CREVICE CORROSION BEHAVIOR OF X70 STEEL IN HCO_3^- SOLUTION UNDER CATHODIC POLARIZATION

The crevice corrosion behavior of XTO steel was investigated with a wedge-shaped crevice assembly under -1000 m V （SCE） cathodic polarization in the solutions with various HCO3 concentrations. The potential, current, pH and the oxygen content within the crevice were measured with or without outside coupled specimen. The results indicated that the polarization potential of XTO steel in the crevice dropped with the increase of time under the cathodic polarization. There was a remarkable influence of HCO3 concentration on the potential of XTO steel in the crevice. When HCO3 concentration was up to 0.125%, the surface of the metal was covered with the corrosion products that resulted in the polarization extent of XTO steel decreased. The pH value in the crevice rose and it dropped gradually from the crevice mouth to the bottom under the cathodic polarization. With the increasing of HCO3 concentration, the hydrolyzation reaction of metal in the crevice bottom aggravated. Most of the dissolved oxygen in the crevice was consumed by the cathodic current. The maximum cathodic current on the metal surface was at the crevice mouth and it was much more than that at the crevice bottom.

Effects of cathodic polarization on SCC behavior of AA7003 under various aging treatments

In this paper,the effect of cathodic polarization on corrosion behavior of AA7003 under three kinds of aging treatments(including peak aging(PA),double peak aging(DPA)and regression re-aging(RRA))was studied in 3.5 wt%sodium chloride solution through slow strain rate testing(SSRT)and electrochemical testing.X-ray diffraction(XRD)and scanning electron microscopy(SEM)methods were also applied to investigating corrosion behavior and fracture morphology.The results showed that under open circuit,stress corrosion cracking(SCC)of AA7003 might by classified as anodic dissolution.In this case,the extent of SCC susceptibility(ISCC)of AA7003 alloy with different aging treatments was as follows:ISCC(PA)>ISCC(DPA)>ISCC(RRA).On the other hand,stress corrosion cracking(SCC)of AA7003 under cathodic polarization might be classified as hydrogen embrittlement(HE)which had been proved in this paper by presence of AlH3 diffraction peak in XRD patterns.In this case,for AA7003 with any of the three aging treatments,hydrogen embrittlement susceptibility(IHE)increases with negatively shifting of cathodic polarization.

Application of Acoustic Emission to the Study on Cathodic Polarization and SCC for High Strength Steels

The ambiguous effect of cathodic polarization on SCC of two high strength steels in 0.1 M Na_2HPO_4 and 0.1 M NaNO_3 has been investigated by means of meas- uring electric resistance(R)and recording acoustic emis- sion(AE)signals simultaneously.Results showed that AE sensitivity strongly depends on K value in different solu- tions.Both anodic and cathodic polarization can acceler- ate crack growth rate at high K values,but it appears that there are only subtle differences in their AE characteristics.AE signals only reflect the macroprocesses of crack growth rather than the elementary ones and can not be used for identification of the micro-mechanisms of SCC.

In situ investigation of atmospheric corrosion behavior of PCB-ENIG under adsorbed thin electrolyte layer

The effects of relative humidity (RH) on a printed circuit board finished with electroless nickel immersion gold (PCB-ENIG) under an adsorbed thin electrolyte layer (ATEL) were investigated in situ via the measurement of cathodic polarization curves, electrochemical impedance spectroscopy, scanning electron microscopy, energy-dispersive X-ray spectroscopy, and X-ray photoelectron spectroscopy to clearly elaborate the corrosion behavior of PCB-ENIG in the atmospheric environment. Results indicated that the cathodic process of PCB-ENIG under ATEL was dominated by the reduction of dissolved oxygen, corrosion products, and H2O. The cathodic current density of PCB-ENIG increased progressively with increasing RH. Moreover, its cathodic current density in the solution was greater than that under ATEL. This result demonstrated that the diffusion process was not the controlling step during the limiting reduction of cathodic oxygen. When the polarization potentials were located in a more negative region, the cathodic polarization current density gradually decreased under 75% and 85% RH. Notably, the anodic process became the controlling step in the extremely thin liquid film during the remainder of the experiment.

Eleciroreduction of Oxygen on Pyrolytk Graphite Electrode with Adsorbed Layer of Cobalt Tetra.sulfonaied Phthalocyaninc In Acetonitrile and Dimethylformamide

The catjpdoc polarization characteristics indicate that the presence of a pre-adsorbed surface layer of CoTSPc innibits the reduction of O2 to O2- on an ordinary pyroiytic graphite electrode (OPG) in AN and DMF solution of 0. 1 mol/L, TEAP, The transfer coefficient a and the heterogeneous rate constant k for this reaction or, OPG with and without pre-adsorbed CoTSPc obtained by rotating disk electrode method were found to be fairly close to thar obtained by cyclic voltammetry. The a remains almost the same, bat the k de creases by a factor of 2-5 with CoTSPc as compared with OPG alone. The possible reason is that the adsorbed CoTSPc as an anion renders the effective potential diffaence less negative, which thus lowers the rase of O2 reduction.

Effects of additives on nickel electrowinning from sulfate system

In order to eliminate the pitting and improve the surface morphology of cathode nickel,the influence of additives of boric acid and dodecyl sodium sulfate(SDS)on the process of nickel electrowinning from sulfate system was studied by cathode polarization tests and nickel electrodeposition experiments.The experimental results show that the addition of boric acid can increase the cathode polarization while SDS can decrease the cathode polarization.Both boric acid and SDS are useful to eliminate the pitting on nickel deposits and improve the morphology of surface.Good deposit morphology with rare pitting and high current efficiency is favored by adding 10 g/L boric acid and 40 mg/L SDS in the electrolyte under the condition of nickel ion concentration of 80 g/L, sodium ion concentration of 10 g/L,pH of 3,current density of 220 A/m 2 and temperature of 70℃.

Study on Electrochemical Characteristics of Electroless Co-Ni-B Alloy with Cerium

The effects of rare earth element cerium on composition and electrochemical characteristics of electroless Co-Ni-B alloy were studied in this paper. The alloy component was analyzed using Inductively Coupled Plasma (ICP) . The plating rate is was determined by electronic balance. The cathode polarization curves and cyclic voltammogram during the electroless deposition were tested by LK998 Ⅱ model electrochemical analytical system. The results show that rare earth element Ce can co-deposit with cobalt-based alloy, and with mass increase of Ce added in aqueous solution, the contents of Co, Ni, Ce in alloy increase and the content of B decreases. Ce can increase deposition rate of alloy in some range. The rare earth makes deposition potential move to positive direction and makes polarizability decrease.

Behavior of arsenic in zinc electrowinning

The effects of arsenic on the cathode polarization process in zinc electrowinning,its kinetics equation,parameters and polarization mechanism were studied by multiple electrochemistry approaches.The experimental results show that,if[As 3+]≥3 mg/L,electrowinning first enters into stationary passivation range,and then enters into precipitation range,which indicates that the depolarization function of impurity arsenic is zinc electrowinning.

Corrosion behavior of pure zinc and its alloy under thin electrolyte layer

The corrosion behavior of zinc and its alloy under thin electrolyte layers （TEL） in 0.1M NaC1 solution was investigated by cathodic polarization curves and EIS. There was only one phase in pure zinc while zinc alloy consisted of eutectic phase and primary phase. Corrosion rate of zinc alloy was faster than that of pure zinc due to the effect of the micro-galvanic couples between the primary phase and the eutectic phase. The results indicated that corrosion rate of zinc alloy was greatly enhanced under TEL than that in bulk solution. Pure zinc exhibited minimum corrosion resistance as TEL decreased to 198 #m. Zinc and its alloy exhibited localized corrosion under TEL while it was more uniform in bulk solution. There were two capacitive loops in high frequency （HF） and middle frequency （MF） respectively, with finite length diffusion in low frequency （LF） presented in EIS. For pure zinc under TEL below 300 pm an additional inductive loop presented in MF-LF. The corrosion products and morphology were respectively examined by X-ray diffraction （XRD）, FTIR （Fourier Transform Infra Red） and SEM-EDS. FTIR micro spectroscopy results indicated that the component of the corrosion products was similar at different section of the specimen surface but different in content.

Effect of denitrifying bacteria on the electrochemical reaction of activated carbon fiber in electrochemical biofilm system

An electrochemical-activated denitrifying bio-film system consisting of activated carbon fiber electrodes immobilized with denitrifying bacteria film as cathode was studied.A revised model for an electrochemical-activated denitrifying biofilm was developed and validated by electro-chemical analysis of cathodal polarization curves and nitrate consumption rate.The cathodal polarization curve and nitrate consumption rate were introduced to verify the rate of electrochemical reaction and the activity of denitrifying bacteria,respectively.It was shown that the denitrification process effectively strengthened the electrochemical reaction while the electron also intensified denitrification activity.Electron was transferred between electrochemical process and biological process not only by hydrogen molecule but also by new produced active hydrogen atom.Additionally,a parameter of apparent exchange current density was deprived from the cathodal polarization curve with high overpotential,and a new bio-effect current density was defined through statistical analysis,which was linearly dependent to the activity of denitrification bacteria.Activated carbon fiber(ACF)electrode was also found to be more suitable to the electrochemical denitrifying system compared with graphite and platinum.