The influence of alloying elements on the corrosion resistance of stainless steels in phosphoric acid medium polluted by sulphide ions
1995; Elsevier BV; Volume: 37; Issue: 6 Linguagem: Inglês
10.1016/0010-938x(95)00005-5
ISSN1879-0496
AutoresSouad El Hajjaji, L. Ariès, J.P. Audouard, F. Dabosi,
Tópico(s)High-Temperature Coating Behaviors
ResumoThe influence of sulphide ions on the corrosion resistance of some special stainless steels (Z2 CNDU 25-25, Z2 NCDU 25-20, Z2 CNDU 25-6, Z1 CN 25-20, Zl CD 29-4) in 40 wt % H3PO4 with 330 ppm SO42− and 1000 ppm Cl− at 80 °C has been investigated using electrochemical (polarisation curves) and spectrometric (SIMS) techniques. The corrosive effect of sulphide ions is confirmed: they increase the anodic current and shift the corrosion potential to more negative values. The presence in the solution of sufficient sulphide ions prevents the establishment of passivity. Critical sulphide ion concentrations above which the alloys Z2 CNDU 25-6, Z2 CNDU 25-25 and Z1 CD 29-4 are no longer able to passivate, are respectively, 1, 5 and 15 ppm S2−; so, the Z1 CD 29-4 alloy with high chromium content (29% Cr) and without nickel has good behaviour in such polluted phosphoric acid. In the passive state, in order of decreasing dissolution rate, the five steels are ranked as follows: Z1 CN 25-20, Z2 CNDU 25-6, Z2 NCDU 25-20, Z1 CD 29-4 and Z2 CNDU 25-25; sulphur is present in the films probably as sulphides or oxysulphides. Contrary to nickel, the presence of chromium and molybdenum is essential to increase the corrosion resistance of stainless steels in phosphoric acid with sulphides as impurities.
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