The influence of the electrode potential on the corrosion behavior of a series of nickel base superalloys has been studied in a 90(mol.%)Na_2SO_4-10 (mol.%) K_2SO_4 melt at 900 C. Acidic fluxing occurs at positive potentials and basic fluxing at negative potentials. A protective scale is formed in aa intermediate (neutral) potential range on high chromium containing alloys such as IN738LC, IN939, IN597 and IN657. The breakthrough potentials for acidic and basic fluxing are dependent on the composition of the alloys. Alloys with low chromium contents such as IN100 and IN713LC do not form stable protective scale at any potential. Numerous sulfide phases have been identified in the scales and subscales, depending on the potential. the severity of the attack and the materials composition. NaCrS_2 only forms under basic conditions. Its presence can therefore be considered as an indication that basic fluxing conditions have been existent.

The A. C. impedance characteristics of iron electrode under anodic polarization controlled potential in neutral Na_2SO_4 solution and in H_2SO_4/Na_2SO_4 solutions of various pH at corrosion potential were investigated. In solutions with pH value higher than 3.5, interfacial capacitance of the iron electrode increases rapidly to 10~3μf·cm~~(-2) order. In neutral Na_2SO_4 solution, it has been shown that the interfacial capacitance is due to Fe(OH)_2 product covered on the iron electrode. Through the analysis of impedance characteristics in higher and lower frequencies of the iron electrode polarized under anodic polarization controlled potential, the equivalent circuit of the iron electrode nder anodic polarization were established, The polarized current density calculated with the A. C. impedance measurement is in agreement with the stationary current density measured in the same condition. Therefore the A. C. impedance measurement is quite suitable for polarized ellectrode.

No matter what kind of localized corrosion cell it is, there is always a potential difference between its cathode and occluded anode. There are actual ly a few components in the potential difference between the cathode and the anode in localized corrosion cell. The character of one of its important components-diffusion potential difference—is analyzed theoretically. For measuring its value, a device is designed to simulate the main structural characteristics of the cell. For the localized corrosion system of iron in 10~(-3)N NaCl solution, along with the propagation of the localized corrosion, the concentration of FeCl_2 in anolyte will increase gradually. In such a case, this diffusion potential difference is linear with the logarithm of the concentration of FeCl_2 in anolyte. At 20℃, it will increase 32mV for each ten-fold of the increase of the concentration of FeCl_2. When the anolyte changes to saturated solution in FeCl_2, it equals 125±2 mV. The results measured experimentally are well coincided with the values calculated theoretically based on the Planck-Henderson's equation. The results prove that, this diffusion potential difference is a nonequilibrium potential difference caused by the difference of the ionic mobilities or the difference of the diffusion coefficients of all ions of both the occluded anolyte and the bulk solution. For Cl~- containing solution, it does not equal the potential difference between two equilibrium electrodes reversible to Cl~- in the anolyte and in the bulk solution respectively.

The components of the potential difference between two SCEs dipped respectively into the bulk solution and the occluded anolyte, and those between the cathode and the anode in localized corrosion cell have been analyzed. A group of quantitative relationships among them are deduced. Then they are verified experimentally by a simulating cell of iron in 10~(-3)N NaCl solution at room temperature. The resuits Show that, the first potential difference mentioned above are mainly composed of the ohmic drop and the diffusion potential difference between the bulk solution and the anolyte in the cell. Once the steady diffusion region between two solutions sets up, the value of the diffusion potential, difference would tend to a constant, while the ohmic drop changes with the electrode potential of the cathode. The final stable value will not change with the internal resistance of the corrosion cell. But for the latter potential difference mentioned above, it also contains third component, i. e., the difference of the electrode potentials between cathode and anode vs. SCEs. On the basis of the results and the polarization measurements, the relationships between the electrode potentials of occluded anode, corresponding to its zero current potential, passivation potential or immunity potential, and the electrode potentials of local cathode could be quantitatively established.

Hydrogen induced delayed cracking of charged smooth torsional specimens was observed on the planes inclined at an angle of 45° (clockwise twisting) or-45°(counter-clockwise twisting)to the torsional axis, after a large enough torque had been sustained for a long time. Calculation shows that if the strain field of an interstitial hydrogen atom in α-Fe has tetragonal symmetry, the interactive energy between the strain field and the torsional stress field has a minimal value on the planes inclined at an angle of 45°. Hydrogen atoms will diffuse to and be enriched on the planes and then hydrogen induced delayed cracking can occur on the planes, when the hydrogen concentration on the planes reaches a critical value. For a charged notched or cracked torsional specimen, i. e. Type Ⅲ crack, above conclusions are also correct.

The effect of macromolecular net structure on corrosion resistance of paint against the attack of pesticide emulsion has been investigated. Many factors, such as mesh density, chain flexibility, chain polarity, sterie restriction, free-volume etc., may influence the permeability of pesticide emulsion. Suitable main and auxiliary materials are selected according to the principle of macromolecular design. A number of prescriptions of paints have been made in this manner, and experimental results show that some prescriptions can satisfactorily resist the attack of pesticide emulsion.

The corrosion behavior of mild steel in soil with various moisture and microbial condition has been investigated. The results showed that with increase in soil moisture from 6.5 to 25%, the weight loss of the steel due to corrosion as well as the soil resistivity, redox potential and count of aerobic bacteria decreased, while the count of sulfate-reducing bacteria markedly increased. When the moisture was near the saturation point, there was little change of corrosion rate, and the "critical soil moisture" for corrosion was at 18～20%. The maximum pit depths occured between 12% and 15% moisture, and the minimum at over 20%. At moisture content of 6.5～20%, corrosion was mostly localized, but over 20% general corrosion predominated, The weight loss of steel in soil with intensive activity of microbes was 40～123% higher than that in microbes inhibited soil at low moisture levels. The causes for steel corrosion under various soil moisture have been discussed.

The kineties on hot corrosion of four Ni-base superalloys, two sheets(GH-30 and GH-128 ) and two cast alloys ( M-38 and K_3 ) , were studied at900℃ by salt coat method. Results showed that hot corrosion process for the more resistant M-38 and GH-30 alloys can be divided into three stages—ineubation, extension and acceleration period, while that of the less resistant GH-128 and K_3 alloys can be divided into two stages—incubation and acceleration period. GH-128 and K_3 alloys have high Mo and W contents, so that hot corrosion is governed by acid fusion. The hot corrosion of M-38 and GH-30 alloys,on the other hand, is governed by a sulfidation—oxidation processes alonggrain boundaries. The penetration of the sheet having fine grain and homogenous composition is less serious than that of the cast alloys which are coarsegrained with a high extent of segregation. Both weight loss and depth of penetration must he employed for the evaluation of hot corrosion resistance of the latter alloys.

The authors have undertaken the analysis of defects in electrodeposited coatings of Au and Ni on Kovar lead of transistors. The corrosion behaviour of Au and Ni plated lead in 3％ NaCl solutions (aerated or not) has been studied. Results point out that under the atmospheric condition, localized corrosion of Au and Ni plated lead is caused by galvanic couple and possessesthe characteristics of occluded hole. Experimental results in fracture morphology etc. show good agreement with the failure of lead in service.