Silicon containing compounds silicates

Even though silicon is extremely abundant, only one silicon-containing compound appears in the list of top 50 industrial chemicals. That is sodium silicate, Na2 Si03, used for the manufacture of silica gel and glass. Nevertheless, with the advent of the electronic age silicon has become an extremely important substance that is the primary ingredient of most semiconductors. Because these are microscale devices, the quantity of production of silicon remains small compared with that of fertilizers and construction materials. Although relatively small in quantity, the value of silicon products is quite high. 

Knowledge regarding renal injury and the development of anti-neutrophil cytoplasmic antibody (ANCA) positivity associated with silica exposure is rudimentary. Moreover, information about the health significance of the occupational exposure to other silicon containing compounds apart from silica and crys-taUine silicates is lacking. 

Based on experimental studies it has been suggested that silicates may stimulate lymphocytes via a T-cell receptor VP-specific T-cell activation pathway resulting in the production of autoantibodies or autoimmune diseases [83, 87, 88]. In this context it must be noted that not only ANCA s but also other autoantibodies such as antinuclear antibodies and rheumatoid factors frequently occur in workers heavily exposed to silicon-containing compounds [64, 75]. 

More systematic studies of silicon electrodeposition began in the 1930 s with Dodero s (17)(18) investigation of the electrolysis of molten silicates at temperatures of 800 to 1250 0. The very high potentials used in these studies would be expected to liberate not only silicon but also alkali and alkaline earth metals. There is no conclusive proof in Dodero s work that silicon was the primary cathode product or the result of a reduction of the silicon containing compounds by alkali or alkaline earth metals that had been produced by electrolysis. His best result was 72% silicon produced from a melt composition of 5 Si02 -1 Na20 - 0.2NaF electrolyzed at 1150 C. 

Silicon is the second most abundant element in the Earth s crust. It occurs widely in rocks as silicates, compounds containing the silicate ion, Si032, and as the silica, Si02, of sand (Fig. 14.33). Pure silicon is obtained from quartzite, a granular form of quartz (another solid phase of SiOz), bv reduction with high-purity carbon in an electric arc furnace ... 

Silicon-containing ceramics include the oxide materials, silica and the silicates the binary compounds of silicon with non-metals, principally silicon carbide and silicon nitride silicon oxynitride and the sialons main group and transition metal silicides, and, finally, elemental silicon itself. There is a vigorous research activity throughout the world on the preparation of all of these classes of solid silicon compounds by the newer preparative techniques. In this report, we will focus on silicon carbide and silicon nitride. 

The spirocyclic pentacoordinate silicon compounds 90,45,58 91 45,58 and 9259 are zwitterionic A5Si-silicates with an Si05 skeleton. The chiral zwitter-ions contain two 2-methyllactato(2-) or two benzilato(2-) ligands. In these molecules, two five-membered SiC>2C2 rings are connected by the silicon spirocenter. Compounds 90 and 91 represent isoelectronic analogs of the zwitterionic A5Sz-silicates 58 and 59 (0/CH2 replacement see Section III,D). 

Beryllium oxide (BeO) is a beryllium compound produced in significant commercial quantities. The chemical process starts with minerals containing aluminum silicate and silicon dioxide and undergoes a number of chemical reactions, some at high temperatures, to end up with BeO. 

A survey of the literature [28, 58-65, 71, 72, 74-80] indicates that the most frequent exposure to silicon involves exposure to silica and silicates mainly in their crystalline forms. Health risks associated with the exposure to other sihcon containing compounds were reported in the mortality study of 16.661 manmade mineral fiber workers employed during 1945 to 1963 at one of 17 U.S. manufacturing plants [75]. Fiber exposure in the plants producing fibrous glass or mineral wool, or both, was associated with increased... 

There is some evidence that chromium (Cr " ), silicic acid (Si(OH)4) or related silicon-based compounds, borate (8407 ), nickel (NP" ), and arsenate (AsOf ) are required inorganic nutrients. However, the available evidence tends to be not convincing to all researchers (Reeves, 1997). The functions of arsenate and nickel are not clear. There is some indication that arsenate is used in the metabolism of sulfur-containing amino acids. An experimentally induced deficiency in arsenate or nickel results in impaired growth. 

Hydrofluoric acid is used in the production of fluorine-containing compounds and for etching glass. The acid reacts with silicates, such as calcium silicate, CaSi03, in the glass to produce a very volatile and thermodynamically stable compound, silicon tetrafluoride, SiF4. 

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