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Master's Dissertation
DOI
10.11606/D.43.1982.tde-08052015-180948
Document
Author
Full name
Hugo Franco
E-mail
Institute/School/College
Knowledge Area
Date of Defense
Published
São Paulo, 1982
Supervisor
Title in Portuguese
EFEITO MOSSBAUER EM LIGAS FERRO-NIQUEL OBTIDAS POR DECOMPOSICAO DE OXALATOS
Keywords in Portuguese
Efeito Mössbauer
Espectroscopia de Mössbauer
Abstract in Portuguese
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.
Title in English
Mössbauer effect in iron-nickel alloys obtained by decomposition of oxalates
Keywords in English
Mössbauer effect
Mössbauer spectroscopy
Abstract in English
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.
 
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Publishing Date
2015-05-13
 
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