Electrochimica Acta 58 (2011) 743–749 Contents lists available at SciVerse ScienceDirect Electrochimica Acta jou rn al hom epa ge: www.elsevier.com/locate/electacta Kinetics of passive film growth on Alloy 800 in the presence of hydrogen peroxide Tirdad Nickchi ∗ , Akram Alfantazi Department of materials engineering, the University of British Columbia, Vancouver, BC, Canada a r t i c l e i n f o Article history: Received 6 July 2011 Received in revised form 10 October 2011 Accepted 10 October 2011 Available online 18 October 2011 Keywords: Alloy 800 Passive film Hydrogen peroxide EIS a b s t r a c t Alloy 800 is one of the potential steel alloys to be used in the cooling system of the next generation of power plants. The corrosion behavior of the alloy is dominated by its passive film. The kinetics of passive film growth is the subject of this study. Long-term open circuit potential tests, along with polarization resistance and electrochemical impedance spectroscopy tests provide data on evolution of passive state on the metal surface. It shows that the metal would possibly be in the active region after 24 h of immersion in the absence of hydrogen peroxide while the alloy undergoes the active–passive transition in solution containing 10 -4 M hydrogen peroxide. Polarization resistance data showed that the passive film continues thickening after OCP stabilization in the case of presence of H 2 O 2 . EIS data generally confirms the overall R p behavior. The time-dependent EIS models were used for more in-depth evaluation of passive film kinetics. © 2011 Elsevier Ltd. All rights reserved. 1. Introduction The supercritical water reactor (SCWR) is currently under devel- opment and is to be installed within the next 20 years. It benefits from the high heat capacity of water at very high temperatures and pressures – called supercritical state. One of the most critical deci- sions to be made for a SCW reactor is the materials selection. In this regard, the degradation behavior of materials as affected by the reactor environment should be studied. The general corrosion behavior of potential alloys in environments simulating the SCW reactor is determined by two factors: 1. The extent of temperature and pressure: higher temperature accelerates the kinetics of reactions, which in turn increases the corrosion rate. 2. The concentration of species such as H 2 O 2 , HO 2 • , O • , decom- posed from water due to gamma irradiation. In order to indirectly study the effects of irradiation, one can study the effect of hydro- gen peroxide on corrosion processes in concentration range of up to 10 -4 M. This value shows the maximum transient concentra- tion of generated hydrogen peroxide in typical irradiation fluxes [1]. The materials selection surveys have shown that a number of ferretic–martensitic steels (for example Ref. [2]), austenitic stainless steels [3], nickel-base alloys [4], titanium [5] and zir- conium [6] are appropriate from the stand point of corrosion as ∗ Corresponding author. Tel.: +1 604 822 6964; fax: +1 604 822 3619. E-mail address: tirdadn@interchange.ubc.ca (T. Nickchi). well as mechanical stability. Other proposed materials are oxide dispersion strengthened steels and refractory materials such as Nb, Mo, Ta, etc. [7]. One of the candidate austenitic alloys to be used in this condition is Alloy 800 [8] due to its superior corro- sion and high temperature creep resistance. Its electrochemical corrosion [9], long-term immersion behavior [10] as well as its oxidation behavior in supercritical water have previously been studied [11]. The aim of our research is evaluation of corrosion of Alloy 800 in the presence of hydrogen peroxide. Our previous study was focused on the short-term electrochemical corrosion behavior of Alloy 800 as affected by presence of hydrogen peroxide [12]. It showed the correlation between the kinetics of hydrogen peroxide reduction and electrochemical response of Alloy 800. The long-term behavior of the alloy is also important as it could be different than its short- term electrochemical response. The long-term behavior of such a passive alloy is controlled by the kinetics of passive layer growth. The kinetics of anodic passive films has extensively been investi- gated. The first theories used the high field model (HFM) [13,14]. Although widely accepted, they do not explain some characteris- tics of passive film growth, to name any reaching the steady state thickness [15]. Other researchers tried to generalize the HFM to incorporate the dissolution [16] and the transfer at oxide/solution interface [17]. The other field of expanding the passive film the- ory is encountering the time dependent behavior. Detailed models considering many physical features of the oxide growth for iron has been proposed [18–20]. Others include simplified time-dependent point defect models [21–23] and the original point defect model, which has recently addressed the time dependent behavior [24]. In this paper we provide data on long-term electrochemical behav- ior of the alloy as affected by passive layer growth. In this regard, 0013-4686/$ – see front matter © 2011 Elsevier Ltd. All rights reserved. doi:10.1016/j.electacta.2011.10.029