Current developments of nanoscale insight into corrosion protection by passive oxide films

Oxide passive films are a key for the durability of metals and alloys components as well as a central issue in corrosion science and engineering. Herein, we discuss current developments of the nanometer and sub-nanometer scale knowledge of the barrier properties and adsorption properties of passive oxide films brought by recent model experimental and theoretical investigations. The discussed aspects include (i) the chromium enrichment and its homogeneity at the nanoscale in passive films formed on Cr-bearing alloys such as stainless steel, (ii) the corrosion properties of grain boundaries in early intergranular corrosion before penetration and propagation in the grain boundary network, and (iii) the interaction of organic inhibitor molecules with incompletely passivated metallic surfaces. In all three cases, key issues are highlighted and future developments that we consider as most relevant are identified.Comment: Current Opinion in Solid State and Materials Science, Elsevier, final accepted preprin

Social Preference Under Twofold Uncertainty

We investigate the conflict between the ex ante and ex post criteria of social welfare in a new framework of individual and social decisions, which distinguishes between two sources of uncertainty, here interpreted as an objective and a subjective source respectively. This framework makes it possible to endow the individuals and society not only with ex ante and ex post preferences, as is usually done, but also with interim preferences of two kinds, and correspondingly, to introduce interim forms of the Pareto principle. After characterizing the ex ante and ex post criteria, we present a first solution to their conflict that extends the former as much possible in the direction of the latter. Then, we present a second solution, which goes in the opposite direction, and is also maximally assertive. Both solutions translate the assumed Pareto conditions into weighted additive utility representations, and both attribute to the individuals common probability values on the objective source of uncertainty, and different probability values on the subjective source. We discuss these solutions in terms of two conceptual arguments, i.e., the by now classic spurious unanimity argument and a novel informational argument labelled complementary ignorance. The paper complies with the standard economic methodology of basing probability and utility representations on preference axioms, but for the sake of completeness, also considers a construal of objective uncertainty based on the assumption of an exogeneously given probability measure. JEL classification: D70; D81

Variational solution of the Gross-Neveu model at finite temperature in the large N limit

We use a nonperturbative variational method to investigate the phase transition of the Gross-Neveu model. It is shown that the variational procedure can be generalized to the finite temperature case. The large N result for the phase transition is correctly reproduced.Comment: 12 p., 1 fig, this is the version which will appear in the Phys Lett B, it differs from the previous one in what concerns the introduction and conclusions (re written), several references have been adde

Progress in corrosion science at atomic and nanometric scales

International audienceContemporary aspects of corrosion science are reviewed to show how insightful a surface science approach is to understand the mechanisms of corrosion initiation at the atomic and nanometric scales. The review covers experimental approaches using advanced surface analytical techniques applied to single-crystal surfaces of metal and alloys exposed to corrosive aqueous environments in well-controlled conditions and analysed in situ under electrochemical control and/or ex situ by scanning tunnelling microscopy/spectroscopy, atomic force microscopy and x-ray diffraction. Complementary theoretical approaches based on atomistic modeling are also covered. The discussed aspects include the metal-water interfacial structure and the surface reconstruction induced by hydroxide adsorption and formation of 2D (hyd)oxide precursors, the structure alterations accompanying anodic dissolution processes of metals without or with 2D protective layers and selective dissolution (i.e. dealloying) of alloys, the atomic structure, orientation and surface hydroxylation of ultrathin passive films, the role of step edges at the exposed surface of oxide grains on the dissolution of passive films and the effect of grain boundaries in polycrystalline passive films acting as preferential sites of passivity breakdown, the differences in local electronic properties measured at passive films grain boundaries, and the structure of adlayers of organic inhibitor molecules

Effect of platinum on the growth rate of the oxide scale formed on cast nickel aluminide intermetallic alloys

Thermo-Gravimetric Analysis ( TGA) and Scanning Electron M icroscopy ( SEM ) data of the initial stages of oxidation of Ni50Al50 and Ni40Pt10Al50 alloys of low and high sulfur content at 900◦ C and 1100◦ C are reported. The results show that the addition of Pt promotes the growth of the transient θ- Al2O3 oxide scale. This effect is particularly sensitive in the initial stages of oxidation at 1100◦ C where Pt considerably increases the total mass gain. It is attenuated in the presence of a high sulfur content in the alloy, indicating a competitive effect of Pt and S on the segregation of Al. The slower θ-to- α transition observed in the presence of Pt leads to an extended lifetime of the θ phase layer, which is proposed to be benecial to the relaxation of the stresses created by the growth of α-Al2O3

2-mercaptobenzothiazole corrosion inhibitor deposited at ultra-low pressure on model copper surfaces

International audienceAdsorption of 2-mercaptobenzothiazole (2-MBT) at ultra-low pressure and room temperature on metallic and pre-oxidized Cu(111) surfaces and its thermal stability were investigated using X-ray photoelectron spectroscopy in order to better understand the interfacial corrosion inhibiting properties. 2-MBT is lying flat in the monolayer with two sulphur atoms bonded to Cu and decomposes partially yielding atomic sulphur when interacting with metallic copper prior to forming molecular multilayers. Decomposition is prevented by surface pre-oxidation with 2D oxide dissociation accelerating the 2-MBT initial adsorption kinetics. 2-MBT further decomposes and partially desorbs above 100 • C. A pre-adsorbed 2-MBT monolayer on metallic copper inhibits surface corrosion

Molecular scale insights into interaction mechanisms between organic inhibitor film and copper

A model experimental approach, providing molecular scale insight into the build up mechanisms of a corrosion inhibiting interface, is reported. 2-mercaptobenzimidazole (2-MBI), a widely used organic inhibitor, was deposited from the vapor phase at ultra-low pressure on copper surfaces in chemically-controlled state, and X-ray photoelectron spectroscopy was used in situ to characterize the adsorption mechanisms upon formation of the inhibiting film. On copper surfaces prepared clean in the metallic state, the intact molecules lie flat at low exposure, with sulfur and both nitrogen atoms bonded to copper. A fraction of the molecules decomposes upon adsorption, leaving atomic sulfur on copper. At higher exposure, the molecules adsorb in a tilted position with sulfur and only one nitrogen bonded to copper, leading to a densification of 2-MBI in the monolayer. A bilayer is formed at saturation with the outer layer not bonded directly to copper. In the presence of a pre-adsorbed 2D oxide, oxygen is substituted and the molecules adsorb intactly without decomposition. A 3D oxide prevents the bonding of sulfur to copper. The molecular film formed on metallic and 2D oxide pre-covered surfaces partially desorbs and decomposes at temperature above 400 °C, leading to the adsorption of atomic sulfur on copper

New insight on early oxidation stages of austenitic stainless steel from in situ XPS analysis on single-crystalline Fe–18Cr–13Ni

International audienceIn situ X-ray photoelectron spectroscopy real-time measurements and angular-dependent high resolution core level analysis were used for the first time to investigate the Cr enrichment and oxide growth mechanisms on a model 304 austenitic stainless steel surface in the very initial stages of oxidation leading to pre-passivation. The oxidation kinetics was followed for increasing oxygen exposure and temperature, revealing an early nucleation regime (for exposure < 10 L) leading to the formation of a strongly Cr-enriched Cr 3+ /Fe 3+ mixed layer followed by an oxide growth regime where preferential iron oxidation takes over and mitigate the initial chromium enrichment