Calcium aluminium silicates, formation

Cement binders are based on silicates, aluminates, aluminium silicates, aluminium ferrites of alkaline earth metals (mainly calcium). The hydration of these compounds or their mixtures with the formation of... 

The usual extraction procedure is to roast the crushed ore, or vanadium residue, with NaCl or Na2C03 at 850°C. This produces sodium vanadate, NaV03, which is leached out with water. Acidification with sulfuric acid to pH 2-3 precipitates red cake , a polyvanadate which, on fusing at 700°C, gives a black, technical grade vanadium pentoxide. Reduction is then necessary to obtain the metal, but, since about 80% of vanadium produced is used as an additive to steel, it is usual to effect the reduction in an electric furnace in the presence of iron or iron ore to produce ferrovanadium, which can then be used without further refinement. Carbon was formerly used as the reductant, but it is difficult to avoid the formation of an intractable carbide, and so it has been superseded by aluminium or, more commonly, ferrosilicon (p. 330) in which case lime is also added to remove the silica as a slag of calcium silicate. If pure vanadium metal is required it can... 

The setting reaction of dental silicate cement was not understood until 1970. An early opinion, that of Steenbock (quoted by Voelker, 1916a,b), was that setting was due to the formation of calcium and aluminium phosphates. Later, Ray (1934) attributed setting to the gelation of silicic acid, and this became the received opinion (Skinner Phillips, 1960). Wilson Batchelor (1968) disagreed and concluded from a study of the acid solubility that the dental silicate cement matrix could not be composed of silica gel but instead could be a silico-phosphate gel. However, infrared spectroscopy failed to detect the presence of P-O-Si and P-O-P bonds (Wilson Mesley, 1968). 

This is by far the most frequently encountered interference in AAS. Basically, a chemical interference can be defined as anything that prevents or suppresses the formation of ground state atoms in the flame. A common example is the interference produced by aluminium, silicon and phosphorus in the determination of magnesium, calcium, strontium, barium and many other metals. This is due to the formation of aluminates, silicates and phosphates which, in many instances, are refractory in the analytical flame being used. 

Although many soil scientists had considered the possible mechanisms which soils employ for the retention [fixation] of phosphorus, it remained for Haseman et al. (1950) to demonstrate that phosphorus could — and in experimental situations did — replace the silicon of micas and clay minerals in order to form crystalline hydrous aluminium phosphates of sodium, ammonium and potassium. Prior to experimentation by this group, associated with the laboratories of the Tennessee Valley Authority (TVA), most authors attributed the retention of phosphorus by soils to combination with calcium to produce fairly insoluble minerals to adsorptive, exchangeable combination with silicate minerals and to formation of phosphates of iron... 

In passing this layer, the precipitation water becomes more acid, and iron and aluminium are dissolved in the upper part of the sand layer. Further down, the acidity is reduced by the dissolution of calcium, magnesium and potassium from the minerals, and iron and aluminium are redeposited as hydroxides (see Figure 12). This is a natural process which during some thousand years has led to formation of the characteristic podsol profile on the top a layer of black humus, then a nearly white layer of leached silicates, and underneath a deposition layer, which takes on first a yellow and then a red colour as the iron is precipitated out. 

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