Diffusion of highly corrosive media (HCM) into protective polymer coating materials

• V.A. Golovin and A.B. Il’in

A.N. Frumkin Institute of Physical Chemistry and Electrochemistry, Russian Academy of Sciences, Leninsky pr. 31, 119071 Moscow, Russian Federation

Abstract: An important element of modern design of chemical technological devices operating under exposure to highly corrosive media (HCM) are polymer protective anti-corrosion coatings. Basic protective mechanism for these coatings is a barrier mechanism. It is based on ensuring a low solubility of the corrosive medium in the polymer and on a low diffusion transfer of the most corrosive components through the coating. So, the study and control of mass transfer, in particular studies of diffusion, constitute the most important task in the design of coating systems for highly corrosive media. A comparative analysis of the laws of sorption and diffusion of water and solutions of salts and acids by the most widely used classes of anti-corrosive polymers, i.e., hydrophobic thermoplastics and moderately hydrophilic cross-linked thermo¬plastics, is made. Data on the concentration profiles of distribution of diffusing acids, regularities of the acids penetration depth and the values of sorption are analyzed. Models of diffusion of highly corrosive media into polymers with binding the medium on chemically reactive polymer groups are considered. It is shown that the binding model can be used to describe the diffusion of acids solutions in a wide range of concentrations and temperatures. A mathematical model of the diffusion of chemically reactive corrosive media into multi-layer composite polymer coatings is suggested and tested experimentally. It is shown that by using a combination of layers of different polymer materials, one can significantly reduce the permeability of the polymer coating, which allows the penetration depth to be reduced tenfold and time “before breakdown” to be extended hundred-fold or more. It is also important that combining layers of a hydrophobic material and a material capable of binding the medium in one coating allows one to simultaneously solve the problem of eliminating the penetration of the most corrosive volatile components at the initial stage of coating operation. The experience of using coatings in various fields of industry is considered.

Keywords: electrolytes, aqueous solution, corrosion inhibitors, sweet and sour corrosion, acid pickling processes

Int. J. Corros. Scale Inhib., 2020, 9, no. 4, 1329-1366 PDF (722 K)
doi: 10.17675/2305-6894-2020-9-4-8

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