Dissolution reaction

A nonuniform distribution of the reactions may arise when the metal s surface is inhomogeneous, particularly when it contains inclusions of other metals. In many cases (e.g., zinc with iron inclusions), the polarization of hydrogen evolution is much lower at the inclusions than at the base metal hence, hydrogen evolution at the inclusions will be faster (Fig. 22.3). Accordingly, the rate of the coupled anodic reaction (dissolution of the base metal) will also be faster. The electrode s OCP will become more positive under these conditions. At such surfaces, the cathodic reaction is concentrated at the inclusions, while the anodic reaction occurs at the base metal. This mechanism is reminiscent of the operation of shorted galvanic couples with spatially separated reactions Metal dissolves from one electrode hydrogen evolves at the other. Hence, such inclusions have been named local cells or microcells. 

KEY TERMS endothermic reaction enthalpy of reaction dissolution enthalpy of formation... 

The first of the four characteristic currents to J4 has a prominent position. It indicates the crossover from a charge supply limited reaction to a kmetically and mass transfer limited reaction. This crossover is accompanied by pronounced changes in charge state, chemical dissolution reaction, dissolution valence, pore formation and anodic oxide formation. Therefore its dependence on other parameters, such as crystal orientation, temperature or H F concentration deserves further investigation. In the literature Jt is usually termed /crl JPS or JPSL. In the following the symbol JPS will be used. 

Reaction rate coefficient for the forward and backward reactions Dissolution or growth distance half-thickness Thickness (temporary parameter)... 

Substrate dissolution rates may be important in the overall kinetics of these reactions. Dissolution rates may be affected by interfacial limitation, but mass transfer in the boundary layer around the particles always plays a key role. Mass... 

Farm and Avnir [113] were the first to use fractal geometry to determine effects of surface morphology on drug dissolution. This was accomplished by the use of the concept of fractal reaction dimension dr [114], which is basically the effective fractal dimension of the solid particle toward a reaction (dissolution in this case). Thus, (5.7) and (5.8) were modified [113] to include surface roughness effects on the dissolution rate of drugs for the entire time course of dissolution... 

In hydrothermal reactions, dissolution-deposition equilibrium takes place. Dissolution of adatoms on the surface occurs preferentially, while preferential adsorption of ions at the vacancies of the surface proceeds. Therefore a nearly perfect surface is formed. Since a nearly perfect growing surface is created, crystals formed by the hydrothermal reaction usually contain fewer defects than the crystals formed by other methods. On the other hand, under solvothermal conditions, dissolution of oxide materials into the organic solvent barely takes place, and therefore the product usually contains various types of crystal defects. 

At the reaction temperatures involved, molten nitrate systems are not particularly corrosive and conventional materials, such as stainless steels, are probably adequate for the reaction, dissolution, and separation steps. If high-temperature volatilization or transfer to a halide system is necessary, then other materials will be required. 

The intensification of the heat transfer through stirring is seldom the primary stirring task. It mostly occurs in connection with the intensification of mass transfer by stirring (dispersion of gases or hquids with a simultaneous exothermic chemical reaction, dissolution of solids with liberation of the latent heat of solution etc.). Occasionally the stirring heat has to be removed, so that the process can proceed under isothermal conditions. 

Zutic, V., and W. Stumm. 1982. On the role of surface complexation in weathering reactions. Dissolution kinetics of hydrous alumina in the presence of organic ligands, p. 613-621. In H. van Olphen and F. Verniale (ed.) Int. Clay Conf. 1981. Developments in sedimen-tology, Vol. 35. Elsevier, New York. 

Salt dissolved in cold water tends to leave a significant amount of precipitate. If the solution is heated, however, the equilibrium state tends to further favor the forward reaction (dissolution), and some or all of the solid salt will be dissolved in the solution. Upon cooling the solution, the salt tends to precipitate as a solid once more. 

Physical Crustal uplift and subsidence Solid-state deformation Erosion by water and wind Rock disaggregation by chemical and biological attack Solid-solution-gas reactions Dissolution, precipitation, cementation, corrosion... 

During charging, the conversion of lead sulfate to sponge lead also proceeds via two reactions, namely, dissolution and deposition. Nevertheless, the nature of each of these reactions differs from that of the corresponding discharge reactions. Dissolution is now the chemical reaction, while the subsequent deposition is the... 

This reaction results as a sum in a kinetic forward (precipitation) and kinetic backward reaction (dissolution) with different reaction rate constants. The equilibrium state is described by the equilibrium constant which is the ratio of the backward ihackward) the forward reaction rate ( <,rwan/)- terms of the concentrations, the equilibrium state is characterized by the equilibrium concentrations of A ) and according to the mass action law. 

Reference materials [133] for processes described as reaction, dissolution and dilution, except for reactions carried out in combustion bombs, are also included in this section. Potassium chloride is currently used as a reference material for the enthalpy of solid-solution calorimetric determinations, and it is available as a certified material. Other recommended reference materials are tris(hydroxylmethyl)-aminomethane (secondary), 4-aminopyridine (secondary), sulfuric acid solution + sodium hydroxide solution (primary). 

Yeff Fsoi (low solution or saturated droplet, no reaction dissolution limited)... 

Figure 6.15 Tafel plots for a metal ion transfer reaction, dissolution and deposition of Cd/Cd ". From the slopes the charge transfer coefficient is determined, a z = 1.09 and (1 — a )z = 0.91. With z = 2 one obtains = 0.55 and (1 — aj = 0.45. The exchange current density is Ig = —2.8.

However, in concurrence with Heller s suggestion (Heller, 1987), bioerosion is herein defined as changes in polymer or matrix structure that occur under physiologic conditions as a consequence of a chemical reaction, dissolution of a water-soluble polymer, dissolution of a water-insoluble... 

The soil solution also interacts with the solid phase, that is, soil particles, through sorption-desorption processes and surface chemical reactions (dissolution-precipitation, oxidation-reduction, etc.). 

This section presents the governing equations for fluid flow in porous media with precipitation reactions, dissolution of minerals, and laminar premixed combustion, as well as similarity parameters. The model is based on Navier-Stokes equations. For modeling precipitation and dissolution, we used the Boussinesq approximation and Darcy s law, which wiU not be considered in the case of combustion in porous media. Darcy s law, in general, defines the permeability or the ability of a fluid to flow through a porous medium [29]. Another difference from the model of combustion lies in the equations for species, which are based on concentrations. 

The role of the reactor in providing heat transfer - which by definition is intensified - is neatly summarised by Hasatani (1998). He pointed out that chemically reacting operations in heat transfer processes (which may include chemical reactions, dissolution, absorption, adsorption and desorption) have the following advantages over conventional heat exchangers/heat transfer systems ... 

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