In virtually all countries through-out the world, stably operating electronic equipment is an important issue from the standpoint of global business strategy. Situations appear to be increasing to use electronic equipment composed of sensitive electronic components with limited margin for corrosion damage in severe climatic conditions such as tropical industrializing countries. One way to ensure the stable operation is to detect symptoms of corrosion damage and then take anti-corrosion countermeasures. We describe the techniques for measuring and diagnosing the corrocivity in environments where electronic equipment is installed and techniques for implementing and evaluating appropriate countermeasure. The information with integrated measurement, diagnosis, countermeasure and evaluation techniques can help cut the costs associated with the corrosion damage of electronic equipment and operate the electronic equipment stably. We can deploy these techniques for quickly assessing the corrosivity in specific environments by utilizing it for corrosion assessments in industrializing countries.
The corrosion potential of copper electrodes increased to 220mV (SSE) and green rusts were produced on them in some hot water tanks in which DO concentration had been kept less than 0.5mg/L by the oxygen decreasing treatment. It was estimated that the cause of the potential increasing might be induced by microorganism because of finding the potential reduction by dosing the biocide in the hot water. After examining the corrosion potential decreasing methods for copper electrodes to inhibit pitting corrosion, the potential of the green rusted copper electrode was decreased by the reduction of the green rust with the hydrazine series water treatment chemicals and the reduced copper electrode showed immunity to the potential increasing after that. The copper potential decreasing was also observed by injecting the chemicals in the hot water.
In order to clarify the applicable conditions as a pipe, in which 80℃ hot water flows, the corrosion resistance of length 500mm or less SUS316L stainless steel flexible pipe with copper alloy joint was evaluated under the conditions simulating an actual environment. The steady corrosion potential Esp was measured during 12 months in the water flow tests keeping a constant value on temperature, residual chlorine concentration, chloride ion concentration and pH. In addition, the localized corrosion potential Vc was measured by a constant potential polarization test. As a result of these tests, localized corrosion did not be found in SUS316L flexible pipe with copper alloy joint under the condition of temperature 80℃, pH7, residual chlorine concentration 1ppm (target value of water quality management in a water treatment plant), chloride ion concentration 200ppm(standard value of water quality management in a water treatment plant).
Noble metals in waste liquid discharged from metal plating process are landfilled as sludge formed by neutralization precipitation. In order to utilize the resource, we have attempted to recover nickel from waste liquid by electrolysis. The efficiency of nickel recovery impair with decreasing of pH in electrolysis due to the use of insoluble anode. To keep pH of electrolyte, we introduced an anion exchange membrane into recovering device. As a result, we confirmed to recover 98% of nickel from waste liquid.
The objective of this study was to clarify effect of Ni on pit depth of 21Cr ferritic stainless steel under the atmospheric environment. The atmospheric exposure test was conducted for 1, 3, 6, 12 and 18 months. After the atmospheric exposure, the depth of each pit was measured by a laser microscope. As a result, the estimated maximum pit depth became shallower by 1.5 mass% Ni addition. The pitting potential measurement test, the anodic polarization measurement test and the corrosion potential measurement test were also conducted. Ni did not have effect on the pitting potential. Ni not only reduced active dissolution but also facilitated repassivation. These electrochemical factors made pit depth shallower.
We have investigated influence of concentrations of LiOH and Li2MoO4 on corrosion behavior of SS400 carbon steel immersed in concentrated LiBr solutions at 393 and 438 K for a short period about 0.2 ks. The corrosion behavior was evaluated by measurement of polarization curve. As a result, the following were obtained: Addition of LiOH to 65 mass% LiBr solution induced suppression of cathodic current around the corrosion potential to shift the corrosion potential lower. Further, two-step active dissolution current was found around the corrosion potential and passive current in the higher potential region. On the other hand, addition of 0.03 mass% Li2MoO4 to 65 mass% LiBr + 0.2 mass% LiOH solution induced small suppression of cathodic current around corrosion potential, and more addition of 0.06 mass% made the cathodic current slightly increase. Two-step active dissolution and passivation phenomena were found in the anodic polarization curve like those in the solution without Li2MoO4. The anodic current density was almost independent of the concentration of Li2MoO4. Corrosion rates of the steel immersed in various solutions at 393 K for the short period were almost the same as 1.5 A・m―2. In the solutions at 438 K, corrosion rate decreased with an increase in LiOH concentration and increased with an increase in Li2MoO4 concentration.
In order to accomplish the high-efficiency electric power generation for waste-to-power plant, further increase in both high-temperature and high-pressure steam conditions of the boiler superheater tube is strongly required. There is a significant problem of hot corrosion in the higher temperature and pressure boilers, in which the complicated corrosion by virtue of both molten salt caused from mainly chlorides and/or sulfates and chloride-rich gas brings about the corrosion-induced severe thickness loss for the superheater tube material. Therefore, preventing of hot corrosive damage is urgent problem to be solved. Present study was conducted to inspect the effect of the natural zeolite powder addition into the flue gas on the corrosion inhibition by means of various techniques such as the electrochemical and X-ray analyses for the characterization of deposited ash and oxide scale constituents. Natural zeolite powder was found to be so effective corrosion mitigation of deposited ash through catching up the corrosive species such as potassium and chlorine as to enhance the formation of protective Cr-rich oxide scale and therefore improve the corrosion resistance of the superheater tube material.
Corrosion monitoring using an electrical resistance (ER) technique is considered to be the most suitable method for evaluating change of corrosion rates of a steel due to change of atmospheric conditions. In this study, exposure tests of steels in Okinawa and Kawasaki confirmed that changes of a corrosion rate throughout a year can be evaluated in detail by the ER technique. Furthermore, it was indicated that the relationship between the corrosion rate and environmental factors (temperature, relative humidity, amount of airborne sea salt, etc.) could be analyzed in detail by the ER technique. The accuracy of the technique was confirmed by comparison of the corrosion losses evaluated by the ER technique with those of test specimens. Based on the results, the accuracy of the corrosion rate evaluated by the ER sensor was higher than that by the conventional ACM (Atmospheric Corrosion Monitoring) sensor. The cause of the lower accuracy of ACM sensor is thought to be that the ACM output has very low sensitivity against temperature, notwithstanding that actual corrosion rate has high sensitivity.