Chemically enhanced dissolution

In situation b the calculations for chemically enhanced dissolution may be applied, see section 5.42.1. Since the relative supersaturation of the reaction product is liable to be high, extensive nucleation could be expected. 

The second CSTR will take care of much of the remaining conversion of the solid, following the mechanism of chemically enhanced dissolution. Since the reactor is now essentially segregated, eqs. (7.13b) and (7.14) have to be used, in... 

Internal boundaries are important in influencing the properties of single crystals in a number of ways. Impurities and other point defects, such as self-interstitials or vacancies, often congregate near to such interfaces. Moreover, because the regularity of the crystal structure is disrupted at the interface, unusual atom coordination can occur, allowing impurity atoms to be more readily accommodated. This in turn leads to differing, often enhanced, chemical reactivity, dissolution, and other physicochemical properties. 

Cosolvent flooding is an experimental method for removing DNAPLs trapped below the water table. It involves injecting a highly concentrated aqueous mixture of solvents, such as alcohols, a chemical that is miscible with either phase in the aquifer. This process has the tendency to increase or enhance DNAPL (or LNAPL) solubility greatly, and to reduce the NAPL-water interfacial tension. Depending upon the phase behavior between the cosolvent and NAPL, a cosolvent flood can be developed to emphasize either enhanced dissolution (i.e., use of methane flooding for the dissolution of TCE) or NAPL mobilization. 

Wang Q, Hikima T, Tojo K. Skin penetration enhancement by the synergistic effect of supersaturated dissolution and chemical enhancers. J Chem Eng Japan 2003 36 92-97. 

Chemical modification By comonomers Enhanced dissolution and dyeing. Flame resistance. Antistatic, Improved hydrophilicity, Dyeing simultaneously with acid and basic colours. 

These findings, together with the observation that etch pits are developed in a similar manner on both deformed and undeformed samples of feldspar and calcite (e.g., see Murphy, 1989), indicate that etch pits may only be weakly related to dislocations. Probably, the dense etch pitting observed in natural samples of quartz and silicates must reflect their aqueous chemical environment (i.e., the presence of ligands, which considerably enhance dissolution) and the presence in these solids of localized chemical impurities such as aluminium, which favor the specific adsorption of F and organic ligands as oxalate, silicilate, and similar. This specific adsorption on chemical impurities may result in localized enhancements of dissolution as illustrated by Figure 17. 

It is reasonable to assume that the absorption rate of the complex is negligibly small compared with HCFU alone, owing to the poor membrane permeability and/or poor lipophilicity of the complex. Therefore, greatly enhanced dissolution rate and improved chemical stability of HCFU by CyDs more than may cancel out these negative effects and result in a net increase in the concentration of HCFU available for gastrointestinal absorption. Above results also suggest that the CyD complexes offer a decrease in dose in oral HCFU therapy. 

We find that until a conversion of 0.8 the first plot yields a straight line, and the other one does not. For the last 10% of the conversion the second plot yields a straigh line, with an inclination of 1/3. These results indicate that in the first part of the process eq. (S.25) applies, and consequently, that the reaction in die bulk is rate determining. The reason that the kinetics change towards the end of the process can only be explained by the fact that die surface area of the solid has become a rate determining factor. Probably chemically enhanced mass transfer takes place here, see section 5.4.2.1, age 153. A correlation of the type of (5.12) applies. By extrapolation of the second line, we find that the apparent dissolution time of the second process is 25 minutes. 

Adsorbent Life. Long term stability under rugged operating conditions is an important characteristic of an adsorbent. By their nature 2eohtes are not stable in an aqueous environment and must be specially formulated to enhance their stabiUty in order to obtain several years of service. Polymeric resins do not suffer from dissolution problems. However, they are prone to chemical attack (52). 

The dissolution of passive films, and hence the corrosion rate, is controlled by a chemical activation step. In contrast to the enhancement of the rate of dissolution by OH ions under film-free conditions, the rate of dissolution of the passive film is increased by increasing the ion concentration, and the rate of corrosion in film-forming conditions such as near-neutral solutions follows the empirical Freundlich adsorption isotherm ... 

Such approximation is valid when the thickness of the polymeric layer is small compared to die thickness of die crystal, and the measured frequency change is small with respect to the resonant frequency of the unloaded crystal. Mass changes up to 0.05% of die crystal mass commonly meet this approximation. In die absence of molecular specificity, EQCM cannot be used for molecular-level characterization of surfaces. Electrochemical quartz crystal microbalance devices also hold promise for the task of affinity-based chemical sensing, as they allow simultaneous measurements of both tile mass and die current. The principles and capabilities of EQCM have been reviewed (67,68). The combination of EQCM widi scanning electrochemical microscopy has also been reported recently for studying die dissolution and etching of various thin films (69). The recent development of a multichannel quartz crystal microbalance (70), based on arrays of resonators, should further enhance die scope and power of EQCM. 

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