Oxidation of stainless steel 304L in carbon dioxide F. Goutier, S. Valette * , A. Vardelle, P. Lefort SPCTS, CNRS UMR 6638, 123, Avenue Albert-Thomas 87060 Limoges Cedex, France article info Article history: Received 14 December 2009 Accepted 22 March 2010 Available online 27 March 2010 Keywords: A. Stainless steel B. SEM B. TEM B. XRD C. High temperature corrosion abstract Oxidation of 304L stainless steel in a carbon dioxide atmosphere at 10 5 Pa has been studied. Between 1193 and 1293 K the oxidation kinetics exhibit first a rapid increase, then a parabolic behaviour with apparent activation energy of (209 ± 8) kJ mol 1 and obeys a Langmuir pressure law. After 1.15 mg cm 2 , the kinetics become almost linear. The reaction products are chromia at the grain boundaries, wüstite (Fe 1x O) on the surface for weight gains greater than 0.30 mg cm 2 and chromite. The very complex reaction mechanism takes into account random buckling for weight gains >1.15 mg cm 2 . Ó 2010 Elsevier Ltd. All rights reserved. 1. Introduction Recent work on atmospheric plasma spraying showed that thin wüstite interlayers at the surface of C40E (low carbon steel) pro- vide excellent adhesion properties to alumina coatings [1]. Indeed, the bonding of wüstite obtained by pre-oxidation of this alloy was as strong with the substrate as with the ceramic coating. It allowed a progressive adaptation of the different lattice parameters, so that no brutal change in the physical properties occurred between the substrate and the deposited layer. This original process, of high potential for the coating industry, has also stimulated interest for oxidation of alloys in order to obtain controlled wüstite layers on their surfaces. For this, detailed knowledge of the oxidation condi- tions is required, implying kinetic studies and an analysis of the oxidation mechanisms. The simplest process for wüstite formation on the surface of iron-based alloys is their oxidation in carbon dioxide [2–4], and since 304L is one of the most commonly used stainless steels, interest was naturally focused on the behaviour of this alloy in CO 2 in order to test the adherence of alumina plasma coatings, deposited on such pre-oxidized substrates. Unfortunately, despite numerous studies on the oxidation of Fe–Cr steels in CO/CO 2 mix- tures, for instance for nuclear applications [5,6], attention was paid mainly to microstructural analysis [7–9] or to the formation of a healing chromia layer [10–12] and nothing is reported about the possible formation of a superficial wüstite layer on the 304L alloy in pure CO 2 . Hence, the aim of the present work was to study the oxidation of 304L stainless steel in carbon dioxide, particularly during the initial oxidation, in order to determine the possible conditions of wüstite formation on the alloy surface, keeping in mind the later alumina plasma deposition. 2. Experimental 2.1. Materials and methods 2.1.1. Steel and gases The composition of the 304L alloy used, provided by Chaumeil S.A. (Brive, France), is given in Table 1. The optical micrographs in Fig. 1 show that its microstructure was homogeneous with a mean grain size of approximately ten micrometers. Carbon dioxide, supplied by Air Liquide France (ONU number 1013 class 2), was deliberately chosen for its low coast and moder- ate quality (at 10 5 Pa and 288 K: purity 99.7 volume%, with 200 volume ppm H 2 O), in order to simulate industrial conditions. In contrast, the argon used for the study of the influence of pressure was a high quality and supplied by Air Products France (purity 99.995 volume% with molecular oxygen and water as main impu- rities, <5 ppm for both). 2.1.2. Thermogravimetry Samples of 304L stainless steel were small disks (10 mm diam- eter, 1 mm thick, with a hole of 1 mm diameter for holding) pol- ished progressively down to a finish with SiC papers grit 4000. The samples were cleaned and suspended in a recording thermo- balance (Setaram B70) equipped with a MoSi 2 furnace where 0010-938X/$ - see front matter Ó 2010 Elsevier Ltd. All rights reserved. doi:10.1016/j.corsci.2010.03.022 * Corresponding author. Tel.: +33 (0) 555 45 75 54; fax: +33 (0) 555 45 72 11. E-mail address: stephane.valette@unilim.fr (S. Valette). Corrosion Science 52 (2010) 2403–2412 Contents lists available at ScienceDirect Corrosion Science journal homepage: www.elsevier.com/locate/corsci