Radiotracer technique was used to study the dezincifieation behaviour of 70/30 brass subjected to stress corrosion cracking (SCC) in 1M NaNO_2, at —0.1V (SCE) under dynamic slow strain-test condition. The results showed that localized anodic dissolution is the essential cause of SCC, while considerable dezincification enhanced the suseptibility to cracking. The maximum dezincification coefficient was obtained during the stage of steady crack propagation before the stress reached the ultimate tensile level (σ_(uts)). After that, the relative increase of dissolved copper gave rise to correspondingly lower dezincification coefficient. The strain rate at the crack tip for the maximum dezincification coefficient was approximately 4 times as high as initially applied strain rate. Calculation based on a volume diffusion model for preferential dissolution indicated that zinc diffusion coefficient in the SCC processes could reach more that 10~(-11)cm~2/s. Finally, the mechanism of dezincification related to the SCC of brass in nitrate solution is discussed.

The effects of various inhibitors on SCC of AISI 321 stainless steel in 0. 5 mol/L HCl+0.5mol/L NaCl solution at 55℃ was investigated by Slow Strain Rate Technique. Typical transgranular SCC which was promoted by anodic polarization was observed in the blank solution. The surface of the steel was in active corrosion state. Three groups of inhibitors were investigated:S, N-containing compounds, primary amines and tetra-amine salts. For the purpose of examining the role of iodide ion, the effect of KI was also investigated. It was found that iodide salts and 2-mercaptobenzothiazole could effectively prevent the test system from SCC. A technique was developed to estimate the effects of inhibitors on anodic and cathodic processes of corrosion in acid solutions quantitatively from electrochimical measurements. By this technique, it was found that those inhibitors which reduced the rate of anodic dissolution of the steel for more than two orders of magnitude could effectively prevent the steel from SCC in the test condition.

High temperature corrosion behavior of Fe-20Cr-5Al and Fe-20Cr-5Al-0.5Y alloys in pure SO_2 atmosphere at 1200℃ was studied. The corrosion kinetics of these alloys was measured. X-ray diffraction was employed to identify the components in corrosion products. The morphologies of corrosion product surfaces, cross sections and fractures were examined by means of SEM, and the element distribution in corrosion product scales was also analyzed. The experimental results show that the alloys underwent pure oxidation without sulfidation observed in the experimental condition during the period of time of 300 hours. A duplex oxide scale was developed on the surface of the yttrium-free alloy while a single layer oxide scale was produced for the yttrium-containing alloy. The adhesion of the oxide scale was found to be remarkably improved by the addition of yttrium in the alloy. The beneficial effect of yttrium is discussed and attributed to the effective blocking of the bulk diffusion of Al~(3+)in the Al_2O_3 scale in the presence of yttrium.

The influence of halide ions on anodic process of iron in alkaline solutions has been studied by electrochemical techniques. The results show that the breakdown potential of passivated film on iron in halide containing solution becomes more positive in the following order Cl~-→Br~-→I~-. The obvious inhibition effect of F~- ion on pitting of iron causedby Cl~- ion was observed. This effect could be explained by the formation of stable, insol uble complex FeF_3.

The effects of strain rate and polarization potential on the sensitivity of SCC of aluminium alloy LC4 were investigated with slow strain rate tensile tests. The fracture area through SCC(A_(SCC)), the maximum tensile strength under SCC(σ_(SCC)) and the corresponding elongation (ε_(SCC)) were used as parameters for evaluating the sensitivity of SCC. The results indicated that the sensitivity of SCC increased with the decrease of strain rate, and A_(SCC) was more sensitive than σ_(SCC). Anodic polarization reduced A_(SCC); weak cathodic polarization increased σ_(SCC) slightly, and strong cathodic polarization decreased σ_(SCC). It showed that both mechanisms of hydrogen embrittlement and anodic dissolution were operative in this system. The fractographs were similar for the specimens fractured under the conditions of open circuit, cathodic polarization or after hydrogen charging, but quite different for those under anodie polarization. It showed that hydrogen embrittlement played a predominant role for this system under the comdition of open circuit.

A systematic study on the intergranular corrosion behaviour of 2Cr13Mn9Ni4 metastable Austenitic stainless steel in H_2SO_4-CuSO_4 solution has been made. The kinetics curve of intergranular corrosion at various sensitizing temperatures was determined. The morphology and distribution of carbide after different combination of sensitizing treatments and cold work have been studied with optical and electron microscopy, and their effect on intergranular corrosion was discussed. Based upon the experimental findings, the intergranular corrosion resistance was found to be dependant on the degree of cold work and on sensitizing treatments.

In this paper the development and applications of a potentionstat/galvanostat with high reference electrode potential (±100V) and high cell voltage(±100V) are described. The principles and circuit diagrams of the high voltage amplifier as well as the big swing voltage follower using general puropse IC operational amplifiers are presented. The method of expanding the range of reference electrode potential for PARC potentiostat of model 173 is shown, and the testing results are given.

A new approach of impressed current cathodic protection for external tank bottom has been developed. An electronically conducting anode coating was applied on the bituminous sand base for above-ground storage tank, followed by a specially formulated CK coating, which contains the solid electrolyte sodiumβ(β″)alumina as an ionically conducting component. Graphite electrodes were embedded in the CK coating to control and/or monitor the cathode potential. The multilayer structure consisting of external tank bottom, CK coating and anode coating enables the completion of current circuit. An appropriate d.c. power source was used to provide current. Compared with conventional cathodic protection techniques, the new approach has significant advantages. Due to the close proximity of cathodically proretted urface to coating anode, the cathodic protection current would not be lost outwards. As a result, the tank to be protected is not necessarily isolated from neighbouring underground metallic structures. At the same time, it also leads to more uniform distribution of protective potential. The feasibility of the proposed technique has been verified both by small simulating tank and by practical applications. Such a cathodic protection system for an above-ground storage tank of 30-m in diameter by 15.8-m in height has already been in operation successfully for two years.

By means of constant load tests and slow strain rate tests, the influence of slurry aluminising on SCC behavior of 304 steel was investigated. The experiments were performed in boiling 42% MgCl_2 solution. Specimens of different thicknesses of aluminised layer were prepared by varying the time of aluminising. In addition, X-ray diffraction, X-ray energy spectrum, electrochemical method and fractography analysis were used to clarify the mechanisms of protection of slurry aluminising against SCC of 304 stainless steel. The results showed that the aluminised layer of 304 stainless steel consisted of duplex structure with the outer layer being principally FeAl_3 and inner layer being FeAl_3 with FeAl. The SCC susceptibility of 304 stainless steel was markedly decreased by aluminising and the extent of reduction was mainly dependent upon the ductility and thickness of aluminised layer. In accordance with experimental data, the mechanisms of protection of aluminising on SCC behavior of 304 stainless steel were suggested, the favourable influence was essentially due to environment separation and galvanic protection.

Evaluation of the protective performance of a series of coatings composed of epoxy resin and certain amount of Al powder added has been made by means of electrochemical impedance spectroscopy and corrosion potential monitoring with emphasis being laid on the influence of the content of Al powder upon the protectiveness of the organic coatings for carbon steels in 3.5%NaCl aqueous solutions. It is indicated that the introduction of appropriate amount of Al powder into the organic coatings leads to a great enhancement of the protective property of the coatings (such as their capability against water penetration) while excessive addition of Al powder is pernicious to the property of the coatings, e, g. weight content ratio of the Al powder (V_(Al))over 30% is found to be detrimental. From our experimental results, optimal weight content ratio of the Al powder is 15%.

The oxidation behavior of Ag-Cu eutectic based active brazing alloys is studied by means of TGA, DTA, sessile drop method and X-ray diffraction technique. The results show that although the oxidation resistance of Ag-Cu eutectic-5at%Ti alloy at 873K is very poor, it can be improved by the addition of Al(5at%) without loss of its excellent wettability (contact angle 15° on sialon ceramic at 1150K for 5min). The oxidation kinetics behavior of the alloy with Al addition does not follow the parabolic law. In fact, the growth of the oxide film on the alloy becomes extremely slow after oxidation for 20 hours at 873K. The beneficial effect of aluminum can be attributed to the formation of an adhesive, protecive oxide film of CuAl_2O_4 on the alloy surface. As compared with the above results, the addition of Cr, Ni or RE is not effective in the improvement of oxidation resistance of the Ag-Cu-Ti brazing alloy.

The effect of molybdate on titanium anodization processes and the essential aspect of passivity of Ti anodized in aulfuric acid is studied with spectro-electrochemical methods. The results indicate that the molybdate could enhance the corrosion resistance of Ti not only by formation of compact surface film of oxides, but also by the adsorption of molybdate inside the pores of oxides to prevent the corrosive anions approaching Ti substrate and the Ti ions of substrate passing out of the films. The ellipsometric spectroscopy is useful for studying the adsorption phenomenon accompanied with the formation of the passive films on surface.

By using tubular test loop for corrosion in high velocity seawater, the potential and corrosion rate of some typical marine carbon steel, marine low alloy steels, 18-8 stainless steel, two copper alloys and one each aluminium alloy and titanium alloy have been measured at different flow rates of seawatrer. The corrosion rate at high velocity is several times higher than that in natural condition and has different characteristics. X-ray diffraction of the rust layer on steels indicates that majority of the rust layer is γ-FeOOH and no Fe_3O_4 is detected. The dependence on galvanic current from four couples on seawater velocity has been studied. The galvanic current in flowing seawater is several to dozens of times higher than that in static condition. When steels are coupled with a noble metal, the galvanic current does not change much with velocity of seawater. When Zn-Al-Cd is used as sacrificial anode to protect iron and steel, special attention should be paid to the effect of velocity.

The intergranular and exfoliation corrosion behavior of five Al-Li alloys were inves-tigated using standard experimental methods,and compared with conventional aluminium alloy 7075. The results showed that the Al-Li alloys were better than 7075 alloy in corrosion resistance. In addition,the corrosion resistance for 8090 alloy is better than that for 2090 and 2091 alloys. The effect of metallurgical factors on corrosion susceptibility was also discussed. It was found that the intergranular and exfoliation corrosion suscepti-bility of Al-Li alloys dramatically depended on the composition, heat treatment and grain orientation of alloys.

The effects of P-content on electrochemical behavior of the cold rolled Fe-P alloys containing 0.007 wt％,0.06 wt％,0.09 wt％ phosphorus,untreated,annealed at 450℃ for recovery and at 700℃ for recrystallization respectively in vacuum have been studied by means of both potentiodynamic and potentiostatic measurements. The results show that phosphorus promotes the anodic dissolution of the iron electrode in 55％ Ca (NO_3)_2 and retards the formation of passive films of the iron. Especially, it is also found that the phos-phorus segregated to the dislocations and grain boundaries making it even more difficult for iron to form passive films after annealing for recovery and recrystallization. Segregated phosphorus at the grain boundaries is responsible for the tendency of enhanced inter-granular corrosion and the reduced localised corrosion resistance of iron.