The steady state corrosion potential of the electroplated nickel-iron alloys with different iron contents has been measuted.The potential diffe- nce curves of any two adjacent layers have also been measured by the galv- anostatic method for anodic dissolution.The corrosion resistance of various multilayer plating systems' has been examined by the EC(Electrolytic Corrosion) test as developed by Saur and Basso. Experimental results show that the corrosion resistance of the multilayer plating system of semibright Ni-10Fe/bright Ni-45Fe/bright Ni-10Fe/ Cr is better than that of Cu/semibright Ni/bright Ni/Cr.

The anodic behaviour of H68A brass in occluded condition was investigated. It is shown that in the occluded area the surface of brass remains in active state,butno autocatalytic dissolution effect can be detected.The potential of brass in occluded area becomes more noble as the concentration of Cu~+ in anolyte increases.If H~+ and Cu~+ can not diffuse outwardly from occluded area, the anodic dissolution of brass in occluded area can not take place when EE_(Cu/CuCl/Cl~-).On the other hand,if H~+ and Cu~+ can diffuse outwardly from occluded area,the anodic dissolution occurs at potential above E_(Cu/Cu_2O/H~+.The product of anodic dissolution in cavity is Cu_2O.At the same time,there are deposits formed at the mouth of the cavity by secondary reactions of Cu~+ diffused outwardly from cavity. The distribution of the corrosion products within and over the pits on brass conpenser tubes seems the latter case as mentioned above,so Cu~+ and H~+ ions must diffuse from pits toward outside in the pitting corrosion process of brass tube and hence these pits can be formed when E References | Related Articles | Metrics

The instantaneous impedance of Al in 1N NaCl at various polarization times has been measured using Laplace transformation method.In the instan of beginning of polarization,the dependence of interfacial resistance R,on polarization current densitg i_p,is as follows: logR_f=K-logi_p Interfacial capacitance Cf,which is independent of i,depends only on film's thickness.In the course of polarization,R_f hardly changes with time, but C_f changes greatly This is due to the fact that the difference between electric resistance on corroded region and that on film region is very small while there is a large difference in capacitance of both regions.

The cathodic polarization curves of various iron rusts(α-,γ-,δ,am- FeOOH;α-,γ-Fe_2O_3,and Fe_3O_4)on platinum electrode have been worked out.The reduction behavior of iron rusts and the cathodic process of steel in atmosphoric corrosion have been discussed.Different iron rusts have diff- terent reduction activities,but with almost the same characteristic poten- tial E_B.In atmospheric corrosion depending upon whether Ecorr is above or below E_B,either the oxygen reduction or the iron rust reduction may be the main cathodic process.In addition,the reduction behavior of several iron rust conversion products on platinum electrode has been investigated.

In this work,isothermal and cyclic oxidation of carbon steel(containing 0.20%wt C)with and without CeO_2 dispersion added by jet injection are investigated at 550°、600°and 650℃ in air.Test retsults show that the addition of CeO_2 dispersion reduces isothermal and cyclic oxidation rates at all three test temperatures. X-ray diffraction analysis of the scale shows that for steel containing CeO_2 dispersion,wustite(FeO) disappears after oxidation at 600℃ and 650℃, and hematite(Fe_2O_3) layer becomes thicker after oxidation at 550℃. Metallographic examination of the scale/substrate interface shows that specimens with CeO_2 dispersion posses“saw-tooth”intrface,which accounts for the better adhesion and spalling resistane of the scale.

The reaction of boiler scale with EDTA aqueous solution under elevated temperature is a complex reaction,but is an acid-base reaction as well. By controlling appropriate conditions,the pH value of the cleaning liquid may automatically rise,from weakly acidic to weakly basic state for the descaling of scale.A new technique called coordinated EDTA cleaning of boiler has been worked out which completes boiler cleaning and inactivation in one step. This technique for boiler cleaning has the following advantages: (1)the cleaning system is simple and more convenient to control, (2)there is less water consumed,(3)it shortens cleaning time, (4)pollution is minimized.

An apparatus controlled by microcomputer for measuring potential dits- tribution on metal surface immersed in an electrolyte has been established. The functions of the measurement system include scanning of microelectrode, acquiring and smoothing of experimental data and displaying of three kinds of potential distribution maps on the plotter. The apparatus has high sensitivity and clear potential distributiaon patterns and is convenient to beused.It is very useful for measuring the electrechemical inhomogenity on metal surface and for monitoring localized cor-rosion.

AES and EPMA have been used to study the passive film and the pit sidewall of Fe-Cr alloys which contain 13%,17% and 28%Cr in 3.5%NaCl solution.By Ar~+ sputtering,the Cr/Fe ratio versus the thickness of the passive film is obtained,and the behavior of Cr in the film has beeninves- tigated.Experiments and analyses show that the Cr/Fe ratio both in the surface passive film and in the pit sidewall of Fe-Cr alloys are markedly higher than that of base materials.The most important factor withregard to protective ability of the passive film is the Cr/Fe ratio in thefilm.The higher the Cr/Fe ratio,the better the protective ability of thefilm is.

Specimens of five Ni-base alloys coated by three coating techniques were tested by crucible method at 700～900℃.It was found that aluminized coating was more resistant to hot corrosion than chromized one on all of teated alloys except GH30.It seems probable that the Al_2O_3 film is more compact than the Cr_2O_3 film,the latter preferentially reacts with O~(2-) ion to form chromate, and the solubility of Cr_2O_3 in molten salt is larger than that of Al_2O_3.Experi- ments showed that the aluminized coating on GH30 was less resistant on account of a larger amount of grain boundaries in β-NiAl phase perpendicular to surface with consequently more serious internal oxidation and hot corrosion along them.