Electroless deposition of NiMoP coating on Q235B steel and its corrosion resistance in simulated concrete pore solution

Abstract

The NiMoP coating is obtained on the surface of Q235B steel by electroless deposition to greatly improve its corrosion resistance in simulated concrete pore solution. Different NiMoP alloy coatings are prepared from the solution with different concentrations of sodium hypophosphite as reducing agent. The direct internal relationship among the composition, structure, thickness, surface morphology, corrosion resistance, and roughness of the NiMoP coating is investigated. It is found that increasing the concentration of sodium hypophosphite in solution is beneficial to increase the deposition rate and thickness of NiMoP coating. As the increase of sodium hypophosphite concentration from 5 gL−1 to 40 gL−1, the grain size of the NiMoP is refined, and the compactness of the coating is gradually improved. However, when the sodium hypophosphite concentration is 80 gL−1, the excessive sodium hypophosphite will promote and enhance the hydrogen evolution, resulting in the decrease of surface compactness and decline of corrosion resistance. The NiMoP alloy coating prepared from solution with 40 gL−1 sodium hypophosphite has the best corrosion resistance with the smallest corrosion current density and the most positive corrosion potential, mainly due to its denser surface morphology, larger thickness and smaller grain size.