Papers by Author: Julian Martínez-Fernández

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: Biomorphic silicon carbide ceramics is very promising as a natural base material for biomedical applications due to their excellent mechanical-biochemical properties and biocompatible behaviour. This innovative material is produced by molten-Si infiltration of carbon templates obtained by controlled pyrolysis of biological precursors. The final product is a light, tough and high-strength material with predictable microstructure. In this study the possibility to produce biomorphic silicon carbide ceramics using marine precursors is demonstrated. Due to the great biodiversity offered by the marine medium, a previous selection of algae (Laminaria ochroleuca Bachelot de la Pylaie, Undaria pinnatifida (Harvey) Suringar, Saccorhiza polyschides (Lightfoot) Batters and Cystoseira baccata (Gmelin) Silva) and marine plants (Zostera marina L. and Juncus maritimus L.) was carried out, taking into account its microstructure, porosity and interconnectivity of each species. The bioceramization process was evaluated in three phases: original material analysis, pyrolysis process and reactive melt Si-infiltration. For each marine precursor, a detailed study by Scanning Electron Microscopy (SEM) of the natural material, the carbon preform and the final SiC biomorphic product is described. The viability to obtain biomorphic SiC ceramic material for all the selected marine precursors is discussed.

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).