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Search Results: 1 - 10 of 681818 matches for " B. R. A. Neves "
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Estabilidade térmica da zeólita A sintetizada a partir de um rejeito de caulim da Amaz?nia
Maia, A. A. B.;Angélica, R. S.;Neves, R. F.;
Ceramica , 2008, DOI: 10.1590/S0366-69132008000300012
Abstract: zeolite a was calcined at 200, 400, 600, 800 and 1000 °c for 2h to evaluate its thermal stability. the zeolite a was synthesized using kaolin waste from kaolin processing industries for paper coating located in the amazon region. both zeolite a and further calcined products were characterized by x-ray diffraction analysis and scanning electron microscopy. the zeolite a structure remained stable up to 600 °c, where only small variations in peak intensities were observed. at 800 °c the diffraction pattern still exhibited zeolite a but with the absence of some peaks. at 1000 °c nepheline, mullite and probably sodalite were formed. the zeolite a was also heated at 900 and 950 °c to check the two exothermic peaks observed in the dta curve. the x-ray diffraction analysis indicated the presence of nepheline, sodalite and mullite.
Extraction Studies of Cd(II), Cu(II), Mn(II), Ni(II) and Zn(II) using N,N’,N,N’-Bis[(2-hydroxy-3,5-di-tert butylbenzyl)(2-pyridylmethyl)]-ethylenediamine as a Novel Ligand
R. Laus, , , , and,A. dos Anjos,R. E. H. M. B. Osório,A. Neves
Pakistan Journal of Analytical and Environmental Chemistry , 2008,
Abstract: In the present study, the use of N,N’,N,N’-bis[(2-hydroxy-3,5-di-tert-butylbenzyl)(2-pyridylmethyl)]-ethylenediamine (H2L) as ligand was evaluated in the liquid-liquid (water-chloroform) extraction of Cd(II), Cu(II), Mn(II), Ni(II) and Zn(II). Experiments were carried out to determine the pH for maximum extraction for each metal ion by ligand, maximum extraction capacity, extraction kinetics and extraction selectivity. The results revealed that the extraction of metal ions is dependent on the pH: maximum extraction maximum was obtained in the pH range of 4.5 - 6.0 for Cu(II) and 8.0 - 9.0 for Zn(II). Cd(II) and Mn(II) were best extracted at pH 9.0 and Ni(II) at 10.0. The ligand H2L was effective for the extraction of Cd(II), Cu(II) and Zn(II) (extraction efficient, %E ~100%), whereas %E of 76% and 23.5% were observed for Mn(II) and Ni(II), respectively. The ligand presented high selectivity for the extraction of Cu(II) at pH 4.0.
Microscopia de varredura por sonda mecanica: uma introdu??o
Neves, B. R. A.;Vilela, J. M. C.;Andrade, M. S.;
Ceramica , 1998, DOI: 10.1590/S0366-69131998000600002
Abstract: during the last few years, the structural analysis of materials has gone through a great advancement which is related to the development of scanning probe microscopy techniques. originated in the last decade, these techniques were strengthened and spread worldwide during the 90s. they constitute a new methodology of analysis, involving both knowledge and technology from a multitude of different areas. their large application spectrum is due, mainly, to: large nanometric-scale resolution; capability of operation in air, liquid or in vacuum environments; and the great quantitative magnification in the z direction. in this paper, the basic ideas concerning the most utilized techniques are described. applications of each technique, evidencing its potentialities in nanostructural analysis, are also illustrated by some examples of works carried out at the laboratório de nanoscopia of the funda??o centro tecnológico de minas gerais - cetec.
ESTUDO DA PASTEURIZA O DA POLPA DE GRAVIOLA
C. K. B. TEIXEIRA,E. C. A. NEVES,R. S. PENA
Alimentos e Nutri??o , 2009,
Abstract: Estudou-se a pasteuriza o da polpa de graviola (Annona muricata L.), visando estabelecer condi es simples e eficientes para sua conserva o. Foram realizadas avalia es microbiológica, enzimática e de cor da polpa, para identificar parametros a serem utilizados no acompanhamento da pasteuriza o. O produto foi submetido a tratamento térmico, em copos de inox, em diferentes tempos (1 a 300 seg) e temperaturas (70°C a 90°C), para identificar o efeito destas variáveis sobre parametros de qualidade do produto. Constatou-se que os tratamentos n o provocaram varia o na atividade da peroxidase, contagem de bactérias, bolores e leveduras e cor da polpa. Em seguida foram realizadas pasteuriza es, em escala piloto, a 80°C e 90°C; sendo os produtos estocados a 25°C e avaliados durante 120 dias. A redu o da atividade da peroxidase e da concentra o de bactérias, bolores e leveduras, a níveis aceitáveis, e a manuten o da cor, demonstraram a eficiência dos processos térmicos. A manuten o destes parametros, nos níveis aceitáveis, durante a estocagem, confirmou a aplicabilidade dos processos, sem a necessidade da adi o de conservante na polpa. A pasteuriza o da polpa de graviola a 80°C ou 90°C, mostrou ser um tratamento térmico adequado para a conserva o do produto, proporcionando 120 dias de vidade- prateleira à temperatura ambiente ( 25°C).
Microscopia de varredura por sonda mecanica: uma introdu o
Neves B. R. A.,Vilela J. M. C.,Andrade M. S.
Ceramica , 1998,
Abstract: A análise estrutural de materiais experimentou um grande avan o nos últimos anos, associado ao desenvolvimento das técnicas de Microscopia de Varredura por Sonda Mecanica, surgidas na década passada e consolidadas nos anos 90. Trata-se de um enfoque analítico inteiramente original, envolvendo conhecimento e tecnologia multidisciplinar, de amplo espectro de aplica o, devido, principalmente, à resolu o em escala nanométrica, à facilidade de opera o ao ar, em meio líquido e em vácuo e à possibilidade de grandes amplia es na dire o z. Neste artigo, s o descritos os princípios básicos das técnicas mais utilizadas, ilustrados através de exemplos de trabalhos realizados pelo grupo do Laboratório de Nanoscopia da Funda o Centro Tecnológico de Minas Gerais - CETEC. S o apresentados exemplos obtidos em diversas tipos de materiais, visando mostrar a potencialidade destas novas técnicas de análise nanoestrutural.
Utiliza??o de rejeito de caulim da Amaz?nia na síntese da zeólita A
Maia, A. A. B.;Saldanha, E.;Angélica, R. S.;Souza, C. A. G.;Neves, R. F.;
Ceramica , 2007, DOI: 10.1590/S0366-69132007000300017
Abstract: zeolite a and hydroxysodalite were synthesized after kaolin wastes from kaolin processing industries for paper coating, located in the amazon region. the waste is mainly composed by kaolinite, which has the same sio2/al2o3 ratio requested for those two zeolites. thereby, synthesis process may occur in two steps: 1) the kaolin was submitted to thermal treatment, through calcination process at 700 °c for 2 h, in order to obtain the metakaolinite phase. the metakaolinite obtained reacted with naoh solution, in hydrothermal conditions, using autoclaves, at the following temperatures: 80, 110 and 150 °c for 24 h. the starting materials were identified and characterized by means of x-ray diffraction (xrd) and scanning electron microscopy (sem) analysis and synthesis products were characterized by means of xrd, sem, thermal methods (dta-dtg) and fourier transformed infrared spectroscopy (ftir). a mixture of zeolite a and hydroxysodalite was obtained through this process at 150°c. in the temperature of 110 oc there was only the zeolite a formation. nevertheless, in the lowest synthesis temperature (80°c) there was no crystalline material formation for the established conditions.
Análise da influência do tratamento de purifica??o no comportamento de inchamento de argilas organofílicas em meios n?o aquosos
Ferreira, H. S.;Menezes, R. R.;Ferreira, H. S.;Martins, A. B.;Neves, G. A.;Ferreira, H. C.;
Ceramica , 2008, DOI: 10.1590/S0366-69132008000100011
Abstract: bentonite clays play important roles in oil based drilling fluids. however, clay impurities and the wrong choose of the quaternary ammonium salt used in the organophilization process can lead to organoclay-fluid low interactions. thus, this work has as aim study the influence of the purification process and quaternary ammonium salts on the swelling behavior in oil media of organophilic clays. the bentonite clay was purified using a sedimentation process and organoclay were prepared using alkyl dimethyl benzyl ammonium chloride (dodigen), distearyl dimethyl ammonium chloride (praepagen), cetyl trimethyl ammonium chloride (genamin) and cetyl trimethyl ammonium bromide (cetremide). the organoclays were characterized by x-ray diffraction and particle size distribution determination. the foster swelling tests were conducted using ester, parafine and diesel oil. the results showed that the purification process reduced the amount of bentonite clay impurities. the purified organoclay treated with praepagen and genamim have foster swelling values in ester, diesel oil and parafine higher than that of the natural organoclay and commercial clay.
Caracteriza??o mineralógica e geoquímica e estudo das transforma??es de fase do caulim duro da regi?o do Rio Capim, Pará
Carneiro, B. S.;Angélica, R. S.;Scheller, T.;Castro, E. A. S. de;Neves, R. F.;
Ceramica , 2003, DOI: 10.1590/S0366-69132003000400008
Abstract: the capim region (pará state, northern brazil) is the most important kaolin district in the amazon region, with the largest brazilian reserves of high whiteness kaolin for the paper coating industry. the main ore (soft kaolin horizon) is located at a depth of about 20 m, being covered by a hard, iron-rich kaolin level, also called flint or semi-flint kaolin, besides a sandy-clay overburden. the beneficiation of this kaolin produces large volumes of wastes, composed mainly of coarse-grained kaolinite, deposited in basins that occupy extensive areas. the main objective of this work is to carry out mineralogical and geochemical studies of the hard kaolin, and to evaluate its thermal transformations through calcination up to 1500 oc. the results show a mineralogical composition dominated kaolinite. the evaluated thermal transformations allows us to describe a series of chemical reactions from kaolinite to metakaolinite and further development of spinel, cristobalite and mullite. for the two analyzed samples, such transformations can start at different temperatures as a result of the different chemical compositions, mainly the iron contents.
X-ray scattering from self-assembled InAs islands
Malachias, A.;Neves, B. R. A.;Rodrigues, W. N.;Moreira, M. V. B.;Kycia, S.;Metzger, T. H.;Magalh?es-Paniago, R.;
Brazilian Journal of Physics , 2004, DOI: 10.1590/S0103-97332004000400009
Abstract: in this work several structural and chemical properties of self-assembled inas islands grown on gaas(001) are studied using surface x-ray scattering with synchrotron radiation. the technique of x-ray diffraction under grazing incidence condition was employed to differentiate coherent and incoherent islands. we used a model of a strained pyramidal island to interpret the x-ray results and correlate size and strain-state of these islands. the degree of gaas interdiffusion in the islands was inferred from the variation of volume of the unit cell. the poisson's ratio of the two materials involved establishes a limit of tetragonal distortion for this material. any variation in this distortion is associated with the presence of ga inside the islands.
Influence of tomato components in the quantification of four pesticides by gas chromatography
Pinho, Gevany P.;Neves, Ant?nio A.;Queiroz, Maria Eliana L. R.;Silvério, Flaviano O.;Marthe, Deyse B.;
Journal of the Brazilian Chemical Society , 2012, DOI: 10.1590/S0103-50532012000200015
Abstract: the matrix effect in gas chromatographic analysis is attributed to the presence of coextractives in organic phase obtained in the extraction process. this work reports the quantification study of increased chromatographic response of four pesticides in organic extracts of tomato extracted by solid-liquid extraction with low temperature purification (sle-ltp). the pesticides chlorpyrifos, λ-cyhalothrin, cypermethrin and deltamethrin showed an increased chromatographic response after the saturation of the chromatographic system with multiple injections of organic extracts of tomato. it was also found that the greater the retention time, the greater the matrix effect, and that the internal standard reduces the matrix effect but does not eliminate it. the matrix effect measured by the analytical curves (in acetonitrile and matrix extract) was 27% for chlorpyrifos, 46% for λ-cyhalothrin, 96% for cypermethrin and 180% for deltamethrin.
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