Papers by Author: Ana Cristina Figueiredo de Melo Costa

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Authors: Criseuda Maria Benício Barros, Sara Verusca de Oliveira, Janaina Benício Marques, Kaline Melo de Souto Viana, Ana Cristina Figueiredo de Melo Costa
Abstract: This research was incorporated the hydroxyapatite in a mineral trioxide aggregate sealer, with the aim of studying this influence in the structure, morphology and radiopacity of the cement to obtain osteoconductive material. The samples were characterized by X ray diffraction (XRD), spectrometry fluorescence X ray (EDX), spectroscopy transform infrared Fourier (FTIR), scanning electron microscopy (SEM) and radiographic appearance. Through the results obtained by XRD for the new sealer observed the formation of phases HAp and MTA evidenced by the presence of phases: CaO, SiO2 and Bi2O verified also by EDX. Through FTIR was observed the presence of absorption bands related to links Ca-O, Si-O and Bi-O present in MTA and P-O present in HAp. The morphology visualized by SEM consists of irregular agglomerates with the formation of pre-sintered particles. The sample MTA/HAp3% presented radiopacity viable for their application as endodontic cement.
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Authors: Ana Cristina Figueiredo de Melo Costa, Kaline Melo de Souto Viana, M.G.C. Porto, E. Souza, Heloysa Martins Carvalho Andrade, Lucianna Gama, Hélio Lucena Lira, J.B.L. de Oliveira
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.
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Authors: Alex Cavalcanti Feitosa, Elvia Leal, D.C. Barbosa, Simoni Margareti Plentz Meneghetti, Ruth Herta Goldsmith Aliaga Kiminami, Ana Cristina Figueiredo de Melo Costa
Abstract: This paper proposes to assess the efficiency of ZnAl2O4 obtained by combustion reaction on the process of esterification and transesterification of soybean oil to biodiesel production. In the synthesis it was used three heating conditions: spiral resistance, muffle furnace, and microwave oven. In order to investigate the influence of the heating source on the structure, morphology, and on the catalytic activity, the samples were characterized by XRD, FTIR, granulometric analysis, TGA, carbon content, TEM, and gas chromatography. The results showed that it was possible to obtain the ZnAl2O4 cubic phase with traces of ZnO. The ZnAl2O4 monophasic was just obtained by the synthesis carried out in the microwave oven and in the electrical resistance. All the samples showed a typical morphology of dense agglomerates and low carbon content. The samples also presented low catalytic activity in the esterification and transesterification process under the adopted conditions.
1919
Authors: P.C. Ribeiro, E.G. da Costa, Lucianna Gama, Ana Cristina Figueiredo de Melo Costa, Ruth Herta Goldsmith Aliaga Kiminami
Abstract: The zinc oxide varistors are ceramic semiconductor devices doped with some metallic oxides such as: bismuth, nickel, manganese, cobalt, and others. The aim of this work is to characterize the varistors, obtained by the Pechini’s method, regarding their microstructure and electrical features. By using chemical synthesis, it has been produced ceramic powders. The powders have been compacted in the form of pellets and sintered at 1200°C/1h. The samples have been characterized by measurements of J x E, XRD and by SEM. The results show that the powders obtained through Pechini’s synthesis method and calcined at 700°C/1h have a particle size of less than 100 nm. The resulting microstructures show heterogeneous morphologies in a shape of pins and presence of inter and intragrain porosity. The electrically characterized results show that the produced varistors present a nonlinearity coefficient of 21 and breakdown voltage of 1590 V/cm.
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Authors: Juliana Pimentel Coutinho, Mirele Costa Silva, Simoni Margareti Plentz Meneghetti, Elvia Leal, Ana Cristina Figueiredo de Melo Costa, Normanda Lino de Freitas
Abstract: The aim of this work is to evaluate the esterification and transesterification activity of ZnAl2O4 catalysts obtained by different ways of heating during the combustion synthesis using glycine as fuel. Samples were prepared according to the propellants and explosives theory using a vitreous silica crucible as container, and as heating source, plate, muffle furnace and microwave oven. After synthesis, the samples were structural and morphologically characterized by: XRD, nitrogen adsorption and carbon content analysis, and employed in the esterification and transesterification reactions, the percentage of biodiesel formed (FAME) was determined by gas chromatography. The samples obtained on the plate, muffle furnace and microwave showed that even using different heating ways, led to the formation of ZnAl2O4 as majority phase, with crystallite sizes of 11, 15 and 10 nm, respectively. The samples present values of surface area ranging from 16 to 77 m2/g, particle size from 17 to 81 nm, and carbon content lower than 11%. The forms used for heating influenced the esterification and transesterification reactions, showing that there was a gap in the production of biodiesel, which is a promising indication that this material has potential to be used as catalysts on the biodiesel production.
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Authors: Normanda Lino de Freitas, Elias Fagury-Neto, Hélio Lucena Lira, Lucianna Gama, Ruth Herta Goldsmith Aliaga Kiminami, Ana Cristina Figueiredo de Melo Costa
Abstract: Among ceramic materials, the alumina has high importance because of its characteristics of resistance and refractory. The possibility to improve the final characteristics of this material, open possibilities for new applications. The aim of this work is to synthesize (α-Al2O3) alumina powders by combustion reaction and to evaluate the effect of the urea content in the final characteristics of the α-Al2O3 powders. Three compositions were studied : a) stoichiometric, b) with 10% of urea reduction and c) with 20% of urea reduction. The initial solution composition was based on the total valence of the reagents by using chemical concepts of the propellant. This powders were characterized by X-ray diffraction (XRD), granulometric determination by laser diffraction, nitrogen adsorption by BET, scanning electron microscopy (SEM), infrared spectroscopy (IR) and helium picnometer. The results showed that the urea reduction change the temperature of the reaction from 525 to 463oC , the characteristics of the powders, and principally the reduction of the particles size.
631
Authors: R.L.P. Santos, M.M. Tavares, Daniel Cornejo, Ruth Herta Goldsmith Aliaga Kiminami, Ana Cristina Figueiredo de Melo Costa
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 Mn0.65Zn0.35Fe2O4 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.
1272
Authors: Ana Cristina Figueiredo de Melo Costa, A.P.A. Diniz, Lucianna Gama, M.R. Morelli, Ruth Herta Goldsmith Aliaga Kiminami
582
Authors: Daniella Cibele Bezerra, Taciana Regina de Gouveia Silva, Edcleide Maria Araújo, Renê Anísio da Paz, Ana Cristina Figueiredo de Melo Costa
Abstract: Composites consist of a mixture or combination of the two or more, micro or macro constituents that differ in shape and chemical composition and, in essence, are insoluble in one another. The polyamide is a polymer that presents dimensional stability, good resistance to impact without notch and excellent chemical resistance. Already the ferrites are absorbers of electromagnetic radiation and have versatility to be used as a composite of ferrites. The composite of polyamide6/ferrite was obtained by mixing 10 and 30wt.% of ferrite added to polyamide 6 in a Torque Rheometer Haake. The objective of this work was to develop of polyamide6/ferrite composites to be used as absorbers of electromagnetic radiation. The results were very promising and showed that occurs interaction between the ferrite and polyamide6.
922
Authors: Joelda Dantas, A.S. Silva, P.T.A. Santos, J.R.D. Santos, D.C. Barbosa, Simoni Margareti Plentz Meneghetti, Ana Cristina Figueiredo de Melo Costa
Abstract: This study aimed to assess the performance of the solid catalyst Ni0.4Cu0.1Zn0.5Fe2O4, synthesized by combustion reaction, over the methyl esterification reaction of the fatty acids present in cottonseed oil. The catalyst was characterized by XRD, FTIR pyridine absorption, Raman spectroscopy, and SEM. The reactions were conducted at 140 and 180°C with molar ratios of 1:3, 1:6 and 1:9, with 2% of catalyst and reaction time of 2 h. The XRD results showed that the single phase ferrite was obtained with surface area of 87 m2/g and with mesoporous characteristic. It was observed from the FTIR pyridine absorption only the presence of Lewis acid sites. The Raman spectra confirm the presence of the inverse spinel phase. The results indicated that at 180°C and molar ratio of 1:9, the conversion of free fatty acids was about 87%.
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