Materials Science Forum Vols. 591-593

Abstract: Induction of an apatite-forming ability on a 100% Y2O3-ZrO2, 100% Al2O3, and 80/20 and 20/80 wt% of zirconia-alumina (Y2O3-ZrO2-Al2O3) composite polycrystals via chemical treatment with 5M H3PO4 have been investigated. The chemical treatments produced Zr-O surface functional groups, which are known to be effective for apatite nucleation in simulated body fluid. It’s believed that Al-OH surface functional groups are not effective for apatite nucleation. I this work was shown that apatite nucleates in substrate of alumina treat and untreated chemically. This implies that Al- OH functional groups are effective for apatite nucleation.

Abstract: In order to improve implant-bone attachment, porous titanium has been used to achieve the ingrowth of bone tissue within the porous structure. Although this biomaterial has shown efficient bone adhesion for orthopedic and dental implants, the ideal surface must have chemical bonds at the implant-bone interface. In this work, samples of pure porous titanium were produced by powder metallurgy technique and submitted to biomimetic process in order to evaluate the material’s bioactivity and to enhance its osteoconductivity. The samples were immersed in modified simulated body fluid (mSBF) which induces the nucleation and growth of a calcium phosphate bioactive film and a chemical bond with titanium. SEM, EDX and FTIR analyses showed that a calcium phosphate deposition occurred without the need of pre-treatments to increase the surface bioactivity. As a result, this research revealed the potential for obtaining a bonelike apatite film on this porous titanium by biomimetic method.

Abstract: The Stacking fault energy (SFE) is an important parameter for metals and alloys. The plastic deformation behavior of face centered cubic (FCC) metals and alloys is directly related to the SFE values. The several methods for determining SFE are critically discussed. The values reported in the 1960s and early 1970s are, in general, 20-30% overestimated. The node dislocation method, due to Whelan, overestimates the SFE. The method based on the critical resolved shear stress is not reliable. The most accurate method is the direct observation of dissociated partials by weak beam in TEM or using HREM (High resolution electron microscopy). Indirect methods based in X-Ray Diffraction and texture may provide reasonable estimates since reliable SFE values of reference metals are available. Selected SFE values for Ni, Cu, Ag, Cu and Al are presented.

Abstract: The aim of this work was to establish a route to produce pre-sintered blocks of Y-TZP (yttria stabilized tetragonal zirconia polycrystal) suitable to be machined in a commercial CADCAM system, used to manufacture crowns and bridge frameworks for dental applications. Two commercial Y-TZP powders were investigated. The powders were pressed with different compaction pressures (40 to 500 MPa) and pre-sintered at temperature ranging from 900 to 1100°C. Vickers hardness, biaxial flexural strength, and linear shrinkage could be correlated to the relative density of pre-sintered samples. Using an empirical equation, pre-sintered blocks with a pre-defined density could be prepared. The blocks withstood the machining in a CAD-CAM system, and the machined and sintered crowns presented good adaptation.

Abstract: Despite of the wide use of hydroxyapatite (HA) for bone repair and regeneration, its brittleness has limited clinical application to less stressed body parts. Thus, evaluation of HA mechanical properties has been an important research matter. The aim of this study is to assess the compressive strength of a stoichiometric HA with 1.66 Ca/P molar ratio, synthesized by hydrothermal method. Cylindrical samples were processed by uniaxial compacting, followed by sintering. Compressive strength of cylindrical samples with 2.0 medium diameter/height ratio was measured according to ASTM C 1424. Load to failure divided by the cross-sectional area of the samples were reported and microstructural characterization was made by MEV-EDS. The compression strength results were compared to values reported in the literature.

Abstract: Reinforcement with yttria stabilized zirconia (YSZ) is an alternative to improve mechanical strength of hydroxyapatite (HAp) ceramic. However, calcium may react with zirconium to form calcium zirconate. In addition, decomposition of HAp to tricalcium phosphate (TCP) occurs with water loss inhibiting ceramic densification. In order to minimize the formation of these compounds, two synthesis routes were compared in this work: coprecipitation of hydrous yttria stabilized zirconia in a calcium phosphate gel medium and powder mixture of individual calcined powders. Composite nominal compositions were fixed at 90 and 95 HAp wt%. Calcium, zirconium and yttrium chlorides and ammonium hydrogen phosphate were the employed precursors. Ammonium hydroxide was the selected precipitation agent. Calcination was performed at 800oC for 1 hour and pellets were sintered in the range of 1150 and 1350oC for 1, 3 and 5 hours. Ceramic samples were characterized by scanning electron microscopy and apparent density measurements. Crystalline phases were quantified by Rietveld analysis of X-ray diffraction patterns. Results indicate that powders prepared by coprecipitation can cause porosity formation due to the higher chemical reactivity during synthesis process.

Abstract: This work has as objective the synthesis for the method by combustion reaction of catalytic supports of α-Al2O3 modified with ZnO and Fe2O3 with and without impregnation of the species it activates (Ni) and your structural and morphologic characterization. The catalytic supports were obtained by method of the synthesis da combustion reaction. The catalytic supports were characterized by XRD, adsorption of nitrogen by BET method and infrared. The results of XRD showed the formation of powders with high cristalinity, characteristic picks of difraction of the phase α-Al2O3 indicating that there was the partial substitution of the ions of Al3+ for Zn2+ and Fe3+ in the hexagonal net of the alumina. The impregnation of the nickel promoted an increasing in the size of the particles, this carried to reduction of the superficial area of the same, of the volume and of the diameter of the pores of the structure of the material. Were accomplished catalytics tests in row of seats scale. The result of catalytic tests showed that the developed catalysts in this work were efficient in the methane conversion process.

Abstract: Ethanol reforming process to produce hydrogen rich-gas stream is performed using Cu/Ni catalyst supported on zirconia and alumina microspheres prepared by hydrolysis method. Theses catalysts were tested in a fixed-bed reactor system employing steam reforming of ethanol. The operating temperature was 550°C and water/ethanol feed ratio 3/1. Although all catalysts were very active for ethanol conversion and very selective towards the desired products, but that one supported on zirconia microspheres was produced slightly better results. The data reveal high activity of the Cu/Ni/ZrO2 catalyst for ethanol steam reforming and presented a good selectivity for H2.

Abstract: The aim of this work is to prepare and characterize Al2O3-ZrO2 powders by Pechine method and to evaluate them as supports for palladium catalysts in the selective reduction of NO with CH4. The effect of aluminum ion on the final characteristics of the zirconia powder is also investigated. The catalytic supports were characterized by X-ray diffraction (XDR), scanning electron microscopy (SEM) and catalytic activity. The XRD data showed the formation of tetragonal zirconia phase, with crystallite size of 6.3 and 6.1 nm for the supports prepared with 0.1 and 0.5 moles of Al3+, respectively. Both supports showed porous and homogeneous agglomerates. Pd/Al2O3-ZrO2 catalysts were active NO reduction by CH4.

Abstract: Zinc oxide was obtained by combustion reaction synthesis method using microwaves energy to provide ignition to the mixture of zinc nitrate, europium and urea. The influence of the europium concentration on the structure, morphology and luminescence characteristics of the ZnO powders was investigated. The proportion of each reagent and fuel was calculated based on the propellants chemistry concepts. The solutions were mixed in a vitreous silica basin and submitted of external heating in a microwaves oven until self-ignition occurred. The resulting powders were characterized by X-ray diffractometer (XRD), granulometric distribution, scanning electronic microscopy (SEM) and emission spectroscopy. The XRD results showed the formation of ZnO:Eu3+ as main phase and Eu2O3 as secondary phase. The powder presented morphology constituted of fine particles agglomerates (<100nm) and red luminescence characteristic from Eu3+ ion.