The paper describes briefly the performance and alteration of various materials used in the engineered barrier system of radioactive waste disposal and rock as natural barrier due to interactions with the groundwater. Cementitious materials, borosilicate glass, metals like stainless steel and Zircaloy, bentonite clay and rock are focused on among candidate materials of the engineered barrier. Studies on long-term alteration of the materials and its effects on the important parameters defining the performance of the materials are surveyed and reviewed.

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The mechanism was studied of calcareous deposit growth on steel surfaces cathodically protected in seawater under a constant cathodic current density. The deposits grew in proportion to the electro-deposition time with keeping the Ca/Mg ratio almost constant. A SEM observation revealed that the deposit was composed of double layers with a clear boundary the inside of which was Mg-rich, and the outside Ca-rich. It was found from electrodeposition experiments added with the isotope of calcium, ⁴⁵Ca, that the particles of CaCO₃ and Mg(OH)₂ were continuously moving in the deposits during the cathodic protection so as to build the boundary between the Mg(OH)₂ and CaCO₃ layers. The cause of this particles movement was attempted to explain from a colloid-chemical viewpoint.

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A new stability index [an improved stability index (SI′)] has been proposed that introduces corrosion inhibiting ability of silica in a broad range of temperature and pH into the conventional index of the corrosive action and scale formation of water, and new empirical equations [Eqs. 1-3] that characterize water were derived using the new index. The derived SI′ was effective in the range of SI>6. The SI′ was balanced at 0, and then SI′=0 differed from SI=6. In addition, a possibility was found for prediction and inhibition of corrosion of ferrous metals based on the equations by controlling the concentration of silica ([SiO₂]).
y=K₀{1-exp(-3.06×10^-1SI′)} (1)
K₀=(2.09T+1.872×10²)exp{-(-1.08×10^-4T+7.62×10^-3)[SiO₂]} (2)
SI′=x-7.21{1-1.71×10^-1exp(-8.59×10^-3[SiO₂])} (3)
[y: corrosion rate (V) (mdd), K0: constant affecting saturation value of corrosion rate (y) (mdd), T: temperature (°C), [SiO2]: silica concentration (mg SiO2/dm3), x: stability index (SI) (-)]

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Aluminum electrolytic capacitors have the tendency that alkali substance gradually concentrates on the cathode terminal end, regardless of load or unload condition. At the time, if the electrolyte consists of the salt containing strong alkali substance such as quaternary alkyl ammonium, the sealing may be affected in the performance.
We investigated the mechanism generating the concentration of the alkali substance. As the result, the obvious difference in electrochemical characteristic difference between two electrode materials, aluminum cathode foil and tab, which are used for the cathode terminal end of the capacitors causes this concentration. Basically, the cathode foil and the tab with different spontaneous potentials each other form a galvanic couple. And the alkali substance comes to concentrate around the cathode terminal end, due to the cathodic reaction which occurs on the tab surface with comparatively noble potential. The reason why the two electrode materials having similar aluminum purity show the obvious difference electrochemically is considered due to the high purification of the aluminum foil surface during etching process of foil.

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Conductive polymer film of polypyrrole (PPy) doped by polymolybdate (PMo) anions was prepared on mild steels by anodic polymerization for corrosion prevention of the steels. The PPy-PMo conductive film prepared exhibits good adherence to the steel substrate. The mass and thickness of the PPy-PMo film linearly increase with electricity during constant current polymerization at 5mA·cm^-2. The density of the PPy-PMo polymer film was evaluated to be 2.5g·cm^-3 from the ratio of the mass to thickness. A corrosion test in neutral and acidic 3.5wt% NaCl solutions was done for the steels covered by the PPy-PMo film. Corrosion of the steels is suppressed by the films: the corrosion rate in the neutral solution decreases by 1/3 compared with that of the bare steel and the rate in the acidic solution by 1/4. The film was gradually reduced during immersion in the solutions with progress of the corrosion reaction of Fe dissolution to Fe²⁺, which is accompanied with the dissolution from PMo in the film to MoO₄^2- in the neutral solution, or with pickup of protons and sodium ions in the acidic solution.

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In order to make the clean antimicrobial surface using metals on which bacteria are too hard to cling and multiply, antimicrobial activity against Saccharomyces cerevisiae, Escherichia coli and Staphylococcus aureus placed on the plate surface of copper, silver and gold which belong to 1B family transition metals has been investigated. The results obtained are summarized as follows: The order of antimicrobial activity was copper>silver>>gold. Copper had the excelent antimicrobial activity against E. coli and S. cerevisiae. Silver had a strong antimicrobial activity against E. coli and a weak one against S. aureus. Gold had a scarce antimicrobial activity. The antimicrobial activity of copper ion against E. coli and S. aureus was weakly found but 640ppm copper ion of a large quantity caused the antimicrobial activity against except S. cerevisiae. 10ppm silver ion caused the antimicrobial activity against all bacteria tested. Contact of copper with E. coli produced a little amount of H₂O₂ which caused the antimicrobial activity as an oxidizing stress. The mechanism of antimicrobial activity of the surface of 1B family transition metal plates was supposed as following. The synergistic effects of both sterilization ability due to H₂O₂ produced in very short time from contact of bacteria with the surface of copper plate and oxidizing ability due to copper ion dissolved from the surface of copper plate caused the great antimicrobial activity of the surface of copper plate. Since the quantity of both H₂O₂ produced and silver ion dissolved from the surface of silver plate was a little, the sterilization ability and oxidizing ability due to silver ion were not so strong as copper's. Consequently, the antimicrobial activity of silver became weaker than copper's. H₂O₂ produced scarcely from the surface of gold plate and gold did not dissolve at all, so that the sterilization ability and the oxidizing ability did not generate.

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