Dissolution, of crystals

Ristic, R.L and Sherwood, J.N., 2001. The influence of mechanical stress on the growth and dissolution of crystals. Chemical Engineering Science, 56, 2267-2280. 

In carbonate diagenesis V we deal usually with a combination of low supersaturation and absence of mechanical agitation. Homogeneous nucleation will certainly not occur. The important factors to be investigated are heterogeneous nucleation and rates of growth and dissolution of crystals. 

Scientists have long recognized that partial dissolution of crystals in the presence of impurities may result in the formation of well-shaped etch pits (60-62). When crystals of calcite, for example, were partially dissolved in the... 

There have been a number of studies on the rate of dissolution of crystals In agitated tanks (eg.26-31). Predominantly the results Indicate dissolution Is mass transfer controlled. For mass transfer In stirred tanks, among the many studies, that of Levins and Glastonbury (32) Is widely considered. 

The dissolution of crystals is a well-known phenomenon. It has sometimes been misunderstood that the reaction is the reverse of the deposition process, but this is only true for a saturated solution in equilibrium with crystals. 

Another question may arise concerning the dissolution of crystals. For example, when a NaCl crystal is dropped into water, it dissolves. How do we decide which ion in the crystal dissolves first —a sodium ion or a chloride ion What is the second ion —and then the third one Answers to such questions cannot be derived from macroscopic observations. However, computer simulation techniques may provide some suggestions in answering such questions. 

Anisotropic dissolution of crystal surfaces results in the formation of surface contour whose geometric features depend on the crystal orientation [81]. During steady-state etching the etched surface profile exhibits a characteristic shape convex or concave [160]. A convex surface will be bounded by fast etching planes while a concave surface will be bounded by slow etching planes. 

Wulff, G. and Kristallogr, Z., On the question of the rate of growth and dissolution of crystal surfaces, Mineral, 34, 449, 1901. 

Solubility curves have traditionally been determined by either crystallization of a supersaturated solution or by dissolution of crystals in an undersaturated solution. Suitable solution conditions, which produce crystals, must be known in advance for both methods. Protein solubility can be determined as a function of many parameters including temperature, salt concentration, salt type, buffer and pH. For the crystallization method, a grid is made of samples of two or three different initial protein concentrations and at least four different values of a given variable (e.g., three protein concentrations at four different temperatures = 12 samples). Aliquots are removed periodically for concentration determination for up to 6-12 weeks after crystals appear. In the case of dissolution experiments, a batch of crystals previously grown in the appropriate buffer is needed. Crystals are placed in undersaturated solutions and allowed to dissolve. Again, for six to... 

The grov h and dissolution of crystals are opposing processes. It follows that an inhibitor for grov h of a particular crystal plane can also influence the dissolution rate of the same plane. This increases the contrast between the protected planes and the exit points of defect lines, since there only a protected crystal plane is involved. In this way, etch craters are formed with whose aid one can count the defect lines (see also Fig. 4.8). 

For the dissolution of crystals smaller than about 60 pm, a rough estimate of the diffusional mass transfer rate may be made because as Re - 0 Sh reduces... 

The heat of crystallization is the heat that has to be supplied or removed during crystallization at constant temperature. It is equal to the negative value of the heat of solution during the dissolution of crystals in an almost saturated solution. The heat of crystallization is accounted for in the enthalpy values. Processes in crystallizers can easily be tracked, if an enthalpy concentration diagram is available for the respective system. The pure component s enthalpy is zero at reference temperature, not the enthalpy of real mixtures however. In such diagrams, the lever rule is applicable. This is shown for the system calcium chloride/water in Fig. 8.3-5, where the specific enthalpy is plotted vs. the mass fractions. 

The first generation of drug nanocrystals accumulated in liver and spleen due to the "relatively" slow dissolution of crystals with a size of a few 100 nm. This accumulation might be beneficial if diseases to be treated are localized in the macrophages and/or liver. However, in most of the cases this effect is not desired. The MPS accumulation can be avoided by using "super fast" dissolving nanocrystals being distinctly below 100 nm in size. However, there are also diseases which do not desire a fast dissolution of... 

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