The diffusion coefficient of the liquid midia in polymer coatings has been calculated by A. C. method. The time dependance of the coating capacitance has been obtained. The change of diffusion coefficient with time and the significance of preparation technique of the coating have been discused.

Aluminium coatings are the most widely used high temperature protective coatings. A small amount of Si can be added in aluminium coatings to further improve the resistance to high temperature corrosion. At present, pack cementation, slurry coating and hot dipping are generally adopted to produce Al and Al-Si coatings. In this work, Si-containing aluminium coatings on Fe and Fe-Cr alloys are made by electrolytic codeposition of Al and Si from fused chloride bath. Smooth, adherent and dense coatings can be produced by fused salt electrolytic co-deposition of Al and Si. The coatings are uniform in thickness which can easily be controlled by the process parameters, such as temperature, time and current density. No subsquent heat treatment is needed after coating. The results of oxidation test at 1000~C and hot corrosion test(using salt-film method) at 900℃ show that Si-containing aluminium coatings have better protective properties then plain aluminium coatings.

Passive films formed on duplex stainless steel 05Cr20Ni 9Mo4Cu2Si 3N in 3. 5% NaCl solution have been studied by ellipsometry combined with AC impedance measurements. It was found that all passive films formed at open-circuit potential and at various anodic potentials(+0. 2 and+ 0. 6V, vs. Ag/AgCl) have a two layer structure, while their growth mechanisms are different. At open-circuit potential the inner absorbing film with a refractive index of ca. 2. 5 is predominantly composed of Fe_2O_3 and Cr_2O_3. At constant potentials inner layer films are adsorbed-films with a refractive index ofea. 1. 2. Under both conditions the outer layer films with arefraetive index of ca. 1. 7 are predominantly composed of FeOOH, CrOOH or Cr(OH)_3 and have amorphous structure possibly. The kinetics of both inner and outer layer film growth at constant potentials follows logarithmic law. The kinetics of the inner layer film growth at open-circuit potential is approximately logarithmic.

The difficulties encountered in Linear Polarization Resistance(LPR) measurements are discussed. A method for determining Differential Polarization Resistance(DPR) is proposed, Its principle is explained, and a DPR measuring device based on this principle is set up. By this technique, the theoretical errors arising from linearizing approximation in LPR measuring techniques will not exist, and other problems encountered in LPR measuring techniques such as how to choose measuring frequency and polarization value properly for a given corroding metallic electrode system will disappear. The effect of nonfaradaic current on results measured may be ignored by this measuring technique, so it is possible to perform the measurement rather rapidly and thus to trace the corrosion potential closely. The DPRs as measured by this technique have been compared with the theoretical PRs and LPRs obtained from polarization curves for Fe in 4 different solutions.

Stress corrosion cracking(SCC) and hydrogen induced cracking(HIC) of Type 321 stainless steel under mode Ⅱ loading were investigated with notched specimens. Experimental results showed that SCC in boiling 42% MgCl_2 solution initiated at the maximum normal stress site, i. e., at= -110° on the notch surface, rather than at the maximum shear stress site, i. e., at=80°, with orientation perpendicular to the direction of the maximum normal stress. However, HIC during dynamic charging initiated at the maximum shear stress site at higher E_Ⅱ or at the maximum normal atress site at lower K_Ⅱ. The threshold value of SCC of the Type 321 steel under mode Ⅱ loading was K_(Ⅱscc)/K_(Ⅱx)=0. 19, which was much lower than that of HIC during dynamic charging, i. e., K_(ⅡH),/K_(Ⅱx)=0. 59. The SCC fracture surface under mode Ⅱ loading different from those of HIC in morphology. These results lend support to the statement that SCC of austenitic stainless steel in boiling 42% MgCl_2 soluion is the anodic path dissolution mechanism and the maximum normal stress rather than the maximum shear stress plays a Controlling part in the SCC initiation.

The effect of chloride ion on the corrosion inhibition of iron caused by dencylamine(DA), dipentylamine(DPA) and dodecylamine(DPA) has been investigated by curve-fitting method of weak polarization data and AC impedance technique. The results are verified by atomic absorption spectrum analysis of solutions. It is indicated that chloride ion has marked synergism with organic amines on corrosion inhibition of iron in acidic solutions and that the corrosion inhibition and the synergism are influenced by both the sort of organic amies and the Cl- concentration in solutions. It is also shown that the effect of organic amines on electrochemical behaviour of iron is changed obviously by the existence of Cl- in solutions.

Corrosion rate and interface capacity of iron in acidic perchloride solutions cantaining decylamine(DA), dipentylamine(DPA) and dodecylamine(DDA) with or without chloride ion have been measured by curve-fitting method of weak polarization data and AC impedance technique. The degree of coverage of organic amines on Fe surface has been calculated as a function of bulk concentration of amines. It has been found that organic amines are adsorbed from the solutions both with and without Cl- on the Fe surface according to Temkin isotherm and Frumkin isotherm in two different regions. The effect of adsorbed organic amine molecules on the interface capacity between electrode and solution is discussed, and a model for discribing the adsorption of organic amine molecules from acidic solutions on the Fe surface is proposed, with which the experimental results of the inhibition of organic amines and the synergistic effect of Cl- ion with them are interpreted.

Potentiodynamic sweep and electrochemical desorption under potentiostatic oxidation are used to investigate the hydrogen in steel. Samples of 08F and mild carbon steel were galvanostaically H-charged for various times with the H-chargingpotential, φ_H, measured. The amount of H-desorbed electrochemically for both steels mentioned above and for 1 Crl8Ni9Ti stainless steel was determined in various H-charging media with different conditions of desorption. Some relationship between cathodic H-entering and anodic H-desorbing, as well as that between the H-ingress and the H-egress can be found.

The method of Second Peak(SP method) of current density on the anodic polarization curves was used to detect the susceptibility of austenitic stainless steels to intergranular corrosion(IGC). The results well agree with surface micromophorogy of specimens after the test and also with the results of Strauss test, but the SP method is fast, accurate and more sensitive. The formation of second pcak of current density on the anodic polarization curvts was discussed.

In the present paper thpe Characteristic of the feature of the rast layer the phase composition and the distribution of the corrosion products were reported by analysis with x-ray diffraction method. The concentration for some alloying elements, fractrographic characteristics, and the behaviour of the electrochemical corrosion of some steels immersed in the sea for 1 to 2. 5 years have been investigated.