The langmuir-blodgett (LB) technique was used to investigate the inhibition of both stearic acid (SA) and hexadecyltrimethyl ammonium bromide (HTAB) in neutral and acidic media. The microstructure of inhibitor-formed film might be controlled on molecular scale. The relationship between the inhibition efficiency and the orientation as weel as the layer number of the LB monolayers of these inhibitors on steel electrodes was examined by electrochemical methods. Their mechanism was discussed on the ground of experimental results and calculation. It is concluded that the mechanism of SA is mainly due to the blocking effect while that of HTAB is due to the synergistic effect of Br-with the electrostatic effect of the positively charged quaternary ammonium ion of HTAB.

The anodic polarization behaviour of type 904L austenitic stainless steel in 85Wt% H3PO4 at 140℃ was investigated using polarization curves, anodic charge curves, potential decay curves and electrochemical impedance spectra. The anodic polarization curve was characterized by four potential regions, i.e. active dissolution (-0.186～-0.12V vs SCE) reginn, active-passive transition (-0.12-0.2V)region, steady-state passive (0.2-0.9V) region and transpassive (>0.9V) region. In the active-passive transition region, the high frequency hot of impedance was a caparitive loop, and the low frequency limit was a Warburg impedance which indicated diffusion control. In steady-state passive region, the complex impedance plane was a capacitive semicircle indicating that the passinging process was controlled by the growth and dissolution of the film. In this region, the resistance of passive film reached its maximum, and the dispersion coefficient and capacitance reaChed their minima, which demonstrated that the films formed had the best corrosion resistance, the highest density, the thickest layer, and the most homogeneous surface. In the transpassive region, the diameter of high frequency capacitive semicircle sharply reduced, which corresponded to the reduction of corrosion resistance of passive film due to its transpassive dissolution; two inductive semicircles were observed at low frequency range, which indicated the adsorption of anion on the electrode surface. It could be concluded from the results of anodic charge curves and potential decay curves that the passive films formed in the steady-state passive region were homogeneous, and their stability increased with the increase of their growth potentials. The authors also discussed the parameters of anodic protection for 904L in hot concentrated phosphoric acid solution, and suggested the best protection potential range was 0.3-0.8V. The lower the temperature of H3PO4, the better the effect of anodic protection.

The influence of warm-rolling at different temperatures prior to aging on the stress corrosion cracking sareptibility of Al-Li-Cu-Mg-Zr alloy 2091 has been studied by slow strain rate tests and constant strain tests with threepoiot loading samples. The examination of microstructure of the alloy by TEM shows that warm-rolling prior tO aging reduces the amount of T2 precipitates and enhances the volume of δ' and S' phare within grains. As a result, the SCC resistance of the alloy is sipecatly improved. The alloy rorolled at 180℃ prior to aging possesses the lowest SCC susceptibility.

Electrolytic plating chromium plain film, alternately multi-layered palladium alld chromium plating film and palladium-containing chromium composite plating film on AISI 430 stainless steel were compared for the purpose of showing the effect of palladium as cathodic modification element in chromium plating film. The electrochemical behaviour of the above coatillgs was examined in comparison to 430SS substrate by voltammetry and impedance spectroscopy. At potentials corresponding to the active-passive transition for chromium film, net cathodic current was measured oil those palladium-containing platings. While chromium may stably exist in either the passive or active state, small amoullt additioll of palladium significantly increases the corrosion resistance of chromium plating in deaerated 5% and 20% sulfuric acid solutions in consequence of spontaneous passivation. The tendency is more propounced for the composite coating. The capacitive circle which appears in the low frequency range of IHz-0.01Hi on the impedance diagrams is considered as ajssociated with the passivation process.

The current fluctuations during pit initiation of two NiCrFeSiB amorphous alloy with different Cr contents in neutral NaCl solutions were investigated using slow potential scanning method. Each curreat fiuctustion gives the information of formation and repassivtion of a single metastable pit. The increase of NaCl concentration in solution resulted in increases of nucleation and growth rates of these metedable pits. The growth rate of the pity was for accelerated by increased potential. AS compared with the alloy of higher Cr content, the nucleation and growth of methetable pits for the low Cr alloy were faster,and its pitting breakdown potential Eb was more cathodic and scattered in a wider potential range. On the average, Q values, the charge quantities calculated from peaks and duration of curreat fluctuation of metastable pits were smaller for the lower Cr alloy than those for the higher Cr alloy, suggesting a sxualler critical she for a metastable pit to grow into a stable one in the former case. The life time of metastable pits followed Weibull probability distribution. The relation between nucleation of metastable pits and growth of stable pits was discussed.

Polytitanosiloxane (PTS) coating was prepared by hydrolysis-polymerizat ion synthesis from precursor sol-solutions consisting of N-[3(triethoxysilyl) propy]4,5 dihydroimidazole, Ti(OC2H5)4, methanol and water by means of twrvstep acid-base catalysis. These solutions were spreed over aluminium substrate, then the quasi-inorganic coatings of different thickness were formed by Pyrolysis-release of carbonaceous species. The following faCtors were considered as playing important roles for corrosion resistance of the coatings:1. film thickness and pyrolysis temperature:2. interface between film and substrate;3. wettability of the coatings.

An apparatus with the occluded specimen connected to the potentiostatically polarized external specimen was used to study the effects of the external potential on corrosion of the occluded cell simulating the propagating cracks or pits. A series of equations describing the relationships between corrosion rates and potentials were derived for systems of type 1Cr13 and OCr18Ni9 stainless steel in 0.5mol/L NaCl solution. Results demonstrated that cathodic polarization of the external specimen caused a reduction in corrosion rate and a decrease in potential of the occluded specimen. It was also found that both corrosion rate and potential with propagating pits or cracks maintained constant even if anodic polarization was applied to the external surface. The potential difference between pit bottoms or crack tiPS and the external surface could be attributed to a summation of a diffusion potential difference and the ohm drop of the ion migration.

Constant load and potentiostatic techniques were used to study the critical SCC potential of aluminium alloy LC4 in 0.5mol/L NaCl solution. It was found that the critical potentials for this system at 30℃, 50℃, 90℃ are -720mV, -760mV, -850mV (SCE), respectively, below which the SCC will not occur. The dependence of the critical potential upon temperature follows a linear equation: Ecri=-655-2.17t (mV). The simulated occluded corrosion cell was modified and used to investigate chemical changes within stress corrosion cracks. When an anodic currellt of 1mV/cm2 was passed through, the pH value of the occluded cell solution dropped down from 7 to 3.3 and the faCtor of Cl- enrichmeat in the solution could be up to 4. Scanning electron fractographs of SCC of alloy LC4 showed a typical intergranular cracking feature.

The expressions of critical size of a stable cleavage crack nucleus in the absence and presence of hydrogen are given respectively as follows:It could be concluded that ac(H) References | Related Articles | Metrics

A relationship between fractal value DF of fracture surface and KISCC for SCC has been astablished,The orientation dependence of KISCC can be explained, on the basis of the dependence of fracture unit df on orientation of the specimen.

Hydrogen could promote stress corrosion cracking (SCC) of a-brass in ammonia solution. For a notched specimen under constant loading, hydrogen shortened the time to SCC fracture particularly upon lower loading. Slow strain rate tensile tests showed that hydrogen reduced both the fracture stress and the time to freture.

Ni-Fe electrodeposits obtained at ambient temperature possess superior corrosion resistance. Its cause was experimentally investigated by means of electronmicroscopy and X-ray distraction analysis. The results showed that both low-iron (5～7Wt%) and high-iron (20～25wt%) alloy deposits were homogeneous nickel-base solid solutiolls. In these deposits lower internal stress, smaller grain size and (100) texture me those obtained in the Watts nickel electrodeposit were obserVed. Besides, a lamellar structure composed of iron-rich and iron-depleted zones alternately made up a galvanic corrosion system which may prevent the underneath steel substrate from corrosion.

This paper describes the chlorination of Ni-13Cr-0.5Ce alloy in Cl2-H2O gaseous mixture at 575℃.The reaction product films were examined by SEM, XRD and XPS. There were Cl2, HCI, H2O, O2 and HOCl in the gaseous environment. The corrosion products consisted of volatile chlorides, oxychloride and oxides. Addition of Ce tO Ni-Cr alloy improved the overall corrosion resistance because of the formation of stable oxides but increased the depths of internal chlorination. The reaction rate followed approximately the parabolic law until the product film reached a steady thickness after which there was a linear decrease in weight change with time. The corrosion rate of Ni-Cr-Ce alloy in the ined Cl2-H2O(g) atmosphere was greater than that in dry chlorine.

The effect of barnacle adhesion on corrosion behaviour of four metallic materials used commonly in marine engineering was studied by means of laboratory observation together with sea exposure. Results showed that the adhered barnacle lowered the general corrosion rate but promoted the locallied corrosion of carbon steel and low alloy steel. With regards to the crevice corrosion susceptible alloys, such as 1Cr18Nil9Ti and monel alloy, barnarle frequently resulted in a blooming corrosion" and crevice corrosion.On the other hand, no sign of corrosion was observed on such passive metal, as Ti, throughout barnacle adhesion.