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Showing 2 results for Pitting

Moayed M.h.,
Volume 2, Issue 3 (9-2005)

In this research pitting Corrosion of a sensitized 316 stainless steel was investigated employing potentiodynamic, potentiostatic techniques. Sensitization process was carried out on as-received alloy by submitting the specimen in electric furnace set at 650°Cfor five hours and then the specimen was quenched 25°C water. Potentiodynamic polarization of as received and sensitized specimens in 1M H2SO4 solution at room temperature and 70°C clearly revealed that the sensitization process has caused a magnificent change on electrochemical behavior of the specimen by changing critical current density for passivation, passivation potential and passive current density. Optical microscopy examination of the specimen surface after oxalic acid electrochemical etching also showed the deterioration of grain boundary of sensitized specimen due to chromium carbide precipitation in compared to as-received one. Several anodic potentiodynamic polarization on rode shaped working electrodes prepared from as-received and sensitized specimen in 3.5% NaCl test solution proved an average ~220 mV drop in pitting potential due to sensitization. Anodic potentiostatic polarization at 400 and 200 mV above corrosion potential also demonstrate the deterioration of pitting resistance of alloy as a result of sensitization. Scanning electron microscopy examination of anodically polarized of sensitized specimen at 700mVprior and after oxalic acid etching revealed large stable pits with lacy cover and also openpits with deep crevice for etched specimens.
H. Fattahi, M. H. Shariat,
Volume 5, Issue 1 (3-2008)

Abstract: In chloride salt solutions, titanium alloys exhibit reasonably high pitting potentials as high as +10 V (vs. Ag/AgCl) at room temperatures. On the other hand, anodic pitting potentials are significantly lower in bromide solutions. In this study, pitting corrosion of commercially pure titanium in aqueous NaBr solution of 0.1 M concentration at room temperature was studied and the effect of an external magnetic field oriented both parallel and perpendicular to electrode surface was investigated. Cyclic potentiodynamic and potentiostatic polarization tests were carried out. Anodic breakdown potential of +1.45 V (vs. Ag/AgCl) obtained in the absence of magnetic field, decreasing to +1.11 V in the presence of a 0.05 T parallel magnetic field. The perpendicular magnetic field actually did not affect the breakdown potential. Applying of an external magnetic field, independent of its orientation, shifted the repassivation potential approximately 150 mV in the positive direction. SEM microscopy observations of sample surfaces indicated that applying of magnetic field results in some variations in the pit shapes and their sizes.

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