Papers by Author: Ana Helena Almeida Bressiani

Abstract: A nanosized magnesium substituted beta-tricalcium phosphate (Mg:β-TCP) was synthesized by an aqueous precipitation method, at room temperature, in one single step. In the present study, the novel and stable Mg:β-TCP resulted in a crystalline and spherical nanoparticles (diameter of approximately 20 nm) with mesoporous structures and a high specific surface area (about 574 m²/g). These special characteristics make this novel crystalline mesoporous Mg: β-TCP nanoparticles ideal candidates for drug delivery system and a promising non-viral vector for gene therapy.

Abstract: Alumina-mullite composites with low shrinkage can be made by reaction bond using mixtures of alumina, aluminum and silicon carbide. In this work, an alternative route is used to produce alumina composites with low shrinkage. Here alumina samples containing additions of 10 and 20 wt% of a preceramic polymer were warm-pressed and treated in the range of 900 -1500°C to produce alumina based composites. The obtained composites were analyzed by linear shrinkage and compared to pure alumina samples sintered at the same temperature range. It were also evaluated the density variation and crystalline phases formed during heat treatment of alumina composites. Results showed that alumina-silicon oxycarbide and alumina-mullite composites were obtained with lower shrinkage than pure alumina samples.

Abstract: Titanium and its alloys are widely used as orthopedic and dental implant materials. However, they cannot bond with bone directly and promote new bone formation. It is desirable to provide a bone-bonding ability to Ti metal and its alloys. This ability can be achieved by surface modification such as chemical treatments. The aim of this study was to evaluate in SBF the apatite-forming ability of Ti subjected to different pre-treatments. Titanium laminated and samples Ti obtained by powder metallurgy were compared. The pretreatments studied were the alkali-treated; alkali and heat-treated; acid and alkali-treated; alkali-CaCl2-heat and hot water treatment. The groups were soaking in SBF for 1, 3, 6 and 9 days in equipment with constant agitation at 36.5°C. The obtained coatings were analyzed by diffuse reflectance spectroscopy on the infrared (DRIFT) and scanning electron microscopy (SEM). The apatite formation was present in all groups; however, the apatite-coating was more effective in samples obtained by powder metallurgy.

Abstract: Titanium alloy are widely used in biomedical applications due to their excellent properties such as high strength, good corrosion resistance and excellent biocompatibility. Researches are being developed with elements such as Nb and Zr that reach all criterions for excellent biocompatibility and provide titanium alloys with Young’s modulus close to human bone. The aim of this work was to produce Ti-27Nb-13Zr alloy with different milling times by powder metallurgy process. The mixtures were performed by high energy milling and sintering in high vacuum furnace with temperature of 1300 °C / 3 h. The microstructures of samples were analyzed by SEM and XRD, while the mechanical behavior was evaluated by elastic modulus and Vickers hardness test. The diffraction results of sintering treatment indicate that the alloys are composed of α and β phases. Images obtained by SEM indicate the formation of equiaxial structures. Vickers hardness measurements from sintered samples with 1300 °C / 3 h indicate mean values around 413, 473 and 609 HV for 2, 6 and 10 hours of milling, respectively. The values of elastic modulus enable use the alloy as biomaterial.

Abstract: In this present work Ti-13Nb-13Zr alloy was produced by PM using planetary ball mill with zirconium oxide grinding bowl and balls to reduce contamination. The effect of milling time upon microstructure and microhardness was studied. Powders have been produced by hydrogenation of Ti, Nb and Zr at 1MPa. Milling speed was 200 rpm during 90 to 360 min. Sintering was carried out at 1150°C during 10h. Powder size distribution was analyzed using CILAS equipment and chemically characterized by X-Ray Fluorescence (XRF). Microhardness was determined by means of a Vickers microhardness tester. Microstructure and phases were analyzed employing scanning electron microscopy (SEM) and X-Ray diffraction.

Abstract: The potential of porous materials for applications in the medical, engineering and pharmaceutical areas has been widely reported. Several processing techniques have contributed to the progress in research involving porous biomaterials. To this purpose, a globular protein based (i.e. ovalbumin) consolidation approach has been proposed. In the present study, a porous hydroxyapatite: -tricalcium phosphate - biphasic ceramics (BCP), was processed by direct consolidation using the protein-action technique. The processed porous ceramic exhibited appropriate pore configuration in terms of size, morphology and distribution. BCP cylindrical samples were implanted in male rabbits tibia to the evaluation of the initial biocompatibility and osseointegration for a 30 days period. The morphological analyses, optical microscopy and scanning electron microscopy evaluated the osseointegration. A rough surface pattern displayed by the ceramics seemed to have improved cell adhesion and proliferation processes. Furthermore, the open porosity of samples was an essential requirement for a suitable bone-implant osseointegration. In conclusion, this study revealed that the porous matrices obtained, promoted suitable development for bone tissue growth and also properties for osseoconduction and osseointegration.

Abstract: Studies of titanium and its alloys commonly used as biomaterials aim to improve bone-implant interface related problems, which may determine the quality, bone repairing time and therefore the implant clinical success. The goal of this study was to evaluate, in rats, osseointegration of macroporous implants produced by powder metallurgy (PM) method with controlled addition of gelatin. As control group, samples of commercially pure titanium (cpTi) and Ti-13Nb-13Zr alloy obtained by the PM process were used. To obtaining the porous samples, at most 15% in weight of gelatin was added to metallic powders, the samples were thermally treated in vacuum furnace, and sintered at 1150°C. The osseointegration evaluation was performed in Wistar rats, males, for a 28 days period. The morphological analyses, optical microscopy and scanning electron microscopy (SEM), evaluated qualitatively the osseointegration. The PM process modified by addition of gelatin provides with success the obtaining of porous metallic implants. Pore size obtained by this technique allowed the necessary nourishing to cell survival, proving that pores and channels form a high interconnectable network represented by the osseointegration and osteoconduction feature of the porous alloy.

Abstract: Machining processes require tool materials with properties such as high hardness at elevated temperature, high fracture toughness and chemical stability with the workpiece. Advances in science and industry, as well as the development of harder materials have permitted cutting tool technology to evolve. In cutting processes, the contribution of different wear mechanisms to total wear is related to the mechanical and chemical properties of the two materials in contact. The high temperatures at tool-workpiece contact zones often result in diffusion of material from the workpiece to the cutting tool. Diffusion experiments were carried out to understand wear mechanisms involved at cutting edges of ceramic tools and the influence of microstructure on diffusion without the interference of mechanical wear processes. The chemical stability was analyzed from static interaction couple experiments at 1100°C with ceramic composite materials and gray cast iron. To investigate the influence of grain size on diffusion, sub-micrometric and nanometric alumina based composites with NbC as the second phase were used. These experiments showed that the influence of grain size on diffusion and the relative inertness of the composites in the presence of gray cast iron.

Abstract: High performance porous structural ceramics have been widely studied. Silicon nitride is an interesting material for this application because bodies with high mechanical strength, achieved as a result of “in situ” anisotropic grain grown, can be obtained. In this study, Si3N4 bodies with different porosity related aspects (percentage, morphology, etc.) are made using the sacrificing template method, by changing the percentage (vol%) and the drying method of the mixture as well as the sintering time. The porosity, apparent density (Archimedes method), microstructure (SEM) and the mechanical strength (in compression) of these bodies were determined. It was thus possible to relate the type and amount of starch with the porosity and mechanical properties of the bodies.

Abstract: The increased interest in nanostructured materials is due to improvements in the mechanical properties presented for these materials. Significant increases in properties such as hardness, wear resistance and in some cases, strength and toughness of nanostructured ceramics have been reported, compared to conventional ceramics. High-energy milling can lead to selfsustaining reactions in a variety of systems. In this study, reactive high-energy milling was used to synthesis niobium carbide (NbC) nanoparticles. The reaction products were de-agglomerated and mixed with commercial ultra-fine alumina powder to produce alumina matrix nanocomposites with 5vol% of nanometric NbC. Alumina/NbC nanocomposite produced using powder obtained by reactive present good microstructural characteristic, high densities, good hardness and higher toughness. What makes this material an interesting alternative for production of ceramic cutting tools.