Chang He

Long‐term polarisation and immersion for copper corrosion were investigated in chloride‐containing sulphide solutions. Results showed that no active state exists for copper in sulphide‐containing solutions, whereas a typical active‐to‐passive transition exists in the second passivation region, indicating a hydroxyl activation effect on copper. After the sulphide passive film broke down, the pitting area was re‐passivated by hydroxide ions; however, if the chloride and sulphide concentrations were both high, then there was no second passivation and the copper would dissolve rapidly. The corrosion resistance and the film thickness both increased with increasing immersion time and an average corrosion rate of 51.2 µm/year was obtained in aerobic solution, which was much higher than in bentonite or under deoxygenated conditions. Moreover, several local corrosion pits appeared after 1‐year immersion and this would occur at the beginning of storage.

The possibility and necessity of using electrochemical tests to characterize the coating performance and guide the development and application of coating products were discussed. An attempt was made to establish the relationship between the electrochemical parameters and the macroscopic behavior of the coating. Waterborne micaceous iron oxide epoxy coatings were prepared and characterized by SEM, Electrochemical Impedance Spectroscopy (EIS) and conventional corrosion tests. The effects of the particle size and the pigment volume concentration (PVC) on the corrosion properties were discussed. Results revealed that the good anticorrosive performance of the paint was obtained when the 600-mesh-sized MIO was used and the pigment volume concentration (PVC) was 39%. The consistency of the two EIS parameters (the partial fitting coating resistance Rpart and the phase angle at 10 Hz) for evaluating the performance of the coatings was confirmed. The electrochemical failure time (EFT) was defined, and then compared with the macroscopic blistering time, which verified the possibility of applying this parameter in the development of coating products.

The corrosion behaviour of oxygen-free copper in anoxic 0.1 M NaCl + 2 × 10−4 M Na2S·9H2O solution (pH = 9.0) was investigated under potentiostatic polarisation for different times. Electrochemical methods, including electrochemical impedance spectroscopy, Mott–Schottky analysis, localised electrochemical impedance spectroscopy (LEIS) and scanning electron microscopy observations, were conducted. The results indicated that the corrosion resistance of oxygen-free copper decreased with increasing applied potential, whereas it increased with increasing polarisation time. The passive film growth kinetics obeyed a logarithmic law (lnD = alnt + b, where D is the layer thickness, b is a constant taken as the initial growth rate, t is the polarisation time and a is the time exponent). Subsequent to the formation of a compact and coherent passive film, the thicker the film was, the more difficult for ion to migrate, which further resulted in a slower film growth rate. The passive film displayed p-type semiconductor behaviour and the acceptor density (cation vacancy) was approximately 1022 to 1023 cm−3. The LEIS results showed that the passive film achieved relative stability after 24 h of immersion under natural conditions, which was longer than the duration of potentiostatic polarisation (4 h at −0.6 VSCE).

The flow field of the molten bath and the decarburisation rate in a 150 t electrical arc furnace (EAF) are discussed based on a three-phase numerical simulation, while the furnace profile of the EAF and the installation location of oxygen lance are fixed. As shown in the results, with increasing charge mass of the molten bath and lowering oxygen lance height, the penetration depth of oxygen jet and the velocity of uncovered steel created by the jet increase, the area of uncovered steel becomes small and the flowrate of steel flowing through the uncovered area increases; thus, the absolute decarburisation rate increases. Simultaneously, the optimum operating mode for this EAF is with a charge mass of 150 t and an oxygen lance relative height of 0·45 m, in which the low speed area on the bottom of the EAF is the minimum and the relative decarburisation rate is the maximum; this contributes to a reduction in the tap to tap time of EAF steelmaking.