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51315-5739-Effect of Temperature on the Repassivation Kinetics of Crevice-Corroded Nickel Base Alloys

Picture for Effect of Temperature on the Repassivation Kinetics of Crevice-Corroded Nickel Base Alloys
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Product Number: 51315-5739-SG
ISBN: 5739 2015 CP
Author: Martin Rodriguez
Publication Date: 2015
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Ni-Cr-Mo alloys show a remarkable corrosion resistance in a wide variety of corrosive environments. These alloys are candidate materials for the corrosion resistant engineered barriers of nuclear repositories. However Ni-Cr-Mo alloys may suffer crevice corrosion in aggressive conditions such as high concentrations of chlorides low pH and high temperatures. The effect of temperature on the crevice corrosion repassivation potential of these alloys has been studied in some detail. There is some uncertainty regarding the crevice corrosion propagation when the temperature decreases. Once the localized corrosion has been started at a certain temperature it is not clear if the attack may proceed at lower temperatures below the corresponding repassivation potential. The aim of this study is to evaluate the effect of a temperature decrease on the crevice corrosion kinetics of Ni-Cr-Mo alloys.Alloys UNS N06625 N06022 N07022 and N10362 were tested in 0.1 mol/L and 1 mol/L NaCl solutions and in 5 mol/L CaCl2 solution. Testing temperatures were 90ºC for 0.1 mol/L and 1 mol/L NaCl solutions and 117ºC for the 5 mol/L CaCl2 solution. Cooling rates of 3.33 ºC/hour and 33.3 ºC/hour were used. The electrochemical cell was placed within a bath of a refrigerated/heating circulator equipped with a Pt100 external sensor connection for measurement and control. The Pt100 external sensor was placed within the electrochemical cell next to the tested alloys specimen. This device allowed a careful control of the testing temperature. Tested alloys were polarized at a fixed potential above the corresponding crevice corrosion repassivation potential for a period of time long enough to start the localized attack. This period of time was typically between 10 and 24 hours depending on the applied potential. After this initial stage the testing temperature was linearly decreased while recording the current. Repassivation was considered to be attained when the current density fell below 0.1 µA/cm2. The repassivation kinetics for each alloy depended on the applied potential and in a lesser extent on the cooling rate.
Ni-Cr-Mo alloys show a remarkable corrosion resistance in a wide variety of corrosive environments. These alloys are candidate materials for the corrosion resistant engineered barriers of nuclear repositories. However Ni-Cr-Mo alloys may suffer crevice corrosion in aggressive conditions such as high concentrations of chlorides low pH and high temperatures. The effect of temperature on the crevice corrosion repassivation potential of these alloys has been studied in some detail. There is some uncertainty regarding the crevice corrosion propagation when the temperature decreases. Once the localized corrosion has been started at a certain temperature it is not clear if the attack may proceed at lower temperatures below the corresponding repassivation potential. The aim of this study is to evaluate the effect of a temperature decrease on the crevice corrosion kinetics of Ni-Cr-Mo alloys.Alloys UNS N06625 N06022 N07022 and N10362 were tested in 0.1 mol/L and 1 mol/L NaCl solutions and in 5 mol/L CaCl2 solution. Testing temperatures were 90ºC for 0.1 mol/L and 1 mol/L NaCl solutions and 117ºC for the 5 mol/L CaCl2 solution. Cooling rates of 3.33 ºC/hour and 33.3 ºC/hour were used. The electrochemical cell was placed within a bath of a refrigerated/heating circulator equipped with a Pt100 external sensor connection for measurement and control. The Pt100 external sensor was placed within the electrochemical cell next to the tested alloys specimen. This device allowed a careful control of the testing temperature. Tested alloys were polarized at a fixed potential above the corresponding crevice corrosion repassivation potential for a period of time long enough to start the localized attack. This period of time was typically between 10 and 24 hours depending on the applied potential. After this initial stage the testing temperature was linearly decreased while recording the current. Repassivation was considered to be attained when the current density fell below 0.1 µA/cm2. The repassivation kinetics for each alloy depended on the applied potential and in a lesser extent on the cooling rate.
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