Papers by Author: Ruth Herta Goldsmith Aliaga Kiminami

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Authors: Elias Fagury-Neto, Ruth Herta Goldsmith Aliaga Kiminami
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.
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.
Authors: Vania Caldas de Sousa, C.R. de Oliveira, A.C. Rodrigues, Márcio R. Morelli, Ruth Herta Goldsmith Aliaga Kiminami
Authors: Ana M. Segadães, Márcio M. Morelli, Ruth Herta Goldsmith Aliaga Kiminami
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.
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.
Authors: Ana Cristina Figueiredo de Melo Costa, A.P.A. Diniz, Lucianna Gama, M.R. Morelli, Ruth Herta Goldsmith Aliaga Kiminami
Authors: M.A. Ribeiro, Laédna Souto Neiva, Ruth Herta Goldsmith Aliaga Kiminami, J.B.L. de Oliveira, L. Gama
Abstract: Because of the unique properties that the system TiO2-ZrO2 has, this system has attracted great interest in catalytic circles. In general, the TiO2-ZrO2 oxides composites have a greater surface area and a stronger acidity when compared to the single oxide and they are used as catalysts supports for many catalytic reactions. This work is to evaluate the effect of calcined temperature in structural and morphological characteristics of Ti1-xZrxO2 nanopowders obtained by Pechini method. For this study, the doping value was 0.25 moles of Zr. The powders were calcined at temperature of 500 to 900°C for one hour. The powders were characterized by XRD, SEM and BET. The X-ray diffraction showed that the powders present a TiO2 anatase phase and another of ZrO2 tetragonal. The crystallite size ranged from 4.8 to 14.6 nm for the temperature of 500 to 900°C, respectively. The analysis of scanning electron microscopy showed soft homogeneous agglomerates with particles around 100 nm. The main particles sizes by BET were ranged from 10 to 20 nm, showing that the synthesis is effective to obtain nanometric powders.
Authors: Valmir José da Silva, P.T.A. Santos, Lucianna Gama, Ruth Herta Goldsmith Aliaga Kiminami, Daniel R. Cornejo, A. Azevedo, Ana Cristina Figueiredo de Melo Costa
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.
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