Change of molecular spectra and magnetism in synthetic Cr-substituted goethite rusts

摘要

For a better understanding of the solid-stateproperties of the Cr-substituted goethite #alpha#-(Fe_(1-x),Cr_x)OOH as the final protective rust layer on weathering steelbearing chromium, Raman and FT-IR spectroscopies and magneticmeasurement have been carried out for the synthetic Cr-substitutedgoethite rusts containing various amount of Cr. It is found fromthe Raman spectroscopy that addition of Cr (III) ions to Fe (II) ionalkaline aqueous solution delays the precipitation of Cr-substituted goethite in the air oxidation process. Despite theincrease of Cr content, the behavior of FT-IR spectra suggests thatthe Cr-substituted goethite keeps a goethite (#alpha#-FeOOH)type oxyhydroxide crystal structure. Ferromagneticity appears overabout 2 mass percent Cr content though the Cr-substitutedgoethites without and with lower Cr content less than 2 masspercent possess the antiferromagneticity. This occurrence ofmagnetization proves that Cr atoms in the lattice of Cr-substitutedgoethite are substituted at the sites of Fe atoms. The particularcontent of about 2 mass percent Cr in the antiferro/ferromagneticchange corresponds to that producing finer particles of Cr-substituted goethite by the action of Cr (III) ions.