Papers by Author: Lucianna Gama

Abstract: The synthesis by combustion reaction stands as an alternative technique for preparing powders with high purity level, nanometric particle size and low cost. Therefore, this study had as objective the synthesis and characterization of ferrite powders with nominal composition NI_1-xZn_xFe₂O₄ (x = 0.6, 0.7 and 0.8 mol) prepared by combustion reaction using urea as fuel. The influence of the quantity of zinc in the final characteristics of the powders was also investigated. The powders were characterized by X-ray diffraction (XRD), nitrogen adsorption (BET) and scanning electron microscopy (SEM). All compositions resulted in nanometric powders of Ni-Zn ferrites with direct formation of the inverse spinel phase, showing the effectiveness of the synthesis method applied. The increase of zinc's concentration caused an increase in surface area, ranging 4 m²g^-1 from 23 m² g^-1. And the SEM micrographs show that the powders have thinner particle morphology with increasing zinc content.

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: The aim of this work is to evaluate the catalytic activity of NiAl2O4 powders, prepared by combustion reaction with different glycine contents, for the steam reforming of methane. The NiAl2O4 powders were prepared according to the theory of propellants and explosives, using glycine reductant in stoichiometric ratio (Φe = 1) and in excess of 10% and 20% (Φe < 1). During the synthesis, parameters such as flame combustion temperature and time were measured. The samples were characterized by XRD, textural analysis by nitrogen adsorption (BET/BJH), TPR and evaluated as catalysts for the steam reforming of methane. The XRD results showed the presence of NiAl2O4 as major phase and traces of NiO and Ni in all the samples. The glycine content increase caused a decrease of crystallite size and an increase of surface area, from 29 to 39 m2/g. The TPR profiles showed reduction peaks of NiO species in weak interaction with the support, and reduction of nickel present in the NiAl2O4. It was observed that higher methane conversions were obtained in the presence of NiAl2O4 samples prepared using glycine excess. However, it was also observed a rapid deactivation of these catalysts due to high coke deposition onto the active surface phases.

Abstract: This work has for aim to synthesize CeO2 catalytic supports doped with Cu2+ by combustion reaction method. Thus were obtained catalytic supports with the composition Ce1-xCuxO2 and the effect caused by doped element in the structure of the CeO2 was evaluated. The concentration value (x) of the Cu doped took over the values of 0.0; 0.3 and 0.5 mol. The catalytic supports developed were submitted to the structural characterization by X-ray diffraction, morphologic analysis by SEM and textural analysis by means of adsorption-dessorption of N2 by BET method. The results showed that the doped element (Cu) was not completely incorporated in the CeO2 structure and was evidenced that how much larger the quantity of Cu larger maid the disorder of the atomic structure of the obtained material. The analyzed supports present mesoporous nature structure.

Abstract: The selective reaction of CO oxidation (PROX) was named as the most attractive way to reduce the CO concentration, thereby purifying the hydrogen. The aim of this work is to make the structural and morphologic characterization of the NiFe2O4 spinel synthesized by combustion reaction, using glycine as fuel, and to evaluate as catalyst in the reaction of selective oxidation of carbon monoxide in the presence of hydrogen, oxygen and carbon monoxide. The powder was prepared by using a vitreous silica crucible on a hot plate at 480°C and according to stoichiometry established by theory of propellants and explosive. The powder was characterized by X-ray diffraction (XRD), FTIR, textural analyses, transmission electron microscopy (TEM) and catalytic measurements. The results from XRD show characteristic peaks of spinel phase without presence of secondary phases. The morphologic results show surface area of 3.1 m2/g and particle size calculated by TEM of 21.72 nm. The catalyst was active and selective for O2, reaching 100% of conversion.

Abstract: The addition of zirconia to alumina can improve the chemical properties, mechanical stability, acidity and surface area of alumina. The aim of this work is to evaluate the influence of 0.005 moles of zirconia addition to the structure and morphology of alumina powders by combustion reaction. The compositions were called AP (alpha-Al2O3) and AZ (Zr0.005Al1.995O3) and were prepared by using a silica container with direct heating on a hot plate at 480oC until selfignition. The powders were characterized by X-ray diffraction and nitrogen adsorption by BET analysis. The composition AZ showed high surface area (47 m2/g) and small crystallite size (60 nm). The alpha-alumina AP showed a wide agglomerates distribution with small agglomerates size when compared with AZ composition.

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: 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: Diluted magnetic semiconductors (DMS), which have both semiconducting and magnetic properties, are those in which transitions metal ions substitute cations of host semiconductor materials [1]. There is a great interest for DMS for use as the material of spintronics. In this study is reported the structural and morphologic characterization of Zn1.95Co0.05O nanoparticles obtained by Pechini method and combustion reaction. The powders resulting were characterized by X-ray diffraction (XRD) for determination of the phases, crystalline phase and lattice parameter; nitrogen adsorption by BET for determination of the specific superficial area and calculation the particle size from the superficial area and scanning electron microscopy (SEM) for morphologic analysis. The XRD results demonstrated the viability of obtaining crystalline and nanosize powders by the both synthesis routes. For all samples the average crystallite sizes was nanosized, but the powders obtained by reaction combustion is smaller. The SEM micrographs shows that the powders obtained for both syntheses are constituted of soft agglomerates.

Abstract: This work involved a morphological, microstructural and magnetic characterization of nanosized powders and sintered samples of Ni-Zn ferrite doped with chromium. The effect of substituting Fe3+ for Cr3+ on the final characteristics of the powders and sintered samples was investigated. The Ni-Zn ferrite powders were prepared by combustion reaction using nitrates and urea as fuel, based on the concepts of propellant chemistry. The samples were uniaxially compacted by dry pressing (385 MPa) and sintered at 1200oC/2h, using a heating rate of 5°C/min. The Ni-Zn powders and compacted samples were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), and the measures of their magnetic properties. The results revealed the formation of the cubic crystalline phase of the inverse spinel of Ni-Zn-Cr ferrite. The average crystallite size was 21 nm and 57 nm while the saturation magnetization was 47.0 and 73.1 emu/g for the powder and the sintered sample, respectively.