The effects of cathodic potential limits and cathodic period on voltammetric characteristics and surface morphology of aluminum in 2mol/L HCl solution at 25℃ were investigated by cyclic triangularwave potentiodynamic method over the potential range from 0.0 to -2.6V vs SCE and SEM analysis of aluminum surface after 200 cycles.The results showed that the magnitude of anodic pitting current decreased rapidly with cathodic potential limit going towards negative,leading to an obvious decrease in the size and density of pits on aluminum.At the same cathodic potential limit,however,the current diminished slowly with increase in the cathodic period,resulting in less change in the size, but significant increase in the density of pits.As cathodic limit became more negative than abort -2.4V vs SCE,the anodic current initially increased, reached a maximum value,and started decreasing to a megligible value,few small pits on aluminum surface were observed by SEM at higher magniication.This result suggested that cathodic potential limit was a key factor in determining anodic dissolution and surface morphology of aluminum although the cathodic time also affect anodic current to a certain extent.Also the process of hydrogen evolution during cathodic half cycle played a dual role (i.e.promotion and impediment) in anodic pitting during AC etching of aluminum.

An important factor in ac etching of aluminum foil in hydrochloric acid solution is a alkalization of the electrolyte near the cathode and precipitation of Al3+ as etch film depositing on aluminum,which influence in lare extent the morphology of etched surface.The mass transport process of hydrogen evolution on aluminum during the negative half-cycle of ac etching of aluminum in HCl solutions has been analyzed. An equation was derived to estimate the surface hydrogen ion concentration as a function of the bulk HCl concentration,curent density and frequency of the applied alternating current on the basis of diffusion equation in which diffusion and electrical migration of H+ in the electrolyte,as well as the variztions of actual hydrogen reduction current density with the surface morphology of aluminum were considered.The analysis showd that the formation of etch film occurs if the actual ratio of concentration of hydrochloric acid to the applied cathodic current density is lower than or equal to the corresponding critical ratio calculated by the inequality, where Co is the bulk HCl concentration in mol?L, i appl is the average value of current density in A/cm2, and f is the frequency of alternating current in Hz.The results published in literature can be interpreted satisfactorily by using the approximate formula.Thus, the etch conditions under which etch film is to be expected could be predicted on the basis of the present results.

The erosion-corrosion behavior of BFe30-1-1 in artificial seawater with different fluid velocities has been studied using rotating cylinder apparatus.The methods adopted in the experimental study included weight-loss test,linear and cycle polarization,free corrosion potential and EIS measurements as well as SEM observaton and EDX analysis.The results showed that the constant of linear polarization for corrosion reaction of BFe30-1-1 in artificial seawater increased with the increasing fluid velocity.Furthermore,the results of both cycle polarization and EIS neasurement showed that the critical fluid velocity of film breakdown for BFe30-1-1 in seawater was about 3m/s.In the lower frequency region of EIS,the capacitive loop disapeared and the inductive loop appeared when flow velocity increased from 2m/s to 3m/s.

The effect of Cl- ion on the anodic dissolution of iron in H2SO4 solutions containing low H2S levle has been stdied by electrochemical polarization curve measurements.Meanwhile,the stable adsorption patterns of Cl- and HS- ions on iron surface were determined with CNDO/2 method.Furthermore,the total energy and binding energy of the competitive adsorption between Cl- and HS- ions under the anodic potential as well as the net charge distribution of iron atoms were calculated.The results showed that certain concentration of Cl- ion could adsorb steadily in the anodic regions of electrode surface,reduce the interfacial concentration of HS- ion,and thereby inhibit the anodic reaction of iron.However,when Cl- ions reached saturated adsorption,the reaction courses changed into iron dissoltion promoted by Fe(Cl-)ads.The critical concentration of Cl- ion for the action transition was 1 mol/L

The inhibition of propargyl alcohol (PA) on iron corrosion in H2S-containing sulfuric acid solutions has been studied using electrochemical potentiodynamic polarization method and impedance measurements.The results showed that PA could greatly retard the corrosion of iron in sulfuric acid containing H2S, which was attributed mainly to the inhibition effect of PA on the anodic dissolution reaction of iron.It wa also found that PA performed its function effectively when the temperature of solution wa between 30℃ to 65℃.However,the ingibition effect of PA decreased enormously ofr the temperature higher than 65℃.In addition,a polymer film of PA could gradually form on iron surface,and its protective ability was related with the surface state of corroded iron.H2S could influence the polymerization of PA and damage the comeatibility and integrity of the polymer.

Results from 12 year atmospheric exposure of 5 types of stainless steel at 7 sites in China were summarized.The exposed steels were selected from commonly used stainless steels.The test sites represented typical encironments such as temperate and subtropical,industrial and marine and rural,humid and hot.Stainless steels under study were corrosion resistant in atmosphere,When Cr content was over 18%,their corrosion behavior became excellent.Mo could raise corrosion resistance.Even in humid and hot marine environment of high corrosivity,the steel with extra low carbon and some molybdenum did not corrode after 12 year exposure.Deposited dust and surface defect were the main places of origin of atmospheric corrosion for stainless steels.Among various environmental factors affecting atmospheric corrosivity,Cl- was most important.The humid and hot environment and the presence of Cl- resulted in extra high corrosion rates.Besides,SO2 had very little effect.

The effects of hydrogen on anodic process,film formation surface character and pitting-resistance of passive film on type 310 stainless steel were theoretically analyzed and experimentally studied by use of electrochemical and STM methods.The results showed that hydrogen can decrease the inner energy of the stainless steel and its corrosion potential,narrow the passivation region and increase its anodic dissolution; decrease the reactive resistance,enhance the passive current density;reduce crystallinity of the film in nanometer scale and the pitting resistance. These influences were more noticable when increasing the pre-charged hydrogen content in the steel.

By means of accelerated corrosion tests and electrochemical measurements,the influence of NaHSO3, NaCl or NaHSO3+NaCl on corrosio behavior of zinc was studied.Its corrosion products were analysed by XRD,and corrosion mechanism of zinc with emphasis on the mixed medium (NaHSO3+NaCl) was discussed.The corrosion process of zinc in Shenyang atmosphere could be simulated by intermittent fogging spraying testing with 10-1mol/L NaHSO3 +10-2 mol/L NaCl.The relationship between weight loss of zinc and test duration could be described by a formula △W=A+Bt.

A study on corrosion and cathodic protection of aluminum alloys POD919 and LD 31 used for deepsea submarine robot was carried out in 3.5% NaCl solution.The related electrochemical parameters of three series of sacrificial anodes were determined by constant current discharge method.The results showed that a zinc alloy sacrificial anode was suitable to the protection of submarine robot.Considering the compactness and complexity of the internal structure of the robot,the effects of crevice dimension on cathodic protection ere also studied.The smaller the crevice dimension,the shorter the protection distance.Based on the achieved results,a proposal concerning the design of the cathodic protection system for robot is suggested.

The martensitic stainless steels of type OCr17Ni4Cu3 are extensively used in the chemical,petroleum and medicinal industry because they possess high strength,good mechanical property,simple heat-treatment process and excelent corrosion resistance.Although inliterature it has been indicated that "stress corrosion cracking for these steels may occur in some environments', no any detailed data and research reports were available.in the present work,the burst of centrifugal drum made of OCr17Ni4Cu3mo2Nb steel was systematically investigated.The results showed that the strength design,operational process,microstructure,chemical composition and mechanical properities of the device were quite right.however,its material,OCr17Ni4Cu3Mo2Nb steel,was foud to exhibit great susceptibility to SCC in 0.5mol/L NaCl+2.5mol/L H2SO4 solution at room temperature.The threshold stress intensity,K ISCC, was only 14MPam1/2 and the threshold stress,σth,was not higher than 150NPa,being 12percentage of its strength.Accordong to the fractography,experimental and calculated results,it was confirmed that the burst of the centrifugal drum was caused by environmental sensitive fracture.When the martensitic stainless steels were used their environmental fracture behavior should be considered carefully and the allowable load should not exceed the σth or K ISCC.