In-situ optical microscopy, potentiostatic and potentiodynamic studies of 316L stainless steel and other metals in sulfuric acid solutions with nickel, chloride and sulfates

Power, Randal J. (2007) In-situ optical microscopy, potentiostatic and potentiodynamic studies of 316L stainless steel and other metals in sulfuric acid solutions with nickel, chloride and sulfates. Masters thesis, Memorial University of Newfoundland.

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Abstract

The corrosion patterns of 316L stainless steel is examined using a custom developed corrosion test cell which allows for in-situ analysis of a sample surface using a conventional microscope and off the shelf digital photography equipment. -- Laboratory prepared solutions of 3.5% NaCl, 3.39M sulfuric acid with 0.25M nickel sulfate and a variety of 1M sulfuric acid, nickel sulfate and nickel chloride based solutions were tested under aerated and deaerated conditions. The results illustrate the wide variety of corrosion behaviors possible for 316L stainless steel under potentiostatic and potentiodynamic test conditions. Analysis of these samples provides both a detailed visual account of the corrosion process in addition to standard electrochemical analysis regarding pitting potentials, corrosion potential, corrosion rate, etc. -- Polarization data and analysis regarding the corrosion patterns observed is presented including in-situ images of grain boundary etching, surface layer changes and pitting. Detailed images and analysis of chromium carbide and sulfide inclusion behaviors in sulfuric acid were performed showing the tendency of sulfide inclusions to dissolve and act as nucleation sites for pits. -- Experimental hydrometallurgical process fluids were also tested, confirming the ability of in-situ optical microscopy to successfully image and providing valuable insights into the corrosion processes taking place. -- Titanium, aluminum, magnesium and electronic materials were tested in predominantly 3.5% NaCl solution to confirm the feasibility of imaging different metals undergoing corrosion.

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