To achieve water repellency and lubricity with corrosion resistance for powder coatings, the surface properties of fluoroplastics (PTFE) particle dispersed saturated polyester coatings were investigated. Lubricity increased with adding about 5 mass% PTFE particles, and the coefficient of friction became 0.07. Water repellency also increased with adding PTFE particles, and the angle of contact was about 140 degree. The surface roughness of powder coatings depends on the kind of PTFE particle. Rough surfaces cause powder coatings to be water repellent under a low PTFE content. Observation with SEM and analysis with EPMA show that PTFE particles segregate on the surface of coating films. This is considered to cause high water repellency and lubricity in a powder coated surface with a relatively low dispersed PTFE content, 20 mass% or less. As a result, PTFE particle dispersed saturated polyester coatings are expected to have excellent water repellency and lubricity, and high corrosion resistance due to the high adhesiveness of saturated polyester on metal without the obstacle of adhesion by fluoroplastics particles.
In order to establish a standard method to identify distribution pattern of corroded surface, a computer aided image analysis has been applied. A standardized method to get a constant input image for the image analyzer was established by using a standard scale. Model patterns showing random, regular and clustered mode, which had been given by Masuko, were analyzed by 5 indexes; variance to mean ratio, homogenuity function, index of clumping, index of mean crowding and index of patchiness. The most effective index to differentiate, the three modes of patterns was found to be the variance to mean ratio.
Invesigated was corrosion behavior of Zn and Zn-Fe alloy electroplated steel sheets in modified Volvo test (atmospheric exposure test with 5%NaCl solution sprinkling). 1) Zn-15% Fe exhibited the best corrosion resistance in the exposure test. 2) It was considered that the excellent corrosion resistance of Zn-15%Fe alloy resulted from the effect of suppresion of oxygen diffusion caused by high coverage of zinc corrosion products and low concentration of iron corrosion products in the corrosion products. 3) As to zinc corrosion products of Zn-15%Fe alloy, it was supposed that 4ZnO·CO2·4H2O existed in the outermost layer, Zn (OH)2 was located in the outer layer, ZnCl2·4Zn (OH)2 or ZnCl2·4Zn (OH)2+ZnCl2 existed in the inner layer in which Zn-Fe alloy coexisted. Iron corrosion products coexisted in the corrosion product layers described above. 4) EG (Zn) corroded ununiformly and formed zinc corrosion products composed of 4ZnO·CO2·4H2O, ZnCl2·4Zn(OH)2 and ZnO with low coverage, and the low coverage decreased the suppressing effect of the products on oxygen diffusion.
Investigated was corrosion behavior of Zn and Zn-Fe alloy electroplated steel sheets under paint film in atmospheric exposure test and modified Volvo test (atmospheric exposure test with 5mass%NaCl solution sprinkling). 1) Creepage width of paint film remained small in the range below 14mass% Fe, and increased with Fe content in deposit in the range above 20mass%Fe in atmospheric exposure test, though it exhibited minimum value at 15mass%Fe in modified Volvo test. 2) The creepage width in both outdoor exposure test and modified Volvo test showed correspondence to corrosion current density of unpainted specimens exposed to each test in the range below 30mass%Fe, indicating that corrosion under paint film is predominantly determined by corrosion rate of the deposit with corrosion products formed in corrosion test. 3) It was considered that wedge effect of iron rust resulting from volume expansion additionally affected the corrosion in the range above 30 mass%Fe. 4) Furthermore, corrosion reaction under paint film was discussed on the basis of EPMA analysis.
High-level radioactive waste in Japan refers to the waste resulting from reprocessing of the spent nuclear fuel. Since radioactivity of this type of waste is high and long lasting, special attention must be given to ensure the long-term protection of man and his environment. The baseline policy of Japan with regard to treatment and disposal of high-level radioactive calls for disposal into geological formations at more than several hundred meters underground. The multi-barrier system of geological disposal is being studied as the most favorable system which conforms to multiple protection concept. This paper shows the concept of the multi-barrier system and safety assessment in Japan and other countries. The long-term performance of the geological disposal sysytem can be assured by designing and constructing an appropriate multi-barrier system.