Effect of Current Density on Microstructure of Mn-Cu Thin Films produced by Electroplating Coating Technique

In the present study, 304 stainless steel (SS) was electrochemically plated with nanocrystalline Mn-Cu alloy coatings from a bath containing ammonium sulfate. The effects of current density on the microstructure, crystallographic structure, and chemical composition of the deposits were studied. The results showed that at low current densities, discontinuous coatings with a large amount of Cu can be obtained. Further increase in current density resulted in amorphous, compact and heterogeneous coatings with a small amount of Cu. The presence of Cu at low contents in precipitated coatings delayed the phase transformation of as-deposited ductile g-Mn to the brittle and hard a-Mn. However, the results did not show any specific changes in the grain size of the coatings with variation of current densities

Mixed Surface Reaction and Diffusion-Controlled Kinetic Model for Adsorption at the Solid/Solution Interface

The effects of diffusion and surface reaction mechanisms have been considered conjointly to investigate the kinetics of adsorption. A new model has been proposed for the modeling of adsorption kinetics at the solid/solution interface in batch systems. Based on generated data points (<i>t</i>, <i>q</i>) by using of the new model, it was found that there is a deviation from linearity as a downward curvature at initial times of adsorption in usual <i>t</i>/<i>q</i> vs time plot, when diffusion contributes to the rate-controlling step of adsorption. Moreover, results of nonlinear fitting to the different experimental data show that the mixed surface reaction and diffusion-controlled model can be useful for kinetics modeling of adsorption in which pure surface reaction or mixed surface reaction and diffusion contribute to the rate-controlling step of adsorption

Fractal-Like Adsorption Kinetics at the Solid/Solution Interface

The kinetics of adsorption processes at the solid/solution interface has been studied by using a fractal-like concept. For the first time, one possible physical meaning for fractal-like adsorption kinetics which indicates that sorption rate coefficient at solid/solution interface is a function of time is presented. So, new kinetic models have been presented by a combination of the fractal-like approach and integrated kinetic Langmuir equation (IKL), mixed 1,2-order equation (MOE), and statistical rate theory (SRT). The fractal-like SRT rate equation has been solved at two limiting conditions, one at initial times of adsorption and the other close to equilibrium. The new parameter (α) which has appeared in these models affects the rate of sorption. Fractal-like IKL (or fractal-like MOE) and also fractal-like SRT models have been used to analyze different experimental data. The obtained results indicate that the variation of initial concentration of solute and stirring rate of solution affect both “α” and the rate coefficient