Alkali aluminium silicates

Acidic refractories (e.g. silica, fire, clay etc.) These are used in areas where slag and atmosphere are acidic. They are stable to acids but attacked by alkalis. Aluminium-silicate refractories These refractories vary widely in their physical, chemical and mineralogical characteristics depending on the nature and proportion of silica and alumina present on them. 

Table 3.2-4 Properties of Alkali aluminium silicates according to DIN EN 60672 [2.6]...

Cleaners containing silicate can cause problems. They should not be used prior to an alkaline process on aluminium, owing to the formation on the surface of alkali-insoluble aluminium silicate. Silicated cleaners can also cause problems before some surface-sensitive zinc phosphating solutions, especially the more modern low-zinc type. 

Caesium is not only of interest as being the first metal to be discovered spectroscopically. As early as 1846 Plattner had examined polluxite, then believed to be merely potassium aluminium silicate, but the analysis, on this assumption, did not work out at 100 per cent. Some alkali appeared to be missing. After the discovery of caesium, Pisanif, in 1864, re-examined the mineral and showed it to contain this new element, and not potassium, whose salts its own so closely resemble. The higher atomic weight... 

The chief source of beryllium oxide is the mineral beryl, or beryllium aluminium silicate, 3Be0.Al203.6Si02, which occurs in Argentina, Brazil and India. When pure, beryllium oxide has a specific gravity of 3.0, and is almost insoluble in water it is soluble in sulphuric acid and in fused alkalis. It has been used as a refractory (melting point over 2500°C) but its toxicity has restricted its use. 

The product of the fusion of silica with sodium carbonate, sodium silicate (strictly called sodium poly trioxosilicate but usually metasilicate), dissolves in water to give a clear, viscous solution known as waterglass . It hydrolyses slowly and silica is precipitated. Besides the metasilicate, other silicates of sodium are known, e.g. the poly-tetroxosilicate (orthosilicate), Na4Si04. Only the silicates of the alkali metals are soluble in water. Other silicates, many of which occur naturally, are insoluble, and in these substances the polysilicate anions can have highly complicated structures, all of which are constructed from a unit of one silicon and four oxygen atoms arranged tetrahedrally (cf. the structure of silica). Some of these contain aluminium (the aluminatesilicates) and some have import ant properties and uses. 

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