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Polyaniline (PANI) polymer coating was electrochemically synthetised by cyclic voltammetry (CV) method on stainless steel bipolar plates of proton exchange membrane fuel cell (PEMFC). Structure and morphology of PANI polymer coating were characterized by means of fourier transform infrared reflection (FTIR) spectrum and scanning electron microscopy (SEM). The corrosion behavior of the coating was evaluated by polarization curve and electrochemical impedance spectroscopy (EIS) in the medium of 1M H2SO4and 2ppM NaF at 70°C to simulate the corrosive condition of PEMFC. It was found that the optimal conditions for PANI polymer coating synthesis could be 10-15 circles when the voltage ranged from-1.2V to +1.2V(Vs.SCE) with a scan rate of 50 mV/s. SEM observation results indicated that the polymer coating presented with uniform and dense feature. FTIR results illustrated that the coating were composed of PANI. Corrosion current densities of 316L SS and PANI-coated steel were 10-5and 10-6A/cm2respectively. Corrosion potential of the coated SS shifted towards more positive values compared to the uncoated plate. EIS results indicated that the radius of the capacity impedance for PANI increased obviously.

PANI coating was electrochemically synthesized by cyclic voltammetry (CV) method on the surface of 316L stainless steel plate. The surface morphology of PANI coating was observed by scanning electron microscopy. The effect of oxygen gas on corrosion behavior of PANI coating in PEMFC environment was investigated. The corrosion performance of the coating was evaluated by potential-time curve and polarization curve as well as electrochemical impedance spectroscopy in a bath containing 1M H2SO4and 2ppM NaF, and the air with a flow rate of 10 ml/min was piped into the testing corrosion cell to simulate the positive cathode condition of PEMFC at 70°C. The potential-time curves illustrated that oxygen gas resulted in the potential decline towards negative direction. Polarization curves showed that corrosion potential of the sample with O2was lower than that of the sample without O2, and the corrosion current density was higher than that of the sample without O2. EIS results indicated that the Nyquist plots were constitute of a capacitive impedance arc and a incline line, and the oxygen gas reduced the anti-corrosion performance of the PANI coating.

A non-chromate conversion coating was prepared from molybdate based bath on the surface of Zn-5%Al hot dip galvanized steel. The influence of the preparation conditions such as temperature, bath pH and treating time on the corrosion resistance of the obtained conversion coating was investigated. The corrosion performance of the film was researched using electrochemical technique in 3.5%NaCl. The results indicate that the anodic branch of the polarization curves present in passivation character. Electrochemical impedance spectroscopy (EIS) illustrate that the radius of the capacity impedance for conversion coating varies distinctly according to the preparation condition. The surface morphology was observed using scanning electron microscopy (SEM), and the results show that the surface of Zn-5%Al hot dip galvanized steel present in eutectic feature after conversion coating treatment. The chemical composition of the coating was detected by energy dispersive X-ray (EDX), and the results illustrate that the conversion coating is composed of Zn, Al , O, P and Mo.

Coating of ME20M magnesium alloys was first carried out using electroless nickel plating technique with an environmentally-friendly pretreatment. The morphology and specific weight loss of the pickling process were investigated. The Ni-P coating was characterized by its structure, morphology, chemical composition, adhesion strength and corrosion resistance. The SEM image shows that the pyrophosphate pickling process can produce a rough surface and the thermal shock test indicates excellent adhesion strength between magnesium alloys and Ni-P coating. The damp heat test and electrochemical measurement prove the Ni-P coating significantly increase the corrosion resistance of ME20M magnesium alloys.

A conversion coating was obtained in the molybdate based bath on hot dip galvanized steel. The influence of the bath service life and bath component variation on the corrosion resistance of the conversion coating were investigated. Corrosion resistance of the coating was evaluated by electrochemical technique in 3.5%NaCl. It is found that the anodic branch of polarization curves presented in passivation character. Electrochemical impedance spectroscopy (EIS) results confirm that the radius of the capacity impedance for molybdate film decreased with treating area, which reveals that the bath life and bath component variation affected anti-corrosion performance of the coating remarkablely. The bath constituent was analysed by inductively coupled plasma atomic emission spectrometry (ICP), and the results show that the bath will lose the passivation ability after treating 1.16m2sample area for new prepared treating solution of 500ml. The surface morphologies of the coatings were observed using scanning electron microscopy (SEM), and the element composition of the coatings was detected using energy dispersive X-ray (EDX). The investigation results indicate that uniform and compact film is formed on the surface of the galvanized steel, and the film is composed of zinc,oxygen, phosphor and molybdenum.

This paper studies the influence of current frequency on the micro-arc oxidation (MAO) process, microstructrue and the properties of the formed alumina coatings. The amount of discharge sparks increases and the spark moves more quickly with increasing the frequency of current pulse. SEM results show that the size of the discharge products decreases. The anodic cell voltage decreases with increasing the frequency of power supply, however, the cathodic cell voltage increases. The thickness and roughness of the coating produced using frequency of power supply 50 Hz are high. Increasing the frequency, the thickness of the coating decreases, but coating surface becomes even, and the coating possesses better corrosion protective property