The corrosion wear of alloy tool steel (SKD 11) coated with TiN (Ti/TiN: single layer and Ti/TiN/Ti/TiN: multiple layers) was investigated in a NaCl solution in comparison with the case of mild steel (SS 400). Corrosion wear tests showed difference in morphorogy of damage between stators and rotors. In the stators, TiN films disappeared with a low load, and wear tracks were observed. As for the damage of rotors, the galvanic corrosion, the wear of substrates and the disappearance of TiN films occured under a load of 9.8MPa or below. With the highest load of 9.8MPa, the disappearance of TiN film, and the adhesion of wear debris and corrosion products were observed. It was found that the SKD 11 substrate was galvanically coupled with TiN films but the corrosion rate of the substrate was less than that of SS 400 by a factor of 2 or 3. The weight loss of SKD 11 with TiN films in corrosion wear tests was caused mainly by wear and partly galvanic corrosion.
The corrosion fatigue strength of the surface modified SNCM 439 steels by the combined use of magnetoron sputtering and argon ion-mixing treatments was studied at a cathodic potential of -1.2V against Ag/AgCl (saturated with KCl) reference electorode in a 3.5% NaCl aqueous solution. The disk of the material of Cr or ZrO2-6vol%Y2O3 was used as a target of magnetoron sputtering. The thickness of coated films obtained on fatigue specimens was about 0.037μm. The fatigue lives of the SNCM439 steels with or without surface modification were remarkably reduced in a 3.5% NaCl aqueous solution because of hydrogen embrittlement, compared with those in air. But, the corrosion fatigue lives of surface coated specimens were improved, depending on the surface treatments. That is, the fatigue life at a stress amplitude of 515MPa for non-coated specimen, ZrO2-6vol%Y2O3 coated specimen, and ZrO2-6vol%Y2O3 coated and ion-mixed specimen was 1.8×104, 9.3×104, and 2.6×105, respectively. The best coating treatment for improving corrosion fatigue lives was obtained by the combined use of magnetoron sputtering and ion-mixing treatments which led to improved adhesion of the film to the matrix and interference in hydrogen entry into the matrix.
The dissolution behavior of magnetite powder (as received) and pellet (prepared by sintering) in solutions containing EDTA or citrate was studied at different pHs (0.3-9) and temperatures (30-95°C). The concentration of dissolved Fe increased with time, and is highest at pH 2.4 with EDTA and at pH 3.7 with citrate. A rate equation of dissolution was derived from a consideration that the dissolution reactions consist of the following two coupled processes: (1) the transfer of Fe ions from solid to aqueous phase by reaction with chelating agents and (2) the transfer of lattice O2- ions by reaction with H+ ions to form H2O. The resulting rate equation in solutions with EDTA (H4Y) is d[FeY]/dt=k′k″[H+]8/3α4([Y]T-[FeY])/(k′[FeY]+k″[H+]8/3) where k′ and k″ are the rate constants for the processes (1) and (2), α4 is the ionization fraction of Y4-, and [Y]T is the total concentration of EDTA. The amount of dissolved Fe vs. pH peaks at a specific pH, which can be explained by the rate equation noted above.
The accelerated evaluation method for microbially influenced corrosion (MIC) resistance of stainless steels was investigated on the basis of the mechanism for MIC. Corrosion potential of stainless steels was determined in natural seawater and in synthetic seawater containing glucose oxidase (GOD) to simulate the bacterial metabolism because the corrosion potential of stainless steels in natural seawater becomes noble by hydrogen peroxide as an intermediate of the metabolism. The corrosion potential ennoblement was reproduced completely in synthetic seawater by adding GOD. This method can be applied to evaluate MIC resistance of stainless steels. The most appropriate test condition was examined to simulate natural seawater environments, and it was determined as 1mg/l of GOD and 10g/l of glucose in synthetic seawater below 50°C. In this condition, results of crevice corrosion tests for one week showed a good correlation with results of the immersed tests in natural seawater for six months. The test method can be also applied to fresh water environments containing low concentration chloride ions. It revealed that SUS 304 stainless steel has a susceptibility to MIC even in fresh water containing 5mgCl-/l at room temperature. This result corresponds with corrosion damages experienced in pipings and structures of stainless steels. These results suggest that this newly developed test method can be applied to evaluate the MIC resistance of stainless steels.
Type 304 stainless steel was modified with an ion implantation technique to obtain higher corrosion resistance. The Cr+ ions were implanted with acceleration energy of 50 or 180keV and with dose rates of 1-5×1017atm·cm-2. At least 100nm surface layer was enriched with chromium more than 40at% by the implantation of 180keV. Anodic dissolution in a sulfuric acid solution was extensively suppressed for chromium implanted steels. No remarkable change, however, was observed for pitting potentials measured in a 3.5% NaCl solution, although the current before initiation of pitting was fairly suppressed for chromium implanted steels.
Chemical decomposition of plastics were reviewed from a viewpoint of waste plastics treatment. The general relationship between molecular structures and chemical degradability of plastics, for example of polyolefines, hydroxyl containing polymers, polyesters and polyamides etc., were introduced. The degradation behavior of plastics by thermal decomposition, depolymerization, hydrolysis and oxidation, which were seemed to have the possibility of actualization as the method of waste treatment, were shown. Biodegradable polymers were also reviewed briefly.