Surface analysis of steel samples polarized anodically in H3PO4- HCl mixtures by SEM and EDAX techniques
Surface analysis of steel samples polarized anodically in H3P04-HCl mixtures by SEM and EDAX techniques
Rita Khare
Department of Chemistry
Government women’s College
Gardanibagh, Patna, Bihar, India
ABSTRACTS Potentiodynamic polarization experiments were performed on 304 stainless steel in 14M H3PO4 containing 0-20000 ppm HCl at 298, 308 and 318 0K. Photomicrographs of the test samples were obtained from Scanning Electron Microscopy after performing anodic polarization experiments on steel samples in 14M phosphoric acid and in 14M phosphoric acid containing critical concentration of HCl at 298, 308 and 318 0K. It is witnessed that severe pitting of the surface occurs when chloride ions are added to phosphoric acid. Morphology of pits is studied and pits are found to be partially hemispherical with some corrosion product spread unevenly. The increase in temperature results in increased number of pits but the size of pits becomes smaller. The composition of passive film formed on 304SS is investigated by the Energy Dispersive x-ray analysis (EDAX) technique. The analysis of alloy samples after interrupting polarization of samples in the passive region at critical concentration of HCl shows the presence of chlorine atoms in the film (0.23 -0.36%) .The result supports the Point Defect Model proposed by Macdonald et al to explain pitting phenomenon.