Electrochemical study of carbon steel protection with a superhydrophobic coating under conditions of 100% humidity and the presence of corrosion stimulants in the air

Issue 25(3) 2020
Pages 17-26

V.I. Vigdorovich, Honored Worker of Science and Technology of the Russian Federation

L.E. Tsygankova, Derzhavin State University, Tambov, Russian Federation

M.N. Uryadnikova, Derzhavin State University, Tambov, Russian Federation

N.V. Shel, Tambov State Technical University, Tambov, Russian Federation

L.G. Knyazeva, All-Russian Scientific Research Institute of Use of Machinery and Oil Products in agriculture, Tambov, Russian Federation

O.V. Alekhina, Derzhavin State University, Tambov, Russian Federation

Keywords: steel, superhydrophobic coating, wetting angle, corrosion, humidity, ammonia, carbon dioxide, hydrogen sulfide, potentiodynamic polarization.

100% humidity and the presence in the air of such corrosion stimulants as CO2, NH3 and H2S are characteristic of livestock buildings. Under these conditions, a surface phase film of moisture is formed on the surface of the metals in which the indicated micro-mixtures of air are dissolved and hydrated almost completely with the formation of NH4OH and acids H2CO3 and H2S. The potentiodynamic polarization method was used to study the corrosion and kinetics of electrode processes on steel with a superhydrophobic coating in a NaCl background solution (used to provide sufficient electrical conductivity) saturated in pairs with CO2 and NH3, NH3 and H2S. Similar studies were conducted with uncoated electrodes. Superhydrophobic coating was obtained on the basis of laser texturing of the surface with subsequent hydrophobization with fluoroxysilane (wetting angle 165±2°, rolling angle 3±1°). The influence of the duration of the
exposure of the electrodes in solution (0,25…168 h) on the kinetics of electrode processes and the corrosion rate of steel is considered. In the presence of CO2 and NH3 dissolution products, the corrosion rate of an electrode with a superhydrophobic coating on the second and third days of exposure is about an order of magnitude, and on the fourth and seventh days it is more than an order of magnitude lower than without coating. During the entire time the electrodes are in solution, the anode process on the superhydrophobic electrode is inhibited compared to an unprotected electrode. The medium containing the dissolution products of NH3 and H2S is more aggressive than the previous solution. Therefore, the corrosion rate of the electrodes without coating and with a coating here is higher than in the latter one. The corrosion rate of electrodes with superhydrophobic coating in the study period is only 1,5…2,5 times lower than that of uncoated electrodes. During the first day of exposure, the anode process is inhibited, and in the next 144 hours, on the contrary, it is facilitated in comparison with an unprotected electrode. Taking into account the corrosivity of the chloride solution, the possible effect of the dissolution products of aggressive air micro-impurities in the absence of background salt was analyzed.