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Master's Dissertation
DOI
10.11606/D.44.1996.tde-14102013-111440
Document
Author
Full name
Flavio Machado de Souza Carvalho
E-mail
Institute/School/College
Knowledge Area
Date of Defense
Published
São Paulo, 1996
Supervisor
Committee
Atencio, Daniel (President)
Lima, Nelson Batista de
Santos, Carlos de Oliveira Paiva
Title in Portuguese
Refinamento da estrutura cristalina de quartzo, coríndon e criptomelana utilizando o método de Rietveld
Keywords in Portuguese
Cristalografia
Abstract in Portuguese
Este trabalho apresenta o refinamento das estruturas cristalinas do quartzo, do coríndon e de um material sintético, análogo ao mineral criptomelana, utilizando o método de Rietveld. Com o quartzo e coríndon, testou-se a aplicabilidade do método e seus procedimentos instrumentais, teóricos, computacionais e os efeitos intrínsecos de preparação de amostras. A partir disto, estabeleceu-se um esquema de trabalho para a realização dos refinamentos. Os dados cristalográficos obtidos para estes minerais concordaram com os apresentados na literatura. Algumas discrepâncias nas intensidades dos picos não puderam ser minimizadas devido a problemas instrumentais, por problemas específicos do difratômetro disponível e, ainda, pela impossibilidade de se tratar os parâmetros térmicos. Para a criptomelana, grupo espacial I4/m, obtiveram-se: parâmetros da cela unitária 'A IND.0'=9,82(1) e 'C IND.0'=2.555(4)'ANGSTROM'; coordenadas atômicas Mn x = 0,3493(5) y = 0,1687(5); 0[1]x = 0,157(1) y = 0,201(2); 0[2] x = 0,534(2) y = 0,160(2) e o fator de ocupação do potássio M = 0,06(2). Os índices de critério para avaliação do refinamento obtidos foram 'R IND.WP'= 18,50; 'R IND.P'= 13,77; S = 0,56; 'D IND.W'-d=0,42; 'R IND.B'= 8,50. De modo geral, os dados foram concordantes com uma estrutura de inomanganato, constituída por quatro cadeias duplas de octaedros de [Mn'O IND. 6'] formando um túnel onde de aloja potássio, cujo fator de ocupação (M) está de acordo com as suas coordenadas atômicas e com a composição química da criptomelana estudada.
Keywords in English
Not available.
Abstract in English
This research presents the Rietveld refinement of the crystal structure of quartz, corundum and a synthetic analogue of cryptomelane. Quartz and corundum were used in order to test the applicability of the method, its instrumental, theoretical and software procedures, as well as the intrinsic effects off sample preparation, and to establish a satisfactory work procedure. A sequence of work was estabished. Crystallographic data obtained for the minerals agreed with those presented in the literature. Some discrepancies on the peak intensities could not be minimized due to instrumental problems, specific problems of the available diffractometer and impossibility to deal with the thermal parameters. For cryptomelane, spatial group l4/m, the folliwing data were obtained: cell parameters 'A IND. 0' 9,82(1) and 'C IND. 0' = 2,555(4)' ANGSTROM'; atomic coordinates Mn x= 0,3493 (5), y = 0, 1687(5); O[1] x= 0,157(1), y=0,201(2); O[2] x= 0,534O(2), y= 0,160(2) and occupation factor of potassium M = 0,06(2). The indices de confidence for evalution of the refinement obtained were 'R IND. WP' = 18,50; 'R IND. P' = 13,77; S= 0,56; 'D IND. W'-d = 0,42; 'R IND. B' = 8,50. The data agreed with a structure of inomanganate formed by four double chains of [Mn'O IND. 6'] octahedra, creating a tunnel, where potassium is found. The occupation factor of potassium is in agreement with its atomic coordinates and the chemical composition of the studied cryptomelane.
 
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CARVALHO_MESTRADO.pdf (3.88 Mbytes)
Publishing Date
2013-10-30
 
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