Dissolution reaction, predict

Thus, it can basically be predicted under what conditions (pH, concentration of redox species) tire metal dissolution reaction (Fe Fe ) proceeds tliennodynamically. From a practical point of view, tire rate of tire reaction and tlierefore tire fate of tire oxidized species (Fe ) is extremely important tliey can eitlier be solvated, i.e., to fonn Fe (H20) complexes, and tlierefore be efficiently dissolved in tire solution, or tliey can react witli oxygen species of... 

Felmy, a, R S. a, Peterson, and R. J. Serne. 1987. Interactions of acidic uranium mill tailings solution with sediments Predictive modeling of precipitation/dissolution reactions. Uranium 4 25-41. 

With sufficient thermodynamic and equilibrium data It Is possible to predict whether or not a dissolution reaction will take place. Also with a knowledge of the free energy change for a reaction one can calculate the potential E at which the reaction will occur from the relationships... 

Refinements of the above volume diffusion concept have been made by a model that includes a contribution of surface-diffusion processes to the dissolution reaction of the more active component at subcritical potentials. By adjustment of different parameters, this model allows for the calculation of current-time transients and concentration-depth profiles of the alloy components [102]. In addition to this, mixed control of the dissolution rate of the more active component by both charge transfer and volume diffusion has been discussed. This case is particularly interesting for short polarization times. The analysis yields, for example, the concentration-depth profile and the surface concentration of the more noble component, c, in dependency on the product ky/(t/D), where is a kinetic factor, t is the polarization time, and D is the interdiffusion coefficient. Moreover, it predicts the occurrence of different time domains in the dissolution current transients [109]. 

The order of nobiKty observed in actual practice may differ from that predicted thermodynamically. The reasons are that some metals become covered with a passivatingfEm of reaction products which protects the metal from further attack. The dissolution reaction may be strongly irreversible so that a potential barrier must be overcome. In this case, corrosion may be inhibited even though it remains energetically favorable. The kinetics of corrosion reactions are not determined by the thermodynamics alone. 

The predicted reaction of the muscovite/ quartz mixture with the evolved fluid was much simpler than the above. Dissolution was predicted to take place along the entire length of the column but at about half the rate found with the young fluid, and with more variation between the inlet and outlet ends. The only products expected to be found in this experiment were hillebrandite, which was predicted to form over the first 240 mm of the column, and foshagite, predicted to form from then on. It was predicted that there would be small net reductions in the porosity throughout the column. 

In the predictions for the reaction of calcite with both young and evolved fluids, a small amount of calcite dissolution was predicted at the inlet end of the column. In the evolved fluid case, this was associated with a porosity increase where no secondary mineral precipitation was... 

The semi-consumable electrodes, as the name implies, suffer rather less dissolution than Faraday s law would predict and substantially more than the non-consumable electrodes. This is because the anodic reaction is shared between oxidising the anode material (causing consumption) and oxidising the environment (with no concomitant loss of metal). Electrodes made from silicon-iron, chromium-silicon-iron and graphite fall into this category. 

Respiration of organic matter and dissolution of CaCOs are the main controls of the distribution of deep ocean Total CO2 and alkalinity. These reactions (and their predicted effects on DIC and alkalinity) can be represented schematically as... 

The distribution of metals between dissolved and particulate phases in aquatic systems is governed by a competition between precipitation and adsorption (and transport as particles) versus dissolution and formation of soluble complexes (and transport in the solution phase). A great deal is known about the thermodynamics of these reactions, and in many cases it is possible to explain or predict semi-quantita-tively the equilibrium speciation of a metal in an environmental system. Predictions of complete speciation of the metal are often limited by inadequate information on chemical composition, equilibrium constants, and reaction rates. 

In situ SAXS investigations of a variety of sol-gel-derived silicates are consistent with the above predictions. For example, silicate species formed by hydrolysis of TEOS at pH 11.5 and H20/Si = 12, conditions in which we expect monomers to be continually produced by dissolution, are dense, uniform particles with well defined interfaces as determined in SAXS experiments by the Porod slope of -4 (non-fractal) (Brinker, C. J., Hurd, A. J. and Ward, K. D., in press). By comparison, silicate polymers formed by hydrolysis at pH 2 and H20/Si = 5, conditions in which we expect reaction-limited cluster-cluster aggregation with an absence of monomer due to the hydrolytic stability of siloxane bonds, are fractal structures characterized by D - 1.9 (Porod slope — -1.9) (29-30). 

There are obvious similarities in the derived relative flux expressions for the MMHS model and the precursor HWPH model. The second term on the right-hand side of Eq. (11) accounts for the increase in dissolution observed near the pKa of the acid. Addition of the ionization reaction [Eq. (9)] provides the added flexibility and accountability so that dissolution at low pH s can be accurately predicted. The agreement between theoretical predictions and experimental results for three carboxylic acids with intrinsic solubilities ranging from 10 2 to 10 M over a pH range of 2-12 was good (see Fig. 2). Computationally, the MMHS model was also quite reasonable to use the roots for a quadratic expres-... 

A paper by Ozturk, Palsson, and Dressman (OPD), reporting a refinement of the MMSH model, did create some controversy. OPD developed a film model with reaction in spherical coordinates and applied quasi-steady-state assumptions to the boundary conditions at the solid surface [11], They theorized that the flux of all species at the solid surface must be zero, except for HA, or the other species (A-, H+, OH ) would penetrate the solid surface. A debate by correspondence in the Letters to the Editor columns of Pharmaceutical Research ensued [12,13], The reader is invited to evaluate which author s arguments are more convincing. What is difficult to evaluate is whether the OPD model produces dissolution results which are different from those which would be predicted using the MMSH model cast in comparable spherical geometry. Simply, these authors never graphically demonstrate how their model predictions compare to the MMSH model. Algebraically, the solutions to both models appear comparable. 

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