titova, Y.V., Shiganova, L.A., Maydan, D.S., and Bichurov, G.V. (2012) The self-propagating high-temperature synthesis of nanostructural powder of aluminium nitride using aluminium fluoride and sodium azide. Izvestia Vuzov. PMiFP, (3), 25-29. 

An alternative fluoride breakdown process for beryl was used during the 1939-45 war by the Sappi Company in Italy. This was based upon the reaction with sodium hydrogen fluoride (NaF.HF) at a temperature of about 680°C. The fluoride reagent is mixed with the ground ore and made into briquettes with a little water, ready for firing in the breakdown furnace. The reaction converts the beryllium to a complex fluoride, believed to be 3NaF.2Bep2, without fluorination of the aluminium and silicon components. 

Certain processes are carried out through the electrolytic route, e g. production of caustic soda by electrolysis of sodium chloride solution, production of aluminium by electrolysis of aluminium fluoride. 

Examples Sodium, aluminium, iron, mercury and brass (copper and zinc) Diamond, polyethene, nylon, silicon dioxide and graphite Iodine, methane, hydrogen chloride, water, benzoic acid, ethanol, ammonia and fullerenes Sodium chloride, magnesium oxide, calcium fluoride and sodium carbonate... 

The book by Prof. Yanko [1] discusses a mechanism of degradation of the flue walls, stating that the main corrosion agents are aluminium fluoride and sodium fluoride. The temperature of evaporation of aluminium fluoride is - 950 °C, while the temperature of evaporation of sodium fluoride is - 1,050 °C. Volatile sodium and aluminium fluoride penetrate the permeable pores of refractory [1] and interact with silica, giving volatile silicon tetrafluoride, while sodium oxide is released in the pores ... 

Cryolite ratio the ratio of molecules of sodium fluoride to aluminium fluoride. In pure cryolite NasAlFs (3NaF AIF3), the cryohte ratio (CR) is 3. The melting point of pure cryolite is 1,010 °C, but the temperature of electrolyte may be reduced either by the additives of fluorides or by varying the ratio of sodium fluoride (NaF) to aluminium fluoride (AIF3). Both variants — additives and variation of cryolite ratio — diminish the melting point of the bath to 930-960 °C. 

Electrolyte, bath, molten bath, frozen bath a substance mainly consisting of cryolite (NasAlFe), with additions of sodium fluoride, aluminium fluoride, calcium fluoride, magnesium fluoride, conducting in molten state electric current and dissolving alumina. 

Hall-Heroult smelting process A continuous electrolytic process used to produce aluminium fmm alumina. The alumina is dissolved in a bath of sodium aluminium chloride called cryolite that contains alumina fluoride and calcium fluoride. The solution is heated to 950 C in a steel tank with a carbon liner. Caibon anodes are lowered into the solution with the liner being the cathode. Electrolytic action separates the alumina into liquid aluminium, which collects at the cathode, and oxygen at the anode, which combines with the carbon to form carbon dioxide gas. It was invented in 1886simultaneously and independently by American chemist Charles M. Hall (1863-1914) and French scientist Paul L. T. ffiroult (1863-1914). 

In addition to cryolite and aluminium fluoride, there is a wide range of inorganic fluorides of commercial importance these include sulfur hexafluoride, used as an electrical insulating gas. Sodium fluoride has been used in the fluoridation of water, although it is being replaced by fluorosilicic acid, and its salts. Tin (IV) fluoride (Snp4) is used in toothpaste to prevent dental decay, and boron trifluoride (BF3) is a widely used catalyst for reactions in the petrochemical industry. 

The trend in architectural applications has been towards more matt finishes, and the sodium hydroxide-based etchants used frequently contain additives such as sodium nitrate or nitrite or sodium fluoride. Chelating agents such as gluconates, heptonates or sorbitol are added to complex the aluminium produced, and other additives such as sulphides may be present in the etchant to complex zinc dissolved from the alloy, and allow it to be used continuously without dumping ... 

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