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S?ntese e caracteriza??o de tungstatos de c?rio e estr?ncio para fins catal?ticosMoriyama, Andr? Luiz Lopes 21 July 2011 (has links)
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Previous issue date: 2011-07-21 / Conselho Nacional de Desenvolvimento Cient?fico e Tecnol?gico / The main goal of this work was to produce nanosized ceramic materials of the
family of the tungstates (tungstates of cerium and strontium), and test them for their
catalytic activity in processes involving the transformation of methane (CH4). The
methodology used for the synthesis of the ceramic powders involved the complexation
combining EDTA-citrate. The materials characterization was performed using simple
and differential thermogravimetry, x-ray diffraction, transmission electron microscopy,
and energy dispersive spectroscopy (EDS). The microstructure analysis was performed
using the refinement by the Rietveld method, and the crystallite size and distribution of
the materials was elucidate by the Scherrer and Williamson-Hall methods. The
conditions of the synthesis process for the three envisaged materials (SrWO4, SrWO4
using tungsten oxide concentrate as raw material, and Ce2(WO4)3) were adjusted to
obtain a single phase crystalline material. The catalytic tests were carried out in the
presence of methane and synthetic air, which is composed of 21% O2 and 79% N2. The
analysis of the conversion of the reaction was done with the aid of an fourier transform
infrared device (FTIR). The analysis showed that, structurally, the SrWO4 produced
using raw materials of high and poor purity (99% and 92%, respectively) are similar.
The ideal parameters of calcination, in the tested range, are temperature of 1000 ?C and
time of calcination 5 hours. For the Ce2(WO4)3, the ideal calcination time and are
temperature 15 hours and 1000?C, respectively. The Williamson-Hall method provided
two different distributions for the crystallite size of each material, whose values ranged
between the nanometer and micrometer scales. According to method of Scherrer, all
materials produced were composed of nanometric crystallites. The analyses of
transmission electron microscopy confirmed the results obtained from the Williamson-
Hall method for the crystallite size. The EDS showed an atomic composition for the
metals in the SrWO4 that was different of the theoretical composition. With respect to
the catalytic tests, all materials were found to be catalytically active, but the reaction
process should be further studied and optimized. / O objetivo principal deste trabalho foi produzir materiais cer?micos
nanom?tricos da fam?lia dos tungstatos (tungstatos de c?rio e de estr?ncio), e test?-los
quanto ?s suas atividades catal?ticas em processos envolvendo a transforma??o do g?s
metano (CH4). A metodologia empregada para a s?ntese dos p?s cer?micos envolveu o
m?todo de complexa??o combinando EDTA-Citrato. A caracteriza??o dos materiais foi
feita atrav?s das t?cnicas de termogravimetria simples e diferencial, difra??o de raios-x,
microscopia eletr?nica de transmiss?o, e espectroscopia de energia dispersiva (EDS). A
an?lise da microestrutura foi realizada atrav?s do refinamento utilizando o m?todo de
Rietveld, e para a estima??o do tamanho de gr?o e de sua distribui??o foram utilizados
os m?todos de Scherrer e Williamson-Hall. As condi??es de obten??o dos tr?s materiais
desenvolvidos (SrWO4, SrWO4 utilizando concentrado de ?xido de tungst?nio como
mat?ria-prima, e Ce2(WO4)3) foram ajustadas para a obten??o de um material cristalino
monof?sico. Os testes catal?ticos explorat?rios foram realizados na presen?a dos gases
metano e ar sint?tico, composto por 21% de O2 e 79% N2. A an?lise da convers?o foi
feita com o aux?lio de um equipamento de infravermelho ? transformada de Fourier. As
an?lises mostraram que, estruturalmente, os materiais SrWO4 produzidos com mat?riaprima
de elevada pureza (99% de pureza) e oriunda do concentrado de ?xido de
tungst?nio (92% de pureza) s?o semelhantes. Seus par?metros ideais de produ??o,
dentro do que foi testado, s?o temperatura de calcina??o de 1000?C e tempo de
perman?ncia de 5 horas na isoterma. Para o Ce2(WO4)3, as condi??es ideais dentro do
que foi testado s?o temperatura de calcina??o de 1000?C e tempo de perman?ncia na
isoterma de 15 horas. O m?todo de Williamson-Hall forneceu duas distribui??es
diferentes para o tamanho de cristalito de cada material, cujos valores oscilaram entre as
escalas nanom?tricas e microm?tricas. Com o m?todo de Scherrer, todos os materiais
produzidos possu?ram tamanho de cristalito nanom?trico. As an?lises de microscopia
eletr?nica de transmiss?o confirmaram o resultado obtido com o m?todo de Williamson-
Hall para o tamanho de cristalito. A EDS indicou a presen?a de diverg?ncias entre a
composi??o at?mica met?lica te?rica e experimental do SrWO4. Com rela??o aos testes
catal?ticos explorat?rios, os materiais se mostraram ativos por?m o processo reacional
ainda precisa ser melhor estudado e otimizado.
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S?ntese e caracteriza??o do Molibdato de Estr?ncio obtido a partir do m?todo de complexa??o combinado EDTA/Citrato para degrada??o fotocatal?tica de corante da ind?stria t?xtil / Synthesis and characterization of Strontium molybdate obtained from the Complexation Method Combining EDTA/Citrate for photocatalytic degradation dye the textile industrySilva, Mait? Medeiros de Santana e 26 August 2016 (has links)
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Previous issue date: 2016-08-26 / Coordena??o de Aperfei?oamento de Pessoal de N?vel Superior (CAPES) / Este trabalho descreve o planejamento experimental 2? com triplicata no ponto central para produ??o do molibdato de estr?ncio (SrMoO4) atrav?s do m?todo de complexa??o combinado EDTA/Citrato onde investigou-se a influ?ncia do pH (6, 7,5 e 9), tempo de calcina??o (3, 4 e 5h) e taxa de aquecimento (5, 7 e 10?C.min-1) em alguns de seus par?metros qu?micos e f?sicos. Com base na curva de termogravim?trica os p?s de SrMoO4 foram calcinados a 650?C.Os materiais sintetizados foram caracterizados por TG/DSC, DRX, EDX, MEV e ERD. Os par?metros de rede da estrutura cristalina foram obtidos com base no m?todo de refinamento Rietveld. Todos os padr?es de DRX foram indexados segundo a ficha JCPDS 01-085-0586, com estrutura tetragonal e grupo espacial I41/a e o par?metro residual do refinamento da estrutura variou entre 1,035 a 1,292, n?o sendo identificadas fases secund?rias e impurezas. Constatou-se a exist?ncia de diferen?as entre as intensidades relativas m?dias dos picos de difra??o de raios-x. Atrav?s de ferramentas estat?sticas, concluiu-se que a taxa de aquecimento foi a vari?vel independente que demonstrou maior influ?ncia nessa diferen?a. As analises de EDX mostraram a presen?a de desvios entre a composi??o te?rica e experimental para os elementos estr?ncio e molibd?nio; o desvio percentual variou de 0,027 a 3,67% em fun??o das condi??es de s?ntese. De acordo com as micrografias obtidas por MEV, os p?s sintetizados s?o compostos de aglomerados de part?culas, com morfologia esf?ricas irregulares e bipiramidais. De acordo com a an?lise do planejamento experimental, tendo como vari?vel dependente a energia de bandgap, os menores valores obtidos (4,18 e 4,17 eV para pH 6 e 9, respectivamente) foram as amostras calcinadas por 3h com taxa de aquecimento igual a 10?C.min-1 em compara??o aos materiais calcinados nas demais condi??es de s?nteses e os modelos estat?sticos gerados se mostraram capazes de descrever os fen?menos observados. Testes explorat?rios na fotodegrada??o da solu??o sint?tica do corante azul de metileno utilizando o material com Egap de 4,17 eV indicam que o p? testado apresenta influ?ncia na diminui??o da concentra??o do corante para os testes realizados em pH 2 e 5 obtendo aproximadamente 95% e 24% de convers?o respectivamente, e para os teste em pH 9 observou-se que a fot?lise direta ? mais efetiva na redu??o da concentra??o do corante alcan?ando em torno 67% de convers?o, por?m o processo reacional necessita ser mais estudado para melhor compreens?o dos resultados. / This work describes the 2? experimental design with center point in triplicate for the production of strontium molybdate (SrMoO4) through complexation combined Citrate/EDTA method where investigated the influence of pH (6, 7,5 and 9), time calcination (3, 4 and 5 h) and heating rate (5, 7 and 10?C min-1) in some of its chemical and physical parameters. Based on thermogravimetric curve of SrMoO4 powders were calcined at 650?C. The synthesized materials were characterized by TG/DSC, XRD, EDX, SEM and ERD. The lattice parameters of the crystal structure were obtained from the Rietveld refinement method. All the XRD patterns were indexed according to JCPDS 01-085-0586 record with tetragonal structure and space group I41/a and the residual parameter structure refinement ranged from 1.035 to 1.292, secondary phases and impurities not being identified. It was found that there are differences between the average relative intensities of the diffraction peaks of X-rays. Using statistical tools, it was found that the rate of heating was the independent variable showed the greatest influence on this difference. The EDX analysis showed the presence of deviations between the theoretical and experimental composition for strontium and molybdenum components; the percentage deviation ranged from 0.027 to 3.67% depending on the conditions of synthesis. According to the SEM micrographs, the synthesized powders are composed of agglomerates of particles with irregular and spherical morphology bipiramidal. According to the analysis of the experimental design, with the dependent variable bandgap energy, the lowest values (4.18 and 4.17 eV to pH 6 and 9, respectively) were the samples calcined for 3 hours at the same heating rate 10 C min-1 compared to the calcined material in other conditions of synthesis and the statistical models generated have been shown to describe the observed phenomena. Exploratory testing photodegradation of the synthetic solution of methylene blue dye using the material bandgap of 4.17 eV indicate that the tested powder has influence on the reduction of dye concentration for tests carried out in pH 2 and 5 getting approximately 95% and 24 % conversion respectively, and the test at pH 9 it was noted that direct photolysis is more effective in reducing the dye concentration reached around 67% conversion, but the reaction process needs more study to better understand the results.
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Obten??o de ferrita de cobalto atrav?s de dois m?todos de s?ntese: m?todo de complexa??o combinando EDTA/Citrato e m?todo hidrot?rmico / Obtaining cobalt ferrite through two synthesis methods: Complexation Method Conbining EDTA/Citrate and Hydrothermal MethodMedeiros, Indira Aritana Fernandes de 17 December 2013 (has links)
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Previous issue date: 2013-12-17 / Coordena??o de Aperfei?oamento de Pessoal de N?vel Superior / In this work it was synthesized and characterized the cobalt ferrite (CoFe2O4) by
two methods: complexation combining EDTA/Citrate and hydrothermal investigating the
influence of the synthesis conditions on phase formation and on the crystallite size. The
powders were mainly characterized by x-ray diffraction. In specific cases, it was also used
scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), x-ray
fluorescence (XRF) and isotherms of adsorption and desorption of nitrogen (BET method).
The study of the crystallite size was based on the interpretation of x-ray diffractograms
obtained and estimated by the method of Halder-Wagner-Scherrer and Langford. An
experimental design was made in order to assist in quantifying the influence of synthesis
conditions on the response variables. The synthesis parameters evaluated in this study were:
pH of the reaction medium (8, 9 and 10), the calcination temperature (combined complexation
method EDTA/Citrate 600?C, 800?C and 1000?C), synthesis temperature (hydrothermal
method 120?C, 140?C and 160?C), calcination time (combined complexation method
EDTA/Citrate - 2, 4 and 6 hours) and time of synthesis (hydrothermal method 6, 15 and 24
hours). By the hydrothermal method was possible to produce mesoporous powders with high
purity, with an average crystallite size up to 7 nm, with a surface area of 113.44 m?/g in the
form of pellets with irregular morphology. By using the method of combined complexation
EDTA/Citrate, mesoporous powders were produced with greater purity, crystallite size up to
22nm and 27.95 m?/g of surface area in the form of pellets with a regular morphology of
plaques. In the experimental design was found that the hydrothermal method to all the studied
parameters (pH, temperature and time) have significant effect on the crystallite size, while to
the combined complexation method EDTA/Citrate, only temperature and time were
significant / Neste trabalho foi sintetizada e caracterizada a ferrita de cobalto (CoFe2O4)
atrav?s dos m?todos complexa??o combinada EDTA/Citrato e hidrot?rmico, investigando a
influ?ncia das condi??es de s?ntese na forma??o da fase e no tamanho m?dio de cristalito. Os
p?s foram caracterizados principalmente por difra??o de raios-x. Em casos espec?ficos,
tamb?m foi utilizado microscopia eletr?nica de varredura (MEV), espectroscopia de energia
dispersiva (EDS), fluoresc?ncia de raios-x (FRX) e isotermas de adsor??o e dessor??o de
nitrog?nio (M?todo BET). O estudo do tamanho de cristalito foi baseado na interpreta??o dos
difratogramas de raios-x obtidos e estimado atrav?s do m?todo de Halder-Wagner-Langford
(HWL) e de Scherrer. Um planejamento experimental foi realizado com a finalidade de
auxiliar na quantifica??o da influ?ncia das condi??es de s?ntese nas vari?veis-resposta. Os
par?metros de s?ntese avaliados neste trabalho foram: pH do meio reacional (8, 9 e 10),
temperatura de calcina??o (m?todo de complexa??o combinando EDTA/Citrato 600?C,
800?C e 1000?C), temperatura de s?ntese (m?todo hidrot?rmico 120?C, 140?C e 160?C),
tempo de calcina??o (m?todo de complexa??o combinando EDTA/Citrato 2, 4 e 6 hrs) e
tempo de s?ntese (m?todo hidrot?rmico 6, 15 e 24 hrs). Pelo m?todo hidrot?rmico foi
poss?vel produzir p?s mesoporosos com elevado grau de pureza, com tamanho m?dio de
cristalito de at? 7nm, com ?rea superficial de 113,44m?/g e na forma de aglomerados com
morfologia irregular. Ao se utilizar o m?todo de complexa??o combinando EDTA/Citrato
foram produzidos p?s mesoporosos com maior pureza, cristalitos com at? 22nm de tamanho,
27,95m?/g de ?rea superficial e na forma de aglomerados com morfologia regular de placas.
No planejamento experimental foi constatado que no caso do m?todo hidrot?rmico todos os
par?metros estudados (pH, Temperatura e tempo) apresentam efeito significativo no tamanho
de cristalito, enquanto que, para o m?todo de complexa??o combinando EDTA/Citrato,
apenas a temperatura e o tempo foram significativos / 2020-01-01
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