Subject soluble silicates

Some metals are soluble as atomic species in molten silicates, the most quantitative studies having been made with Ca0-Si02-Al203(37, 26, 27 mole per cent respectively). The results at 1800 K gave solubilities of 0.055, 0.16, 0.001 and 0.101 for the pure metals Cu, Ag, Au and Pb. When these metal solubilities were compared for metal alloys which produced 1 mm Hg pressure of each of these elements at this temperature, it was found drat the solubility decreases as the atomic radius increases, i.e. when die difference in vapour pressure of die pure metals is removed by alloy formation. If the solution was subjected to a temperature cycle of about 20 K around the control temperamre, the copper solution precipitated copper particles which grew with time. Thus the liquid metal drops, once precipitated, remained stable thereafter. 

In contrast to calcium carbonate, all seawater is undersaturated with respect to BSi. As shown in Table 16.1, the imdersaturation is very large and increases with depth because the solubility of BSi increases with pressure. Thus, all siliceous hard parts are subject to dissolution. Nevertheless, about 25% of the BSi created in the surfece waters survives the trip to the seafloor via pelagic sedimentation. Direct observations of this transport... 

Regardless of the t)q)e of soluble metal silicates used, they are subject to the same molecular speciation in aqueous solution resulting in a mixture of monomeric tetrahedral ions, oligomeric linear or cyclic silicate ions, and polysilicate ions. Sodium metasilicate, an example of a soluble metal silicate, can be prepared in anhydrous form or in the presence of water of crystallization as the penta- or nona-hydrate. It is readily soluble in water [8]. 

Shallow-mantle xenoliths, hosted in alkali basalts, commonly contain C02-rich fluid inclusions (e.g., Roedder, 1965, 1984 Frey and Prinz, 1978 Murck eta/., 1978 Miller and Richter, 1982 Fastens, 1987 Frezzotti et al., 1994 Bumard et al., 1998 Ertan and Leeman, 1999 Andersen and Neumann, 2001). In most cases, these fluid inclusions are related to metasomatic processes to which the samples were subjected. As outlined previously, the C02-rich nature of these inclusions may be a natural consequence of degassing from an ascending melt that contains both H2O and CO2, because the greater solubility of H2O in silicate melts would allow it to remain in solution in the residual melt. Alternatively, as proposed by Andersen and Neumann (2001), the high CO2 content in these inclusions could be the result of removal of water via reactions between the original fluid and the host mineral surrounding the inclusion. 

It is important to acquire information on the hydration processes that occur when cement is subjected to low temperatures. Even at temperatures below zero cement hydrates slowly, as water does not freeze due to the presence of soluble materials in the pores. The products that form at low temperatures are calcium aluminate hydrates at earlier periods and after several months, the products of hydration of tricalcium silicate. A weak endothermal peak at about 330°C could be due to the presence of silica gel and this is preceded by the appearance of calcium hydroxide and C-S-H gel.t l... 

Sorption reactions of silica in soils were postulated many years ago (Sreenivasan [1935]). In the early work, however, somewhat high concentrations of sodium and potassium silicates were used, and such systems would be subject to hydrolysis and polymerization reactions and also to pH changes. Thus, in recent studies on the sorption of soluble silica by soils (Eliassaf [1962] Beckwith and Reeve [1963] McKeague and Cline [1963]), dilute solutions (100 to 135 ppm) of monomeric silicic acid have been employed, and results indicate that the residual concentration of monosilicic acid is controlled by an adsorption equilibrium which is pH dependent. Sesquioxides make a considerable contribution to the capacity of soils to sorb soluble silica (Nejegebauer [1958] Beckwith and Reeve [1963]), and the apparent increase in solubility of silica in soil suspensions with increased acidity has been discussed in terms of... 

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