ИСТИНА

Experimental and theoretical studies of processes of spontaneous enrichment of solid alloy surfaces with their individual components (surface segregation) at the interface with electrolyte solutions attract keen attention of scientists and technologists. This is associated with the fact that it is the surface segregation of components that plays the key role in catalytic and corrosion processes, destruction of materials in corrosive media, at phase transitions in multicomponent systems, in developing special procedures for metal surface treatment, in solving certain technological problems in microelectronics, etc. In the present study, an Ag-Cd binary alloy that pertains to alloys allowing the formation of intermetallic compounds was chosen as the study object. The main component of the alloy (Ag) is characterized by the reversible work of surface formation substantially higher as compared with Cd present in the alloy as a minor additive (up to 1 at. %; the range of solid solutions of Cd in Ag). The studies were performed using the impedance method and a method of cyclic voltammetry in a special cell equipped with a tool for the in situ mechanical renewal of the metal surface. Transients of current and differential capacitance of this electrode were measured from the moment of its renewal in a surface-inactive electrolyte (NaF) solution under potentiostatic conditions. It was shown that with the longer contact between the newly formed alloy surface and the solution, the amount of cadmium atoms on the surface increased. This indicates that cadmium is the surface active component of the alloy under study. Moreover, the effective rate of the process of electrode surface enrichment with cadmium atoms is very high for solid-phase processes (characteristic time is 30 – 40 minutes). The analysis of the obtained results that involved the calculation of the surface coverage with Cd atoms as a function of time from the moment of surface renewal at different electrode potentials (charges) was carried out. The obtained results allowed us to conclude that the process of surface segregation can be described by the mechanism involves two stages: (1) quick diffusion of the surface active component of the alloy (Cd) to the surface and (2) a slower stage associated with the formation of an intermetallic-like compound AgCd in the surface layer. The results of studying the effect of segregation at the alloy/electrolyte interface are compared with the data obtained by Auger spectroscopy at the interface of the same alloy with vacuum. The study was carried out with the financial support by the Russian Foundation for Basic Research (grant no. 15-03-05243-a).