Influence of Solution pH, Anion Concentration, and Temperature on the Corrosion Properties of Alloy 22

Abstract

We introduce an acid addition technique for the rapid assessment of the influence of solution pH, anion ͑such as chloride͒ concentration, and temperature on the dissolution of metals. We demonstrate the technique with the characterization of the dissolution of alloy 22 ͑Ni-22Cr-13Mo-3W-3Fe͒ exposed to chloride-containing hydrochloric, sulfuric, and nitric acid environments as a function of pH ͑from pH 5 to pH −1͒ and temperature ͑25-90°C͒. A combination of electrochemical techniques ͑electrochemical impedance spectroscopy and linear polarization resistance͒ and atomic force microscopy are used to characterize the influence of the various solutions on the dissolution of alloy 22. Below 50°C, corrosion rates are less than 1 m/yr independent of acid type, pH, and temperature. In contrast, between 50°C and the upper explored limit of 90°C, dissolution rates in sulfuric and hydrochloric acid scale approximately linearly with temperature at rates that depend on the solution pH. In nitric acid, corrosion rates are lower at comparable pH values due to the oxidizing effects of nitrates. An increase in the open-circuit potential in conjunction with electrochemical impedance spectroscopy data suggests that nitrates promote a stable passive oxide film that inhibits alloy dissolution in all environments tested.Nickel-based alloys are employed in a wide range of applications where long lifetimes are vital such as in implant materials and nuclear waste storage. The robustness of alloys in these types of environments is due to the formation of a protective "passive" oxide film at the alloy interface. The nature and composition of these oxide films depends on the alloy composition and the pH, temperature, and electrolyte composition of the formation environment. Alloys can be tailored to fit a specific set of environmental conditions by selection of constituent elements that have strengths that compensate in the areas where other elements fail. For example, for Ni-Cr-Mo alloys, it is generally well established that the Mo provides resistance against reducing acidic environments, Cr against oxidizing conditions, Cr and Mo against localized attack, and Ni, Cr, and Mo against stress corrosion cracking due to chloride ions. [1][2][3][4] This combination of corrosion resistance in both reducing and oxidizing environments makes these alloys particularly well suited as long-term storage materials. As a result, the Ni-Cr-Mo alloy, alloy 22 ͑Ni-Cr22-Mo13-W3-Fe3͒, is the candidate material for the outer wall of nuclear waste packages at the proposed Yucca Mountain nuclear waste repository ͑Nevada, USA͒. Over the past decade, a number of studies have been undertaken to characterize its general and localized corrosion properties. 5-8 These studies demonstrate that alloy 22 is exceptionally corrosion resistant in a broad range of concentrated brines including chloride, fluoride, carbonate, sodium, and calcium with pH values ranging from ϳ2.7 to 13 and temperatures from 25 to 120°C. 9 To date, little work has been done to characterize the allo...

Characterization of the Corrosion Products of Crevice Corroded Alloy 22

“…This result agrees with other researchers' results. 17,26 At a depth of 10 nm and more, all the elements in the alloy existed in the metallic state.…”

Electrochemical Behavior of the Passive Films Formed on Alloy 22 (UNS N06022) in Acidic Solutions

“…Moreover, the excellent passive behavior of these alloys is B Arash Fattah-alhosseini a.fattah@basu.ac.ir 1 Department of Materials Engineering, Bu-Ali Sina University, 65178-38695 Hamedan, Iran well known in numerous solutions with pH values ranging from 1 to 13 [1][2][3]. For that reason, it is important and interesting to study the electrochemical behavior of the passive films formed on these alloys in diverse environments [3][4][5][6][7][8][9][10].…”

Modified Point Defect Model for the Electrochemical Behavior of the Passive Films Formed on Alloy C (UNS N10002) in Borax Solutions

“…Therefore, there is a permanent interest in A. Fattah-alhosseini (B) Faculty of Engineering, Bu-Ali Sina University, Hamedan 65178-38695, Iran e-mail: arash.fattah@gmail.com; a.fattah@basu.ac.ir studying the passivation of these alloys in various conditions [4][5][6][7][8][9][10].…”