In this study, the corrosion properties of Ti-6Mo-6V-5Cr-3Sn-2.5Zr alloy were investigated as a function of the cold rolling ratio and annealing temperature. The annealing treatment was carried out at temperature of 680°C, 730°C, and 780°C. The highest corrosion potential observed in the specimen with a 10% rolling ratio was 179 mV, which was more positive than that of the non-rolled specimen (–0.214 Vssc). The lowest corrosion current density (1.30×10–8 A/cm2) was observed in the non-rolled specimen which suggested that the integrity of its passive oxide layer was superior to that of the cold-rolled specimens. Time-dependent EIS evaluation revealed that the consistency of the passive oxide layer was highly affected by the subjected rolling ratio over time.
The corrosion inhibition behaviour of 1-Ethyl-3-methylimidazolium-methanesulphonate (EMIM[MS]) and 1-Ethyl-3-methylimidazolium acetate (EMIM[Ac]) on API 5L X-52 carbon steel in 2 M HCl was investigated using weight loss, potentiodynamic polarization and electrochemical impedance methods. The corrosion rates of carbon steel decreased in the presence of these ionic liquids. The inhibition efficiencies of the compounds increased with concentration and showed a marginal decrease with a 10°C increase in temperature. Polarization studies showed the compounds to be mixed type inhibitors with stronger anodic character. The adsorption mechanism of both compounds on the metal surface was via physical adsorption and the process obeyed the El-Awardy kinetic-thermodynamic model. The associated activation energy of corrosion and other thermodynamic parameters were calculated to elaborate on the thermodynamics and mechanism of the corrosion inhibition process. EMIM[MS] was found to inhibit the corrosion of carbon steel better than EMIM[Ac] and is attributed to the presence of the highly electronegative sulphur atom in its structure and its larger molecular size.
Nifedipine, a pyridine derivative was investigated as corrosion inhibitor for API 5L X-52 steel in 2 M HCl solution by potentiodynamic polarization, electrochemical impedance spectroscopy and quantum chemical calculations. Statistical tools were used to compare results of the experimental methods. The results showed that nifedipine is capable of inhibiting the corrosion of API 5L X-52 steel in 2 M HCl solution. Potentiodynamic polarization results reveal that nifedipine functions as a mixed-type inhibitor and presents an inhibition efficiency of about 78% at 500 ppm. Impedance data reveal an increasing charge transfer resistance with increasing inhibitor concentration and also shows comparable inhibition efficiency of about 89-94% at 500 ppm. Thermodynamic parameters imply that nifedipine is adsorbed on the steel surface by a physiochemical process and obeys Langmuir adsorption isotherm. The calculated molecular properties namely the highest occupied molecular orbital energy, lowest unoccupied molecular orbital energy, chemical hardness, energy gap, dipole moment, electronegativity and global nucleophilicity index all show a positive relationship to the observed corrosion inhibition efficiency.
Al2Cu phase has been obtained by melting pure metals in the electric arc furnace. It has been found that the intermetallic phase undergoes selective corrosion in the H3PO4 aqueous solutions. Aluminium is dissolved, the surface becomes porous and enriched with copper. The corrosion rate equals to 371 ± 17 g·m–2·day–1 (aerated solution) and 284 ± 9 g·m–2·day–1 (deaerated solution). The surface of Al2Cu phase after selective corrosion was characterised by using electrochemical impedance spectroscopy. It was found that the surface area of the specimens increases with temperature due to higher corrosion rate and is between 2137 and 3896 cm2.
Sodium orthovanadate was tested as a corrosion inhibitor of intermetallic Al2Cu in 1 M H3PO4. The Al2Cu – H3PO4 – Na3VO4 system was studied using the following methods: inductively coupled plasma optical emission spectrometry, scanning electron microscopy with energy dispersive x-ray spectroscopy, x-ray diffraction, electrochemical impedance spectroscopy, polarisation and open circuit potential. It was found that the corrosion rate decreased as the inhibitor concentration increased. The highest inhibition efficiency 99% was obtained when sodium orthovanadate initial concentration was equal to 100 mM, pH = 1.11, due to precipitation of a protective layer of insoluble salt, containing vanadium, phosphorus, sodium and oxygen, on the surface. At pH = 0.76 the protective layer was not formed and inhibition efficiency decreased to 76%. Selective corrosion of the intermetallic phase caused a significant increase of an electric double layer capacitance and decrease of a charge transfer resistance.
In this work, we developed the lanthanum strontium cobalt ferrite and it’s composite with yttrium iron cobaltite (mass ratio of 1:1) cathodes as a thin layer on Ce0.8Sm0.2O1.9 electrolyte. Two kinds of electrode pastes were prepared, with and without 6 mm polystyrene beads as an additional pore former. The performance of cathode materials was investigated by electrochemical impedance spectroscopy as a function of electrode morphology, oxygen partial pressure, potential, and temperature. The polarization resistance of the more porous electrodes was lower than those electrodes prepared without additional pore former in the whole potential range at 800°C, slightly lower at 700°C and 600°C. The addition of yttrium iron cobaltite decreased the performance of both types of cathodes. The lower polarization resistance of porous cathodes is due to the facilitated gas diffusion through their structure.