Characterization of Steel Rusts by Gas Adsorption

Abstract

Two kinds of steel rusts were characterized by N₂ adsorption. The artificial rusts of α-, β-, γ-FeOOH, Fe₃O₄ and poorly crystallized iron oxide were synthesized from aqueous solutions of iron salts dissolving different metal ions such as Cu(II), Ni(II), Cr(III) and Ti(IV). Another series of rusts were obtained by exposing five kinds of weathering steels in various environments for 17 years. The specific surface area of these rust particles reflecting the particle size was obtained from the adsorption isotherms of N₂. The particle size of synthesized rusts was increased by the addition of the metal ions, depending on the kinds of steels and metal ions. The particle size of weathering steels was affected by the exposure environment but not by the kind of weathering steels. Irrespective of the kind of steels, the atmospheric NaCl increased the size of rust particles and the particle size increased with the increase of corroded amount. It was shown that the gas adsorption method gives useful information on the steel rusts.