Surface modification of stainless steels: green technology for corrosion protection

Abstract

Many methods of corrosion protection rely on toxic chemicals such as hexavalent chromium (Cr6+), which is the species responsible for protection in conversion coatings, anodizing baths and as a pigment in polymer coatings. Despite many attemps to replace Cr 6+ and other harzardous chemicals in corrosion protection, very little progress has been made. Passive layers containing Ce and Mo have already been formed on materials such as A17075 and A12024, and their corrosion behaviour has been shown to improve by imlaibition of both anodic and cathodic reaction. In this work the results of applying these coatings to SS304 and 316 will be presented. The layers were studied by electrochemical impedance spectroscopy (EIS), X-ray photo-electron spectroscopy (XPS), and the corrosion behaviour was followed by EIS and d.c. current methods. © 1997 Elsevier Science S.A.Keywords: Stainless steel; Corrosion protection; Impedance; Surface analysis In~oducfionRare-earth metal salts, particularly those containing cerium, are effective corrosion inhibitors for iron [1,2] and aluminum [2][3][4][5] in aggressive environments, and have been successfuly used in surface modification of various aluminum alloys [6--8] and stainless steels [9,10], inhibiting both anodic and cathodic reactions. Similar results have been reported for stainless steels, but questions have been raised concerning the validity of some of these data [ 11 ].Inhibition of anodic and cathodic reactions involved in the corrosion mechanism has been attributed to the formation and precipitation of cerium oxides or hydroxides over cathodic sites having a blocking effect [4][5][6][7][8][9][10]. The mechanism by which cerium forms a ceriumenriched hydroxide, particularly on stainless steel, is not clear. Indeed, the complexity of this process is evident, in that the valence state of cerium in the corresponding films varies between 3 and 4, depending on the pH and 1Paper presented at 23rd International Conference on metallurgical coatings and thin films, San Diego, CA, USA.0257-8972/97/$17.00 © 1997 Elsevier Science S.A. All rights reserved _PII S0257-8972(96) 03142-8 the degree of aeration of the solution [5]. For aluminum alloys [6][7][8], adding molybdenum to cerium improves the corrosion behaviour significantly in some cases.In this work, the electrochemical behaviour of SS304 and SS316L following various cerium and cerium/ molybdemum pre-treatment steps was studied in an effort to gain more information on the process by which cerium and molybdenum can modify the properties of the passive film formed on stainless steels. The coatings were analysed by EIS (electrochemical impedance spectroscopy) and XPS in order to identify the cerium species which play the main role in the enhacement of the passivation behaviour. The corrosion behaviour was followed by EIS and d.c. current methods. Experimental approachCerium-containing layers were prepared by immersing the SS samples in the following solutions: 50mM Ce(NO3)3, 10 mM Ce(NO3)3, 10 mM CeC13 or 40 mM C%(CyH3CO) main...

Protective effect in sulfuric acid media of alumina and ceria oxide layers electrodeposited on stainless steel

“…It is interesting to note that an analogous effect of cerium has been established in the cases, when cerium is a bulk component of steel (in case of metallurgical production of Ce-containing steels) [16,17], as well as in a series of cases of steels notcontaining cerium but superficially modified in Ce-containing solutions [5,[18][19][20][21][22], or when cerium is implanted by ion beam bombardment [23][24][25][26][27][28][29][30]. A very good protective effect has been established, when stainless steels articles are being exploited in media, inhibited by ceria compounds [31].…”

High-Performance Coating Materials

“…This finding strongly validated that the useful lifetime of air-cooled condensers is extended conspicuously using an appropriate amount of APST precursor. Several recent papers [53][54][55][56][57][58] documented that, among the rare-earth metal salts, the environmentally benign cerium (Ce) salt compounds displayed high potential as a promising alternative corrosion inhibitor for replacing the toxic hexavalent chromium (Cr…”

Development of TiC/ Cr₂₃C₆Composite Coating on St 304 Substrate through TIG Process

“…Through solidification process, titanium carbide and chromium carbide particles (dark areas) are formed, then the liquid phase transforms to the super saturated titanium carbide (fine dark particles), and iron carbide (gray fragments) that were distributed in the background γ phase [24]. TiC → Ti + C (7) Cmatrix + Cgraphite → 2C (8) 3Fe + 2C → Fe3C + C (9) 23Cr + 6C → Cr23C6 …”

“…Surface modification is one of the most important and effective industrial methods for improving wear properties of such steels. A number of methods have been applied to improve the surface properties including chemical and physical vapor deposition, ion implantation, and electron and laser beam [7][8][9][10]. The chemical and physical vapor deposition forms a thin layer on the surface, thus involving high production time.…”