Abstract
The electrical conductivity of mixtures of synthetic α-, β-, γ-FeOOH, and Fe3O4 crystals has been measured to elucidate the high-order structure in the FeOOH/Fe3O4 systems as model rusts. The electrical conductivity of FeOOH/Fe3O4 binary systems showed minimum values for the samples containing less than 50% volume fraction of Fe3O4. The electrical conductivity change in low Fe3O4 content range was characteristic to each FeOOH polymorph. The electrical conductivity change suggests that FeOOH cyrstals form an aggregate which is loosened by coexisting Fe3O4 crystals. Above 50% of the Fe3O4 fraction, the electrical conductivity of the binary system increased steeply with the Fe3O4 content, implying that a chain-like structure of Fe3O4 crystals is formed. Electrical conductivity changes for the systems of α-FeOOH/γ-FeOOH/Fe3O4 and α-FeOOH/β-FeOOH/Fe3O4 also suggest the roles of each component played in the high-order structure of the ternary systems. The correlation between the electrical conductivity and high-order structure was discussed with reference to properties of the rust layer formed in atmospheric corrosion.
