Papers by Author: António Ramirez de Arellano-López

Abstract: Rhombohedral r-plane fracture surfaces in sapphire are analyzed by optical microscopy and by atomic force microscopy. Features of special interest include steps, lines and angles on the surface that appear to have crystallographic origins. A classification and description of these features is given over a scale ranging from hundreds of micrometers to tens of nanometers. Preferential directions in the surface are identified and related to the crystalline orientation of the sample; an attempt is made to identify the underlying phenomenology behind the appearance of each kind of feature.

Abstract: There is a need to develop new tough bioactive materials capable to withstand high loads when implanted in the body and with improved fixation, which led to the production of bioactive coatings on metallic substrates. A new approach, which consists of biomorphic silicon carbide (SiC) coated with bioactive glass, was recently presented. This new material joins the high mechanical strength, lightness and porosity of biomorphic SiC, and the bioactive properties of PLD glass films. In this work, a multiple evaluation in terms of biocompatibility of this new material was carried out starting from the biomorphic SiC morphology and porosity, following with the bioactivity of the coatings in simulated body fluid, and ending with a deep biocompatibility study with MG-63 cells. Different ranges of porosity and pore size were offered by the biomorphic SiC depending on the starting wood. The PLD glassy coatings had a high bioactivity in vitro and both the biomorphic SiC coated and uncoated presented high levels of biocompatibility.

Abstract: Laser scanning confocal microscopy (LSCM) is a microscopic technique which allows for height discrimination. The ability to gather 3D data, along with adequate resolution (around 400 nm), makes the technique suitable for fractography; however, its applications in this area are not sufficiently explored. In this work, LSCM and SEM are applied to the study of fracture surfaces in sapphire and ruby fibers submitted to tensile stress in high-temperature conditions. The obtained qualitative and quantitative information demonstrates the validity of LSCM as a fractographical technique, allowing for clear identification of fractographical features and providing novel insight in the phenomenon of subcritical crack growth (SCG).

Abstract: Glass coated microwires with two metallic nucleus compositions Co57Fe 6.1Ni10B15.9Si11 and Fe36,4Co41,7B11,8Si10,1 with 3 different glass coating compositions (Pyrex – 74.5% SiO2, 15% - B2O3, 3%- Na2O, 2%- Al2O3 1.5% -K2O; Nonex – 73% SiO2, 16.5% - B2O3, 6% - PbO 3 %-Na2O, 1.5% -K2O; and F1 – 70.2% SiO2, 27% - B2O3, 0.8 %-Na2O, 2%- LiO2 1% -K2O;) with very similar geometry (metallic nucleus diameter 7 µm, total diameter 19 µm) have been successfully fabricated and studied. Ferich microwires in as-prepared state show rectangular hysteresis loops, which is connected with the strong internal stresses induced by the fabrication process. Co-rich compositions show inclined hysteresis loop with smaller value of coercive field. The coercivity, Hc, of Co-rich microwires is the highest and of Ferich samples is the lowest in the case of Pyrex coated microwires. The Nonex coated microwires are in the intermediate position while the F1 coated Co-rich microwires have the lowest Hc while the Fe-rich samples have the highest Hc. The mechanical tests show that the best tensile strain yield is observed in samples coated by Nonex glass followed by Pyrex and F1. In this way the variation of the glass coating material allows to tailor both magnetic and mechanical properties of glass coated tiny microwires.