In situ observation of preferential anodic dissolution of phosphorus compound in Fe-P alloys using Raman spectroscopy

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 degrees 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 PO43-, HPO42-, 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 HPO42- 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.