Materials Science Forum Vols. 530-531

Abstract: Triaxial porcelains for utilization in electric applications use alumina in its composition replacing quartz in order to improve mechanical strength. This property is a critical parameter for the application of this product. As a consequence of that, in this work, it was evaluated the mechanical strength, analyzing porcelain hardness and toughness by the indentation test, a fast way for measurement of strength. It was studied the different models used in the measurement of these parameters found in literature. It was verified which procedures are better for this type of material, comparing to values of toughness obtained by the method of Fracture Mechanics using notched samples. It is also presented technical characterization and photomicrographs of the analyzed samples.

Abstract: Surgical implant coatings and grafts for tissue replacement have been made by porous surface materials to improve the implant to bone attachment. In this work, porous titanium samples were produced via powder metallurgy techniques and submitted to the biomimetic process in order to enhance its osteoconductivity. This process allows a nucleation and growth of a calcium phosphate film which makes a chemical bond with titanium. Therefore, it avoids the looseness of this film from substrate. The samples were chemically treated, heat treated at different temperatures and soaked into a modified body fluid solution (mSBF) during periods of 2 and 7 days. Samples with and without pretreatments and not soaked in mSBF were used as controls. SEM and EDX analyses detected a calcium phosphate phase on the sample surfaces treated at 400°C and 600°C and soaked in mSBF for 2 and 7 days. The results demonstrated the potential of the methodology applied for obtaining a bonelike apatite film on porous titanium samples processed by powder metallurgy.

Abstract: In this work, the effects of alumina additions on the properties of the ZrO2-Al2O3 ceramic composites were investigated. Samples of ZrO2 with Al2O3 additions varying between 0 and 30wt-% were prepared. The powder mixtures were milled, compacted by uniaxial cold pressing and sintered at 16000C, in air, for 2 hours. The sintered samples were characterized by their relative density, phase composition and microstructure. As mechanical properties at room temperature, their Vickers hardness and fracture toughness were determined: In all sintering conditions and Al2O3 amounts, the samples presented relative density higher that 99%. The Al2O3 addition produces a linear increase of the hardness, reaching values between 1350 and 1610 HV for the addition of 0 and 30% of alumina, respectively. The fracture toughness was near to 8 MPam1/2 in all conditions. The phase composition, microstructure and relative density were correlated in order to interpret the mechanical properties obtained.

Abstract: In this study, the tricalcium phosphate [β-Ca3(PO4)2] behaviour using MgO and TiO2, respectively as additives has been investigated. The introduction of these additives is to control the phase transition of TCP during thermal process. The tricalcium phosphate (β,α) phases change when the temperature of sintering increase and/or during cooling down. To investigate the phase transition we examined tricalcium phosphate powder doped using 5 mol % of MgO or TiO2. The β-TCP and additives powders were mixture with acetone and dried using rota-vapour to eliminate all the solvent at 45°C for 3 h. After this procedure the powders were uniaxially pressed at 50 MPa and sintered in air-atmosphere at 1100°C to 1200°C for 5 h. All the sintered compacts were measurements by relative density, porosity, shrinkage, shrinkage rate, and the polished and fracture surfaces were investigated using a scanning electron microscope (SEM). To verify the transition phase the differential thermal analysis (DTA) and X-ray diffraction studies were carried out. The experimental results of relative density showed 92 % (MgO) and 90 % (TiO2) at 1200°C.

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: 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: 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: 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: Phase composition of calcium phosphate ceramics is a characteristic directly related to the biological response of implants due to the differences in mechanical and biochemical properties of these compounds. In this sense, it was evaluated in this work the crystalline phase evolution of calcium phosphates samples synthesized by wet precipitation route. Fixing Ca/P atomic ratio as 1.67, precipitation was carried out from heated aqueous solutions of calcium chloride and ammonium hydrogen phosphate, in ammonium medium (pH = 10). After washing and drying steps, calcination was performed at 600 to 1100 oC for 1 and 3 hours. Milled and pressed powders were sintered at 1250 oC for 1 hour. Samples were characterized by X-ray diffraction, chemical analysis, scanning electron microscopy, gaseous adsorption, laser diffraction and apparent density measurements. Results indicate the formation of a biphasic calcium phosphate ceramic containing hydroxyapatite as a major phase and β - tricalcium phosphate, the later obtained by heat treatment above 600 oC.

Abstract: Zirconia has received much attention as catalysts for its high surface area and acid-base property. The textural and acid-base properties of ZrO2 depend on both, the synthesis procedure and the calcinations temperature. The aim of the present study is the preparation and characterization of nickel/cupper/zirconia and cobalt/cupper/zirconia microspheres using hydrolysis process. This process is based on homogeneous hydrolysis of droplets of a concentrated ZrO2(NO3)2-urea solution after adding hexamethyletetramine. Gelation was conduced successfully and the gel spheres were dried at 80 °C. The dried gel spheres were thermally treated at 550 °C. Characterization of the samples was performed using X-ray diffraction (XRD), BET nitrogen adsorption, scanning electron microscopy (SEM), thermogravimetric (TGA) and UV-Vis spectroscopy. The performance of the microspheres was investigated as catalysts in steam reforming of ethanol. Theses catalysts exhibit a good selectivity for hydrogen.