Single particle dissolution rate

Thus, experimental studies relating dissolution rates to defect concentrations are needed. This has been done recently in two different types of experiments where the importance of line defects has been measured. Casey et al. (1988) and Holdren et al. (1988) have measured the rate of dissolution of rutile and labradorite powders that were shocked with an explosive charge to induce a high density of dislocations (> 1011 cm-2). Concurrently, in order to avoid artifacts due to fine particles, Schott et al. (1989) have performed with the rotating disc apparatus dissolution runs of single crystals of calcite in which dislocations were induced in a constant-strain apparatus. Examples of the results are shown in Fig. 15. Surprisingly, it can be seen that dislocations have only a small effect on the dissolution rates the dissolution rates of samples with over 6 order of magnitude in dislocation density differ only by a factor less than 3. 

Simplified Model. The dissolution rate of a single particle of volume V is given by ... 

Dissolution rate data for potash alum are plotted in accordance with equations 6.108 and 6.110 with e = 0.95, in Figure 633, where it can be seen that the results lie reasonably close ( 20%) to the predicted values. However, it should be noted that equation 6.110 is very sensitive to values of e as e —> 1, so it cannot be applied with any reliabihty to very lean beds of dissolving particles and certainly not to the dissolution of single particles. 

The scope of kinetics includes (i) the rates and mechanisms of homogeneous chemical reactions (reactions that occur in one single phase, such as ionic and molecular reactions in aqueous solutions, radioactive decay, many reactions in silicate melts, and cation distribution reactions in minerals), (ii) diffusion (owing to random motion of particles) and convection (both are parts of mass transport diffusion is often referred to as kinetics and convection and other motions are often referred to as dynamics), and (iii) the kinetics of phase transformations and heterogeneous reactions (including nucleation, crystal growth, crystal dissolution, and bubble growth). 

The influence of particle size on the absorption rate from aqueous suspension enemas has probably never been investigated. Dissolution of the active substance is assumed to increase with decreasing particle size (see Sect. 29.2.1). For the requirements on particle size for a stable suspension enema reference is made to Sects. 29.2 and 29.3 as well as to Sect. 5.10 because of similarity with oral suspensions. A particle size of maximal 180 pm generally satisfies. Suspension stability is less important than for oral use since an enema is dispensed in single-dose containers. However,... 

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