X-ray absorption studies of chlorine valence and local environments in borosilicate waste glasses

Iodine valence and local environments in borosilicate waste glasses using X-ray absorption spectroscopy

“…shows an affinity for Ca 2+ , and can be bonded to itself, Na, or oxygen [33]. According to the XAS results found here, iodine shows no inclination to bond with Ca 2+ , even though there are significant Ca concentrations in two of the glasses investigated, KI-2 and 10S-G-86F (Table 1).…”

“…Iodine-sites in the borosilicate glasses investigated here have relatively simple configurations compared with chorine-sites in similar waste glasses [33]. Iodine nearest-neighbors are Na + or Li + , the most common network modifying cations in the glass.…”

Bromine speciation in hydrous silicate melts at high pressure

“…It may originate either from a water molecule, an -OH group or an oxygen from the silicate melt network as seen for Cl in Cl-bearing borosilicate glasses (McKeown et al, 2011). Although the small increase with pressure in the white line intensity of the melts spectra could be consistent with a change of Br environment from bromide to bromate, there is no other evidence for such a dramatic change with pressure.…”

“…We cannot therefore attribute any of the above correlations to the peak that increases with pressure at 3.8 Å in the Fourier transform of the EXAFS data. The presence of Si in the immediate environment of Br is unlikely according to MAS-NMR and XAFS studies on analog high pressure Cl-bearing (alumino)silicate glasses (Stebbins and Du, 2002;Sandland et al, 2004;Evans et al, 2008;McKeown et al, 2011) that indicate that Cl is mainly coordinated to the networkmodifying cations (e.g., alkali and alkaline-earth). In addition, Dalou and Mysen (2015) explained in a recent study that there is no interaction between Si 4+ and Cl − in hydrous aluminosilicate glasses quenched from 1.5 GPa.…”

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.…”