A Strict thermodynamic definition of the critical pitting potential (φcb)has been proposed. A model of pitting initiation was developed and the equation of φcb=α-blnα_(X~-)was derived from the definiton and the model, α_(X~-) being the activity of the active anion. It is shown that φcb, α_(X~-),c and T_c (critical temperature) are correspondent to one another, Furthermore, the kinetics equation of pitting initiation was established and the equationof φb=φcb+H was obtained. The functional relations between induction time τ and α_(X~-) under various stationary applied potentials have been determined. The theory developed in the paper can explain many authors' experimental results, It is poossible for one to determine φcb practically.

A simulated occluded cell was used to study the changes within crevices or cracks of Cr18Ni9 austenitic stainless steel in Cl~-+NO_3~-(or NO_2~-)solution. It was found that in the occluded cell pH dropped more slowly than in plain Cl~- solution and approached a limiting value at about2. The ratio of migration rate of Cl~- to NO_3~- in g-eq. was approximately the same as that of the concentrations of Cl-/NO_3~- in original solution. When 1F quantity of electricity passed, about 0.5～0.7 g-eq. of Cl~-+NO_3~- migrated into the occlude cell. Migration of NO_2~- was negligible. Addition of sufficient NO_3~- or NO_2~- also caused critical potential to move in the more positive direction and the crack tip s into the passive state.

The surface structure of glass fiber treated with different silane coupling such as A151, A186, KH550, and the diffusivity of medium in epoxy/glass composite material as well as the adhesive shape of interface have been studied by means of SEM, Single Filament Test, XPS and Specific resistance. The results show that interface with covalent bond reacted with-SiOH both on the surface of glass and in the epoxy matrix is better than that without covalent bond. This type of covalent bond interface had: a) stronger interface adhesion; b) a good shape of interface adhesion; c) lower diffusivity of medium in composite materials; and d) good corrosion-resistant properties of interface.

The effect of the solution temperature and concentration within pits on pitting growth rate of 18-8 austenitic stainless steel has been studied quantitatively under uniform corrosion condition. The practical polarzation curves (PPC) of the sample was measured in the simulated solutions within the pits. The ideal polarization curves and corrosion current densities were obtained by extrapolating the Tafe's lines of the PPC to corrosion potentials. The requirements for repassivation of pitting nuclei were discussed in detail. According to the experimental results, the authors attempted an initial approach to a method for measuring the practical rate of pitting growth.

By using the potentiostatic etching method, the behavior of non-sensitized intergranular corrosion (IGC) for as-received 316L stainless steel (SS) at different potential regions were studied in autoclave containing urea solution. The propagation of non-sensitized IGC and the relation of IGC to potential values were investigated in sulfuric acid at ambient temperature. It is found that only general corrosion occurs for as-received 316L SS both in the active potential region and in the active-passive transition potential region, but both general corrosion and IGC occur simultaneously in the transpassive potential region. With potentiostatic etching in the transpassive region, IGC is deepened and broadened with increased etching electric quantities (with etching time), and the cross section of corroded specimen is in "V" shape. Under the condition of potentiostatic etching with equal electric quantities in the transpassive region, the nobler the etching potential, the greater will be the IGC rate (V_(IGC)) and the total corrosion rate(V_t), the less will be the ratio of IGC rate to total corrosion rate (V_(IGC)/V_t). The non-sensitized IGC of austenitic SS may be lightened by using high purity SS.

To determine the suitability of inhibitors containing WO_4~(2-), many tests based on orthogonal design methods are studied using polarization and weight-loss technique. Optimum results show that inhibitors containing WO_4~(2-) are suitable under various conditions. By adding inhibitors, the corrosion rate of mild steel is below 0.1 mpy in the presence of high concentration of Cl and SO_4~(2-) ions (Cl~-+SO_4~(2-)=5, 000ppm). BASIC programs on IBM PC are designed. The integral average value of polarization resistance is calculated using the programs. Scanning potentiodynamic technique describes corrosion on mild steel and inhibitors' behavior in Cl~- and SO_4~(2-) environment. The film on iron exposed to inhibitors have been studied using XPS and Ar~+ ion sputtering. Correlation are found between protective quality and film composition.

Stress corrosion cracking of high strength forged aluminium alloy LD10, containing 4.4％ Cu, 0.6％ Mg and 0.8％ Si, has been studied. It is found that the response of SCC resistance and strength to heat treatment of Al-Cu-Mg-Si alloy is different from that of Al-Zn-Mg-Cu alloy in some aspects. For Al-Zn-Mg-Cu alloys, a two-step aging improves the resistance against SCC, but always with decreased tensile strength. On the other hand, after two-step aging (1600℃×8h+190℃×2h) Al-Cu-Mg-Si alloy can reach a high resistance against SCC (K_(1SCC) is large than 17 MPam~(1/2) SCC growth rate is about 10~(-10)m/see) and a high tensile strength.Attention is fucused on the microstructure at grain boundaries because of the intergranular fracture characteristics of SCC. It is found SCC sensitivity on LD10 alloy varies with the precipitation phases: GP zone and θ″ phase are sensitive to SCC; the continuous θ′ phase is most sensitive to SCC; while the discontinuous stable θ phase is not sensitive to SCC at all.

The electrochemical behavior within the SCC cracks of 30CrMnSi steel in 3.5％NaCl solution or in 5％K_2Cr_2O_7+0.1％NaCl solution was studied. The distribution of potential, pH value and Cl~- concentration under different polarized potentials was measured. It was found that the crack tip potential versus pH value and the potential-versus Cl~- concentration relationships are both linear. Based on the electrochemical model of microcell and multi-electrode system, the electrochemical difference between corrosion crack and crevice was explained and the correlation between electrochemical behavior within the crack and the cracking sensitivity was established.

Effect of hydrogen on anodic dissolution and passivation of 304 stainless steel has been studied in 1N H_2SO_4+0.1N HCl solution at controlled potentials. Ion concentrations of Fe, Cr and Ni dissolved in the solution are determined using plasma emission spectroscopy. Thus, the amount of net corrosion of the steel containing hydrogen is obtained. The results show that hydrogen promotes strongly anodic dissolution of 304 stainless steel in the transpassive potential region, (E=1.0V, SCE). The rate of dissolution increases with hydrogen content. The ion concentrations of Fe, Cr and Ni in fhe solution under different charging time are analyzed. The ion ratio of Fe, Cr and Ni is about 78:16:6 for uncharged specimen, while it is the same as that of the chemical composition of the steel for hydrogen charged specimen, i.e., Fe:Cr:Ni=72:19:9. This result reveals that hydrogen decreases the stability of passive film. In the passive potential region(E=0.5V), however, hydrogen has little effect on the anodic behavior. The ion ratio is 82:11:7 for both hydrogen charged and uncharged specimens. The amount of net corrosion of the specimens with hydrogen is about equal to that of the specimen without hydrogen.

The kinetics of corrosion of Ni-(0～12.5)at％Al-0.2at％ La alloy and of aluminided Ni samples in SF_6 are studied. Results show that there is a linear relationship between the weight loss and time; the loss increases with increase of temperature and a sharp accelereted corrosion exists at 850℃; the weight loss obviously decrease with increase of Al content and the aluminided Ni shows only slight corrosion.

In order to find out the causes of failure of the secondary superheater tubes in waste heat boiler in the production of sulfuric acid from sulfur, samples from an uncoated 12CrMoV tube after ten months' service, an aluminium-sprayed 12CrMoV tube and an 18-8 stainless steel tube both after one year service in the Nanjing Fertilizer Plant have been examined by metallography, EMPA, X-ray diffraction and chemical analysis. Results obtained indicate that service failure of the secondary superheater tubes was mainly caused by the corrosion of tube surface, the nature of corrosion was high temperature sulfidation and oxidation.The uncoated 12CrMoV tube suffered from severe corrosion, and the corrosion products consisted of nonprotective oxide and sulfide of iron, while the aluminium-sprayed 12CrMoV tube and the 18-8 stainless steel tube had much better performance in this corrosion environment, because of the formation of protective Al_2O_3 and Cr_2O_3 scale which appeared to prevent ingress of oxygen and sulfur to the metal.On the basis of experimental results, possible mechanisms of corrosion and methods of solving the corrosion problem are proposed.

Exploration of the causes of failure of secondary superheater tubes made of 12CrMoV in waste heat boiler has been carried out. The results show that corrosion of tube surface is responsible for the service failure of secondary superheater tubes, though erosion and superheating of tubes may be involved in the failure processes.The structure, chemical composition and morphology of corrosion products on the damaged tube were studied by means of X-ray diffraction metallography, EMPA, IR, DTA and chemical analysis. The corrosion products are mainly composed of Fe_2O_3, Fe_2 (SO_4)_3 and sulfide of iron. Therefore, it is snggested that the mechanism of corrosion is sulfidation and oxidation caused by high partial pressure of SO_3 from decomposition of Fe_2 (SO_4)_3 at elevated temperatures in the system.On the basis of experimental results, possible methods to combat corrosion are proposed.