Leaching of some sulphide minerals of nickel under acidic oxidising conditions

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Solidification behaviour and mechanical properties of cast Mg-alloys and Al-based particulate metal matrix composites under intensive shearing

This thesis was submitted for the degree of Doctor of Philosophy and awarded by Brunel University.Magnesium alloys, as the lightest of all structural metallic materials, and aluminium-based particulate metal matrix composites (PMMCs), offering unified combination of metallic and ceramic properties, have attracted increased interest from the automotive, aerospace, electronic and recreation industries. Current processing technologies for PMMCs do not achieve a uniform distribution of fine-sized reinforcements and produce agglomerated particles in the ductile matrix, which are detrimental to the ductility. At the same time, molten magnesium alloys contain impurities and oxides and when cast conventionally, the final components usually exhibit a coarse and non-uniform microstructure with various casting defects. The key idea in this thesis has been to adopt a novel intensive melt conditioning process, allowing the application of sufficient shear stress that would disperse solid particles present in the melt and offer unique solidification behaviour, improved fluidity and die-filling during casting. The Melt Conditioned High Pressure Die Casting (MC-HPDC) process, where intensive shearing is directly imposed on the alloy melt, which is then cast by the conventional HPDC process, has been used to produce PMMC and magnesium alloy castings. The MC-HPDC process for PMMCs leads to a uniform dispersion of the reinforcement in the matrix, confirmed by quantitative statistical analysis, and increased mechanical performance as indicated by an increase in the hardness and the tensile properties of the composites. We describe a solidification path for aluminium containing magnesium alloys, where intensive shearing prior to casting leads to effective dispersion of solid oxide particles, which then effectively act as nucleation sites for magnesium grains, resulting in significant grain refinement. The MC-HPDC processed magnesium castings have a significantly refined microstructure, with reduced porosity levels and casting defects. Evaluation of the mechanical properties of the castings reveals the beneficial effect of intensive shearing. After careful optimization, the MC-HPDC process shows promising potential for the direct recycling of high purity magnesium die casting scrap, producing casting with mechanical properties comparable to those of primary magnesium alloys

Update on the sudden hearing loss

Aims: Sudden hearing loss is defined as a sensory neural hearing deafness of at least 30 dB in three consecutive speech frequencies that as occurred within the 3 days. It is a medical emergency and the treatment should start as soon as possible; up to now therapies are empirically addressed to improve hearing. Materials and Methods: We have evaluated 558 patients with a diagnosis of sudden hearing loss. In our study, we have investigated possible prognostic factors of hearing loss and their influence on the recovery of the pathology. Results and Discussion: Sudden hearing loss requires an immediate therapeutic intervention. The corticosteroid therapy remains the most accredited one at which are reported the most satisfactory results. We have recognized as negative prognostic factors hearing loss on acute frequencies in the audiometric exam, the presence of a severe-deep hearing loss and a delay in starting therapy. Conclusion: The sudden hearing loss is an otologic emergency which requires an immediate therapeutic intervention. The most accredited therapy remains the corticosteroid therapy. Frequencies we have recognized as negative prognostic factors hearing loss on acute frequencies. The presence of a severe-deep hearing loss, and a delay in starting therapy