Stainless steels and ozone

The corrosion behaviour of several stainless steels and some pure metals has been investigated in water solutions with dissolved ozone. Dissolved ozone increases the redox-potential of solutions to about +1200 mV vs. SCE and the corrosion potential of stainless steel to the transpassive region. The corrosion rate of stainless steels increases as the amount of alloying elements increases. The corrosion of stainless steels is mainly general but also peeling of oxide layers and pitting was also observed. As the pH of the solution is decreased, the corrosion rate of higher alloyed steels increases at higher pH than lower alloyed steels. Dissolved ozone increases the thickness of the oxide layers greatly up to 260 nm and greatly changes the composition of the layer. Chromium concentration is negligible in the oxide layers. Molybdenum concentrates in the outer layer, even more so with lower alloyed steels. Iron and alloying elements have oxidised to their highest valencies. The main components in the oxide layers are iron oxides and on the surfaces also MoO6 occurs.