Abstract
Laser Raman spectra were investigated for hopeite crystal films formed on galvannealed steel. Four clear peaks due to PO43- for the crystalline state of hopeite were found at 800-1300cm-1. Orthophosphate (PO43-), which is a regular tetrahedron, has four basic vibration modes-ν1, ν2, ν3 and ν4-, of which, ν1 and ν3 are observed at 800-1300cm-1. Here, the main peak corresponds to ν1 and the other peaks correspond to ν3 untied and split. A reference sample of 85%-H3PO4 showed two peaks in the same region, the main peak corresponding to ν1 and the sub-peak corresponding to ν3 degenerated. It was found that a basic vibration mode of ν3 appears at 1150cm-1.Raman spectra were observed for hopeite dissolved in HCI solution. Three peaks were found in the region, but the spectral pattern was quite different from that of crystalline hopeite, and was similar to that of H3PO4 aq. soln.. The peak intensity ratio of I1075/I890 differed between liquid-state hopeite and H3PO4 aq. soln., but the band frequencies of the three peaks were consistent with each other. It was confirmed that the three peaks correspond to the P(OH)3 and PO stretching vibrations of [H3PO4] and the PO2 stretching vibration of [H2PO4-] formed by the dissociation of H3PO4. The PO2 stretching vibration observed at 1075cm-1 depends on the dissociation state of H3PO4.
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