Evaluation of the corrosion performance of 316 L stainless steel for hydrometallurgical processing of Voisey's Bay nickel concentrate

Snow, Gerald P. (2005) Evaluation of the corrosion performance of 316 L stainless steel for hydrometallurgical processing of Voisey's Bay nickel concentrate. Masters thesis, Memorial University of Newfoundland.

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Abstract

The susceptibility of 316 L stainless steel to pitting corrosion in a solutions of sulfuric acid has been investigated using both potentiodynamic and potentiostatic polarization techniques. The effects of Cl, SO₄²⁻, Ni ²⁺, Fe³⁺ and aeration were studied and the results are presented in terms of pitting potential, free corrosion potential and pit morphology. -- It was determined that the potentiostatic polarization techniques resulted in pitting potentials closer to the true pitting potential when compared to values obtained using potentiodynamic polarization. Validation of the pitting potential was done by c comparing the data from the respective polarization tests to the surface of the test sample in question. Solutions containing chloride ions resulted in the lowest pitting potentials and highest amount of anodic dissolution. It was found that etch pits developed at lower potentials closer to the pitting potential, whereas polished pits developed at higher potentials. -- A scanning electron microscope (SEM) was used to analyze micro-pits on the surface of the polarized samples. From the analysis it was clear that pits developed with a cover which served as a diffusion barrier promoting stable pit growth. A profile of stable pits were examined by cross sectioning the polarized samples and it was concluded that the morphology of developed pits are not hemispherical in shape but rather saucer shaped with an average width-to-depth ratio of about 6.

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