Papers by Author: Ana Helena A. Bressiani

Abstract: The shear bond strength between a ceramic material (Titankeramik®, Vita Zahnfabrik, Germany) and two biocompatible titanium alloys was investigated. Ti-13%Nb-13%Zr (TNZ) and Ti-35%Nb-7%Zr-5%Ta (TNZT) alloys were obtained based on the blended elemental technique followed by a sequence of cold uniaxial and isostatic pressing and sintering. Characterization involved microstructural analysis (SEM) and crystalline phase identification (XRD). Subsequently, samples were machined to 4 x 4 mm with a base of 5 x 1 mm. The base metals were blasted with Al2O3 particles followed by the application of a coupling agent and opaque ceramic. After ceramic firing, the specimens were loaded in a universal testing machine (0,5mm/min). XRD revealed the presence of α and β-phases for TNZ, and peaks related to β phases and Nb and Ta for the TNZT alloy. SEM evaluation (TNZ) depicted remaining pores and biphasic microstructure formation. SEM micrographs of the TNZT alloy revealed good densification and a homogeneous β structure. Shear bond strength data (MPa) were statistically analyzed (one-way ANOVA and Tukey test, α=.05) revealing that TNZT (37.6 ± 2.91) presented significant higher values (p=0.0002) compared to TNZ (26.03 ± 2.92). In conclusion, it seems that Ti alloy composition plays a significant role on ceramic bonding.

Abstract: Comparing to hydroxyapatite (HA), which forms a strong chemical bond with the bony tissues, metallic materials are not able to bond with bone. For this reason, a great variety of complex coating methods, such as pulse-laser deposition, ion-beam assisted deposition and plasma-spray has been used to form a HA layer onto metallic surfaces. This study evaluated the performance of the biomimetic technique on apatite-based coating formation on two Tialloys. Ti-13Nb-13Zr and Ti-35Nb-7Zr-5Ta were obtained via powder metallurgy. The Tibased alloys were biomimetically coated using a technique which was modified from the conventional ones using a sodium silicate solution as the nucleant agent. Both alloys presented similar behavior in the evaluated conditions which means the formation of a homogeneous and well defined HA coating. These results show that these new non-toxic Tialloys seem to be very promising for biomedical applications.

Abstract: Calcium phosphates with different Ca/P molar ratio can be obtained depending the precipitation conditions such as pH and temperature. In this work the effect of the pH’s variation during the H3PO4 addition in the synthesis of hydroxyapatite-HA, (Ca/P molar ratio 1.67) by neutralization method, was studied. The H3PO4 addition’s rate was 1.0, 1.5, 8.0 mL.min-1 and in other experiment the H3PO4 was added at a time. After the addition was completed the pH ranged from 7-12. The suspensions were kept during 24 hours for ripening. The precipitate was separated from the suspension by vacuum filtration, washed with distilled water and dried at 70°C/24h. Afterwards the materials were analyzed by thermogravimetric analysis (TGA) with heating rate of 10°C/min in air. The calcination of the powders was accomplished at 800°C/3h with heating rate of 10°C.min-1. The powders were characterized by X-ray diffraction (XRD), infrared spectrometry (FTIR), specific surface area (BET), and scanning electron microscopy (SEM). The results indicated that the ratio of addition of the acid can influence both the morphology and the formation of the phases (HA and TCP) in the obtained powders.

Abstract: In the last years, the porosity in ceramic materials for implants production has motivated the development of various technologies. Calcium phosphate ceramics, in special the tricalcium phosphate - TCP, are very promising as bone substitutes and scaffolds for tissue engineering. The macroporosity incorporation in TCP ceramics by porogenic, foaming and consolidator agent, as globular protein (ovalbumin) was the focus of this work. Preliminary studies of zeta potential were made to have a suitable suspension. Ovalbumin amounts (5-7 wt%) were added to the ceramic slurries and suspensions with a solid percentage higher than 60 wt% were obtained. The interaction albumin/surfactant with detergency properties was evaluated by pH and viscosity measurements. The foam was produced by mechanical stirring. The results suggested that the presence of the surfactant increase the volume and stability of foam. After drying, burnout and sintering (1200oC/30 min.) the phase composition of the foams was determined by X-ray diffraction. The microstructure and porosity were evaluated by scanning electron microscopy. SEM micrographs of the foam show that the structure consists of a permeable porous network, being observed spherical and interconnected pores.

Abstract: The sintering behavior of silicon carbide using alumina, silica and yttria as additives was investigated. Powders containing 90 vol. % SiC and 10 vol. % additives (keeping 1Y2O3:1Al2O3 molar ratio) were sintered at 1950°C/1h, in a dilatometer or a graphite resistance furnace. Thermal treatments were also done from 1500°C/1h up to 1800°C/1h, in order to evaluate the formation of transient crystalline secondary phases. The sintered samples were characterized through XRD, SEM and TEM analysis. The results showed that sintering behaviour is clearly related to the additive composition investigated, as demonstrated by linear shrinkages and linear shrinkages rate curves. Temperatures of particle rearrangment, solution-reprecipitation of SiC grains, as well as secondary crystalline phase(s) formation and dissolution could be revealed after dilatometric analysis. These temperatures are in good agreement with XRD results. Microstructural observations through SEM and TEM analysis are also related to the sintering behaviour.

Abstract: The influence of polymer precursor additions on liquid phase sintering of SiC:Al2O3:Y2O3 has been evaluated. Two polymer precursors were used: polymethylhydrogensiloxane and D4Vi (1,3,5,7-tetramethyl-1,3,5,7-tetraviniylcyclotetrasiloxane). The ceramic phase had the following composition in wt%: 91.6 SiC, 4.2 Al2O3 and 4.2 Y2O3. The composites were prepared using the following ceramic phase to polymer ratios in wt%: 82.7: 17.3; 74.0: 26.0 and 71.5: 28.5. Density measurements were carried out using a helium picnometry and the Archimedes method. The crystalline phases were identified by X-ray diffraction analysis and the microstructures were observed by optical and scanning electron microscopy.

Abstract: Silicon nitride was the first nitride developed for engineering applications. The excellent combination of thermomechanical properties makes silicon nitride a good candidate for applications where high hardness and mechanical properties are fundamental. However, the low fracture toughness of this material limits its use as structural material. The improve of mechanical properties of silicon nitride comes from many factors, like refined microstructure by restraining grain growth, localized stress, crack tip bridging, etc. Within these factors, microstructure formation of the silicon nitride is critically important for the final properties. The design of silicon nitride based composite materials is of particular interest because of their improved high temperature strength and fracture toughness. In this work, Si3N4-TaC particulate composite was investigated. For this study was prepared a basis composition (CB) with 90%wt a-Si3N4, 6%wt and 4%wt Y2O3 and Al2O3, respectively. TaC (20%vol) was added into CB and after mixture, in high-energy milling, the powder was compacted into pellets. The kinetics of sintering was studied by means of dilatometry. The shrinkage rate versus time and temperature curves exhibit two well-defined peaks. The first peak refers to the particle rearrangement process and the second, more pronounced, to solutionreprecipitation process. It is quite clear that the presence of TaC particles has small influence on sintering kinetics of silicon nitride. It was observed the complete a®b-Si3N4 phase transformation. The microstructure shows good homogeneity both in regard of grain size and secondary phase distribution.

Abstract: The use of yttria concentrates was investigated in this study for synthesis and processing of zirconia based ceramics applied as solid electrolyte materials. Terbium, dysprosium, holmium, erbium and ytterbium are the chemical elements, classified as heavy rare earths, that can be found in those concentrates due to their association with yttrium ores. The ceramic characteristics were compared to zirconia-yttria and zirconia-yttria-heavy rare earth oxide systems, containing 3 and 9 mol% of dopant. Powders were prepared by the coprecipitation route and ceramic processing conditions were established to attain relative densities up to 95%. The characterization of assintered pellets was performed by apparent density measurement by Archimedes method, X-ray diffraction, scanning electron microscopy and electrical resistivity measurement by impedance spectroscopy. It was observed that the presence of heavy rare earths in a concentrate containing 85 wt% of yttria has no significant influence on the total ionic resistivity of zirconia based ceramics.