Characterization of Delhi iron pillar rust by X-ray diffraction, Fourier transform infrared spectroscopy and Mossbauer spectroscopy

Rust samples obtained from the region just below the decorative bell capita l of the Delhi iron pillar (DIP) have been analyzed by X-ray diffraction (X RD), Fourier transform infrared spectroscopy (FTIR) and Mossbauer spectrosc opy. The identification of iron hydrogen phosphate hydrate in the crystalli ne form by XRD was unambiguous. Very weak diffraction from the oxyhydroxide s/oxides of iron was observed indicating that these phases are most likely to be present in the amorphous form in the rust. The present XRD analysis o f rust obtained from an inaccessible area of the DIP has also been compared with earlier analyses of DIP rust obtained from regions accessible to the public. FTIR indicated that the constituents of the scale were gamma-, alph a-, delta -FeOOH, Fe3-xO4 and phosphate, and that the scale was hydrated. T he unambiguous identification of the iron oxides/oxyhydroxides in the FTIR spectrum implied that they are present in the amorphous state, as XRD did n ot reveal these phases. The FTIR results have also been compared with earli er FTIR spectroscopic results of atmospheric rust formation. Mossbauer spec troscopy indicated that the rusts contained gamma -FeOOH, superparamagnetic alpha -FeOOH, delta -FeOOH and magnetite, all in the amorphous form. The M ossbauer spectrum also confirmed that iron in the crystalline iron hydrogen phosphate hydrate, whose presence was confirmed by XRD, was in the ferric state indicating that it was a stable end corrosion product. (C) 2000 Elsev ier Science Ltd. All rights reserved.