A multi-monitoring system has been constructed to research atmospheric corrosion behavior of metal continuously and multifariously. The system consists of a microscope, a surface potential apparatus, a corrosion monitor and a chamber which can control both temperature and relative humidity. Initial corrosion behavior of carbon steel under a thin electrolyte layer has been studied using this system. As the result of monitoring of impedance and surface potential for relative humidity, the surface potential shifted to less noble and the corrosion rate increased with an increase of relative humidity. Furthermore, the change in the surface potential and corrosion rate for the average thickness of a thin electrolyte layer calculated thermodynamically has been researched. The surface potential shifted to noble with a decrease of electrolyte layer thickness, and the corrosion rate showed a maximum at a thickness of about 80 μm. Based on the results of surface potential and corrosion rate, the initial corrosion behavior of carbon steel under a thin electrolyte layer has been discussed.
We have developed a novel proton-conduction film by recasting an aqueous solution comprising an acid polymer and a base polymer. This technique is called the polyelectrolyte complex method, in which a film is generally formed by using a concentrated acidic solution, because it is hard to obtain a stable one from a neutral solution. First, poly (sodium-p-stylenesulfonate) (PSSNa) was partially changed to a proton form (PSS) by using cation exchange polymer beads prior to the blending with polyethyleneimine (PEI). By using thus-prepared neutral aqueous blend solution, it has been possible to prepare a stable polyelectrolyte complex film that demonstrates a higher ionic conductivity than that of Nafion. This report also describes ionic conductivity dependence on a SS/EI mole ratio and acid-activation processes of the film.
The surface charge of 316 L stainless steel particles treated at various temperatures under oxygen or gaseous ozone of 0.2 to 15% (vol/vol) was determined as a function of pH by potentiometric titration. The apparent points of zero charge (pzc’sapp) of ozone-treated stainless steel particles were situated at points corresponding to more acidic pH values compared with the pzc’sapp of oxygen-treated particles. The degree of the shift in the pzcapp of stainless steel particles depended on the ozone concentration and temperature. The combined ozone/heat treatment was found to induce the surface dehydroxylation of stainless steel particles. Cr6+ species were generated in the passive film on stainless steel particles through ozone oxidation. The generated Cr6+ species were readily dissolved into aqueous solution, whereas the amount of dissolved Cr6+ species decreased markedly by heating again at 200℃ under atmospheric pressure. It was demonstrated that the situation of pzcapp and the surface charge density of stainless steel particles could be controlled, to some extent, by the combined ozone/heat treatment followed by post-ozone heat treatment. Controlling the surface charge of stainless steel particles resulted in a lower affinity for pectin adsorption. It was also shown that the combined ozone/heat treatment resulted in the formation of relatively thick and dense passive film on stainless steel particles, thereby giving a higher resistance to surface dissolution in aqueous solution than oxygen-treated particles.
The gas carburizing atmosphere for surface treatment of steel can be regulated using the carbon potential, which is obtained by measuring the dew point, oxygen concentration or carbon dioxide concentration. The carbon potential which is calculated with carbon dioxide concentration is consistent with the carbon content of carburized steel foil. However, since a zirconium oxide oxygen sensor is easier to handle and its response is better than others, it is generally used for controlling the carbon potential, Methane is the main component of natural gas and it is stable at high temperature, so that the majority of tends to remain in the furnace. Since the retained methane decomposes on the oxygen sensor tip, the oxygen concentration around it decreases. Therefore the measurement of carbon potential with an oxygen sensor has been considered to be difficult when natural gas is used as the enriched gas. In this study, the carbon potential is regulated by taking account of the difference of the carbon potentials which are calculated with carbon dioxide concentration and with oxygen concentration; therefore the carbon potential can be controlled by the oxygen sensor, using natural gas for enriched gas. Target surface hardness and effective case depth are obtained when gas carburizing is carried out using this method, In addition, when the carrier gas is generated with natural gas and air, the carbon oxide concentration is 20.5 volume%, and the hydrogen concentration is 39.0 volume%; therefore the carburizing speed is higher than that when the carrier gas is generated with propane or butane.
AB5 type LaNi3.5Co1.1-xCrxAl0.4 (x=0, 0.1) alloy powders were prepared by two-stage rapid quenching as negative electrode materials for Ni-MH batteries. The crystal structures, morphologies and electrochemical properties were examined. The results of X-ray diffraction analysis showed that both of these alloys had a typical hexagonal CaCu5-type crystal structure. In recovered powders, a small quantity of the powders with uneven form were mixed with the flaky form powders that we have intended. The charge-discharge cyclic stability and discharge rate performance of chromium-containing LaNi3.5Co1.0Cr0.1Al0.4 alloy electrodes were much better than those of chromium-free LaNi3.5Co1.1Al0.4 alloy electrodes. Additionally, we examined the arranged packing effect of the flaky powders in the disc electrodes on the discharge rate performance. We confirmed that the performance could be improved by the arranged packing technique.
The durability of heat-resistant metal (Fe based alloy and Ni based alloy) and surface-modified materials (spraying, calorizing) were evaluated by oxidation tests at high temperature achieved by the combustion of natural gas in order to determine which metal was superior in durability and economic efficiency. In the result, it was found that the most durable and useful material was the SUS 310 S with CoNiCrAlY coated by HVOF.