Leaching mechanism

The attack of water is related to the leaching mechanism described for acids. Table 4 rates glasses based on their resistance to water attack. Low alkah, high alumina, or borosiUcate glasses generally have high water durabiUty. 

However, given that other, supposedly stable and leach-resistant catalysts that we had previously studied seemed to operate solely by a leaching mechanism, with no supported Pd apparently active for the reaction (vide supra) and that other authors had found precatalysts of this type to operate by solely a leaching mechaiusm in Heck conversions of aryl iodides (19), we decided to investigate this system further using the solid poison testing method. 

Cocke, D. L. Molla, M. Y. A. 1993. The chemistry and leaching mechanisms of hazardous substances in cementitious solidification/stabilization systems. In Spence, R. D. (ed) Chemistry and Microstructure of Solidified Waste Forms. Lewis, Boca Raton, 187-242. 

The scope of this work was not intended to include study and analysis of leaching mechanisms beyond this point, but the data do show that the mechanism is dependent on time, sampling frequency, and type of element. Also, over the long testing period, two different mechanisms account for the release of material. More work is needed to increase our understanding of these high-level waste glass-solution interactions. 

A long term leaching study to compare the behavior of a titanate waste with glassy waste forms and to attempt to elucidate a leaching mechanism has been in progress for l6 months (15) ... 

Rusin, P., Ehrlich, H. L. Developments in Microbial Leaching - Mechanisms of Manganese Solubilization. Vol. 52, p. 1... 

White, W. B. Freeborn, W. P., in "Materials Characterization Center Workshop on Leaching Mechanisms of Nuclear Waste Forms, Summary Report Mendel, J. E., compiler PNL-4382 Pacific Northwest Laboratories, Richland, Washington pp. 247-254. 

The leaching mechanism (predominantly kinetically or diffusion controlled). 

For the purposes of describing leaching tests, the description of the leaching mechanisms hence the description of the types of tests are simplified into those which are relevant to granular materials and those which are suitable for monolithic materials. 

Table 3 Characteristics of leaching mechanisms for granular and monolith materials...

Aeration. Aeration is best nearthe face of the dump, providing optimal conditions of temperature and bacterial activiQr. Aeratkm by convection throu the dump is an essential part of the leaching mechanism. In r ions of high oxidation potential, iron is oxidized by bacterial activi to the ferric state resulting in the precipitatimi of ferric oxides and Jarosites. 

The research was focused on the acid leaching mechanism of goethite with nickel incorporated into goethite structure totally. Therefore, it was necessary to examine the synthesized nickeliferous goethite. 

The formation of allophane clays and silica gels seems however to be different a leaching mechanism for the allophane and the polymerization of silicic acid for the silica gels. However, in both cases, the network is obtained by the aggregation of colloidal... 

Palladium nanoparticles and other heterogeneous catalysts are often invoked as catalysts in cross-coupling processes [194, 195). Direct evidence in support of an oxidative-addition-promoted leaching mechanism has been recently obtained in the Suzuki-Miyaura reactions with nanoparticle catalysts, suggesting that true surface catalysis remains largely unknown with these heterogeneous catalysts [196]. 

DiaUo AK, Ornelas C, Salmon L, Aranzaes JR, Astruc D (2007) Homeopathic catalytic activity and atom-leaching mechanism in Miyaura-Suzuki reactions under ambient conditions with precise dendrimer-stabilized Pd nanoparticles. Angew Chem Int Ed 46 8644... 

The leaching mechanism operates primarily in media having pH = 7 or less (water or acidic). On the other hand, when pH > 7, i.e., in alkaline solutions, the corrosion is primarily due to the network dissolution. Since both the mechanisms are thermally enhanced, chemical durability of glass decreases at elevated temperatures. 

The elastomers utilize a diffusion-dissolution mechanism because true solutions of the pesticide in the elastomer solvent are obtained. When true solutions are not possible, as in thermoplastic polymers, a leaching mechanism would be used. Large loadings were required to create the proper porosity that would allow the pesticide to escape to the surrounding medium. Other additives have other functions. An example is given in Table 3. Unfortunately, copper sulfate does not provide the proper release for mollusk control and is less effective than the various tin compounds discussed. ... 

TON increases when the amount of nanoparticle catalyst is decreased or when the solution is diluted. The efficiency reaches 54% yield using 1 ppm Pd nanoparticles, i.e. the amount of nanoparticle catalyst is homeopathic. On the other hand, with high loading of catalyst, the yield is not quantitative, reaching only 70% at 1% Pd atom catalyst. These phenomena are taken into account by a leaching mechanism whereby one or two Pd atoms escape from the nanoparticle surface subsequent to the oxidative addition of the aryl halide onto the nanoparticle surface, then become extremely active in solution until it is quenched by the mother nanoparticle [66]. A similar mechanism had been proposed earlier by de Vries for the Heck reaction at high temperature (150-170°C) [67-69],... 

Chemical conversion electrolytic anodization (oxides) fused salts chemical-liquid chemical-vapour thermal plasma leaching mechanical shot peening thermal... 

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