Corrosion behaviour of graphite and stainless steels in phosphoric acid.

Abstract

Corrosion behaviour of graphite and stainless steels was examined in phosphoric acid by electrochemical methods (polarization curves, impedance spectroscopy and SVET). Potentiodynamic curves showed that graphite exhibit an excellent resistance in the acid solution. Effect of the presence of chloride and sulphide ions in 40% H3PO4 solution was also investigated at 20°C and 80 °C. At elevated temperature, the current densities increased in the presence of aggressive impurities. Although stainless steels exhibited a good passive behaviour, the best corrosion resistance in chloride and sulphide contaminated H3PO4 was shown for the graphite. Subsequently, the current density at the surface was detected by scanning vibrating electrode technique (SVET). From the data obtained, graphite surface manifested a distinctive behaviour from that of stainless steels.