High temperature corrosion mechanism of type 304 stainless steel embedded in corrosion ash

High frequency impedance (Z(10kHz)) at 10 kHz and low frequency impedance ( Z(10mHz)) at 10 mHz for Type 304 stainless steel were monitored in synthesi zed ash at 873 K, as well as the corrosion potential. The mixture of Al2O3 particles (120 mu m in diameter) and molten salt (NaCl + KCl + Na2SO4 + K2S O4 + ZnSO4) was used as the synthesized ash. The value of (Z(10mHz) - Z(10k Hz))(-1) was well correlated with the average corrosion rate obtained from the mass loss measurement. The corrosion rate of Type 304 stainless steel s howed a maximum at molten salt contents of 20 similar to 30 mol%. The corro sion potential shifted to less noble values as the amount of molten salt in creased up to 40 mol%, and it became constant when the molten salt content exceeded 40 mol%. The corrosion mechanism was discussed on the basis of the obtained corrosion rates and corrosion potential data. Also, in the corros ion ashes collected at actually operating incinerators, the corrosion rate of Type 304 stainless steel was monitored by AC impedance technique. The co rrosion rate and amount of molten salt were estimated by comparison with im pedence data in the synthesized ash.