The electrochemical corrosion behavior of three intermotallic compounds,i.e.Ni3Al(B),Ni3Al(B)CrZr and Ni3Al(B)-Cr-Mg-RE,in 62 Li2CO3-38K2CO3(mol%)molten salt was studied.It was found thatthe anodic polarization curves of three Ni3Al(B) baSed alloys showed characteristiCS of active -passivetranspaseive stages, while two dual-phase Ni3Al(B)-Cr blloys exhibited an additional prepassiverange,similar to pure nickel, due to the contribution of Ni(M)phase.The potential range of passive statefor the alloys under study was-220~+240 mV(vs.Ag/AgCl).Based on the results of XRD and AES,thedissolution-oxide formation process at various potential stages was discussed respectively.

The anodic polarization curves of three intermetallic compounds,i.e.N i3 Al(B)t Ni3 Al(B)- Cr-Zr andNib Al (B)-Cr-Mg-As t in 58L iCI-42KCl (mol%)molten salt with or without"impurity" at 4 50℃ were studied.The results indicated that no Flade potential was observed and that electrochemical passivation didnot occur in the pure molten salt.However,these intermetallic compounds showed passivation behaviorand their anodic current densities were lowered in the molten salt with Li2CO3 as impurity.ObviouslyLi2CO3 was an effeCtive inhibitor in these cases. On the contrary,the anodic current densities were higherin the molten salt with metallic chides, such as MgO,ZnO or MnO2.Because of the difference in solubilityproduct of the metallic chides,in some cases the anodic polarization curves showed diffusion control or passiVation. The possible action of CO,O2 and O2-during electrochemical corrosion in LiCl-KCl moltensalt was discussed. The observed variation of the shape of polarization curves might be attributed to threepaths of Oxide formation.

Using Kelvin Probe as reference electrode, a study was made on electrochemical measurements onelectrode covered with very thin electrolyte layer. Two experimental improvements including the application of piezo-electric ceramics sheet as the actuator and the measurement of the voltage component of theA.C. signal have been adopted and resulted in satisfactory performance with high potential resolution andlow signal to noise ratio.The electrode potential measured with this device exhibits a linear corrljlation tothat measured with conventional reference electrode. This arrangement can be employed with confidencefor various steady-state electrochemical measurements of metals under thin electrolyte layer.

An electrochemical investigation on the oxygen reduction under thin electrolyte layer was made usingKelvin probe as reference electrode.It was found that as the electrolyte layer thickness decreased duringelectrolyte evaporation,the rate of oxygen reduction first increased,then stagnated and finally decreased,thus showing a maximum.Althougy oxygen salting out effect had some influence on the rate of oxygenreduction,it was not main cause responsible for the decrease in cathodic limiting current in the case ofvery thin electrolyte layer. With decreasing water layer thickness upon drying, the oxygen reduction ratewas in trun accelerated by the faster oxygen diffusion, hindered by the limited rate of oxygen dissolutionat the gas/liquid interface, and reduced due to nonuniform current distribution on electrode surface as thewater layer thickness became very thin.

High temperature chlorination behavior of Ni-20Cr alloy in a (HCl+H2) gas mixture was studied.Thermodynamic calculations predicted that there are two different regimes of stable chlorination productsdepending on gas ration of PHcl/PH2 and temperature.In the regime of lower ratio of PHcl/PH2 andhigher temperature,the only important chlorination product is volatile CrCl2(g), and in the regime of higherratio of PHcl/PH2 and loWer temperature,the condensed phase CrCl2(c)becomes thermodyllamicallystable. The chlorination kinetics study was carried out in the two different regimes by TGA measurements.A time dependent mass loss rate was observed in first experimental regime. Further analysis of tile kineticdata indicated that the chlorination rate limiting process is a linear gas phase transport in series witha parabolic process of the substrate diffosion of Cr. In the second experimental regime,the growth ofcondensed product leads to m~ gain behavior. The surfaCe of the alloy after chlorination in the firstregime showed pitting morphology. A surfaCe scale was visible for the alloy after chlorination in the secondregime. These obserVations are consistent with the expectation of the thermodynamic analysis and theresults of kinetic measurements.

Fatigue craCk.growth rates (FCGR)of tempered and normalized specimen of high strength steel38MnCrNiMo exposed to air,distilled water and 3.5%NaCl solution were evaluated. The effects of appliedpolarization potentials on FCGR in 3.5%NaCl solution were examined. The corrosion fatigUe fracturesurfaCe features and metallographic microstructure were also observed. The results indicated that thefatigue crack growth for the steel was controlled by hydrogen embrittlement(HE)and the FCGR oftempered specimens was lower than that of normalized specimens in air,distilled water and 3.5% NaCI' solution. The HE sensitivity of fatigue crack growth for the sted in corrosive environments was aLsodiscussed.

The exfoliation behaviour of LY12 alloy in the EXCO solution was studied by metallography and electrical resistance methods.The main experimental results are as follows. During the exfoliation development,pitting occurred at first,then followed by intergranular corrosion.Exfoliation took place as a result of the combination of corrosion and tensile stress.A logarithmic relationship between corrosion depth and immersion duration was observed. However,the first and the second steps have different slopes.The peak aged LY12 alloy was found more susceptible to exfoliation than the naturally aged alloy.

The effect of iron as alloying element on the crevice corrosion resistance of titanium was studied using immersion test,electrochemical measurement, SEM and EPMA techniques.The results indicated that the addition of iron into titanium decreased repassivation potential for crevice corrosion (ER), reduced the incubation time of crevice corrosion and increased the crevice corrosion rate. The potentiostatic tests showed that ER is in accordance with critical potential of crevice corrosion.The EPMA analysis and SEM observation showed that the intermetallic compound TiFe precipitated at intergranular boundaries in titanium.Corrosion occurred preferentially st these places and penetrated along the intergranular path to the interior.TiFe induced the crevice corrosion and promoted active active dissolution inside the crevice.

The photoelectrochemical response of anodic oxide flm on nickel in pH 8.4 borax-borate buffer solution has been investigated. Experimental results show that both passive film and high valence oxide film are n-type semiconductors.The passive film is formed by direct oxidation of nickel on the surface.Its flat band potential and carrier density are -0.68V and 1.3x1020cm-3 respectively.For the high Valence oxide film, a dissolution-deposition process is proposed.During the formation, growth and breakdown of the anodic film, the corresponding changes in photocurrent are monitored. At the initial stage Cl-penetrates into the film, which results in a sudden change in its electronic character and then photocurrent increases remarkably.

Hot corrosion behavior of singlecrystal superalloy DD3 in air at 900℃ was studied using specimens coated with po(wt.)Na2SO4+10(wt.%)NaCl.The kinetic processes consisted of three stages.The basic fluxing of metal/oxide predominated in stage Ⅰ.Stage Ⅱ was a transitional process form basic fluxing to acidic fluxing.The presence of W and Mo oxidex at corrosion front during stage Ⅲ showed acidic fluxing reaction.Optical microscopy,electron scanning microscopy and EPMAwere employed for the micro-morphology study of hot corrosion.After corrosion test for an hour,some bubbles were observed on the surface of the superalloy.The corrosion product was in the form of loose scale thickening with time.A specimen of 3mm thickness crumbled seriously into powder after 100 hours hot corrosion. These results indicated that the hot corrosion of single-crystal supperalloy DD3 was catastrophic.

The results of research on quantum chemical study for corrosion inhibitors were reviewed.The following aspects were mainly discussed:relations between the inhibition efficiency and quantum parameters(such as HOMO energys LUMO energy,electron density et al),inhibition mechanism and electron distribution of the inhibitors.The protonation effect on the results of quantum chemistry calculation was also analysed.Finally,the quantum chemistry methods used for investigation of corrosion inhibition were outlined.

The corrosion behavior of copper and the inhibition of BTA for copper in 3% NaCl solution have been investigated by photo-electrochemical and XPS met hods. The results show that the surface film of copper in the solution is composed of Cu(I),O2-and Cl-However,CuCl has not been found as the primary component in the surfaCe film.The inhibition of BTA could be attributed to the formation of a protective and adsorptive film on Cu2O.The adsorption of BTA does not change the semiconductive properties of Cu2O on copper.