ELECTROLYTIC DEPOSITION OF MgO ON STAINLESS STEEL SUBSTRATE

Abstract

The main objective of this thesis was to fabricate and characterize magnesium oxide coating on stainless steel alloy (SAE 316L). Electrolytic processing, followed by sintering was used for making it. Coating the heater tubes used in refinery industry with magnesium oxide is expected to increase the oxidation and corrosion resistance of the tubes. Fabrication of magnesium oxide coating was a two-step process. First, a magnesium hydroxide coating was deposited on the SAE 316L stainless steel substrate in an electrochemical bath and then the magnesium hydroxide was converted to magnesium oxide during sintering. The substrate was electropolished in a 15% sulfuric acid solution before immersing in the electrochemical bath. Electrolytic processing parameters such as deposition time and voltage were optimized and others like the distance between anode and cathode, concentration of magnesium ions in the solution and the surface area of the cathode and the anode were kept constant. The microstructure and texture of the magnesium hydroxide coating was analyzed using scanning electron microscopy (SEM) and X-ray diffraction (XRD). Sintering parameters were also optimized. Corrosion and oxidation resistance of the fabricated coating were compared to that of the uncoated sample in both high and room temperature. The hardness of the magnesium oxide coating was measured using a nano-hardness tester. The developed coating has uniform and crack free surface.