THE LONG-TERM GROWTH OF THE PROTECTIVE RUST LAYER FORMED ON WEATHERING STEEL BY ATMOSPHERIC CORROSION DURING A QUARTER OF A CENTURY

The rust layers formed on weathering and mild steels by atmospheric co rrosion in an industrial region for a quarter of a century have been c haracterized using various analytical techniques. In particular, analy sis of a local portion of the rust layers by means of Raman spectrosco py gives important information on the structure of the layers. It is e lucidated that the inner stable and protective rust layer which covere d the surface of weathering steel mainly consists of nano-particles of alpha-FeOOH containing a considerable amount of Cr. The relative chan ge of the amount of rust constituents for low alloy steels supports we ll a newly proposed schematic progress of long term alteration in stab le and protective rust layer formed on a weathering steel in an indust rial environment, i.e. the gamma-FeOOH, as an initial rust layer, is t ransformed into a final stable rust layer of alpha-FeOOH, probably via an amorphous oxyhydroxide substance, during the long term atmospheric corrosion of a weathering steel.