Selective dissolution critical potential

For a supercritical fluid to be suitable as a solvent in extraction, a high solubility of the solute is required, tf the objective is to separate components, the solvent should also have selective dissolution properties. Moreover, the pressure effect on the solubility is a factor. High compression costs may be incurred if the conditions for desirable solubility require excessively elevated pressures. The critical temperature of a potential solvent is also important. If the solvent is to be around its critical point for optimal performance, it is preferred that its critical temperature not be too far from ambient temperature. 

The nature of copper dissolution from CuAu alloys has also been studied. CuAu alloys have been shown to have a surface Au enrichment that actually forms a protective Au layer on the surface. The anodic polarization curve for CuAu alloys is characterized by a critical potential, E, above which extensive Cu dissolution is observed [10]. Below E, a smaller dissolution current arises that is approximately potential-independent. This critical potential depends not only on the alloy composition, but also on the solution composition. STM was used to investigate the mechanism by which copper is selectively dissoluted from a CuAu electrode in solution [11], both above and below the critical potential. At potentials below E, it was found that, as copper dissolutes, vacancies agglomerate on the surface to form voids one atom deep. These voids grow two-dimensionally with increasing Cu dissolution while the second atomic layer remains undisturbed. The fact that the second atomic layer is unchanged suggests that Au atoms from the first layer are filling... 

The article to be polished is made the anode with a current density in the range 100—800 mA cm in a bath of phosphoric acid at 60°C for a period of 5—10 min. The cathode material is not critical and may be steel, copper or lead. The mechanism of electropolishing is thought to involve both selective anodic dissolution (the potential distribution will favour corrosion of the surface at peaks rather than in troughs) and oxide film formation. The conditions are somewhat more forcing than those used in anodizing. 

Investigation of the anodic dissolution below the critical potential is likely to provide more relevant information on the mechanism of selective dissolution [178]. The emphasis is generally put on the current-time relationships, which are supposed to reflect the mechanism of transport within the surface layer. Dynamic polarization curves and current-time decays have been investigated for Cu-Au and Ag-Pd in LiCl... 

The value of can be estimated from potential-time transients or AES analysis, and the value of Sb is determined by weight loss and solution analysis. The potential increases with the dissolving charge passed at the interface in the selective dissolution stage, then reaches a critical value and exhibits a plateau where either both components dissolve in stoichiometric proportion or only one keeps dissolving with formation of surface roughness. On Ag-Pd alloys the values at the critical potential, estimated by electrochemistry and... 

For a two-level factorial design, only two excipients can be selected for each factor. However, for the filler-binder, a combination of brittle and plastic materials is preferred for optimum compaction properties. Therefore, different combinations such as lactose with MCC or mannitol with starch can count as a single factor. Experimental responses can be powder blend flowability, compactibility, blend uniformity, uniformity of dose unit, dissolution, disintegration, and stability under stressed storage conditions. The major advantage of using a DOE to screen prototype formulations is that it allows evaluation of all potential factors simultaneously, systematically, and efficiently. It helps the scientist understand the effect of each formulation factor on each response, as well as potential interaction between factors. It also helps the scientist identify the critical factors based on statistical analysis. DOE results can define a prototype formulation that will meet the predefined requirements for product performance stability and manufacturing. 

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