Papers by Author: Walter José Botta Filho

Abstract: This work presents the structural comparison of Al₉₀Fe₇Nb₃ alloys obtained by different techniques: (i) partly amorphous powder alloy produced by mechanical milling and their consolidation by hot extrusion (cylindrical bar), (ii) from millimeter portion by casting centrifuged system (square shape), and (iii) from millimeter portion by melt-spinning (ribbon shape). The cylindrical consolidated alloy presented an Al matrix with Al₃Nb and Al₁₃Fe₄ nanophases (intermetallic compounds), the square consolidated alloy resulted in the same structure composed of Al matrix with Al₃Nb and Al₁₃Fe₄ in micro-phase scale. On the other hand, the ribbon alloy exhibits an amorphous matrix with primary Al nanocrystals (fcc-Al phase).

Abstract: Samples of a 2Mg-Fe (at.%) mixture were produced by high energy ball-milling (HEBM) with ball to powder ratio = 20:1, in an argon gas atmosphere, in 190 ml vials (sample-1) to produce powders and in 300 ml vials (sample-2) to produce plates. Both samples were cold-pressed into preforms. The preforms were then extruded at 300°C at a ram speed of 1mm/min., with the following extrusion ratios: sample-1 at 3/1 to ensure porosity and sample-2 at 5/1 to increase the adhesion of the plates. The resulting bulks from samples 1 and 2 were hydrogenated for 24h in a reactor under 15 bar of H₂ to produce the Mg₂FeH₆ complex hydride, and at 11 bar of H₂ to produce both the complex hydride and MgH₂ hydride. In addition, sample-1 was severely temperature-hydrogen cycled to verify its microstructural stability and the influence of grain size on the sorption properties. XRD patterns showed Mg(hc), Fe(ccc) and Mg₂FeH₆ in both samples, and sample-2 also contained MgH₂ and MgO (attributed to processing contamination). DSC results demonstrated that the initial desorption temperature of sample-1 was lower than that of sample-2. However, sample-2 showed faster desorption kinetics, presenting a desorption peak about 73°C below that of sample-1. This could be attributed to the activation/catalyst effect of the MgH₂ hydride. The improvement in sorption properties was attributed mainly to porosity and to the type of employed catalysts.