A mechanism of reanodizing porous anodic films on aluminium in(NH_4)_2MoS_4 aqueous solution at various constant current densities is proposed by analysing the voltage time transients. It is suggessted that the acidity change of the solution in pores causes the change of aggressiveness of solution to the film. The change of aggressiveness, in conjuction with the action of electric field assisted dissolution, results in the thickness variation of barrier layer in different stages of reanodizing. The V-t transients reflect the change of the barrier layer thickness. A model of ion migration in pore channels is postulated.

It is proposed that a critical concentration of hydrogen ion in pores of the anodic film exists, above which the film material at pore bases dissolves during reanodizing process. A formula on the critical hydrogen ion concentration is derived, based on ion diffusion model.Good agreement is reached between the experimental results and the theoretical predictions from the formula.The improved sample preparation technique in ultramicrotomed sectioning used in this work, allowed direct observation of pore bases of thick porous films(20～30μm) in TEM. Morphological features of the microstructure of the film and the deposited loose molybdenum sulphide are described.

The effect of thiocyanate ion on the electrochemical behavior of armc6 iron in deoxygenated acidic perchlorate and sodium sulphate solutions(total ionic strength 1N) has been investigated by means of galvanostatic polarization measurements under steady-state conditions. The results of investigations show that the electrochemical behavior of iron in perchlorate solutions in the absence and presence of SCN~- is identical with that obtained in the corresponding sodium sulphate solutions. In different SCN"-concentration ranges thiocyanate ion exerts quite different influence on the electrochemical behavior of iron. At low SCN"-concentration range(C_(SCN~-≤0.05N) thiocyanate ion inhibits both iron anodic dissolution and hydrogen evolution reactions, in higher SCN~-- concentration solutions(C_(SCN~-≥0.lN) thiocyanate ion acts as an accelerator for iron anodic dissolution but impedes hydrogen evolution process on iron electrode. Kinetic models which may elucidate the experimental results are proposed.

The effect of carbon content and various amount of titanium additions, as well as heat treatment conditions, on stress corrosion cracking(SCC) susceptibility of Cr18Mo2 ferritic stainless steel in 143℃ boiling MgCl_2 solution was investigated by slow strain-rate technique. Results indicate that with the lowering of carbon content, both intergranular and pitting corrosion rates are reduced and, correspondingly, the SCC susceptibility decreases. The amount of appropriate titanium additions that gives Ti/(C+N)ratios ranging from 9.1 to 13.0 has the most inhibitory effect on SCC,Excessive addition of titanium will cause precipitation of cr phase near the grain boundaries, resulting in higher susceptibility to SCC. The intergranular corrosion rate of Crl8Mo2 steel considerably increases if the steel is heat-treated at 1100℃. Under such a condition, SCC becomes very pronounced and the fracture is decidedly intergranular. In contrast, the intergranular corrosion remarkably decreases and the pitting corrosion becomes the predominant factor responsible for the susceptibility to SCC if the heat treatment of the steel is performed at 850℃. In the latter case, transgranular cracking is observed and SCC susceptibility of the steel greatly decreases. Experimental results obtained for the effect of strain rate show that the strain rate of 9×10~(-7s~(-1) gives rise to the most susceptible cracking. The parameters including fracture time t, elongation e; and reduction in area RA can be used to properly evaluate the SCC susceptibility of this ferritic stainless steel,

The corrosion behaviour of Fe~-Cr alloys in the presence of a thin layer of Na_2SO_4-MgSO_4-CaSO_4 was studied in air in the temperature range of 700～800℃ by means of thermogravimetry and some physical analysis techniques such as X-ray diffraction, SEM, EMP, etc. It was found that the molten ternary sulfates accelerated the oxidation of the alloys. The experimental results lead to a proposition that the accelerated oxidation is related to the chromium depletion resulting from sulfidation and easier diffusion of metal ions through the sulfides formed.

The corrosion kinetics and corrosion product morphology of commercial pure iron and some Fe-Cr alloys were studied in O_2-0.1 %(SO_2 + SO_3) environment at 700～800℃ when there existed a thin layer of ternary sulfa tes, Na_2SO_4-MgSO_4-CaSO_4, on the surface of the alloys,The experimental results showed that the presence of sulfates induced hot corrosion of commercial pure iron and some Fe~-Cr alloys, and that hot corrosion in O_2-0.1%(SO_2+SO_3) was much more severe than that in air. On the basis of the experimental results, a sulfidation mechanism is proposed to explain this kind of hot corrosion.

Cr-Mo alloy films were formed by electrolysis in a patented bath at different temperatures. Corrosion rates of Cr-Mo alloy coatings in 5 % H_2SO_4 solution at 60℃ and in 10%FeCl_3.6H_2O solution at 4013 were determined. The pitting potentials of Cr-Mo alloy coatings in3%sodium chloride solution at 30℃ were determined,Internal stress,micro-hardness and wear resistance of Cr-Mo alloy coatings were tested. Results show that excellent corrosion and wear resistant coatings were formed by electrolysis in the bath temperature of 30℃. This has something to do with the higher content of Mo or less internal stresses in Cr-Mo alloy coatings at the bath temperature of 30℃.

Based on the stability conditions of steady state and the characteristics of linear systems, the equations of fardaic admittance measured under potentiostatic condition can be derived and the equivalent circuits of faradaic impedance can be discussed for irreversible electrode reactions where the diffusion effect can be ignored. The possible equivalent circuits for faradaic processes with one and two state variables besides electrode potential are discussed.

The isothermal oxidation behaviour of Ni_3Al-0.lB alloy containing Zr or Cr additions has been studied over a temperature range of 850-1150℃ and for periods up to 100 h. The structure of scale and phase transformation of the surface zone beneath the scale have been investigated by X-ray diffraction, scanning electron microscopy and electron microprobe analyzer ete. The results show that isothermal oxidation kinetics of the alloys at variour temperatures all obey the parabolic law. The additions of Zr, Cr or Cr + Zr obviously improye oxidation resistance at 850 to 950℃ and worsen it at 1050 to 1150℃. The addition of Zr leads to the formation of adherent scale at all temperatures, since the internal oxides are developed like "tree roots'' between the oxide scale and the substrate. But, Zr clearly increases the diffusion of oxygen along A1_2O_3 grain boundaries at elevated temperature. The oxidation scale is generally made of NiO, NiAl_2O_4 and A1_2O_2, There is a little Cr_2O_3 in Cr containing alloy.

Corrosion behavior of vapour plated titanium(VP-Ti), ion plated titanium(IP-Ti), titanium nitride(TiN), and yttrium-modified titanium nitride [Ti(Y) N] films has been studied in the corrosive media which contained 0.0N.0.1N, or 0.5N Cl-respectively. IP-Ti film exhibits better corrosion resistance than VP-Ti film, due probably to negative bias that enables the IP-Ti film to be more compact and more uniform, Pole figures of TiN and Ti(Y) N films show that there is a strong texture of TiN(110) for TiN film, and TiN(112) Tor Ti(Y)N film. The latter crystal plane is closer to TiN(1ll) with the highest degree of microcompactness, that may be responsible for the better corrosion resistance observed.

The potential of atmospheric corrosion cell(Fe/Cu) wetted by artificial acid rain in pH range of 4 — 7 at dif f erent conccntrabions, was mas measured in different relative humidity range of 30～90%. Atmospheric corrosion occurred at lower relative humidity with decrease in pH and increase in concentration of acid rain. The data obtained in this work also indicated that concentration of acid rain has more significant influence than pH of acid rain on atmospheric corrosion.