instrumental techniques applied to mineralogy and geochemistry

More documents

Recommendations

Info

X-ray Absorption Spectroscopy in Mineralogy and in the Earth and Environmental Sciences Jesús Chaboy Nalda Instituto de Ciencia de Materiales de Aragón (ICMA) and Departamento de Física de la Materia Condensada, CSIC-Universidad de Zaragoza, 50009 Zaragoza (Spain) Introduction X-ray absorption spectroscopy (XAS) has proven to be an outstanding structural tool by allowing the determination of the local environment around a selected atomic species in a great variety of systems. An important advantage of this technique is its utility for heterogeneous samples in such a way that a wide variety of solid and liquids, including whole soils and liquids, can all be examined directly and non-destructively. Additionally, since the local structure does not depend on long-range crystalline order, the structure of amorphous phases (and that of dissolved species) is easily achieved. XAS is useful for concentrations from about 10 ppm to major elements. As such, it is useful to speciate trace elements such as contaminants adsorbed to pure minerals, soils and sediments, and is also a valuable tool for studying the mineralogical composition of the soil or sediment (especially when used in conjunction with other techniques such as X-ray diffraction). Our purpose here is to present a brief review of the principles underlying x-ray absorption spectroscopy. The main strengths of this technique mainly focused on Mineralogy and in the Earth and Environmental Sciences are highlighted and illustrated by showing different selected examples. X-ray Absorption Spectroscopy (XAS): basic principles The basic process of X-ray absorption is the excitation of electrons from deep core levels of a selected atom by the absorption of a photon. When X-rays pass through any sort of material, a proportion of them will be absorbed. The absorption of x-rays by atoms is smoothly varying with photon energy except at some discrete energies where
44 Jesús Chaboy abrupt increases occur, called absorption edges. These edges correspond to the x-ray photon attaining enough energy to free or excite a bound electron in the atom. The absorption of x-rays on the high energy of the absorption edges does not vary monotonically in condensed matter but has a complicated behavior which extends past the edge by an amount typically of the order of 1 keV. The small oscillations can superimposed on the edge step gradually die away as the X-ray energy increases. The oscillations are known as EXAFS (Extended X-ray Absorption Fine Structure) are due to the interaction of the photoelectron with the surrounding atoms. Usually the x-ray absorption spectrum is divided in several regions depending on the energy of incoming photons: * the pre-edge, edge and the near-edge (XANES) regions, which extend about 20 eV below the edge to 30-100 beyond the edge. * the EXAFS region which extends from 30-100 eV to 600-1000 eV beyond the edge. The physical origin of the absorption features in the pre-edge and edge regions depend on the material, i.e. Rydberg states in free atoms, bound valence states or bound multiple scattering resonances in molecules, unoccupied local electronic states in metals and insulators. Thus, analysis of these near-edge features in the spectrum of a particular sample can provide information about vacant orbitals, electronic configuration and the site symmetry of the absorbing atom. FIGURE 1. X-ray absorption spectra of LuFe 11 Ti at the Lu L-edges, involving different final state symmetry: L 3 (2p 3/2 {d 3/2 , d 5/2 }), L 2 (2p 1/2 d 3/2 ), L 1 (2s 1/2 {p 1/2 , p 3/2 }).
Page 2 and 3: SEMINARIOS DE LA SOCIEDAD ESPAÑOLA
Page 4 and 5: FOREWORD On the occasion of the Spa
Page 6 and 7: INDEX Electron back-scattered diffr
Page 8 and 9: 8 Elisabetta Mariani et al Introduc
Page 10 and 11: 10 Elisabetta Mariani et al success
Page 12 and 13: 12 Elisabetta Mariani et al number
Page 14 and 15: 14 Elisabetta Mariani et al FIGURE
Page 16 and 17: 16 Elisabetta Mariani et al FIGURE
Page 18 and 19: 18 Elisabetta Mariani et al In-situ
Page 20 and 21: TEM in Geology. Basics and applicat
Page 44 and 45: X-ray Absorption Spectroscopy in Mi
Page 56 and 57: Raman, Conventional Infrared and Sy
Page 82 and 83: 84 Clemente Recio Isotope Terminolo
Page 84 and 85: 86 Clemente Recio collector gas sou
Page 86 and 87: 88 Clemente Recio Something similar
Page 88 and 89: 90 Clemente Recio beers. Some brand
Page 90 and 91: 92 Clemente Recio The source of the
Page 92 and 93:
94 Clemente Recio By using GC-C-IRM
Page 94 and 95:
96 Clemente Recio about 25% of tota
Page 96 and 97:
98 Clemente Recio such as blood and
Page 98 and 99:
100 Clemente Recio relatively simpl
Page 100 and 101:
102 Clemente Recio following admini
Page 102 and 103:
104 Clemente Recio and high N in dr
Page 104 and 105:
106 Clemente Recio although 15 N d
Page 106 and 107:
108 Clemente Recio spectrometers th
Page 108 and 109:
110 Clemente Recio O’Brien, D.M.
Page 110 and 111:
112 Kjell Bilström time in old geo
Page 112 and 113:
114 Kjell Bilström ratios ( 204 Pb
Page 114 and 115:
116 Kjell Bilström Certain samples
Page 116 and 117:
118 Kjell Bilström Molybdenite is
Page 118 and 119:
120 Kjell Bilström analyzed with r
Page 120 and 121:
122 Kjell Bilström radiogenic sign
Page 122 and 123:
124 Kjell Bilström plants inherits
Page 124 and 125:
126 Kjell Bilström in some cases a
Page 126 and 127:
128 Kjell Bilström Besides, minera
Page 128 and 129:
130 Kjell Bilström References Bear
Page 130 and 131:
Analytical techniques applied to fl
Page 132 and 133:
Page 134 and 135:
Page 136 and 137:
Page 138 and 139:
Page 140 and 141:
Page 142 and 143:
Page 144 and 145:
Page 146 and 147:
Page 148 and 149:
Page 150 and 151:
show all

instrumental techniques applied to mineralogy and geochemistry

Create successful ePaper yourself

Delete template?

Save as template?