Modeling of the surface treatment of passive metals
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MODELING OF THE SURFACE TREATMENT OF PASSIVE METALS M. V. Ved’, M. D. Sakhnenko, O. V. Bohoyavlens’ka, and T. O. Nenastina
UDC 541.13:621.35
On the basis of analysis of the specific features of physicochemical reactions leading to the local destruction of the surface of passive metals, we conclude that it is impossible to construct an adequate kinetic model of its evolution. For modeling the processes of formation of the surface of metals inclined to passivation, we propose to use the formalization of discrete states with subsequent analysis of the dynamics of these processes. We have constructed a simulation model of the transformation of the morphology of an electrochemically active surface under the action of polarization by pulse current and proposed a scheme of the corresponding technological process and a quantitative criterion for the completion of treatment.
The preliminary treatment of the metal surface plays an important role in the formation of multilayer systems, serviceable over a wide range of working conditions. To achieve corrosion resistance, it is necessary to decrease the porosity and to ensure the uniformity of coating distribution over the surface of the substrate, whereas catalytic materials require a large specific area of the surface. The most efficient methods for the complex solution of these problems are connected with the electrochemical preparation of the surface. As is well known, changing the electrolyte composition and the modes of electrolysis, in particular, pulse modes, one can control nucleation and the rate of growth of a new phase [1]. Since etching of the surface depends not on the total salt concentration (within the range 0.5 – 1 moles / liter) but on the ratio between the concentrations of activators and inhibitors of pitting formation and on the polarization current density [2], one also can regulate the dissolution rate and morphology of the surface of metals inclined to passivation by using nonstationary modes of polarization and electrolytes of a certain composition. Proceeding from these prerequisites, we can generalize the principles of control of surface treatment for obtaining a uniformly developed surface of the substrate with a large specific area. Principles of Modeling The anodic dissolution of a series of aluminum alloys, nichrome, and alloyed steels in chloride-containing solutions usually proceeds according to the pitting mechanism, which envisions the course of several joint and coupled reactions. For controlling the dynamics of this multivariant process in the classical version, it is necessary to determine its mechanism as an assemblage of separate stages, to establish their kinetic parameters, to identify the limiting stage, and to choose ways for influencing the course of this process and factors suitable for its control. The algorithm of construction of such a controlled technological process is rather complex. Hence, for the solution of this problem based on the general system theory, we represent the topology of local (pitting) development of the s
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