The corrosion protection ability of the novel asphalt-type coating films, which were composed of asphalt emulsion, polymer compounds, and inorganic or organic pigments, was evaluated. The important factors for the asphalt-type coating films on film formation ability and corrosion protection ability were the compatibility between pigments and vehicles, the degree of polymerization and the surface activity of vehicles. It was found that the suitable components of the asphalt-type coating films for good corrosion protection were asphalt emulsion, acrylic elastomer (lower molecular weight) and phenol or polyester resin.
The effect of permeated oxygen on the corrosion of coated steel plates was investigated for five cationic electrodeposition paints. The oxygen permeability coefficient (P. C.) of peeled paint films was measured by the electrode method and mass spectrometry. As evaluations of corrosiveness, the maximum width of corroded part at the cut line on the coated panels after salt-spray test and the peeling-off areas after the immersion test in saline water were employed. A good correspondence was observed between the oxygen P. C. by the electrode method and mass spectrometry especially in the range of high oxygen permeability. However in the low range, the P. C. by mass spectrometry was more precise than that by the electrode method. A linear correlation was profed between the logarithm the oxygen P. C. and the corrosiveness. In particular, the correlation was excellent between the oxygen P. C. by mass spectrometry and the corrosiveness after the immersion test.
The degradation of corrosion protective films of vinyl chloride resin, long oil alkyd resin containing lead cyanamide (Pb (CN) 2), tar epoxy resin, and polyurethane resin was evaluated by electrochemical impedance spectroscopy (EIS) and scanning vibrating electrode technique (SVET). In this study, the film resistance (Rf) determined by EIS was closely correlated to the frequency at maximum phase angle (θmax) measured with EIS. The breaking time (tb1) of Rf-time curve also related to the breaking time (tb2) of fθmax-time curve. The relationship between the Rf by EIS and the current density (i) by SVET was also found clearly. The rapid measurements of fθmaxby EIS and i by SVET were effective in the evaluation of the degradation of paint films.
In order to offer the effective painting maintenance for railway steel bridges, we tried to predict the service life of paint films. The steel bridges were classified into ten groups from the factors such as the kinds of steel plates (mill-scale or blasted), environments (sea or others) and the periods after painting (newly-constructed or repainted). From the results of the degradation of the paint films for about 100 steel bridges in conventional lines, the equation for the service life of each group was estimated by the regression analysis with conditional variance.
Several coating systems for outdoor structure (four different top coats) were subjected to outdoor exposure tests and accelerated weathering tests. The properties of the films were evaluated by surface appearance, gloss retention, SEM observation, and three-dimensional surface roughness measurement. In addition to those, the adhesion strength of the films to a substrate and the dynamic contact angle on the topcoating surface were measured. Correlations among those properties were obtained. It was found that the top coatings became rough when the resins were decomposed by ultra-violet ray, which made the surface to retain more water. It was also found that the corrosive factor, such as water, oxygen, and chloride, penetrated undercoating from degraded top coating, which reduced the adhesivity and intercepting ability of the film. As a conclusion, we assume that the topcoating that has poor weathering property affects anticorrosive property of the coating system.
Composite acrylic resins modified with ultrafine inorganic particles (100 nm or less) were tested for corrosion resistance and undercoating applicability asa surface treatment material for hot dip galvanized (HDG) steel sheet. It was proved from the results of the salt spray and thaw cyclic corrosion tests, etc. that a composite acrylic resin containing SiO2 (silica) was superior to the other composite resins having ultrafine Al2O3, BaSO4, CaCO3, Fe2O3, TiO2, or ZnO. The corrosion resistance of the composite silica resin was determined by the type of reaction process, the specific suface area, and the hydroxyl (≡Si-OH) content of ultrafine silica particle. An ultrafine silica made by a wet process provided better corrosion resistance than that by a dry process. What was more, the particles with larger specific surface area, higher the hydroxyl content, and higher hydrophilicity had greater effectiveness for corrosion resistance. The corrosion resistance on the salt spray test of each composite?resin?coated chromated HDG steel sheet was about an order better than that of unchromated HDG steel because of a synergetic effect of chromating. Especially, the composite silica resin was distinguishable from the others. Thus, the composite silica resin appears to be most suitable for HDG steel for its excellent corrosion resistance as well as its good adhesivity on the steel.
The interfaces between carboxyl group of poly (acrylic acid) (PAA) and metal substrates have been investigated. The metal substrates used had various types of IEPS (Iso Electric Point of Surface) value. Three types of surface-analysis techniques were used in an attempt to ascertain the bonding mechanism between carboxyl group and metal. The differences among the interfaces were detected by XPS from the shift in the binding energy of the 0 (1 s) peak of carboxyl group. This shift was observed only when a strong ionic interaction between carboxyl group and metal exists. The results obtained by RA-FTIR and SSIMS were also in good agreement with those by XPS. It has been determined that when a PAA treatment is used in epoxide resin/PAA/metal joint systems, the joint durability is promoted. In such cases a strong ionic interaction between carboxyl group and metal exists