The composition of the passive layers formed on Zn electrode in naturally aerated and de-aerated 0.1 M KClO4 solution were studied using X-ray photoelectron spectroscopic measurements (XPS). A correlation between the presence of dissolved O2 and the formation of an interior passive layer was carried out. Librated Cl− from the perchlorate reduction reaction was detected in its solutions during Zn electrode polarization. The librated Cl− concentration reached its maximum value at −1.4 V. Moreover, in the studied potential range the perchlorate reduction rate increases in absence of dissolved oxygen. Chrono-amperometry and electrochemical impedance spectroscopy (EIS) were performed for the stationary and the rotating disc Zn electrodes in naturally aerated and de-aerated 0.1 M KClO4 solution. EIS technique showed a change in the electrode impedance with the experimental conditions as a result of changing the reactions occurring in the electrode vicinity. The obtained data were fitted to three different equivalent circuits depending on the electrode potential. The protective nature of the passive layers formed in different experimental conditions was found to decrease with rotating the electrode and de-aerating the solution. 相似文献
In this work, the influence of the outer solution cation mobility on the electrochemical behaviour of PVC Plastisol freestanding films was studied. For that purpose, the paint films were immersed in 0.5 M and 0.05 M chloride solutions with different cations (Na+, K+, Cs+). The electrochemical impedance spectroscopy (EIS) was the technique chosen for this study and estimated values of film capacitance and resistance were calculated.
For PVC Plastisol films, it was observed that the ion diffusion depends on the outer solution concentration. To explain such results different mechanisms for the ionic diffusion were considered. For higher concentration solutions the ions of the outer solution must diffuse into the film, while for lower concentration solutions the dissolution inside the film occurs followed by ionic diffusion from the film to the outer solution.
The water uptake was determined by EIS and gravimetry techniques. The Brasher and Kingsbury (BK) and the low frequency solution (LF) models were used to estimate this parameter by the EIS technique. A direct dependency between water uptake and solution concentration was obtained by this technique, while by gravimetry an inverse relation was obtained. However, the LF model presented water uptake values better correlated with the gravimetric ones comparatively to the BK equation. For the more concentrated solutions, the cation mobility influenced the water uptake estimated by EIS, whereas, such dependency was not observed with the gravimetric technique.
The results obtained in this work suggest that the outer solution resistivity and consequently the film resistance influence the water uptake measurements and should take part in any improved model used for water uptake determination. 相似文献
The present research brings new insights on the role of admixed corrosion inhibitors in the processes of cement hydration and rebar corrosion. The admixing of NaCl and the corrosion inhibitors in fresh mortar was found to alter the morphology and microstructure of the hardened mortar at the steel-mortar interfacial region. The admixing of the inhibitors increased the risk of carbonation of cement hydrates at the steel-mortar interfacial region, but partially displaced chloride ions. Chloride and the admixed inhibitors facilitated the formation of different cement hydrates and affected chloride binding at the steel-mortar interfacial region. The admixing of all three inhibitors was found to increase the polarization resistance of steel, indicating reduced corrosion rate of the steel over 48-day exposures to salt ponding. 相似文献
This paper describes the effect of corrosion process in the magnetic flux density of FeNbCuSiB alloys and correlates with the Si content in the alloys and in the surface oxide layer after a corrosion process. The corrosion resistance of FeNbCuSiB alloys was studied by ordinary weight loss tests, the potentiodynamic polarization technique and spectroscopy impedance. The photoelectron spectroscopy was used in order to identify the compositional changes in the surface oxide layer. Two alloy compositions, Fe77.5Cu1Nb3Si2.5B16 and Fe73Cu1Nb3Si16.5B6.5, with different Si content were analyzed in two different conditions, amorphous and crystalline states, respectively. The Fe77.5Cu1Nb3Si2.5B16 alloy displayed lower corrosion resistance than the Fe73Cu1Nb3Si16.5B6.5 alloy. The increase of the Si amount in the alloy composition results in an improvement in the corrosion resistance. The enrichment of the Si content on the surface oxide layer was found to be responsible for the improved corrosion resistance. Losses in magnetic properties depend not only on the Si content but also on the structural state. 相似文献
Electrophoretically deposited hydroxyapatite (HAP) coatings on type 316L SS was developed at the optimum coating parameters of 60 V and 3 min. Sintering of the coating enhances the metal-ceramic bond strength, but HAP structure is sensitive to temperature as it decomposes to other calcium phosphate phases. Sintering of HAP coatings in air at 900 °C for 1 h indicate the formation of a composite surface containing oxides of the alloy and decomposition products of HAP, mainly tricalcium phosphate. Open circuit potential-time measurements, potentiodynamic cyclic polarisation and electrochemical impedance experiments performed in Ringer’s solution indicate that the corrosion performance of HAP coatings were severely affected by the sintering atmosphere and temperature. Higher capacitance and low polarisation resistance values obtained from electrochemical impedance spectroscopic studies further indicate that the coatings are more prone to dissolution on comparison with the pristine type 316L SS. The sintering of the coatings in vacuum at 600, 800 and 900 °C for 1 h did not alter the phase purity of the coatings, and shifted the electrochemical parameters towards noble direction. Sintering of the coatings in vacuum lead to the formation of an adherent, stoichiometric HAP coating with enhanced corrosion resistance. 相似文献
The present paper studies the effect of ion implantation of 2 × 1016 ions/cm2 of Ce+ and 2 × 1016 ions/cm2 of La+ at 150 keV on the corrosion behaviour of hot-dip galvanised steel. After implantation, galvanised steel was characterised by means of XPS previous to and following immersion in the medium. The results revealed incorporation of cerium and lanthanum on the surface as Ce2O3 and La2O3, respectively. Electrochemical impedance spectroscopy was carried out in order to evaluate its corrosion behaviour in 0.6 M NaCl during 1 month of immersion. The corrosion resistance was improved by an increase in the charge transfer resistance of the implanted specimens in the medium. This effect could be associated with changes in the morphology/microstructure of the corrosion products layer rather than in its composition variations. 相似文献
The corrosion behavior of the 70/30 Cu-Ni alloy in stagnant, aerated pristine and sulfide-containing simulated seawater as a function of exposure time was investigated with polarization curve measurement and electrochemical impedance spectroscopy (EIS). It was demonstrated that the compact protective oxide film formed on the 70/30 Cu-Ni alloy resulted in the decrease of corrosion rate in aerated pristine seawater; while the corrosion rate of 70/30 Cu-Ni alloy in aerated sulfide-containing seawater increased dramatically due to the catalysis of the sulfide ions or sulfide scale for both the cathodic and anodic reactions. The impedance spectra and the corresponding equivalent circuits confirmed that a duplex layer of a surface film was formed on the 70/30 Cu-Ni alloy in aerated pristine seawater after a period of time and that the inner layer was responsible for the good resistance of the alloy; while only a porous and non-protective corrosion product layer formed on the 70/30 Cu-Ni alloy in aerated sulfide-containing seawater, which made small values of charge transfer resistance (Rct) to last for a abnormally long time by interfering with the growth of the protective oxide film. The composition of the surface film on the alloy in pristine and sulfide-containing seawater for different exposure times were investigated thoroughly by XPS. It was found that the duplex corrosion product layer formed on the alloy in pristine seawater was composed of an inner Cu2O and an outer CuO layer. The porous and non-protective corrosion product layer formed on the alloy in aerated sulfide-containing seawater was a mixture of CuCl, Cu2S, NiS, Cu2O and NiO with trace amounts of CuO and Ni(OH)2 and that the most significant component was Cu2S. In addition, SEM was used to analyze the topography of the 70/30 Cu-Ni alloy in both solutions after different exposure times. 相似文献