Dissolution, definition

If two salts which do not react chemically to produce a double salt (contact with a quantity of solvent insufficient for complete dissolution, the composition of the solution is independent of the proportions of the two solids and is definite at a fixed temperature, as we see from the phase rule ... 

When we speak of the dissolution of an estate, we are applying the common definition and we know that the estate will be broken up into parts. In chemistry, when we discuss the ease of solute dissolution, we are implying a full range of chemical and physical processes that take place when a solute dissolves. 

The second difference relates to the definition of a cutoff time point for the evaluation of the difference factor and the Rescigno index. When cumulative data are available, evaluation of the difference factor or the Rescigno index usually requires a reference data set in order to define the cutoff time point for index evaluation (30). For the evaluation of fl and the , i.e., when the difference factor and the Rescigno index are evaluated from non-cumulative data, this difficulty does not exist, provided that the release process has been monitored up to the end (i.e., until dissolution of the drug is complete). At this point, it is worth mentioning that a similar conclusion cannot be drawn for the similarity factor (31) because application of this index to non-cumulative data is set apart by the careful scaling procedure required, in addition to the existence of a reference data set. The reason is that this index can continue to change even after dissolution of both products is complete. 

The use of (T/100) as a variable has the advantage of making the parameters A, A2, A3, and A4 of similar magnitude. The application of standard thermodynamic definitions to the equation allows the equation parameters to be used to calculate the thermodynamic characteristics of the dissolution process summarized in Table I. When all four parameters of the equation... 

A definite number of main chain cleavages should occur in the soluble part of the film when a developer is specified and the least amount of photons required for the dissolution of the film in the developer used. If the definite number is K, the following formulae are obtained ... 

The basicity of the molten carbonate is defined as equal to -log (activity of O ) or -log aM20, where a is the activity of the alkali metal oxide M2O. Based on this definition, acidic oxides are associated with carbonates (e g., K2CO3) that do not dissociate to M2O, and basic oxides are formed with highly dissociated carbonate salts (e.g., U2CO3). The solubility of NiO in binary carbonate melts shows a clear dependence on the acidity/basicity of the melt (18,19). In relatively acidic melts, NiO dissolution can be expressed by... 

There are limited data on the chemical resistance of various oxide materials in the literature (Samsonov 1982, Ryshkewitch and Richerson 1985). Furthermore, many of the studies are concerned with solid, nonporous materials. Nevertheless, these may provide an indication of the general trends. Until a definitive and quantitative database of chemical stability of various inorganic membranes becomes available, some simple dissolution-type test methods using membrane samples may be employed on a comparative basis to estimate the extent of attack by a chemical under the application conditions. An example of such a simple test is given below. 

The presence of water does not only create conditions for the existence of an electrolyte, but it acts as a solvent for the dissolution of contaminants [10], Oxygen plays an important role as oxidant element in the atmospheric corrosion process. The thickness of the water layer determines the oxygen diffusion toward the metallic surface and also the diffusion of the reaction products to the outside interface limited by the atmosphere. Another aspect of ISO definition is that a metallic surface is covered by adsorptive and/or liquid films of electrolyte . According to new results, the presence of adsorptive or liquid films of electrolyte perhaps could be not in the entire metallic surface, but in places where there is formed a central anodic drop due to the existence of hygroscopic particles or substances surrounded by microdrops where the cathodic process takes place. This phenomenon is particularly possible in indoor conditions [15-18],... 

Pores may be present as structural features (e. g. between domains) or as a result of aggregation of particles. They may also be the result of partial dehydroxylation (oxide hydroxides) or dissolution. Although the shapes of pores can be quite variable, there are some definite, basic forms. The commonest of these are 1) slit shaped, the walls of which may or may not be parallel 2) ink bottle which are closed upon all sides but one from which a narrow neck opens and 3) cylindrical. Upon partial dissolution, pores bounded by well-defined crystal planes (e. g. 102 in goethite) develop (Chap. 12). 

Al substitution (0.09-0.16 mol mol ) had no definite effect on the photochemical dissolution of substituted goethite in oxalate at pH 2.6 (Cornell Schindler, 1987). On the other hand, Al substitution depressed the initial (linear) stage of dissolution of synthetic goethites and hematites in mixed dithionite/citrate/bicarbonate solutions (Fig. 12.22) (Torrent et al., 1987). As the variation in initial surface area has already been accounted for, the scatter of data in this figure is presumably due to variations in other crystal properties such as disorder and micropores. Norrish and Taylor (1961) noted that as Al substitution in soil goethites increased, the rate of reductive dissolution dropped (see also Jeanroy et al., 1991). 

By the above definition, b is positive for crystal dissolution, and negative for crystal growth. During convective crystal dissolution, the dissolution rate u is directly proportional to b. During diffusive crystal dissolution, the dissolution rate is proportional to parameter a, which is positively related to b. Hence, for the dissolution of a given mineral in a melt, the size of parameter b is important. The numerator of b is proportional to the degree of undersaturation. If the initial melt is saturated, b = 0 and there is no crystal dissolution or growth. The denominator characterizes the concentration difference between the crystal and the saturated... 

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