How to Use Composition Ratio Index Obtained by Internal Standard Quantitative X-ray Diffraction Analysis for Evaluation of Rust Status on Weathering Steel

In order to discuss how to use internal standard quantitative X-ray diffraction analysis of rust, recently proposed techniques which utilized α/γ, α/γ* ratios for corrosion stability evaluation of weathering steels were assessed. Reported correlation between α/γ (or α/γ*) values and corrosion rates on good exposure test pieces obtained at limited number of sites in industrial and rural atmospheres, did not always stand when this technique was applied to the cases of much wider environmental ranges. Thus, a further improved method for approximate assessment of inactivity of rust, in which both (α+am)/γ* value and thickness of rust are taken into account, is proposed based on the discussion in terms of rust formation processes, corrosion protection mechanisms, and actual performances of weathering steels.