ISSN 0033-1732, Protection of Metals, 2008, Vol. 44, No. 1, pp. 32–38. © Pleiades Publishing, Ltd., 2008. Original Russian Text © A.B. Shein, O.S. Ivanova, R.N. Minkh, 2008, published in Zashchita Metallov, 2008, Vol. 44, No. 1, pp. 38–44. 32 INTRODUCTION Composition of a corrosive environment produces a many-sided effect on the characteristics of partial elec- trochemical processes on metals and alloys. As the main factors, changes in the chemical composition of the metal surface and an effect on the structure of sol- vent and electric double layer, as well as an effect on the electronic structure of the superficial metal layer, are distinguished. This classification is conditional, since in all the cases, the final result is the change in the ener- getic profile of the reaction. The effect of anions, particularly halide ions, on the mechanism and kinetics of the anodic dissolution of the metals of iron family was a subject of numerous studies [1–3]. It was found that it may vary depending on the integral characteristics of the solution. The anodic pro- cess may either be accelerated or decelerated depend- ing on the pH of solution, on the kind of anions and their concentration, as well as on the presence of some other anions. According to the classical concepts for- mulated by Ya.M. Kolotyrkin [4, 5], anions, which have a high metal affinity, form superficial complexes weakly bound to the lattice and easily soluble. By con- trast, anions, which are not inclined to form such com- plexes, but able to adsorb at the surface, occupy free sites, thus hampering the metal dissolution. Here, due to the competitive character of the adsorption, one should necessarily take into account the surface activity of ç 2 é molecules and ç 3 é + and éç – ions. A nonzero order of the anodic dissolution of metals of the iron family in halide ions indicates their direct involvement in the process. The n Hal value depends both on the concentration of anions and the pH of electro- lyte. For example, the effect of the chemisorbed halide- ion layers is of two kinds, namely they may stimulate or inhibit the anodic process, as was shown in [6–9]. According to the experimental data, chloride ions at a low concentration decelerate the anodic process, while at a high concentration, stimulates it. The magnitudes of both effects decrease with an increase in pH. A substantial complication of the effect of the solution anions on the mechanism and kinetics of the anodic pro- cess should be expected in the case of alloys, whose com- ponents may interact with the electrolyte anions in differ- ent ways. Earlier, we have studied in detail the anodic pro- cess on metal silicides of the iron family [10–12]. The object of this work is the comparative estima- tion of the effect of a number of anions (F – , Cl – , Br – , I – , and SCN – ) on the parameters of the anodic dissolution of nickel and nickel silicide. EXPERIMENTAL Materials taken for the studies were nickel silicide and individual nickel and silicon. In preparing the sili- cide, high-purity substances were used, namely semi- conductor zone-melted KPZ-1 silicon (99.99 wt % Si) and nickel (99.99 wt % Ni). The main device for pro- ducing cast silicide specimens was an OKB-8093 (Red- met-8) oven for industrial growth of monocrystals. The directed crystallization was carried out according to Chokhralskii method with the use of a seed monocrys- tal. Techniques of making and treating the electrodes were described earlier in [10–12]. Choosing this particular silicide was predetermined by the fact that, according to the earlier data, similarly to the individual metal, NiSi has a pronounced range of active dissolution in the voltammetric curves. Silicides The Effect of Anions on the Anodic Dissolution of Nickel Silicide in Sulfate Electrolytes A. B. Shein, O. S. Ivanova, R. N. Minkh Perm State University, ul Bukireva 15, GSP, Perm, 614990 Russia E-mail: Anatoly173@yandex.ru Received July 24, 2006 Abstract—Anodic dissolution of nickel and nickel silicide in a 0.5 M H 2 SO 4 solution in the presence of halide and thiocyanate ions is studied with the use of cyclic voltammetry. Main regularities of the effect of anions on the mechanism and kinetics of the anodic dissolution of the metal and its silicide are found. The results obtained reveal different nature of the passivation processes and different compositions of the oxide films formed on Ni and NiSi. PACS numbers: 81.65.Kn; 81.65.Rv; 82.45.Bb DOI: 10.1134/S0033173208010037 PHYSICOCHEMICAL PROCESSES AT THE INTERFACES