A study of the influence of physico-chemical processes in a metal base/nonmetallic coating system on the operational properties of coatings in a chemically active medium

Mathematical description and analysis of the corrosion of metals under lacquer coatings in seawater

“…It saturates the coating and penetrates into the uncoated microareas of the metal, which later turn into corrosion centers. In [1], it was discovered that the times for which they are filled with different components of seawater are practically equal and much shorter than the service life of the coating. This is why, in what follows, we can speak about the diffusion of seawater.…”

“…As a result, the volume of the center increases. The results of theoretical analysis performed in [1] (and corroborated by the experimental data) show that, for some values of strength and thickness of the film, concentration of the passivator, and linear adhesion on the solid-coating interface, there exist initial values of the radius of the center for which pressure inside the center becomes equal to the osmotic pressure, the process of osmosis terminates, the volume of the blister does not increase, the protective concentration of passivators does not decrease, and corrosion is absent. Thus, for each set of parameters of the system in seawater, one can analytically determine the radii of centers (uncoated regions) where the metal does not suffer corrosion under the lacquer coating.…”

“…where P is pressure and A 1 is linear adhesion [1], we arrive at the following solution of Eq. (8): All physical characteristics of the coating are measured as soon as the cavities are completely filled with seawater in the process of diffusion.…”

“…It is shown that, for the examined type of coatings, the corrosion rate first linearly increases with time but then, on attainment of a certain level, its subsequent increase is substantially decelerated. If the corrosion rate of the uncoated metal is higher than 0.05 mm/yr, then the rate of corrosion under coatings is lower by at least an order of magnitude.Some model representations of the mechanism of aging and fracture of lacquer coatings in seawater, the corresponding boundary-value problems formulated on the basis of the relevant mathematical model, and analytic-numerical methods for their solution can be found in [1,2]. These results were obtained for small deflections (blisters) of a lacquer film over the corrosion center and an almost linear law of increase in the corrosion rate to a certain fixed value.…”

A study of the influence of osmotic and corrosion effects on the working capacity of nonmetallic coatings in chemically active media

“…The surfaces z = 0, x = h are respectively the coatingmetal interface and the coating-medium interface. The rest of the notation used coincides with that of [1]. The distribution of the weight concentration Cv of water in the film at time rw, i.e., the initial condition of the problem under consideration, is determined by formula (6) of [1].…”