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[en] Research highlights: → Surface roughness of AZ91 magnesium alloy plays a critical role in the passivation behaviour of the alloy. → The passivation behaviour of the alloy influences the pitting tendency. → Increase in surface roughness of AZ91 magnesium alloy increases the pitting tendency of the alloy. -- Abstract: In this study, the influence of surface roughness on the passivation and pitting corrosion behaviour of AZ91 magnesium alloy in chloride-containing environment was examined using electrochemical techniques. Potentiodynamic polarisation and electrochemical impedance spectroscopy tests suggested that the passivation behaviour of the alloy was affected by increasing the surface roughness. Consequently, the corrosion current and the pitting tendency of the alloy also increased with increase in the surface roughness. Scanning electron micrographs of 24 h immersion test samples clearly revealed pitting corrosion in the highest surface roughness (Sa 430) alloy, whereas in the lowest surface roughness (Sa 80) alloy no evidence of pitting corrosion was observed. Interestingly, when the passivity of the alloy was disturbed by galvanostatically holding the sample at anodic current for 1 h, the alloy underwent high pitting corrosion irrespective of their surface roughness. Thus the study suggests that the surface roughness plays a critical role in the passivation behaviour of the alloy and hence the pitting tendency.
[en] The addition of chromium and molybdenum to nickel creates alloys with exceptional corrosion resistance in a diverse range of environments. This study examines the complementary roles of Cr and Mo in Ni alloy passivation. Four nickel alloys with varying amounts of chromium and molybdenum were studied in 1 molar salt solutions over a broad pH range. The passive corrosion and breakdown behavior of the alloys suggests that chromium is the primary element influencing general corrosion resistance. The breakdown potential was nearly independent of molybdenum content, while the repassivation potential is strongly dependant on the molybdenum content. This indicates that chromium plays a strong role in maintaining the passivity of the alloy, while molybdenum acts to stabilize the passive film after a localized breakdown event
[en] Equilibrium states of quantum systems are characterized by a condition of passivity suggested by the second principle of thermodynamics. Ground states and β-KMS states for all inverse temperatures β>=0 are completely passive. It is proved that these states are the only completely passive ones. For the special case of states describing pure phases, assuming the passivity, the results of R. Haag, D. Kastler and E.B. Trych-Polhmeyer are reproduced
[en] We discuss some features of thermodynamics in the presence of multiple conserved quantities. We prove a generalisation of Landauer principle illustrating tradeoffs between the erasure costs paid in different ‘currencies’. We then show how the maximum entropy and complete passivity approaches give different answers in the presence of multiple observables. We discuss how this seems to prevent current resource theories from fully capturing thermodynamic aspects of non-commutativity. (paper)
[en] Highlights: • Corrosion behavior of the Zn-Mg alloys in saturated Ca(OH)2 solution was studied. • The Zn-Mg alloys were passivated with more negative corrosion potential. • Mg alloying caused inhomogeneity of the passivation layer. • The Zn-Mg alloys were less resistant to corrosion compared to pure zinc. - Abstract: The influence of Mg addition on the corrosion behavior of Zn-x%Mg (x = 0.5, 1.5 and 3) alloys in saturated Ca(OH)2 solution was investigated with pure zinc as a reference. The Zn-Mg alloys were passivated but less resistant to corrosion. Mg alloying caused more negative corrosion potential of the Zn-Mg alloys and inhomogeneity of the passivation layer. Alternately preferential dissolution of the primary Zn-rich dendrites (PZD) and Zn-Mg eutectics (ZME) regions was observed. This was probably linked to the galvanic coupling between the PZD and ZME regions, and/or the Mg-rich passivation layer less resistant to corrosion than the Ca-rich passivation layer.
[en] A comprehensive investigation of quantum confinement in nanowires has been carried out. Though applied to silicon nanowires (SiNWs), it is general and applicable to all nanowires. Fundamentals and applications of quantum confinement in nanowires and possible laws obeyed by these nanowires, have been investigated. These laws may serve as backbones of nanowire science and technology. The relationship between energy band gap and nanowire diameter has been studied. This relationship appears to be universal. A thorough review indicates that the first principles results for quantum confinement vary widely. The possible cause of this variation has been examined. Surface passivation and surface reconstruction of nanowires have been elucidated. It has been found that quantum confinement owes its origin to surface strain resulting from surface passivation and surface reconstruction and hence thin nanowires may actually be crystalline-core/amorphous-shell (c-Si/a-Si) nanowires. Experimental data available in the literature corroborate with the suggestion. The study also reveals an intrinsic relationship between quantum confinement and the surface amorphicity of nanowires. It demonstrates that surface amorphicity may be an important tool to investigate the electronic, optoelectronic and sensorial properties of quantum-confined nanowires. (topical review)
[en] This paper studies the problem of delay-dependent passivity for uncertain neural networks (UNNs) with discrete and distributed delays. Without considering free weighting matrices and multiple integral terms, which may cause more numbers of linear matrix inequalities (LMIs) and scalar decision variables. By constructing a suitable Lyapunov–Krasovskii functional (LKF) and combining with the reciprocally convex approach, some sufficient conditions are established in terms of LMIs. Compared with existing results, the derived criteria are more effective due to the application of delay partitioning approach which takes a full consideration of all available information in various delay intervals. Two simulation examples are given to illustrate the effectiveness of the proposed method.
[en] The considerable evolution which the main parts of the theory of the electrochemical corrosion (local in particular) have undergone due to their coniection with the main provisions of the electrode reaction kinetics and complex electrochemical and physical surface investigations is reviewed. Different variants of action of technologic metal impurities both solved and segregated over grain boundaries, and those forming separate phases are analyzed. The regularities of selective dissolution and the mutual effect of dissolution, oxidation processes and the transfer of separate alloy components in different variants of corrosion of chromium-nickel steels in active and passive states and depending on the metal crystal structure and substructure are studied. Prospects for further investigations are outlined
[en] Research highlights: → The influence of load on passivity of steel in concrete pore solution is studied. → The passivity of steel in pore solution decreased as the load amplitude increased. → A micro-crack model is presented to explain passive behaviour of steel under loads. - Abstract: The influence of stress on passive behaviour of steel bars in concrete pore solution was studied with electrochemical impedance spectroscopy and X-ray photoelectron spectroscopy. The passive ability of steel decreased as the applied load increased and higher load had much greater influence on passivation than repeated loading of small magnitude. A micro-crack model was presented to explain the damage of passive layer by loads. Lower load caused micro-cracks in the passive film which might be completely recovered after unloading. Under higher load more micro-cracks were produced in the passive film and some may penetrate the film, leading to irreversible damages.