Anodic dissolution of Ag,Au-, Cu,Au- and Ag,Zn-alloys with rough surfaceunder limited capacity of vacancy sinks

摘要

The role of such surface effects as a microroughness, a displacement of interface and avacancy subsystem relaxation in the anodic selective dissolution of binary homogeneous alloyswas estimated by the method of consecutive approaches. Firstly, problems of the nonstationarytwo-dimensional diffusion to a surface of microrough electrode have been solved inpotentio- and galvanostatic conditions of polarization [1,2]. There was analyzed in what waygeometrical parameters and morphological type of a surface, and also of diffusion coefficientD influence current I and potential E dependence of time. It was found that a type of microunevennesspractically does not influence values of current and transition time. On the contrary,the roughness factor fr, the diffusion coefficient and the mean value of distance λ between microunevennessesplay the main role in current and potential transients. Totality of these parametersdetermines the time when a linear dependence of the current (at E = const) and of theroot of transition time (at I = const) on roughness factor is observed. If the measurements arecarried out in this time interval, then it is very simple to take into account the roughness effect:in chronoampero- and chronopotentiometry equations it is necessary to use the productSg?fr instead of geometrical surface Sg. These results were used in the investigation of selectivedissolution of Ag,Au-alloys (in chronoammetrical conditions), Cu,Au- and Ag,Zn-alloys(in chronopotentiometrical conditions) in couple with conclusions of theory of binary homogeneousalloys anodic dissolution under limited capacity of vacancy sinks [3]. It has been determinedthat in all investigated systems the electronegative component dissolution is controlledby interdiffusion in alloy solid state. Estimation of interdiffusion coefficient and meanvalue of distance between microunevennesses allowed to conclude that experiment was carriedout in the interval where fr linearly influence the current and the root of transition time.That is why the values of kinetic parameters of process (interdiffusion coefficient, nonequilibriumvacancy concentration) will be less than their values without taking into accountthe roughness. The influence of other factors of alloy surface layer during a selective dissolution(displacement of interface, non-equilibrium of vacancy subsystem) was analyzed.