Dissolution kinetics, effects

In a detailed study the dissolution kinetics of shock-modified rutile in hydrofluoric acid were carefully studied by Casey and co-workers [88C01], Based on the defect studies of the previous sections in which quantitative measures of point and line defects were obtained, dissolution rates were measured on the as-shocked as well as on shocked and subsequently annealed powders. At each of the annealing temperatures of 200, 245, 330, 475, 675, 850, and 1000 °C, the defects were characterized. It was observed that the dissolution rates varied by only a factor of 2 in the most extreme case. Such a small effect was surprising given the very large dislocation densities in the samples. It was concluded that the dissolution rates were not controlled by the dislocations as had been previously proposed. 

Hodge, F. G. and Wilde, B. E., Effect of Chloride Ion on the Anodic Dissolution Kinetics of Cr-Ni Binary Alloys in Dilute H2SO4 , Corrosion, 26, 146 (1970)... 

T Higuchi, S Dayal, I Pitman. Effects of solute-solvent complexation reactions on dissolution kinetics Testing of a model by using a concentration jump technique. J Pharm Sci 61 695, 1972. 

KG Mooney, MA Mintun, KJ Himmelstein, VJ Stella. Dissolution kinetics of carboxylic acids I Effect of pH under unbuffered conditions. J Pharm Sci 70 13-22, 1981. 

Bisrat et al. concluded that for sparingly soluble, suspended drugs, diffusional transport plays a major role in the dissolution kinetics [19]. They studied the effect of particle size and viscosity on dissolution rate and apparent diffusional distance (.h-App) of oxazepam and griseofulvin. The term apparent diffusional distance was used as a simplified measure of the distance over which diffusion dominates and was calculated as follows ... 

This paper presents new data on dissolution kinetics. The effects of alkali concentration, size of the cation, and salt addition were studied. The influence of segmental mobility on dissolution was elucidated by measuring the temperature coefficients of the dissolution rates. Experiments were also carried out to study the relation between the chemical structure of a polymeric Inhibitor and Its effectiveness 1n retarding dissolution. Based on these results,... 

Figure 4. Effect of added NaCl on dissolution kinetics at fixed NaCl concentrations.

Zutic, V., and W. Stumm (1984), "Effect of Organic Acids and Fluoride on the Dissolution Kinetics of Hydrous Alumina. A Model Study Using the Rotation Disc Electrode", Geochim. Cosmochim. Acta 48, 1493-1503. 

Figure 2 Effect of sample pretreatment on feldspar dissolution kinetics (modified from Ref. 11). See text for discussion.

The fourth explanation for non-linear kinetics differs from the previous three in that it concerns the composition of the solution rather than any intrinsic property of the solid reactants or products. Changing solution composition can produce apparent or true parabolic dissolution kinetics either through the influence of changing pH and COj equilibria, or through the effect of chemical affinity and the reverse reaction rate. These phenomena have been discussed in detail by Helgeson and Murphy (V7) and Helgeson and others ( 1 8). 

Cerpa, A. Garcia-Gonzalez, M.T. Tartaj, P. Re-quena, J. Garcell, L. Serna, C.J. (1999) Mineral-content and particle-size effects on the colloidal properties of concentrated lateri-tic suspensions. Clays Clay Min. 47 515-521 Cervini-Silva, J. Sposito, G. (2002) Steady-state dissolution kinetics of aluminum-goethite in the presence of desferrioxamine-B and oxalate. Environ. Sci. Technol. 36 337-342 Cesco, S. Rdmheld.V. Varanini, Z. Pinton,... 

Scheckel, K. G. Ryan, J. A. 2002. Effects of aging and pH on dissolution kinetics and stability of chloropyromorphite. Environmental Science Technology, 36, 2198-2204. 

Ahn, T. M. 1996. Long-Term Kinetic Effects and Colloid Formations in Dissolution of LWR Spent Fuels. US Nuclear Regulatory Commission, NUREG-1564. 

Ks do not match with each other. This is partly the result of the effects of the specific surface which was different in the two methods. However, the mechanisms of the dissolution kinetics seem to be identical. The reaction rate of the acid with carbonate mineral would be controlled by diffusion of the reactant into and the products out of the pores. Therefore, the availability of only the contact surface is not adequate. The type of surface in terms of relevant diffusion model and the closest theory to that model, such as film, penetration, or any other, should also be specified. 

Kinetic effects were determined by measurements of dissolution and penetration rates. A constant penetration velocity was observed for almost all compositions for both binary solvent mixtures. In all studies, case II transport assumptions provided good agreement with experimental results. For MEK-IPA, penetration rates increased with increasing MEK concentration. For MIBK-methanol, however, a maximum penetration rate was observed at a 60 40 MIBK/methanol ratio. 

Solution Composition. Changing solution composition can also cause apparent or true parabolic dissolution kinetics through the influence of changing pH and C02 equilibria or through an effect on chemical affinity and reverse rate (Helgeson et al., 1984). 

Morse J.W. (1974) Dissolution kinetics of calcium carbonate in seawater. V Effects of natural inhibitors and the position of the chemical lysocline. Amer. J. Sci. 274, 638-647. 

Walter L.M. (1983) The dissolution kinetics of shallow water carbonate grain types Effects of mineralogy, microstructure and dolution chemistry. Ph.D. dissertation, Univ. Miami, Miami, FL. 

Walter L.M. and Hanor J.S. (1979) Effect of orthophosphate on the dissolution kinetics of biogenic magnesian calcites. Geochim. Cosmochim. Acta 43, 1377-1385. 

The method of soil suspensions extracts is based on metal desorption/dissolution processes, which primarily depend on the physico-chemical characteristics of the metals, selected soil properties and environmental conditions. Metal adsorption/ desorption and solubility studies are important in the characterization of metal mobility and availability in soils. Metals are, in fact, present within the soil system in different pools and can follow either adsorption and precipitation reactions or desorption and dissolution reactions (Selim and Sparks, 2001). The main factors affecting the relationship between the soluble/mobile and immobile metal pools are soil pH, redox potential, adsorption and exchange capacity, the ionic strength of soil pore water, competing ions and kinetic effects (e.g. contact time) (Evans, 1989 Impelhtteri et al., 2001 McBride, 1994 Sparks, 1995). 

Bonny, J. and Leuenberger, H., Matrix type controlled release systems I. Effect of percolation on drug dissolution kinetics, Pharmaceutica Acta Helvetiae, Vol. 66, No. 5-6, 1991, pp. 160—164. 

The expected Tafel slope of 60mV/decade is not always found. There are a number of reasons for this, aside from kinetic effects in the bulk of the semiconductor. The kinetic effects associated with faradaically active surface states is of considerable significance, as shown below, but another common problem is that part of the potential change may appear across the Helmholtz layer rather than across the depletion layer. A well-known case in point is germanium, for which the surface is slowly converted from "hydride to "hydroxylic forms as the potential is ramped anodically. This conversion gives rise to a change in the surface dipole and hence Aij/ AT. In fact, the anodic dissolution of p-germanium is found to follow a law [106]... 

---