Materials Science Forum Vols. 727-728

Abstract: Among bioceramics materials, bioglasses which exhibits either a bioactive or resorbable behavior has been studied for many applications, such as bone substitutive and regeneration. When in contact with body fluid, the bioglasses can induce the formation of a hydroxyapatite surface layer. In this paper, we studied the bioactivity of a bioglass containing 48 wt %SiO₂, 27 wt% Na₂O, 19 wt % CaO and 6 wt %P₂O₅. After fusion and annealing, the samples were immersed in SBF for different periods, up to 14 days. The samples were characterized through XRD, DRIFT and SEM before and after bioactivity experiments. The overall results suggest the formation of a surface layer of consisting of hydroxyapatite, which was crystallized within seven days after in vitro experiments, leading to a suitable bioactivity. Moreover, the samples showed a glass network with high cohesion due to calcium addition, leading to materials with high corrosion resistance.

Abstract: As alternative for alumina and zirconia implants, silicon nitride based ceramics are considered promising candidate due to its biocompatibility and mechanical properties. However, this materials exhibit a bioinert character, leading to clinical failures. To overcome this problem, a biomimetic coating of hydroxyapatite is proposed in this paper, so that the surface can be bioactive and, consequently, the osteointegration process can be enhanced. Silicon nitride samples were sintered with different additives (Y, La and Yb) and the surfaces before and after coating were characterized by diffuse reflectance infrared Fourier transformed (DRIFT), X ray diffraction (XRD) and scanning electron microscopy (SEM). The results showed that the surfaces of bioinert silicon nitride samples sintered with different additives could be transformed into bioactive by the formation of a hydroxyapatite layer through biomimetic process.

Abstract: The aim of this work is to evaluate the catalytic performance in steam reforming of methane of the NiAl₂O₄ catalysts prepared by combustion reaction with different urea levels. The catalysts were prepared with urea in the stoichiometric proportion, and with excess of 10% and 20%. The samples were characterized by DRX, textural analysis by nitrogen adsorption, SEM, TPR, and then, catalytically evaluated in the methane reforming reaction. The results showed the presence of NiAl₂O₄ and traces of NiO for all the samples. The increase of the urea content caused an increase in the particle size and a reduction in the surface area, from 171 to 35 m²/g. All the samples presented irregular morphology. The TPR curves showed peaks of reduction of the NiO species, and reduction of nickel present in the NiAl₂O₄. Regarding the conversion of methane to synthesis gas, it was observed that the increase of the urea content allowed obtaining higher conversion. However, it was also observed a rapid deactivation of these catalysts due to high coke deposition on the active phases surfaces.

Abstract: The aim this work is to synthesize the CeO₂ in the ceramic powder form through three different methods of synthesis, they are: method of combustion, Pechini method and hydrothermal method. Will be evaluated the influence exerted by these methods of preparing of the metallic oxide on the structural features presented in the same. Three samples of CeO₂ were synthesized in this work, they were analysed by x-ray diffraction, SEM and adsorption and desorption of N₂ by BET method. According to the results has been observed that the synthesis method has great influence on the structural characteristics of CeO₂ obtained. The sample of CeO₂ synthesized by Pechini method showed a structure with a higher percentage of crystallinity and average pore diameter smaller when compared to samples of CeO₂ synthesized by means of the combustion method and of the hydrothermal method. The sample synthesized by the combustion reaction method presented larger agglomerated of unitary particles.

Abstract: This work shows the influence of the fuels aniline, carbohydrazide and glycine on structural and morphological characteristics of ZnAl₂O₄ synthesized by combustion reaction. Samples were prepared according to the propellants and explosives theory using a vitreous silica crucible and a muffle furnace as heating source. During the synthesis was measured the time and temperature of the reaction. After The samples were structurally and morphologically characterized by the following techniques: XRD, nitrogen adsorption / desorption (BET / BJH), and SEM. The higher temperature was achieved by the synthesis using aniline, whose value was of 876°C. XRD results showed that all the samples presented the ZnAl₂O₄ spinel as majority phase and, ZnO and Al₂O₃ as segregated phases. The samples also showed low surface area, varying of 23.6 to 28.7 m²/g, and particle size of 45 to 55 nm, besides mesoporous characteristic and irregular agglomerates formation.

Abstract: This work proposes to study the influence of dilution on the synthesis of ferrites Mn_0.65Zn_0.35Fe₂O₄ using glycine. It was used the reactants/H₂O proportions of 1:0; 1:3.5; 1:7; 1:10, and 1:14 (100 mL of H₂O). During the synthesis were measured the time and temperature of combustion. The samples were characterized by X-ray diffraction and X-ray fluorescence. The dilution in the samples increased with the increasing of the reaction time and flame temperature. For samples synthesized with 1:0, 1:3.5; and 1:7 ratio were observed traces of hematite, and to the remaining samples only the single phase of the Mn_0.65Zn_0.35Fe₂O₄ spinel. The crystallite sizes ranged from 32 to 42 nm.

Abstract: Research in Mn-Zn ferrites have been growing in recent years, mainly because of the properties in high frequency application such as high saturation magnetization, low core losses, which are sensitive to the structure, processing conditions, such as sintering temperature, time and atmosphere. This study aims to evaluate the microstructure and magnetic characteristics Mn_0.65Zn_0.35Fe₂O₄ ferrite sintered in N₂ atmosphere and to microwave energy at 1200°C/2h. The samples were compacted by uniaxial pressing at 200 MPa and sintered in a microwave oven with a heating rate of 50°C/min and sintering time of 30 min. For samples sintered in N₂ atmosphere was used heating rate of 5°C/min with sintering time of 2 hours. The samples were characterized by apparent and bulk density, XRD, SEM and magnetic measurements. The results indicate the formation single phase of Mn-Zn ferrite for sample sintering in N₂ atmosphere, and to sintering by microwave oven observed the phase ferrite Mn-Zn with trace of secondary phase hematite. The density and saturation magnetization were 3.14 and 3.12 g/cm³, 5 and 83 emug^-1 for the samples sintered by microwave energy and N₂ atmosphere respectively.

Abstract: This aim of this work is to evaluate the influence of citric acid/metallic cation ratio of 3:1, 4:1 and 5:1 used in the TiO₂ synthesis by Pechini method in the structure, morphology and photocatalytic activity of methyl red dye. The prepared samples were characterized by X-ray Diffraction (XRD) using Rietveld refinement method, textural analyses, and photocatalytic activity. The results obtained by XRD technique confirm the efficiency of the Pechini method in the preparation of TiO₂ samples with nanosize particle. All samples present anatase phase and presence of rutile as secondary phase with content of 15.6, 10.5 and 18.3%. The isothermal adsorption showed that samples have mesopores characteristics and morphology with irregular shape agglomerates. The sample 4:1 presented better photocatalytic performance discoloring 70% of dye in 24h, indicating that the presence of 10.5% of rutile phase jointly with anatase phase improve the photocatalytic activity.

Abstract: This work involved the synthesis and characterization of Cu_0.5Zn_0.5Fe₂O₄ ferrite powders prepared by combustion reaction for use as soft magnetic materials. The powders were characterized by nitrogen adsorption (BET), XRD, Rietveld refinement, SEM, TEM and magnetic measures. The results indicate that the combustion reaction yielded crystalline powders containing spinel ferrite as the primary phase and traces of Fe₂O₃ as secondary phase. The crystallite size and lattice microdeformation calculated from Rietveld refinements were 36 and 0.24 nm, respectively. The micrographic analysis revealed particles smaller than 100 nm and fine particle agglomerates. The particles were approximately spherical and their size, calculated by TEM, was 29 nm. The magnetic parameters indicated that the Cu-Zn ferrite powders presented closed hysteresis loops and soft magnetic properties.

Abstract: This paper aims to synthesize and characterize nanosized nickel and zinc ferrites (NiFe₂O₄ and ZnFe₂O₄) samples by a combustion reaction method, using glycine as fuel. The performance in HT-WGRS reaction the samples was investigated. The results showed that the combustion reaction was effective in the production of major phases of the spinel ferrite (crystallite sizes of 44 and 27 nm) and presence of the secondary phases, such as Ni and ZnO, with surface area 3 and 115 m²/g for NiFe₂O₄ and ZnFe₂O₄, respectively. HT-WGSR activity was achieved (80%) to NiFe₂O₄ ferrite in the temperature range of 300 - 500°C.