A short historical review was given of the important pieces of research on cavitation, which was followed by the describing in orderly sequence how a method to predict quantitatively the extent of damage caused to ductile metallic materials by cavitation attack was established. The useful effect of the methodology on cavitation research was also given.
Biological activity has a major influence on corrosion, scaling and fouling in cooling water system. Recently, this area is getting more attention within the industry. This article will review the characteristics on the typical microbio organizms, the possible mechanisms of biological corrosion, treatment program for biological control and environmental solution.
The chemical state of the tungsten (W) in the rust of low alloy steel was analyzed by EPMA and XPS, and the electrochemical behavior of rust was investigated by alternating current (AC) impedance method after wet/dry cyclic corrosion test with chlorides. The 1.0mass%W-bearing steel showed higher corrosion resistance than carbon steel in the corrosion test. EPMA and XPS showed that the tungsten existed as WO4 compounds in the rust of W-bearing steel. A Fe-W binary potential-pH diagram was made to investigate the thermodynamic stability of Fe-W oxides, and this showed that WO4 was stable in the rust, which confirmed the physical analysis. An AC impedance measurement was made to obtain the corrosion reaction resistance (Rt) of the rust, and it was found that Rt of W-bearing steel was much larger than that of carbon steel. The corrosion of the W-bearing steel is suppressed by (1) the insoluble FeWO4 formed near the base metal suppressing the anodic reaction, (2) the WO42- ions in the rust changing the selective permeability to prevent the transport of Cl- ions.
A new method has been proposed for evaluation of repassivation behavior of pits formed on stainless steel. The conventional cyclic polarization technique is less effective for detailed examination of repassivation because of difficulty of controlling the extent of growth of pits in spite of the fact that repassivation potential varies with the depth of pits. According to the new method, a specimen is exposed in the iron (III) chloride solution for predetermined duration to cause pits with desired maximum depth and then subjected to potential control. After the designed control of potential, the specimen was released for open circuit condition to follow the potential. The potential response well reflected if pits repassivated during the potential-controlled period. This method is effective for the detailed study of repassivation behavior of pits since it enables determination of repassivation condition as a function of potential, time and pit depth. This technique was applied to study the effect of agitation of a solution or ultrasonic irradiation on the repassivation behavior of pits. The result showed that repassivation kinetic of pits was not influenced by such physical stimulation.