Silicate glasses structure

Silicate glasses, 72 571-572, 608 durability of, 72 584-585 modulus of elasticity of, 72 590 thermal properties of, 72 588 Silicate glasses, atomic structure of, 22 453-454... 

There are a number of papers which report the use of Si NMR in studies of the structures of various soluble silicates and alkali silicate glasses. (93, 97-103) Early workers concluded that in soluble sodium metasilicate solutions only simple monomeric silicate structures are present. (104) The presence of polymeric structures was subsequently identified using Raman spectroscopy (105-107) and trimethylsilylation experiments. (108) Marsmann (97) first reported the existence of dimer, linear trimer, tricyclic, and polymeric structures based on Si NMR... 

The silicate ceramics include materials that vary widely in composition, structure, and use. They range from simple earthenware bricks and pottery to cement, fine porcelain, and glass. Their structural strength is based on the same linking of silicate ion tetrahedra that gives structure to silicate minerals in nature. 

In alumino-silicate glasses, the structural disposition of Al is guided by the same considerations as that of Pb. In pure alumino-silicates, Al is found both in tetrahedral and in octahedral positions (Prabakar et al., 1991). The tetrahedral Al is in network positions, while octahedral Al is present as aP and is surrounded by NBOs as confirmed in NMR experiments. This is because if both Al atoms in AI2O3 have to occupy tetrahedral positions, it requires four oxygens, 2[A104/2] , which it does not possess and [Si04/2]° cannot provide it. Therefore, AI2O3 behaves as if it has become. 

Based on your knowledge of the silicate structure, would you expect the viscosity of Na2Si205 to be greater or smaller than that of Na2Si03 at their respective melting points Which would you expect to be the better glass former Explain. 

Anhydrous sodium silicate glasses which are composed of between 12 and 21 wt. % Na20 are difficult to form into useful, dur-ableglass objects because of their rapid phase separation or crystallization. However, they hydrate easily in an autoclave to contain up to 40 weight percent water. These sodixam hydrosilicates are thermoplastic in behavior, but more Importantly the molecular water provides a means for dealkalizing the silicate structure. 

R. Hill, D. Wood, M. Thomas, TrimethylsUylation analysis of the silicate structure of fluoro-alumino-silicate glasses and the structural role of fluorine, J. Mater. Sci. 34 (1999)1767-1774. 

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