Minerals, usage calcium

The calcium silicate hydrate formed in both cases appears to be a very poorly crystallized version of the natural mineral tobermorite. The use of the name tobermorite for the calcium silicate hydrate obtained in the hydration of Ca8Si05 and Ca2Si04 is not fully justified nevertheless, because in all publications from this laboratory that name was used, the usage is retained in this paper. 

The diversity of sources of inorganic chemicals was touched on in the introduction to this chapter and the book entitled The Modern Inorganic Chemicals Industry discusses, in detail, the production of a number of important inorganic chemicals. Comment here therefore will be restricted to a summary of world consumption (Table 2.6) and major uses of the more important inorganic raw materials, plus a brief study of the changing raw-material usage for sulphuric acid production and the reasons for this. Between 1960 and 1975 four alternatives were utilized in sulphuric acid production. They are sulphur, anhydrite (a calcium sulphate mineral), zinc concentrates... 

PVC has inherently poor stability to heat, even the heat of processing. When thermally decomposed it releases HCl gas and becomes brown and brittle. The acid gas acts as a catalyst to accelerate further breakdown. Calcium carbonate absorbs and neutralizes this acid and therefore acts as a low cost stabilizer. This is a major reason for using this mineral in preference to others. Ultrafme ground grades, coated or uncoated, give the best stabilization. Table 6 shows calcium carbonate usage in PVC. 

The compounds used are semirigid and, in some cases, ABS blends. In the case of a straight PVC compound, 30-40 phr of a low-volatility phthalate or trimellitate plasticizer is used. From 15 to 20 phr calcium carbonate is supplemented with 1 phr titanium dioxide, 1-2 phr antimony trioxide for improved flame resistance, 2-3 phr ESO, colorants as required, and about 0.1 phr (or less) stearic acid. The stabilizers used are barium/zinc or calcium/zinc powders supplemented with mineral acid absorbers and also a source of perchlorate anion. The latter is active in scavenging amine catalysts migrating fiom the PUR layer, which rapidly discolor PVC. If need be, minor amounts of dispersion resin or of acryhc processing aid can be added to compounds such as the above to improve flowability. Although principally used in the United States for instrument panels, European and Japanese usage in arm and head rests has also been reported. 

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