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  • About
  • The Global ETD Search service is a free service for researchers to find electronic theses and dissertations. This service is provided by the Networked Digital Library of Theses and Dissertations.
    Our metadata is collected from universities around the world. If you manage a university/consortium/country archive and want to be added, details can be found on the NDLTD website.
1

EFEITO MOSSBAUER EM LIGAS FERRO-NIQUEL OBTIDAS POR DECOMPOSICAO DE OXALATOS / Mössbauer effect in iron-nickel alloys obtained by decomposition of oxalates

Franco, Hugo 11 August 1982 (has links)
Investigamos o fenômeno da segregação de fases em ligas ferro-níquel de estrutura cúbica de faces centradas, na região do invar (~35 a 50% Ni ). As amostras foram preparadas pela decomposição térmica de oxalatos mistos Fe1-x Ni xC2O4.2H20, a temperaturas selecionadas; este método de preparação assegura que o equilíbrio termodinâmico é atingido muito mais rapidamente que pelos métodos convencionais. As amostras foram examinadas por espectroscopia Mössbauer; evidências anteriores mostraram que as duas f ases resultantes da segregação diferem notavelmente em suas propriedades magnéticas, mas são idênticas do ponto de vista estrutural, o que impossibilita a sua distinção pelas técnicas usuais de raios X. Amostras foram preparadas com concentrações entre 36 e 50% Ni e a temperaturas entre 350 e 600°C. O aparecimento de uma linha central no espectro Mössbauer foi usado como critério para a ocorrência de segregação. Dessa forma, mapeamos a fronteira do \"gap\" de miscibilidade nessa região do diagrama de fases do Fe-Ni. / We have investigated the phenomenon of phase segregation in iron-nickel alloys with a face-centered cubic structure, in the invar region (~35 to 50% Ni ). The samples were prepared by thermal decomposition of mixed oxalates, Fe1-x Ni xC2O4.2H20, at selected temperatures. This method ensures that thermodynamic equilibrium is reached much more rapidly than by conventional methods. The samples were examined by means of Mössbauer spectroscopy; previous evidence has shown that the two phases resulting from segregation differ markedly in their magnetic properties but are structurally identical, which renders their distinction impossible by usual X-ray techniques. Samples were prepared at concentrations between 36 and 50% Ni and at temperatures ranging from 350 to 600°C. The appearance of a central line in the Mössbauer spectrum was taken as the criterion for segregation occurrence. We thus mapped the miscibility gap boundary in this region of the Fe-Ni phase diagram.
2

EFEITO MOSSBAUER EM LIGAS FERRO-NIQUEL OBTIDAS POR DECOMPOSICAO DE OXALATOS / Mössbauer effect in iron-nickel alloys obtained by decomposition of oxalates

Hugo Franco 11 August 1982 (has links)
Investigamos o fenômeno da segregação de fases em ligas ferro-níquel de estrutura cúbica de faces centradas, na região do invar (~35 a 50% Ni ). As amostras foram preparadas pela decomposição térmica de oxalatos mistos Fe1-x Ni xC2O4.2H20, a temperaturas selecionadas; este método de preparação assegura que o equilíbrio termodinâmico é atingido muito mais rapidamente que pelos métodos convencionais. As amostras foram examinadas por espectroscopia Mössbauer; evidências anteriores mostraram que as duas f ases resultantes da segregação diferem notavelmente em suas propriedades magnéticas, mas são idênticas do ponto de vista estrutural, o que impossibilita a sua distinção pelas técnicas usuais de raios X. Amostras foram preparadas com concentrações entre 36 e 50% Ni e a temperaturas entre 350 e 600°C. O aparecimento de uma linha central no espectro Mössbauer foi usado como critério para a ocorrência de segregação. Dessa forma, mapeamos a fronteira do \"gap\" de miscibilidade nessa região do diagrama de fases do Fe-Ni. / We have investigated the phenomenon of phase segregation in iron-nickel alloys with a face-centered cubic structure, in the invar region (~35 to 50% Ni ). The samples were prepared by thermal decomposition of mixed oxalates, Fe1-x Ni xC2O4.2H20, at selected temperatures. This method ensures that thermodynamic equilibrium is reached much more rapidly than by conventional methods. The samples were examined by means of Mössbauer spectroscopy; previous evidence has shown that the two phases resulting from segregation differ markedly in their magnetic properties but are structurally identical, which renders their distinction impossible by usual X-ray techniques. Samples were prepared at concentrations between 36 and 50% Ni and at temperatures ranging from 350 to 600°C. The appearance of a central line in the Mössbauer spectrum was taken as the criterion for segregation occurrence. We thus mapped the miscibility gap boundary in this region of the Fe-Ni phase diagram.
3

An investigation into the Mossbauer effect in Fe57

Woodrow, Janice Emily Jean January 1964 (has links)
In this thesis the Mossbauer effect in metallic iron has been studied as a function of the length of time of diffusion of the Co⁵⁷ source into metallic iron, of the source temperature over the range 156°K to 478°K, and of the absorber thickness. In each case, the line shape, width, intensity and shifts were measured. Measurements showed that the appearance of an appreciable Mossbauer effect, .122, arises within the first ten minutes of diffusion time at 900°C in a hydrogen atmosphere and that additional time is required to reduce the line width and to increase the intensity to .145. The observed temperature shift of the resonantly absorbed 14.4 kev radiation followed that which was predicted by the Josephson effect. However, corrections for an isomer and a hydrostatic compression shift were made to the data before comparing the measured shift with the theoretical shift. The results indicated a Debye temperature of Θ[subscript D] = (420±20)°K for both the source and absorber used. The measurements made over the temperature range indicated that the internal magnetic field H̰ followed the saturation magnetization curve (the Weiss Law) closely. For small temperature differences between the source and absorber, ΔΘ < 50°K, measurements were made indicating that the minimum line width occurred at ΔΘ = 24°K. These results indicated that the internal magnetic field at ΔΘ = 0°K for the source was .01x10⁵oe greater than that of the absorber. For ΔΘ ≥ 100°K, the Mossbauer line displayed a hyperfine structure arising from the temperature dependent difference in the internal magnetic field at the nuclei. The line profile, width, shift and intensity were measured for four absorber thicknesses - .0002", .00035", .00055", and .001". The detailed comparison of these line characteristics with the theoretical values required an extension of existing treatments, a discussion of which is given in chapter five. In each case it was observed that the Mossbauer line was accompanied by two small peaks, one on either side of the main line. The position of these peaks indicated that they were associated with a small or zero internal magnetic field at the site of some of the Fe⁵⁷ atoms. / Science, Faculty of / Physics and Astronomy, Department of / Graduate
4

Precision measurements of the Mössbauer fraction of Fe⁵⁷ in Pt, Pd and Cu

Nees, Wilbur Lee 01 June 1968 (has links)
Precision measurements of the Mössbauer fraction of the 14.4 kev Fe⁵⁷ transition were made using the black, wide absorber technique. The Fe⁵⁷ was diffused, as a dilute Mössbauer impurity, into 99.995% purity single crystal chips of Pt, Pd and Cu. By comparing the Debye form of -ln f, corrected for anharmonicity, with our data, we extracted a high and low temperature Debye theta, as well as an anharmonicity coefficient, є, for the three materials. We estimated the accuracy of our data to be ± 1%. From the data we concluded that the Fe⁵⁷ in Cu has stronger force constants and is more anharmonic than pure Cu, while Fe⁵⁷ in Pt and Pd has smaller force constants and about the same anharmonicity as the pure host materials.
5

Estudo das ligas quaternárias Al-Fe-Si-B produzidas por mecanossíntese / Study Quaternary Alloys Al-Fe-Si-B Mechanical Synthesis

Jesus, Denis Rezende de 22 April 2003 (has links)
Este trabalho tem como objetivo a síntese da liga Fe IND.78-X Al IND.X Si IND.9 B IND.13, com o X=0, 10, 20, 30 e 50, através da moagem utilizando para isto um moinho de bolas de alta energia. As técnicas de difração de raios-X, microscopia eletrônica de varredura, SQUID, análise térmica diferencial (DTA) e espectroscopia Mössbauer são utilizadas na verificação da dependência da estrutura e propriedades magnéticas com o tempo de moagem e diferentes concentrações de Al. Com a moagem uma solução sólida com estrutura BCC é formada, com os átomos sendo distribuídos de forma aleatória na rede. O tamanho de grãos descresce rapidamente nos primeiros estágios de moagem e depois, com a continuação da moagem, permanece aproximadamente constante. Os espectros Mössbauer apresentam linhas alargadas, uma característica dos materiais submetidos a moagem, e forma ajustados considerando sítios paramagnéticos, sextetos cristalinos e distribuições Gaussianas de campos hiperfinos. As medidas magnéticas mostram que as ligas possuem propriedades de material magnético mole. A magnetização e a coercividade diminuem com o tempo de moagem, indicando um aumento no número de átomos não-magnéticos em torno do átomo de ferro e a diminuição do tamanho do grão, respectivamente. Com o aumento da concentração de Al, o tamanho do grão da solução sólida tende a diminuir e o sistema perde seu ordenamento magnético. As curvas DTA mostram uma transformação exotérmica associada à cristalização de fases amorfas e ao ordenamento da solução sólida Fe(Al, Si, B) para formar outros compostos. O tratamento térmico dos pós moídos forma os intermetálicos FeAl, FeAl IND.2. As amostras submetidas a tempos de moagem maiores dão origem a fases nanocristalinas e amorfas com alto grau de contaminação pelos componentes de moinho. / The purpose of the present work is the synthesis of Fe IND.78-xAl IND.xSi IND.9B IND.13 alloy, with x=0, 10, 20, 30 and 50, by mechanical alloying in a high energy planetary ball mil. The effect of the milling time and Al content on the structure and magnetic properties has been studied by X-ray diffraction, scanning electron microscopy, SQUID, differential analysis thermal (DTA) and Mossbauer spectroscopy. After milling a Fe-Al-Si-B solid solution with a bcc structure is formed. The atoms are assumed to be randomly distributed in lattice, the grain size decrease dramatically at the early milling stages with further milling to remain relatively stable at the late stages. The Mossbauer spectra show lines broad, a characteristic of milled materials, and were fitted by considering paramagnetic phases, crystalline sextet and Gaussian distributions of hyperfine fields. The magnetic measurements show soft magnetic properties. The magnetization and coactivity decrease with milling time, indicating an increasing number of nonmagnetic atoms around the iron atoms and decrease of grain size, respectively. With increasing Al content, the grain size of the solid solutions decreased, and the system loses its magnetic order. The DTA curves show the exothermic transformation associated to crystallization of amorphous phase and ordering of the Fe(Al,Si,B) solid solutions to form other compounds. The annealing of milled powders form the ordered FeAl and FeAl IND.2 intermetallic. Long milling times resulted in Nano crystalline and amorphous phases highly contaminated by the milling tools.
6

Estudo das ligas quaternárias Al-Fe-Si-B produzidas por mecanossíntese / Study Quaternary Alloys Al-Fe-Si-B Mechanical Synthesis

Denis Rezende de Jesus 22 April 2003 (has links)
Este trabalho tem como objetivo a síntese da liga Fe IND.78-X Al IND.X Si IND.9 B IND.13, com o X=0, 10, 20, 30 e 50, através da moagem utilizando para isto um moinho de bolas de alta energia. As técnicas de difração de raios-X, microscopia eletrônica de varredura, SQUID, análise térmica diferencial (DTA) e espectroscopia Mössbauer são utilizadas na verificação da dependência da estrutura e propriedades magnéticas com o tempo de moagem e diferentes concentrações de Al. Com a moagem uma solução sólida com estrutura BCC é formada, com os átomos sendo distribuídos de forma aleatória na rede. O tamanho de grãos descresce rapidamente nos primeiros estágios de moagem e depois, com a continuação da moagem, permanece aproximadamente constante. Os espectros Mössbauer apresentam linhas alargadas, uma característica dos materiais submetidos a moagem, e forma ajustados considerando sítios paramagnéticos, sextetos cristalinos e distribuições Gaussianas de campos hiperfinos. As medidas magnéticas mostram que as ligas possuem propriedades de material magnético mole. A magnetização e a coercividade diminuem com o tempo de moagem, indicando um aumento no número de átomos não-magnéticos em torno do átomo de ferro e a diminuição do tamanho do grão, respectivamente. Com o aumento da concentração de Al, o tamanho do grão da solução sólida tende a diminuir e o sistema perde seu ordenamento magnético. As curvas DTA mostram uma transformação exotérmica associada à cristalização de fases amorfas e ao ordenamento da solução sólida Fe(Al, Si, B) para formar outros compostos. O tratamento térmico dos pós moídos forma os intermetálicos FeAl, FeAl IND.2. As amostras submetidas a tempos de moagem maiores dão origem a fases nanocristalinas e amorfas com alto grau de contaminação pelos componentes de moinho. / The purpose of the present work is the synthesis of Fe IND.78-xAl IND.xSi IND.9B IND.13 alloy, with x=0, 10, 20, 30 and 50, by mechanical alloying in a high energy planetary ball mil. The effect of the milling time and Al content on the structure and magnetic properties has been studied by X-ray diffraction, scanning electron microscopy, SQUID, differential analysis thermal (DTA) and Mossbauer spectroscopy. After milling a Fe-Al-Si-B solid solution with a bcc structure is formed. The atoms are assumed to be randomly distributed in lattice, the grain size decrease dramatically at the early milling stages with further milling to remain relatively stable at the late stages. The Mossbauer spectra show lines broad, a characteristic of milled materials, and were fitted by considering paramagnetic phases, crystalline sextet and Gaussian distributions of hyperfine fields. The magnetic measurements show soft magnetic properties. The magnetization and coactivity decrease with milling time, indicating an increasing number of nonmagnetic atoms around the iron atoms and decrease of grain size, respectively. With increasing Al content, the grain size of the solid solutions decreased, and the system loses its magnetic order. The DTA curves show the exothermic transformation associated to crystallization of amorphous phase and ordering of the Fe(Al,Si,B) solid solutions to form other compounds. The annealing of milled powders form the ordered FeAl and FeAl IND.2 intermetallic. Long milling times resulted in Nano crystalline and amorphous phases highly contaminated by the milling tools.
7

Evaluation of nanoparticles iron-molybdate catalyst using physical properties measurements

Al-Ghanem, Hussain 12 1900 (has links)
Mössbauer spectroscopy, X-ray spectroscopy, SEM, EDX, heat capacity and SQUID measurement were carried out in conjunction with a catalytic study on mixed Fe-Mo oxides, some of which have been used in selective oxidation of certain hydrocarbons. With the specific activity being sensitive to the catalytic particle size and morphology, an aerogel process was employed to prepare seven samples covering Fe/Mo ratios from 1/2 to 2/1and some of the samples were annealed at 300oC and 500oC . Mössbauer data have been analyzed, with each set well fitted to reflect one Fe3+ and two or more non-equivalent Fe2+ sites. There isomer shift, quadruple splitting and molar fraction are analyzed in terms of temperature and Fe/Mo-ratio dependence. The Fe-rich samples exhibit magnetic ordering at low temperatures, revealing multiple sextets corresponding to different magnetic hyperfine fields. Two samples with the Fe:Mo ratio 1:1 and 2:3 were study in more detail their X-ray diffraction pattern reveal that they crystallize with the β-FeMoO4 structure. SEM gives unusual morphology and the material form into hallow sphere with 2um in diameter. EDS confirms that the metal ion is fairly uniformly distributed and close to the nominal values. Finally heat capacity and SQUID measurements confirm the antiferromagnetic phase transition near 13K for the heat treated samples. / "December 2006."
8

A Mössbauer effect investigation of metamagnetic FeCO₃

Koon, Norman Carroll 12 1900 (has links)
No description available.
9

A study of iron in clay minerals using Mössbauer spectroscopy

Pecuil, Thomas Edward 08 1900 (has links)
No description available.
10

Síntese, Dopagem e Caracterização da Polianilina Com Sais de Fe(II) e Fe(III)

FORNAZIER FILHO, Y. 10 June 2009 (has links)
Made available in DSpace on 2016-08-29T15:35:23Z (GMT). No. of bitstreams: 1 tese_3511_YONIS FORNAZIER FILHO.pdf: 1751555 bytes, checksum: 31f7faa26a87c7ecea8cd5e2bf1fdaf5 (MD5) Previous issue date: 2009-06-10 / Neste trabalho foi feita a síntese e caracterização da polianilina na forma de sal esmeraldina (Pani-ES), utilizando-se anilina e (NH4)2S2O8 em meio ácido à temperatura de 0°C. Obteve-se um polímero sólido, com um rendimento de 60,4% e com massa molecular de 246,13 kg/mol, determinada pela técnica de viscosimetria. Ao polímero sintetizado foram adicionados sais de Fe(II) e Fe(III) para estudar as mudanças nas suas propriedades estruturais, térmicas e de condutividade. As amostras foram estudadas pelas técnicas de análise elementar, espectroscopia no Infravermelho (FTIR), no Ultravioleta-Visível (UV-VIS) e Mössbauer, Difração de Raios-X, MEV, EDS, Análise Térmica (TG e DSC), e medidas de condutividade das soluções de polianilina e resistividade por pressão das amostras poliméricas sólidas. Os resultados, obtidos com o uso destas técnicas experimentais mostraram que os íons Fe(II) interagiram com os nitrogênios benzenóides. Os dados de Mössbauer e resistividade comprovaram essas observações, sugerido que ocorre a formação de um complexo Pani-Fe(II). Por outro lado, os íons Fe(III) adicionados a Polianilina não mostraram interação significativa com a cadeia polimérica. Portanto, foi observado que é possível a interação de íons Fe(II) e Fe(III) com a polianilina na forma sal esmeraldina, sendo mantida suas propriedades condutoras.

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