The phase analysis of the rusts generated beneath the primer containing micaceous iron oxide (MIO) and micaceous iron oxide
in combination with red lead (RL), zinc phosphate (ZP), basic lead silicochromate (BLSC) and zinc chromate (ZC) has been carried
out by Mössbauer spectroscopy at room temperature. The rust beneath the coating obtained after immersion of the painted panel
for six months in 3% NaCl, consists mainly of nonstoichiometric magnetite together with small fractions of γ-, α-FeOOH except
in the case of panel painted with RL containing MIO showed only a central doublet indicating the formation of γ-FeOOH and
SPM α-FeOOH. Non-stoichiometry of magnetite as calculated from the ratio of B/A sites of the peaks of magnetite in the spectrum
has been found depending on the nature of anticorrosive pigment present in the primer coating. The order of non-stoichiometry
has been found to be in order of ZC>BLSC>ZP>MIO.
Corrosion products of mild steel exposed to four different cultures of sulfur reducing bacteria (SRB) grown in a synthetic
medium have been studied by transmission Mössbauer spectroscopy (TMS). Cultures of SRB studied are two hydrogenase positive
strains,Desulfovibrio desulfuricans (DD) andDesulfovibrio vulgaris (DV) and two hydrogenase negative strainsDesulfotomaculum orientis orientis (DO) andDesulfotomaculum nigrificans (DN). The corrosion products generated on the coupons as well as in the broth were studied. In all the cases, the corrosion
products removed from coupons showed the presence of green rust 2 (GR2), ferrous sulfides, γ-FeOOH and superparamagnetic (SPM)
α-FeOOH in different proportions. The corrosion products from the broth showed a symmetrical central doublet, which indicates
the presence of γ-FeOOH and SPM α-FeOOH along with ferrous sulfides. The corrosion products from coupons suspended in sewage
water also showed the presence of GR 2 and ferrous sulfides together with oxyhydroxides. FTIR spectrum supports the presence
of these phases in corrosion products. The formation of GR 2 on coupons seems to be the first step for the SRB induced corrosion.
The corrosion rate has been found in the order of DO>DN>DV>DD.
Authors:A. Nigam, R. Tripathi, M. Jangid, and M. Chacharkar
The corrosion of mild steel as a result of interaction with various types of local natural water samples and distilled water is studied with the help of Mössbauer spectroscopy. The data are supplemented with the studies on IR and magnetic properties as and when required. Distilled water and potable water behave in almost similar fashion wherein ferrihydrite and FeOOH are observed to be the precursors of magnetite, the end corrosion product. In case of brakish water, the additional species, viz., FeCl2, FeOOH and an intermediate possibly FeOCl are accounted, and possible mechanisms are suggested.
Authors:A. Nigam, R. Tripathi, M. Jangid, M. Chacharkar, and Madan Lal
Tungsten ores from Degana, Rajashthan State, India are studied using Mössbauer spectroscopy. The low grade ore exhibits two types of mineral assemblages as per chemical states of iron. The relation between ferrous/ferric ratio and tungsten concentration also supports the existence of two types of mineral assemblages. The Mössbauer spectroscopy of concentrate ore samples has shown the absence of iron. The energy dispersive X-ray fluorescence spectroscopy on the contrary has evidenced the presence of iron in concentrate ore samples but at lower concentration on comparison with low grade ores. These differences in behaviour in the above spectroscopic studies may be additionally due to higher attenuation of -radiations and higher atomic weight material in the ore concentrates.