Mirtha Rodríguez

Determination of the Crevice Corrosion Stabilization and Repassivation Potentials of a Corrosion-Resistant Alloy

Abstract Ni-Cr-Mo alloys are highly resistant to general and localized corrosion, but they may suffer crevice corrosion in aggressive environmental conditions, such as high-chloride concentrations,...

Effect of fluoride ions on crevice corrosion and passive behavior of alloy 22 in hot chloride solutions

Abstract Alloy 22 (UNS N06022) is a Ni-Cr-Mo-W alloy highly resistant to localized corrosion. Alloy 22 may be susceptible to crevice corrosion in pure chloride (Cl−) solutions under aggressive environmental conditions. The effect of the fluoride (F−) over the crevice corrosion induced by chloride ions is still not well established. The objective of the present work was to explore the crevice corrosion resistance of this alloy to different mixtures of fluorides and chlorides. Cyclic potentiodynamic polarization (CPP) tests were conducted in deaerated aqueous solutions of pure halide ions and in different mixtures of chloride and fluoride at 90°C and pH 6. The range of chloride concentration [Cl−] was 0.001 M ≤ [Cl−] ≤ 10 M and the range of fluoride to chloride molar concentration ratio [F−]/[Cl−] was 0.1 ≤ [F−]/[Cl−] ≤ 10. Results show that Alloy 22 was susceptible to crevice corrosion in all the pure chloride solutions but was not in the pure fluoride solutions. Fluoride ions showed an inhibitor behavior ...

Crevice corrosion testing methods for measuring repassivation potential of alloy 22

Abstract Alloy 22 (UNS N06022) belongs to the Ni–Cr–Mo family, and it is highly resistant to general and localised corrosion; however, it may suffer crevice corrosion in aggressive environmental conditions. The susceptibility to crevice corrosion is measured by the value of the repassivation potential. The objective of this work is to compare different electrochemical methods for determining the repassivation potential of alloy 22; these include cyclic potentiodynamic polarisation, Tsujikawa–Hisamatsu electrochemical, potentiodynamic–potentiostatic–potentiodynamic and potentiodynamic–galvanostatic–potentiodynamic methods. The potentiodynamic–galvanostatic–potentiodynamic technique was found to be the most conservative laboratory technique, which gave the lowest repassivation potential in a relatively short testing time. The polytetrafluoroethylene (PTFE)-wrapped ceramic crevice formers formed more severe crevices, leading to higher repassivation potentials than the solid PTFE crevice formers. Torque values higher than 2 N m were needed for obtaining reliable repassivation potentials. Surface roughness did not affect significantly the repassivation potential.

Crevice corrosion of nickel superalloy in deaerated chloride/sulphate solution at 90°C

Alloy 22 is a nickel base alloy highly resistant to all forms of corrosion. It was designed to resist to most aggressive environments for industrial applications. Electrochemical studies such as Potentiodynamic-Galvanostatic-Potentiostatic (PD-GS-PD) tests and Electrochemical Impedance Spectroscopy (EIS) and Scanning Electron Microscopy (SEM) observations were performed to determine the corrosion behaviour of alloy 22 (N06022). The effect of sulphate ion in chloride containing solutions at 90°C, were studied in this work under aggressive conditions where this material might be susceptible to crevice corrosion. The electrolyte solution, which consisted of 0.1M and 1M NaCl and different sulphate concentrations. It was observed that there were complete inhibitions of crevice corrosion for R crit =[SO4 =]/[Cl-]=1 in the 0.1mol/L NaCl solutions and R crit =2 in the 1mol/L NaCl solutions. The corrosion rate obtained was about 0.1μm/year at 24 hours of immersion.

Cutaneous metastases from primary carcinomas of unknown origin. Contribution with3 cases and brief review

Metastases of unknown primary site occurs in about 5-10% of patients diagnosed with cancer. Usually appear after diagnosis of the primary cancer, but may be the first clinical sign of a tumor of unknown origin or the first sign of relapse of cancer. Cancer treatment is based on the recognition of the primary neoplasm, which raise diagnostic and therapeutic challenges. Skin biopsy should be considered in newly emerging lesions in cancer patients in addition to those lesions of sudden onset that are slow to heal, prone to bleeding or vascular appearance, that are not resolved with appropriate treatment. We present three cases of cutaneous metastases as the first manifestation, from which the primary tumor was found.