• K Seshan

      Articles written in Bulletin of Materials Science

    • Preparation and characterisation of γ-Fe2O3 as tape recording material

      K Seshan M R Anantharaman Venkatesh Rao A L Shashimohan H V Keer D K Chakrabarty

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      Optimum conditions for the preparation of tape recording quality γ-Fe2O3 by the thermal decomposition of ferrous oxalate dihydrate have been established. Formation of the intermediate Fe3O4 which is most important in forming γ-Fe2O3 takes place only in the presence of water vapour. Various stages of decomposition have been characterised by DTA, TG, DTG, and x-ray powder diffraction. The method for the preparation of acicular γ-Fe2O3 that matches very well with the commercial tape recording material has been developed.

    • Synthesis and characterization of γ-Fe2O3 — a magnetic tape material

      M R Anantharaman K Seshan D K Chakrabarty H V Keer

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      Acicular FeC2O4 · 2H2O was precipitated from glycerol and starch media. Thermal decomposition of this oxalate in dry and moist nitrogen yielded primarily FeO and Fe3O4 respectively. Characterization was attempted through DTA, TG, x-ray diffraction, TEM and magnetization studies. It was found that the oxalate can be completely decomposed to Fe3O4 in moist nitrogen (PH2O ∼ 35 torr) at 775 K and then oxidised by dry air to acicular γ-Fe2O3 at 575 K. The resulting material has saturation magnetization (∼ 70 emu/g), coercive field (∼ 300 Oe) and squareness ratio (∼ 0·60–0·65), which values art comparable with those of the commercial samples.

    • Development of pure and doped gamma ferric oxide

      M R Anantharaman K Seshan S N Shringi H V Keer

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      Optimum conditions and experimental details for the formation of γ-Fe2O3 from goethite have been worked out. In another method, a cheap complexing medium of starch was employed for precipitating acicular ferrous oxalate, which on decomposition in nitrogen and subsequent oxidation yielded acicular γ-Fe2O3. On the basis of thermal decomposition in dry and moist nitrogen,dta, xrd, gc and thermodynamic arguments, the mechanism of decomposition was elucidated. New materials obtained by doping γ-Fe2O3 with 1–16 atomic percent magnesiu, cobalt, nickel and copper, were synthesised and characterized.

    • X-ray photoelectron spectroscopy studies on ethylene oxychlorination catalysts

      R Vetrivel K Seshan K R Krishnamurthy T S R Prasada Rao

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      Copper chloride on alumina catalyst used for oxychlorination of ethylene represents a typical system where copper is in a dynamic equilibrium between Cu+ and Cu++ oxidation states. Surface studies on redox, structural and compositional properties have been undertaken to monitor the changes that occur on the catalyst during use and pinpoint causes for its deactivation. For this, a fresh and a spent catalyst were been chosen for characterization. A core consisting of copper in Cu+ state and present as CuAlO2 is formed at the centre of the catalyst sphere. Formation of such a nonreversible phase under reaction conditions upsets the redox equilibrium. XPS also shows the absence of potassium in the core and its precipitation as a new phase on use, probably KCl, formed by the decomposition of active component KCuCl3. These factors facilitate deactivation.

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