• M R ANANTHARAMAN

Articles written in Bulletin of Materials Science

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

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

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

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.

• A new inexpensive method for the preparation of acicular precursors for magnetic recording media

Magnetic materials meant for audio/video recording applications necessitate that polycrystalline materials be in acicular shape. So preparation of acicular precursors for magnetic storage materials assumes significance. The employment of aqueous solutions do not produce needle shape crystallites. Glycerol is one of the complexing media used for the precipitation of ferrous oxalate dihydrate. An inexpensive method using starch for preparation of acicular particles is described. The influence of an additive namely Gd on acicularity is also investigated.

• Ultra-high Seebeck coefficient of nanostructured Sb-substituted PbTe and fabrication of a thermoelectric generator module

Compounds belonging to the series PbSb$_x$Te$_{1-x}$ and Pb$_{1-x}$Sb$_x$Te ($x = 0.1, 0.3, 0.5$) were prepared in thenanostructured form by employing high-energy ball-milling and subsequent hot-pressing. The amphoteric property of antimony was utilized to substitute lead and tellurium in the compounds having the formula PbSb$_x$Te$_{1-x}$ and Pb$_{1-x}$Sb$_x$Te to make them p and n. All the compositions were evaluated for their figure of merit (ZT) and power factor afterascertaining their Seebeck coefficient, electrical and thermal conductivities. These compositions exhibited very high Seebeck coefficient both in low- and room-temperature regimes. Thermoelectric generator modules were constructed using combinations of n- and p-type PbSbTe and the voltage developed was measured and compared with the calculatedvalues, and they are found to be in good agreement. Different combinations of p- and n-types from the series were tested,and the best among them were identified.

• # Bulletin of Materials Science

Volume 45, 2022
All articles
Continuous Article Publishing mode

• # Dr Shanti Swarup Bhatnagar for Science and Technology

Posted on October 12, 2020

Prof. Subi Jacob George — Jawaharlal Nehru Centre for Advanced Scientific Research, Jakkur, Bengaluru
Chemical Sciences 2020

Prof. Surajit Dhara — School of Physics, University of Hyderabad, Hyderabad
Physical Sciences 2020

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Posted on July 25, 2019

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