Local structure of iron in tektites and natural glass: An insight through X-ray absorption fine structure spectroscopy

Abstract

The local structure of iron in tektites from six strewn fields, and impact -and non -impact -related glass were studied using the Fe K -edge X -ray absorption near edge structure (XANES) and extended X -ray absorption fine structure (EXAFS) techniques, in order to obtain quantitative data on Fe -O bond length and Fe coordination number. X -ray absorption fine structure (XAFS) spectra and Fe -O bonds in standard minerals such as hematite, fayalite, and magnetite were compared. The degree of oxidation was measured based on the valencies of iron in the samples. Tektites contain a greater proportion of ferrous than ferric iron [0.04 (1) /ƩFe] are higher than that in tektites. Based on the measured Fe -O distance, it was inferred that 4 -and 5 -coordinated Fe exist in tektites, whereas volcanic glass contains 5 -and 6 -coordinated Fe. Impact -related glass possesses various local structures caused by the combination of 4 -, 5 -, and 6 -coordinated Fe. During formation, tektites experience high temperatures and a reducing atmosphere when they were ejected into the outer space. In contrast, the impact -related glass, which was ejected into the atmosphere or which remained close to the crater, experienced a more complex environment, with air pressure, density, and temperature varying across the atmospheric layers. Thus, impact -related glass presents more complicated oxidation states and structure compared to tektites. Volcanic glass, on the other hand, has a relatively stable redox condition; and thus, it undergoes only a small change in the degree of oxidation. This study indicates that the local structure and oxidation state of Fe may change due to the environment that the glass experienced during its formation. These different kinds of natural glass can be distinguished from each other using the study of the local structure.

Chemical speciation of U, Fe, and Pu in melt glass from nuclear weapons testing

“…Overall, these results confirm that Fe in the melt glasses is predominantly 4-coordinate Fe(II). The bond lengths observed for the melt glasses and tektite are near the endpoints of the previously reported range for tektites collected from various strewnfields [52,63].…”

“…4, the k-space Fe K-edge EXAFS collected from the soil and glass samples are shown with spectra collected from staurolite, containing 4-coordinate Fe(II) [55]; grandidierite, containing approximately 90% 5-coordinate Fe(II) and 10% Fe(III) [60]; and a tektite from the Australasian strewnfield [61]. Tektites have been proposed as naturally occurring analogs to nuclear melt glass [56,57], and are reported to predominantly contain Fe(II) in distorted tetrahedral coordination [43,62,63]. Table III show EXAFS fitting results.…”

XAFS study of Zr in Cretaceous–Tertiary boundary clays from Stevns Klint

“…A condition such as high-temperature melt was quenched rapidly in the space with little oxygen pressure condition may be supposed. This consideration is consistent with the result of Wang et al (2013): since tektite glasses are formed in the space under low oxidation conditions, iron ions in tektite has abnormally high ratio of Fe 2+ /(Fe…”

XAS and XRF investigation of an actual HAWC glass fragment obtained from the Karlsruhe vitrification plant (VEK)

“…XAS (X-ray Absorption Spectroscopy) studies of glass materials are numerously reported in the material sciences literature, covering such disparate applications as the investigation of historic artifacts (e.g., [6]) or geological specimen (e.g., [7]), characterization of optical glasses for solid state lasers (e.g., [8]) or the encapsulation of radiotoxic residues from nuclear fuel reprocessing (notably the work of McKeown et al [9][10][11][12][13][14][15][16]). These studies benefit from the ability of X-ray Absorption Fine Structure (XAFS) measurements to provide direct chemical speciation (e.g., determination of oxidation states and coordination geometries) through analysis of the Xray Absorption Near Edge Structure (XANES) -without the need for any sample pretreatment -while the Extended X-ray Absorption Fine Structure (EXAFS) reveals structural details on the local coordination environments (bond lengths, neighboring atom types) of glass matrix constituents -unlike standard X-ray Diffraction (XRD) analysis, which is severely hampered by the amorphous nature of elemental networks in glassy materials lacking any long range order.…”