Papers by Author: M.T.D. Orlando

Abstract: Samples of the superconducting ceramics Hg0.82Re0.18Ba2Ca2Cu3O8+ were prepared by solid-vapor reaction technique. The preparation of the ceramic precursor started with a mixture of Ba2Ca2Cu3Ox and ReO2 powders with molar ratio 1:0.18. The precursor material was submitted to annealing under three different partial pressures of oxygen using a mixture of oxygen/argon at ratios: 5/95 (sample A), 10/90 (sample B) and 15/85 (sample C). X-ray powder diffraction analysis of the precursors identified the phases BaCuO2+x, Ba2Cu3O5+x, Ba4CaCu3O8+x, Ca2CuO3 and Ca5Re2O12 at different ratios in the samples, indicating an increment in the oxygen content from sample A to sample C. Finally, the precursors with different oxygen contents were blended with HgO at molar ratio 1:0.82 and treated in a sealed high pressure furnace to produce the high Tc superconducting ceramics. Rietveld refinement of XRD data showed differences in the crystal structures of the samples. The measurement of thermopower at room temperature resulted in distinct values, confirming the different oxygen sample doping.

Abstract: Fine magnetic powder has been produced using the hydrogenation disproportionation desorption and recombination (HDDR) process. The first goal of this work involved an investigation of a range of disproportionation/desorption temperatures between 800 and 900°C with the purpose of optimizing the HDDR treatment for a Pr14Fe80B6 alloy. The cast alloy was annealed at 1100°C for 20 hours for homogenization. The optimum disproportionation temperature for achieving high anisotropy was 820°C. The influence of the reaction temperature on the microstructure and magnetic properties of Pr14Fe80B6 HDDR powders and magnets has been shown. A second stage of this study involved the characterization, for each temperature, of the HDDR processed powder using X-ray diffraction analysis. Samples of the HDDR material have been studied by synchrotron radiation powder diffraction using the Rietveld method for cell refinement, phase quantification and crystallite sizes determination. Scanning electron microscopy (SEM) has also been employed to reveal the morphology of the HDDR powder.