The vast scale of the industry can be gauged from the

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Unformatted text preview: es and then heated in a rotary kiln to 1500" to give a sintered clinker; this is reground to 325-mesh and mixed with 2-5% of gypsum. An average-sized kiln can produce 1000-3000 tonnes of cement per day and the world's largest plants can produce up to 8000 tonnes per day. The vast scale of the industry can be gauged from the US production figures i n the table below. Price (1990) was $45-55 per tonne for bulk supplies. In the same year China emerged as the world's largest cement producer (200 million tonnes per annum). Total world production continues to grow dramatically, from 590Mtpa in 1970 and 881 Mtpa in 1980 to nearly 1200Mtpa in 1990, of which Europe (including the European parts of the former Soviet Union) accounted for some 40%. - Production of Portland Cement in the UStVmillion tonnes (Mtj 1890 0.057 1900 1.45 1910 13.1 1920 17.1 1930 27.5 7.3.5 Other inorganic compounds Chalcogenides At normal temperatures the only stable chalcogenides of A1 are A12S3 (white), A12Se3 (grey) and A12Te3 (dark grey). They can be prepared by direct reaction of the elements at -1000" and all hydrolyse rapidly and completely in aqueous solution to give Al(OH)3 and H2X (X = S, Se, Te). The small size of A1 relative to the chalcogens dictates tetrahedral coordination and the various polymorphs are related to wurtzite (hexagonal ZnS, p. 1210), two-thirds of the available 6' K irk- Othmer Encyclopedia of Chemical Technology, 4th edn., Vol. 5, Interscience, New York, 564-98 (1993). 1940 22.2 1950 38.5 1960 56.0 1970 66.4 1980 68.2 1990 70.0 metal sites being occupied in either an ordered (a)or a random ( p ) fashion. A12S3 also has a y-form related to y-A1203 (p. 243), and very recently a novel high-temperature hexagonal modification of A12S3 containing 5-coordinate A1 has been obtained by annealing a-Al2S3 at 5 50"C;(62) n this new form half the A1 atoms i are tetrahedrally coordinated (A1- S 223 -227 pm) whereas the other half are in trigonal bipyramidal coordination with AI-S,, 227-232 pm and AI-Sa, 250-252pm. The chalcogenides of Ga, In and T1 are much more numerous and at least a dozen different structure types have been established by X-ray 62 B. KREBS, A . SCHIEMANN M . LACE,Z . anorg. allg. and Chem. 619, 983-8 (1993). Other inorganic compounds 1.. 735 crystallography.(63) The compounds have been extensively studied not only because of their intriguing stoichiometries, but also because many of them are semiconductors, semi-metals, photoconductors or light emitters, and T15Te3 has been found to be a superconductor at low temperatures. (See p. 1182 for high-temperature super conductors, including Tl2Ca2Ba2Cu30lo+, which has one of the highest known superconducting transition temperatures, T , = 125 K.) The chalogenides, as expected from their position in the 6 3L. I . MAN, R. M. IMANOVnd S . A . SEMILETOV, a Sov. Phys. Crystallogr. 21, 2 55-63 (1976). 253 periodic table, are far from ionic, but formal oxidation states remain a useful device for electron counting and for checking the overall charge balance. Well-established compoun...
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This note was uploaded on 10/12/2012 for the course CHEMISTRY CHM1040 taught by Professor Jhon during the Spring '12 term at Florida A&M.

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