Far Infra-Red Absorption Spectra of Ferric Oxides and Oxyhydroxides

Abstract

Far infra-red spectroscopy is believed to be a very powerful tool for identifying metallic compounds and studying their structures. Ferric oxides and oxyhydroxides are important corrosion products of iron alloys, but their far infra-red spectra have never been reported. For this reason, the far infra-red spectra of α-, β- and γ-FeOOH and α- and γ-Fe₂O₃ were observed in the region of 25∼220 μ. In addition, the diffuse reflection spectra of these compounds were measured, since diffuse reflection spectroscopy may also be a convenient method for identification of the compounds.
The measurement of the far infra-red spectra of powdered samples was carried out using a JASCO DS-501G grating far infra-red spectrophotometer. Fine powders of the compounds were dispersed in MgO, and the diffuse reflection spectra of the dispersed samples were observed over the region of 240∼1100 mμ.
It has been observed that the compounds show the characteristic absorption bands in the far infra-red region. The measurement of far infra-red spectra has proved to be an excellent method for identifying these compounds. An absorption band at 286 cm⁻¹ of α-FeOOH and those at 266 cm⁻¹ of β- and γ-FeOOH are assigned tentatively to be the absorption due to the out of plane deformation vibration of the -O-H group. The results also show characteristic absorption curves for each compound in the diffuse reflection spectra, indicating the applicability of diffuse reflection spectroscopy for the said purpose.