A. Canizares

In-Situ Raman Observation of the First Step of Uranium Dioxide Weathering Exposed to Water Radiolysis

ABSTRACT The effect of irradiation is a key point in the knowledge of the behavior of some compounds such as uranium-based ones. Regarding this topic, the authors developed an original in-situ Raman spectroscopy device coupled to a cyclotron ion beam. This original instrument allows observing the kinetics of uranium dioxide weathering by α radiolysis of water. The authors then observed that an altered layer made of Studtite and Schoepite phases grows linearly during the irradiation and extends for several hours after irradiation. Kinetics of production of some molecular species during radiolysis were also reported.

Structural Relaxation Dynamics and Annealing Effects of Sodium Silicate Glass

Here we report high-precision measurements of structural relaxation dynamics in the glass transition range at the intermediate and short length scale for a strong sodium silicate glass during long annealing times. We evidence for the first time the heterogeneous dynamics at the intermediate range order by probing the acoustic longitudinal frequency in the GHz region by Brillouin light scattering spectroscopy. Or, from in-situ Raman measurements, we show that relaxation is indeed homogeneous at the interatomic length scale. Our results show that the dynamics at the intermediate range order contains two distinct relaxation time scales, a fast and a slow component, differing by about a 10-fold factor below Tg and approaching to one another past the glass transition. The slow relaxation time agrees with the shear relaxation time, proving that Si-O bond breaking constitutes the primary control of structural relaxation at the intermediate range order.

On the rigid to floppy transitions in calcium silicate glasses from Raman scattering and cluster constraint analysis

Calcium silicate glasses xCaO − (1 − x)SiO2 exhibit a threshold in Raman line-shapes which can be related, on the basis of Maxwell constraint counting, to the onset of network rigidity as the concentration of calcium oxide x is decreased. The present results are more deeply characterized by a size-increasing cluster approximation that allows to perform Maxwell mechanical constraint counting beyond the usual meanfield treatment. This permits to discuss under which structural conditions an elastic intermediate phase should be obtained in the future.

Growing Negative Pressure in Dissolved Solutes: Raman Monitoring of Solvent-Pulling Effect

Negative pressure in liquids is both an experimental fact and a usually neglected state of condensed matter. Using synthetic fluid inclusions, namely closed vacuoles fabricated inside one solid host by hydrothermal processes, a Raman study was performed to examine how a superheated solvent (under negative pressure) interacts with its dissolved solutes. As a result, this contribution not only illustrates this well-known tensile state but also displays evidence that a stretched solvent is able to pull on its dissolved solutes and put them also under a stretched state. The dielectric continuum hypothesis may lead to expect a stretching effect in solutes similar to the solvent’s, but our measurements evidence a damping mechanical effect (growing with tension), most probably related to solvation shells. One practical consequence is that the (experimentally known) supersolvent properties of superheated solutions are certainly related to the change of the chemical potential of solutes which results from the damp...

High-temperature Raman spectroscopy of the Cs2O–B2O3–MoO3 system for CsB3O5 crystal growth

Raman spectroscopy at high temperature has been applied to study in situ the microstructure of the solution in a Cs2O–B2O3–MoO3 growth system. A crystal–solution interface was observed. The BO groups consist of spiral chains based on B3O4O2 rings in the solution (O is a bridging O atom). The Raman spectrum of the solution indicates that MoO4 tetrahedra existed in the growth system. The nonbridging O atoms of the chains combined with the MoO4 groups, which decreased the viscosity. The Raman spectra near the interface show that at the boundary an isomerization reaction from three- to four-coordinated boron occurred. The formation of B3O7 triborate groups occurred. The morphology of the CsB3O5 crystal resulting from spontaneous crystallization was observed to correspond to our expectations.