P. N. Moorthy

Compositional characteristics of magnetite synthesised from aqueous solutions at temperatures upto 523K

Abstract A comparison has been made of the compositions of magnetites prepared by different aqueous routes namely: a) by employing a mixture of Fe 2+ Fe 3+ , b) by oxidising at 363K a suspension of Fe(OH)2 & c) by giving a hydrothermal treatment at 523K to a Fe(OH)2 slurry. Exposing a carbon steel (CS) specimen to a pH 10 solution at 473K with & without complexing agents has resulted in a preferential formation of magnetite on the alloy surface while haemetite remained as crud in solution. Wet chemical analysis, X-ray, TG and Mossbauer studies were carried out to characterise the ferro-ferrites obtained.

Synthesis and characterization of mixed fluoride Y1−xSr2+1.5xF7 (−1.0 < x < 0.5)

A series of mixed fluorides with the general formula Y1−xSr2+1.5xF7 (x = −1.0 < x < 0.5) was synthesized and characterized by powder X-ray diffraction (XRD). It was found that the compound with the stoichiometry Y0.5Sr2.75F7 shows a cubic symmetry (fluorite-type structure) with a = 5.776 A. On decreasing the Sr2+ content or increasing the Y3+ content in Y1−xSr2+1.5xF7, a phase with tetragonal symmetry with a = 11.416 A and c = 13.291 A was observed in the composition YSr2F7, whereas in the composition Y2Sr0.5F7, a phase with hexagonal symmetry with a = 6.882 A and c = 7.032 A was observed. The existence of phases such as YSr2F7 and Y2Sr0.5F7 was confirmed. We observed a coexistence of rhombohedral and hexagonal phases beyond a particular nominal composition in this series of compounds.

Dissolution Behaviour of Chromium Substituted Haematites in an Oxidative/Reductive-Complexing Agent Environment

The dissolution behaviour of 3.5-12.5 at% Cr substituted haematites in a citric acid-EDTA-ascorbic acid (CEA) reductive-complexing formulation with and without alkaline permanganate (AP) oxidative pre-treatment is presented. In the direct treatment, with increasing Cr content of the oxide, employing CEA formulations containing increased concentrations of ascorbic acid could either completely or significantly solubilise the oxide. In the 3.5-10 at% Cr in the oxide, the concentrations of reducing agent employed in the CEA formulation to achieve a solubility of >40% in iron have been demarcated. The AP pre-treatment resulted in a release of only <4% of Cr from the oxide irrespective of the Cr content of the oxide and the concentrations of the permanganate. Nevertheless, such a pre-treatment was found to improve the percentage dissolution of the oxide significantly in the subsequent treatment with the reductive-complexing formulation. With AP pre-treatment, CEA formulations containing a lower concentration of the reducing agent dissolved as much oxide as the one by CEA formulations containing a higher concentration of the reducing agent in the direct treatment. Both with and without pre-treatment methods of dissolution yielded a preferential solubilization of Fe over Cr.