Solutions, chemistry supersaturated

The formation and growth of precipitates and crystals are very important in analytical chemistry and in other areas of science. Shown in the photo is the growth of sodium acetate crystals from a supersaturated solution. Because supersaturation leads to small particles that are difficult to filter, it is desirable in gravimetric analysis to minimize the supersaturation and thus increase the particle size of the solid that is formed. 

Calculation of Saturation Indices from solution chemistry can also be a useful elimination tool (Plummer et al., 1991). Models that precipitate minerals that are undersaturated and dissolve minerals that are supersaturated may not be realistic. The modelers must be cautious, however, in using this criterion. Inverse modeling calculates the net mass changes along a flow path, often a few kilometers apart. It does not consider the point to point mass transfer or equilibrium state along the flow path. A mineral phase may precipitate in one segment of the path, but dissolve in another. 

At the start, amorphous solid is in equilibrium with solution species. This initial equilibrium is then maintained while product crystals grow from the supersaturated solution. Finally, when all the amorphous precursor has been consumed, the crystalline zeolite equilibrates with its mother liquor. This simple analysis enables the solution chemistry, and in particular the effects of solubility and pH, to be understood at a fundamental level [62]. 

The foregoing relations show that supersaturation plays a key role both on nucleation as well as on growth steps for a given material. Solution chemistry provides a useful tool for predicting the occurence of a deposition reaction by using the approach of conditional solubility diagrams. 

The first and most widely studied area of chemical-chemical interactions is on the surface of the skin. The types of phenomena that could occur are governed by the laws of solution chemistry and include factors such as altered solubility, precipitation, supersaturation, solvation, or volatility as well as physical-chemical effects such as altm ed surface tension from the presence of surfactants, changed solution viscosity, and micelle formation (Idson et al., 1983 Williams and Barry, 1998 Barry, 2001 Moser etal., 2001). For some of these so-called solvatochromatic effects, chemicals act independmit of one another. However, for many the presence of other component chemicals may modulate the effect seen. 

Slade, L. and Levine, H. 1985. Intermediate moisture systems concentrated and supersaturated solutions pastes and dispersions water as plasticizer the mystique of bound water thermodynamics versus kinetics (Number 24). Presented at Faraday Division, Royal Society of Chemistry Discussion Conference - Water Activity A Credible Measure of Technological Performance and Physiological Viability Cambridge, July 1-3. 

Biomineralization,4 where inorganic materials are formed under near ambient conditions, has inspired new approaches to coating polymers. Biominerals often show superior properties due to an elaborate microstructure of crystalline domains in an organic matrix.5 In biomineralization the interaction of supersaturated solutions and surface chemistry is often crucial. 

While this book treats several topics similar to those found in an analytical chemistry text, it endeavors to consider the spatial and temporal scales of the reactions in nature as distinctly different from those of the laboratoiy. For example, in chemical analysis, precipitates (frequently of metastable and active compounds) are formed from strongly oversaturated solutions, whereas in natural water systems, the solid phase is often formed under conditions of slight supersaturation often crystal growth and aging may continue over geological time spans. Interfacial phenomena are particularly important because chemical processes of significance often occur only at phase discontinuities. 

Precipitation of cement in all environments is controlled by a number of factors, including the presence of saturated solutions, the degree of supersaturation of pore fluids (which affects the amount of cement precipitated as it controls both the crystal fabric developed and the amount of CaO available for precipitation), the composition of the solution, the rate of pore-water movement and the chemistry of the substrate. 

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