Joao Batista Marimon da Cunha

Influence of iron on mineral status of two rice (Oryza sativa L.) cultivars

Received: 02 April 2007; Returned for revision: 02 July 2007; Accepted: 14 August 2007Iron is an essential nutrient for plants. In aerobic conditions, Fe is highly unavailable for plant uptake, and Fe deficiencycan be severe in plants grown in calcareous soils. In waterlogged soils, however, Fe availability increases and can reachtoxic concentrations. Rice is an important staple crop worldwide and faces iron deficiency or excess, depending on thegrowth conditions. To contribute to the study of mechanisms involved in response to Fe deficiency and resistance to Feexcess, experiments were carried out with rice cultivars BR-IRGA 409 (I409, susceptible to Fe toxicity) and EPAGRI 108(E108, resistant to Fe toxicity) grown in culture solutions and submitted to Fe excess, control concentration ordeficiency (500, 6.5 or zero mg L

Conductivity dynamics of metallic-to-insulator transition near room temperature in normal spinel CoFe2O4 nanoparticles

Herein, we report the preparation of minute CoFe2O4 nanoparticles which exhibit an unusually normal spinel characteristic and a metallic behavior at room temperature that has not yet been reported in the literature for such materials. A study on the synthesis and characterization of these nanoparticles and the effect of cation distribution on electrical properties was conducted. A xerogel was treated at 300 °C for 20 hours and the as-synthesized powder was structurally and electrically characterized. X-ray diffraction studies indicate that the synthesis pathway was successful in producing crystalline nanoparticles under such mild conditions. TEM images demonstrate that CoFe2O4 consists of monodispersed nanocrystalline particle aggregates with a particle size of ∼10 nm. Mossbauer spectroscopy investigation shows a normal spinel configuration, which is highly unusual for cobalt ferrite. Impedance analyses confirm that the material has a metallic characteristic at temperatures close to room temperature which arises as a consequence of octahedral site occupancy. Above 100 °C, the material displays a metallic-to-insulator transition, which has been related to the predominant OLPT conduction mechanism. An endothermic peak in the DSC curve indicates the occurrence of a structural transition which was associated with the Verwey-type reordering of charged metallic atoms.

Mössbauer effect characterization of some Brazilian iron ores

Characterization of iron ores from different Brazilian locations is illustrated here with the application of Mössbauer spectroscopy to ganga, criptomelane, hematite and chalcosine ores.