Papers by Author: C. Leroux

Abstract: Porous Titanium Scaffolds were produced by using a rapid prototyping technique. These scaffolds were either coated or not with a calcium phosphate coating via an eletrodeposition method. Rat bone marrow mesenchymal stem cells were cultured on the scaffolds at a density of 106 cells/scaffold for a period of 3 days. Cell proliferation was measured by using the Alamar Blue assay. The scaffolds were observed by SEM and polarized light microscopy. Constructs were then implanted subcutaneously for 4 weeks in syngenic rats. Cells proliferated well after seeding. After subcutaneous implantation, histology and SEM revealed the presence of uniform coatings as well as Ca and P deposits in the non-coated scaffolds suggesting mineralization.

Abstract: Two porous titanium implants with interconnected pore size of 800 and 1200 m in diameter, were fabricated by a rapid prototyping method. Their dimensions and structure accomplished the expected design with accuracy and reproducibility. The porosity of titanium was around 60%. The compressive strength and Young’s modulus were comparable to those of cortical bone with values around 80 MPa and 2.7 GPa, respectively. The implants were implanted bilaterally in the femoral epiphysis of 12 New Zealand Rabbits. After 3 and 8 weeks, abundant bone formation was found in the titanium porous structure. This work demonstrates that macroporous titanium with controlled shape and porosity is a good candidate for orthopaedic and maxilofacial applications.

Abstract: Rare earth oxides have been widely investigated in catalysis as structured and electronic promoters to improve the activity and thermal stability of catalysts. Cerium has an important role in three-way catalysis and fluid catalytic cracking, two significant catalytic processes by their economic relevance and tonnage. Cerium and other rare earths have been studied as possible heterogeneous catalysts at selective oxidation of hydrocarbons. Cerite and monazite are minerals with high concentration of cerium element. Extraction of cerium metal using conventional leaching processes has shown low yields or high costs. The main purpose of this research work is to optimize the parameters in cerium purification stage from this mineral using leaching process. To separate particles with different granulometries, the mineral is ground and fractioned with sieves of 80, 200, 250 and 400 mesh. In order to put off organic components and oxidize cerium(III) to cerium(IV), samples were roasted at 1073K by twenty-four hours. The roasted samples were solubilized by acid attack (leaching) for approximately twenty-four hours; according to the acid used hydrochloric or sulfuric), cerium and other trivalent elements are solubilized as chloride or sulfate solution. Cerium was extracted by selective precipitation at pH~3,4 using ammonium or natrium hydroxide as pH changer. After filtration and drying, the precipitated product was characterized by XRD (x-ray diffraction), and then process efficiency was determined (cerium percentage and the different phases in the powder). Particles granulometry, roasting process (time and temperature), as well as leaching parameters (acid used, time, temperature and concentration of reagents) were the main variables studied.

Abstract: The structural analysis of thin cerium dioxide films doped with Cu, produced by laser ablation for applications in catalytic and gas sensors, was the general aim of the study. The thin films deposited on a (100) silicon substrate were nanocrystalline structure with a well-developed texture. The morphology, as well as the preferred films orientation, is changed with the volume fraction of Cu. The observed changes affect the catalytic properties of the materials obtained which was confirmed by the catalytic tests undertaken with CH4.