Displacement deposition prediction

Predictions of the Feasibility of the Reaction. Complexed Metal Ions in Displacement Deposition... 

Recently XAS investigations were used to explore the Cu UPD process as a function of applied potential on carbon-supported Au nanoparticles [23]. Analysis of both the Cu and Au extended X-ray absorption fine structure (EXAFS) indicated only partial monolayer coverage at potentials where a complete Cu monolayer is predicted for single crystals. The structure of deposited Cu was found to be more consistent with Cu cluster formation at defects in the Au surface than the presence of a smooth monolayer due to lower than expected numbers of Au-Cu neighbors and Cu-Cu neighbors fitted in EXAFS analysis. The absence of a uniform mono-layer of Cu on the nanoparticles implies that subsequent displacement of Cu by Pt is unlikely to result in the formation of a uniform Pt shell [23]. 

A related phenomenon is the common occurrence of secondary deposition in molten salts. Thus, a metal may be deposited as a result of a chemical reaction between a metallic ion in the melt and another preferentially-deposited, reactive metal corresponding to the solvent cation(s). (Notably, there is still discussion as to whether sodium or aluminum is the primarily deposited metal during operation of the Hall-Heroult cell. " ) Such occurrences can be rationalized in theoretical terms if the primary deposition of the solute metal is precluded by an observed limiting current exceeding that predicted, or if its deposition potential is displaced in a cathodic direction by activation overpotential. Some authors have preferred an explanation which involves underpotential deposition (vide infra). 

Equation (14.19) is applicable to the case where a thick layer of a liquid is placed atop the resonator surface. Physically, it predicts that only a thin layer of liquid will undergo displacement at the surface the bulk wave device, and device response will be a function of the mass of this layer. Bruckenstein has observed that the response of a resonator which has both an elastic solid deposited layer and liquid atop the surface will be a linear sum of the responses expected for each individual perturbation (12). 

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