Dissolution/precipitation mechanism

Central pore being filled by the dissolution precipitation mechanism... 

Oxidation/reduction of Pb electrode has been studied using in situ spectroscopic techniques - Raman [114, 130-132], fourier transform infrared (FTIR) [133-135], Auger [136], and photocurrent spectroscopy [131, 137-141]. El-Kpsometric studies underlined nonuniform PbS04 film growth a dissolution-precipitation mechanism with nucleation and three-dimensional growth has been proposed as a result of large oversaturation of Pb(II) ionic species [142]... 

SFC is complementary to other classical techniques of liquid or gas chromatography. The migration of the analyte is explained by a dissolution-precipitation mechanism that depends on the solvation power of the mobile phase. Thus, it is governed by the pressure that determines the density of the supercritical phase. Resistance to mass transfer between the stationary and mobile phases is less than that found in HPLC because diffusion is faster. The C factor in Van Deemter s equation is smaller so the velocity of the mobile phase can be increased (see Fig. 6.3). Moreover, because the viscosity of the mobile phase is similar to that of a gas, it is possible to use capillary columns like those used in capillary GC. However, the... 

E = —0.65 Y). The mechanism of formation of these thick layers and their reduction is still not fully understood. They presumably grow with a dissolution/precipitation mechanism. 

Pure A1 reacts with SiC to form AI4C3 at and close to the interface by a dissolution-precipitation mechanism according to the overall reaction ... 

It is generally agreed on the basis of TEM evidence (e.g., Rask et ai, 1997) and on the basis of chemical substitution in the several structural sites of illite (e.g., Lanson and Champion, 1991 Awwiller, 1993 Lynch et ai, 1997) that the illitization of smectite, like other replacement reactions in late diagenesis, proceeds through a dissolution/precipitation mechanism. Similar to other replacement minerals, illite also occurs as cements in sandstones as well as in shales, where it forms overgrowths on detrital illite particles and discrete crystals (cements) (e.g., Lanson and Champion, 1991 Rask et at, 1997). 

Dissolution-precipitation mechanisms dissolution of aluminum species in the solvent used for the solvothermal reaction. 

Hydrothermal reaction takes place because of the water adsorbed on the particles surface Therefore crystallization of the product occurs by means of the dissolution-precipitation mechanism. 

A dissolution-precipitation mechanism for this reaction was proposed by Kozawa and Yeager. ... 

It should be noted that Eq. (3) is only a simplified reaction scheme for the anodic reaction. Actual anodic discharge reaction may take place via a dissolution-precipitation mechanism with soluble complex ions such as Cd(OH)3, Cd(OH)4 as intermediates, as shown below ... 

As opposed to the positive electrode, the redox process at iron does not proceed in the solid phase but via a dissolution-precipitation mechanism simplified below to... 

The observations can be generalized. Besides the homogeneous oxide growth by Reaction (2), a dissolution/precipitation mechanism may contribute to the passivation. If it takes place by corrosion of an ion with lower valency (e.g. Fe " "), the following reaction (inverse of Reaction 17) includes oxidation and the necessary ETR (15). Then, the supporting passive film has to be electronically conducting. On the other hand, if it consists of passive corrosion (11) and following chemical precipitation (inverse of 18) without a redox process, electronic conduction is not necessary. 

FIGURE 17.17 Illustration of the dissolution-precipitation mechanism that could be operative in ceramics containing a glassy phase at the GB. 

Pinceloup, R, Courtois, C., Vicens, J., Leriche, A., Thierry, B. Evidence of a dissolution-precipitation mechanism in hydrothermal synthesis of barium titanium powders. J. Eur. Ceram. Soc. 19, 973-977 (1999)... 

A similar lack of knowledge exists on the influence of strong CaCl2/HCl solutions on phase transformation. For other hydrometallurgical systems it was found that the DH to HH, DH to AH and HH to AH transformations typically proceeded via a dissolution-precipitation mechanism [22-26]. Increases in temperature [24], the presence of seed of the more stable phase [23-25,27] and low water activity [25] accelerate the transformation process. The time signifying the onset of the conversion process (otherwise known as induction time) has been reported to vary from hours to several days depending on solution composition and temperature. 

A detailed study of each particular system is needed to distinguish between the two mechanisms. However, as far as the kinetics of the process is concerned, the dissolution-precipitation mechanism could be treated along the same lines of reasoning as used in the previous parts of this chapter, while a direct formation of insoluble product has a number of specific features which are treated elsewhere (Volume IV, Chapter 10, Volume VIII, Chapters 3 and 4) and are outside the scope of this review. 

A good example of the dissolution-precipitation mechanism is found in the case of formation of calomel by anodic dissolution of mercury in chloride solutions. It has been realized that the low-solubility product of calomel in aqueous solutions gives far too low a concentration of mercurous ions in... 

Many electrocatalytic processes involve a complex combination of surface charging processes (H or OH or O deposition and removal) and net Faradaic reactions, in which the surface species are themselves involved and cause effects associated with inhibition of the main reaction sequence or of coreactions. The Faradaic reactions may also be partly diffusion controlled, which leads to the most complex behavior. In cases where surface oxide films arise which are substantially thicker than a monolayer, e.g., as at Ni or Ag electrodes, the time-dependent current in a sweep experiment reverts to a square root dependence on sweep rate and this effect arises either because of a dissolution-precipitation mechanism of oxide layer growth or because of solid state diffusion effects. 

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