Linha de ressonância da radiação gama e estrutura hiperfina do 57Fe em minerais de uma jazida de manganês e em óxidos de ferro de um sistema natural magnetita-hematita

Abstract

This work is divided into two major parts: the first, theoretical, is about the algebraic form of nuclear gamma resonance line, of Mössbauer effect, the second, is one of experimental character, which is related to the measure of the hyperfine parameters, of minerals ferrugionos, of a mine under exploration commercial of manganese and a detailedstudy of a natural system of magnetic iron oxide and its products of the magneticcrystallographic-structural transformation, in the original geological environment in lithology of hematitic phyllite. In the first part of the work, the emission lines and absorption gamma have Lorentzianshape, with a natural line width, ..n. It is shown that the Mössbauer resonance line is also a Lorentzian with a width equal to 2..n. The theoretical foundations are laid in a way they offer a deductive configuration, reached more directly, as well as an alternative to more complex arguments, found in the scientific literature. In the second part of the study, of experimental character, there were two main focuses.Initially, selected samples of manganese ore containing ferruginous minerals and described as being originated from a silica-carbonate rock, called queluzito, Mining Morro da Mina in Conselheiro Lafaiete, Minas Gerais, the samples were characterized, from the point of chemical structures, crystallographic and Mössbauer hyperfine of 57Fe. Then a second problem involving a complex mineralogical system, consisting of magnetite crystals typical of a hematitic phyllite from the region of Diamantina, Minas Gerais. Samples of these crystals were analyzed in detail, as well as from the point of view of chemical, crystallographic, and magnetic hyperfine in the search of experimental evidence to sustain aplausible model for the transformation of the precursor, magnetite in hematite, in its original geological environment. The obtained collection of experimental data show that manganese mine has at least two forms of siderite, a purer (FeCO 3) and another with isomorphous substitution of iron by calcium ( Fe1- x..Ca,Mg..xCO3 ), spessartine ( .. .. 3 2 3Fe2+ , Mn2+ Al SiO ), rhodochrosite (MnCO3) and rhodonite (..Fe2+, Mn2+, Ca..SiO3 ). The system mineralogical magnetite - hematite has some very special characteristics: they are millimetric octahedral crystals, characteristic of magnetite, and are magnetic, although the value of saturation magnetization .. .. 1,2 J T kg-1 is much smaller than thecharacteristic of magnetite pure (.. >90 J T kg-1). However, the X-ray diffraction patterns of the crystals powder, revealed the existence of hematite only. The Mössbauer spectra also correspond to hyperfine parameters characteristic of hematite. The origin of the magnetization of the material, even in of the preserved crystals as in the powdered, isnt still clearly understandable, but the present results of the X-ray diffraction, the Mössbauer spectroscopy and the magnetic measurements, provide new data to previously reported in the scientific literature, so that one can build a physical model capable of explaining the transformations (i) crystallographic structure of a cell cubic magnetite to the trigonalhexagonal structure of the hematite, and (ii) structural-magnetic, of the ferrimagnetic precursor to a weakly ferromagnetic, of the hematite or some other intermediate magnetic structure, which would follow the crystallographic phase change. Of the two cases treated experimentally the data hyperfine Mössbauer value extraordinarily the physical interpretation and the structural modeling of the studied systems,in a way it allows the access and the achievement of local information of the hyperfine structure, by the probe nuclear 57Fe.