Metals and Rust

In the presence of electrolyte anode surface rust is stronger than the cathode. All of these metals can be cathodic with respect to the metals, which are located above them. From this it follows that the metal coating, which are cathodic to the base metal may be used only in thick coatings that are deposited on machine parts. For example, stainless steel is widely used for pump shafts and shafts of steam turbines. Brass, bronze, nickel, stainless steel and copper are not used for thin-film coatings, since the foundation will soon crumble under the penetration of fluid through the pores of the coating. Metals anodic to iron, which can used as the deposited metal, are only cadmium, zinc and aluminum (magnesium is chemically active). Since these metals to protect iron, subjected to destruction, while spraying their porosity is not influence the choice of metal for spraying. All other metals that are commonly used for spraying, are cathodic with respect to iron and to protect it, providing only the complete nonporous barrier coating, which, moreover, will protect the iron mechanically.

Therefore, most often for corrosion protection of iron and steel thermally sprayed metals using zinc and aluminum. Zinc coating thickness of 100-150 microns, well suited for many types of atmospheric conditions. Due to the fact that aluminum tends to oxidize, and thus protect themselves from further destruction, it is believed that it was necessary to use thicker layer of metal, minimum thickness of metal coating for atmospheric corrosion must be 150-200 microns. Must always consider and seek to avoid adverse electrochemical action, result of dissimilar metals which can connect to the electrolyte. For example, a storage tank of cold water to cover the necessary corrosion protection of zinc, then the coating will last. But if capacity to put the copper coils / coils, the presence of copper will cause electrochemical reaction and thus accelerate the corrosion of zinc coatings and service life will be much less.

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