Search

The use of high-pressure synthesis conditions to produce I-bearing aluminoborosilicate represents a promising issue for the immobilization of 129I radioisotope. Furthermore, iodine appears to be more solubilized in glasses under its iodate (I5+) form rather than its iodide (I−) form. Currently, the local atomic environment for iodine is poorly constrained for I− and virtually unknown for I5+ or I7+. We used I K-edge x-ray absorption spectroscopy conducted at 20 K for determining the local atomic environment of iodine dissolved as I−, I5+, and I7+ in a series of aluminoborosilicate glasses. We determined that I− is surrounded by either Na+ or Ca2+ in agreement with previous studies. The signal collected from EXAFS reveals that I5+ is surrounded invariably by three oxygen atoms forming an IO3− cluster charge compensated by Na+ and/or Ca2+. The I–O distance in iodate dissolved in glass is comparable to the I–O distance in crystalline compounds at ∼1.8 Å. The distance to the second nearest neighbor (Na+ or Ca2+) is also constant at ∼3.2 Å. This derived distance is identical to the distance between I− and Na+ or Ca2+ in the case of iodide local environment. For one sample containing iodate and periodate, the distinction between the local environment of I5+ and I7+ could not be made, suggesting that both environments have comparable EXAFS signals. [ABSTRACT FROM AUTHOR]

The solubility, speciation, and local atomic environment of chlorine have been determined for aluminoborosilicate glasses equilibrated with various sources of chlorine (NaCl and PdCl2) at high pressure (0.5–1.5 GPa) and high temperature (1350–1400 °C). The Cl solubility reaches up to 11 mol% in borosilicate glass and appears to be strongly influenced by the concentration of network-modifying cations (Ca and Na) and increases with increasing CaO + Na2O content. The Cl solubility is enhanced in Ca-bearing rather than Na-bearing borosilicate glass, suggesting a higher affinity of chlorine for alkaline-earth cations. Cl K-edge XANES and Cl 2p XPS spectra reveal that chlorine dissolves in glasses only as chloride species (Cl–) and no evidence of oxidized species is observed. Using PdCl2 as a chlorine source leads to a pre-edge signal for PdCl2 in the XANES spectra. The EXAFS simulations show that the Cl– local environment is charge compensated by Na+ or Ca2+ at a distance to first neighbor on the order of 2.7 Å, which is comparable to the observed distances in crystalline chloride compounds. The coordination to charge compensating cation is lower in the case of Ca2+ (~1.1) than Na+ (~4.3). [ABSTRACT FROM AUTHOR]

From the first initiatives [[1]] to the most recent developments of synchrotron-based techniques for the study of cultural and natural heritage materials, many synchrotron facilities have developed their own scientific programs in this field [[2]]. Ender to hard X-rays 3-23 keVMacro: 250 × 200 µm Micro: 5 to 10 µmXRF, XRD, DANES, DAFS, EXAFS, XANES imaging or punctual measurementsU X-ray tomography Synchrotron X-ray micro- and nanotomography allow the study of the detailed 3D morphology of bulk samples, with a spatial resolution that can go down to the sub-micrometer range for "standard" parallel-beam projection microtomography setups, and down to less than 50 nm in nano-tomography methods using more recent and more complex schemes, such as hard X-ray transmission X-ray microscopy (TXM). D micro spectral imaging with XRF, XANES, and XRD 3D computed tomography with absorption and phase contrast (in the future)T. [Extracted from the article]

This study aims at the characterisation of red and orange glass tesserae from the 4th-century Roman villa of Noheda (Spain). Due to the limited number of analyses available for such ancient materials, many questions remain unanswered about the production processes in the Roman period. Six samples were chosen for their hue variations, including two samples showing banded patterns of red and orange. Differences in copper speciation were investigated by X-ray absorption spectroscopy and compared with colour and compositional variations obtained by EPMA. The shapes and sizes of colouring crystals could be investigated using scanning and transmission electron microscope imaging. The brown-red colour is due to metallic copper nano-particles and corresponds to a low-copper and low-lead group usually described in the literature. The orange samples and bands are coloured by copper oxide C u 2 O nanoparticles with remaining Cu+ in the glass and have greater contents of Cu. Compositional analyses reveal that the same base glass is used in the red and orange bands with additions of Cu, Sn, Pb and probable Fe. Furthermore, based on our results and on the literature review, a high-copper low-lead group of glasses highlights the variability of compositions observed in cuprite colours. [ABSTRACT FROM AUTHOR]

• Iodine is dissolved as iodide (I−) in high pressure borosilicate glasses. • Both alkali and alkaline-earth cations act as a charge compensator to I− species. • The absence of iodate (I5+) suggests that there is a complex interplay between I− species and oxygen species within the glass structure. The 129I radioactive isotope is a by-product of nuclear plants activity. Owing to its strong volatility, there is currently no ideal protocol to immobilize 129I in nuclear waste borosilicate glasses. Recently, we have proposed the use of high-pressure syntheses to dissolve iodine in various glass compositions; however, I speciation and dissolution mechanism could not be determined. We have adopted an approach combining X-ray Photoelectron Spectroscopy (XPS) and X-ray Absorption Spectroscopy (XAS) methods to determine I speciation and molecular environment in glasses containing from 0.5 to 2.5 mol.% I. The XPS spectra reveal that I is mostly dissolved as iodide (>85% I−) with a small proportion of elemental iodine (<15% I0) and the absence of iodate species (I5+). For borosilicate glasses, the XAS results and subsequent spectrum simulations suggested that Na and Ca are involved in the I− vicinity with averaged derived coordination number (CN) of 3.6 and 2.0 and bond length to the nearest neighbour (r X-I) 2.98 and 2.85 Å, respectively. These results suggest that the coexistence of both I− and I5+ species is not requested for electric neutrality but instead, we explain the I speciation by the possible interplay with oxygen species from the borosilicate matrix. In addition, the results imply that the borosilicate network is affected by the I dissolution. [ABSTRACT FROM AUTHOR]