Search results for "CORROSION"
showing 10 items of 456 documents
Calcium phosphate/polyvinyl acetate coatings on SS304 via galvanic co-deposition for orthopedic implant applications
2021
Abstract In this work, the galvanic deposition method is used to deposit coatings of brushite/hydroxyapatite/polyvinyl acetate on 304 stainless steel. Coatings are obtained at different temperatures and with different sacrificial anodes, consisting of a mixture of brushite and hydroxyapatite. Samples are aged in a simulated body fluid (SBF), where a complete conversion of brushite into hydroxyapatite with a simultaneous change in morphology and wettability occurred. The corrosion tests show that, compared with bare 304, the coating shifts Ecorr to anodic values and reduces icorr Ecorr, and icorr has different values at different aging times due to chemical interactions at the solid/liquid i…
The use of microcapillary techniques to study the corrosion resistance of AZ91 magnesium alloy at the microscale
2011
Abstract The AZ91 alloy is composed of Mg 17 (Al, Zn) 12 precipitates, an eutectic phase around these precipitates, AlMn intermetallic particles and an α-Mg solid solution (matrix). The corrosion behaviour of AZ91 was investigated at the microscale by means of the electrochemical microcell technique, which uses extremely small capillaries (diameters between 5 and 10 μm). Experiments were conducted in 0.1 M NaClO 4 at 25 °C. The β-Mg 17 (Al, Zn) 12 precipitates were found to have the highest corrosion resistance, whereas the eutectic phase was very active (pitting potential of approximately −1400 mV vs. Ag/AgCl). The α-Mg solid solution displayed better corrosion resistance than the eutectic…
Characterizing archaeological bronze corrosion products intersecting electrochemical impedance measurements with voltammetry of immobilized particles
2017
Application of electrochemical impedance measurements to microparticulate deposits of copper corrosion products attached to graphite electrodes in contact with 0.10 M aqueous HClO4 electrolyte is described. The impedance measurements were sensitive to the applied potential and the amount of solid sample and were modeled taking into account the contribution of the uncovered base electrode. Several pairs of circuit elements provide monotonic variations which are able to characterize different corrosion compounds regardless the amount of microparticulate solid on the electrode. Application to a set of archaeological samples from the archaeological Roman site of Gadara (Jordan, 4th century AD) …
Analogy between the effects of a mechanical and chemical perturbation on the conductivity of passive films
2002
Abstract In order to study the passivity breakdown of a type 316L stainless steel, the electrochemical impedance and surface stresses were measured under straining conditions. The Mott–Schottky analysis, performed at high frequency, appears as very useful method to study, below the apparent yield strength, the effects of a mechanical stress on the capacitance values. The results obtained in sodium chloride media indicate that the semiconducting properties of passive films formed in a tensile stress field reflect a higher vacancies concentration than those formed in a stress-free state, suggesting that the passive film conductivity is increased. It was also shown that the Mott–Schottky plots…
The combined effect of refractory coatings containing reactive elements on high temperature oxidation behavior of chromia-forming alloys
2003
Abstract The high temperature oxidation behaviors of chromia-forming alloys (F17Ti and Fe–30Cr alloys) have been studied at 1273 K under isothermal conditions and at 1223 K under cyclic conditions, in air under the atmospheric pressure. To extend the oxidation lifetime, coatings have been applied onto the alloy surfaces. Al2O3 and Cr2O3 films doped with Sm2O3 or Nd2O3 were prepared via the metal-organic chemical vapor deposition technique. Single Cr2O3, Al2O3, Nd2O3 and codeposited Cr2O3–Nd2O3, Al2O3–Nd2O3, Al2O3–Sm2O3 coatings drastically improved the chromia-forming alloy high temperature oxidation behavior, since they decreased the oxidation rate and enhanced the oxide scale adhesion. Re…
The effect of rare earths deposited on steel surfaces, by different processes (sol/gel, electrophoresis, OMCVD), on high temperature corrosion behavi…
1993
Abstract In this paper, different methods of rare earth oxides deposition on the surface of AISI 304 steel are described: sol/gel, electrophoresis in aqueous or organic medium, OMCVD of rare earth β-diketonates. After the deposition, all the samples were reheated. This treatment was absolutely essential for a strengthening effect of the protective oxide scale. Oxidation of coated and non-coated samples was performed under isothermal and cyclic conditions. The effect of rare earth deposition is significant in isothermal conditions. However, in thermal cyclic conditions, the effect of a rare earth deposited on surface is spectacular. Scale spallation is then completely avoided under the chose…
Cut-edge corrosion of a Zn–55Al-coated steel: A comparison between sulphate and chloride solutions
2011
Abstract Ex situ observations and in situ measurements of current and pH distributions over cut-edge coated steels revealed that Zn–55Al coatings are sacrificial only in chloride solutions, because of an activation of both Zn- and Al-rich phases present in the coating. In sulphate solutions, an efficient cathodic protection occurs only for short times of immersion, because only Zn-rich phases are active in this medium. The low solubility and strong acidification induced by Al(OH)SO4 allows only short distance cathodic protection, but cannot prevent red rust precipitation on the steel surface.
Role of plastic deformation and microstructure in the micro-electrochemical behaviour of Ti–6Al–4V in sodium chloride solution
2013
Abstract The role of alloying elements and the influence of plastic deformation on the micro-electrochemical behaviour and the pitting corrosion susceptibility of TiAl6V4 have been investigated in 10 g/L NaCl using the electrochemical microcell technique. Local electrochemical measurements have revealed that both the increase of surface roughness and the increase of dislocation density have impact on the electrochemical behaviour of TiAl6V4 after plastic deformation. It has been shown the surface roughness induced by slip band emergence is the predominant parameter responsible for the increase of the cathodic current. It has also been shown that cathodic reactions occur preferentially at su…
In situ investigation of sacrificial behaviour of hot dipped AlSi coating in sulphate and chloride solutions
2013
Abstract The electrochemical behaviour of the cut-edge of hot-dipped aluminium–silicon-based alloy coated steel is studied in immersed conditions in sulphate and in chloride media. Preliminary studies performed on steel-pure Al bi-electrode demonstrate that a significant galvanic current can develop at short times (t
Modeling bimetallic corrosion under thin electrolyte films
2011
A finite element model (FEM) was developed to calculate the potential distribution in the electrolyte in the case of bimetallic corrosion between iron and zinc electrodes, taking into account mass transport of oxygen in the solution. This model was first compared with experimental results obtained by scanning vibrating electrode technique (SVET) on a galvanized steel cut-edge in immersion conditions in a 0.03 M NaCl electrolyte. A good agreement was obtained between the calculated and experimental current densities. The model predicted the evolution of the galvanic coupling as function of the electrolyte thickness and for various iron–zinc surface area ratios. Different coupling regimes wer…