SURFACE PASSIVE FILM CHARACTERISTIC OF Q235 CARBON STEEL IN PURE MOLYBDATE SOLUTION

In pure Na2MoO4 solutions with different concentrations of MoO[Formula: see text] (0.01, 0.04, 0.06, 0.08 and 0.10 mmol/L), a passive film was formed on the surface of Q235 carbon steel spontaneously, and the influences of MoO[Formula: see text] concentrations on the passive film characteristics were investigated. The electrochemical and microstructural techniques of electrochemical impedance spectroscopy (EIS), Mott–Schottky plot (MSP), scanning electron microscope (SEM) and X-ray photoelectron spectroscope (XPS) were applied to characterize the passive film characteristics, including resistance, defect, microstructure and composition. The resistance and defect of passive film respectively increased and decreased with increased MoO[Formula: see text] concentration up to 0.08[Formula: see text]mmol/L, which was the critical MoO[Formula: see text] concentration of complete passivation for the Q235 surface. The passive film formed in the 0.08[Formula: see text]mmol/L Na2MoO4 solution showed a dense microstructure and was composed of Fe2(MoO[Formula: see text] mainly. Further, in this work, the relation between characteristic and anti-corrosion of passive film was also discussed.

Surface Stabilities of n-type GaN Dependent on Electrolyte under Photoelectrochemical Reactions

ABSTRACTThe n-type GaN has stability problem of the surface anodic corrosion during the photoelectrochemical reaction for H2 generation. The photoelectrochemical surface stabilities of n-type GaN dependent on the electrolytes were investigated. The flatband potential in HCl obtained from Mott-Schottky plot shifted 0.1 V to positive direction compared with that in H2SO4. The variation of saturated photocurrent of 1 to 3 cycles in H2SO4 was much larger than that of HCl, NaOH and KOH. The surface morphologies also changed by the electrolytes. These results show the absorbed materials on the GaN electrode surface during the photoelectrochemical reactions were changed by the electrolyte and affected the surface reactions.

On the Flat-Band Potential and the Frequency Dispersion of Capacitance and Its Removal in an Normal-Cadmium Telluride in Alkaline Selenide, Polyselenide Photoelectrochemical Cell

When seepage of the electrolyte between the semiconductor crystal and its insulation was prevented, the equivalent series capacitance CS of an n-CdTe|Se2-, Sen2-,OH-|Pt cell was almost independent of frequency (<2% increase of CS per decade decrease of frequency) in the range 104-2 Hz. Attributing CS wholly to the space-charge capacitance resulted in a linear Mott- Schottky plot and this yielded a flat-band potential of -2.0�0.1 V v . s.c.e . and a built-in potential of 1.08�0.06 V. This was consistent with the observed current-voltage curves in both dark and light. Two conditions under which frequency dispersion was observed were (a) electrolyte seepage and (b) surface damage. The insulating techniques which allowed seepage were similar to those of other workers. The effects of these imperfections on the Mott- Schottky plot are considered. Attempts to extract useful information from frequency dispersion data showed that it is difficult or impossible to obtain a unambiguous equivalent circuit solely on the basis of goodness-of-fit of calculated to observed impedances. The ambiguity can be removed only when sufficient information beyond impedance-frequency data is available. For electrodes with seepage, a model due to Tomkiewicz led to the correct value of the built-in potential.