In Situ Observation of Preferential Anodic Dissolution of Phosphorus Compound in Fe-P Alloys Using Raman Spectroscopy

抄録

The solution chemistry of P in the Fe-P alloy electrodes containing P of 0.104, 0.028, and 0.004 mass% has been investigated by using in situ Raman spectroscopy in an electrochemical cell under controlled potential in 0.1 kmol·m^-3 NaOH at 25°C. It is found that the segregation site of the precipitate with the chemical composition of F₃P dissolves preferentially. Using in situ Raman spectroscopy three dissolution species of PO₄^3-, HPO₄^2-, and H₂PO₄^- were detected on the surface at the segregation site, and these concentrations depend on the location of the precipitate of P compound whether at grain boundary or in grain. The detection of HPO₄^2- and H₂PO₄^- both of which are unstable in the solution of NaOH suggests that the localized corrosion at the segregation site of P induces decrease of pH.