Impacts of composition and beta irradiation on phase separation in multiphase amorphous calcium borosilicates

Borosilicate glasses for nuclear waste applications are limited in waste loading by the precipitation of water-soluble molybdates. In order to increase storage efficiency, new compositions are sought out that trap molybdenum in a water-durable CaMoO4 crystalline phase. Factors affecting CaMoO4 combination and glass-in-glass phase separation in calcium borosilicate systems as a function of changing [MoO3] and [B2O3] are examined in this study in order to understand how competition for charge balancers affects phase separation. It further examines the influence of radiation damage on structural modifications using 0.77 to 1.34 GGy of 2.5 MeV electron radiation that replicates inelastic collisions predicted to occur over long-term storage. The resulting microstructure of separated phases and the defect structure were analyzed using electron microscopy, XRD, Raman and EPR spectroscopy prior to and post irradiation. Synthesized calcium borosilicates are observed to form an unusual heterogeneous microstructure composed of three embedded amorphous phases with a solubility limit ~ 2.5 mol% MoO3. Increasing [B2O3] increased the areas of immiscibility and order of (MoO4)2 − anions, while increasing [MoO3] increased both the phase separation and crystallization temperature resulting in phases closer to metastable equilibrium, and initiated clustered crystallization for [MoO3] > 2.5 mol%. β-irradiation was found to have favorable properties in amorphous systems by creating structural disorder and defect assisted ion migration that thus prevented crystallization. It also increased reticulation in the borosilicate network through 6-membered boroxyl ring and Si ring cleavage to form smaller rings and isolated units. This occurred alongside an increased reduction of Mo6 + with dose that can be correlated to molybdenum solubility. In compositions with existing CaMoO4 crystallites, radiation caused a scattering effect, though the crystal content remained unchanged. Therefore β-irradiation can preferentially prevent crystallization in calcium borosilicates for [MoO3] < 2.5 mol%, but has a smaller impact on systems with existing CaMoO4 crystallites

Characterization of immiscibility in calcium borosilicates used for the immobilization of Mo 6+ under Au‐irradiation

Funder: FfWGFunder: Cambridge Philosophical SocietyAbstract: The aim of this paper was to assess factors affecting primary and secondary phase separation in simplified calcium borosilicate glasses studied for nuclear waste applications. Several glasses with varying [MoO3] and [B2O3] were synthesized and exposed to Au‐irradiation to examine compositional effects on glass structure and domain size of separated phases induced by accumulated radiation damage resulting from α‐decay over a ~1000 year timeframe. The produced glasses fell within the immiscibility dome of CaO−SiO2−B2O3 and showed a unique microstructure of embedded immiscibility with three identifiable amorphous phases according to electron microscopy, Raman spectroscopy, and diffraction. These glasses were then bombarded with 7 MeV Au3+ ions to a dose of 3 × 1014 ions/cm2 creating an estimated ~1 dpa of damage. Several changes to the morphology, spatial distribution, and size of secondary phases were observed, indicative of significant structural reorganization and changes to the chemical composition of each phase. A general mechanism of coalescence to form larger particles was observed for [MoO3] < 2.5 mol%, whereas segregation to form smaller more evenly distributed particles was seen for [B2O3] ≤ 15 mol% and [MoO3] ≥ 2.5 mol%. These microscopic changes were concurrent to surface‐bulk diffusion of Ca and/or Mo ions, where the direction of diffusion was dependent on [B2O3] with a barrier identified at ~20 mol%, as well as cross‐phase diffusion of said ions. These modifications occurred in part through the formation of distorted ring structures within the borosilicate network, which enabled the increased dissolution of isolated (MoO4)2− units. Au‐irradiation was therefore able to increase the solubility of molybdenum and alter the structure and composition of secondary phases with the extent of modification varying with [MoO3] and [B2O3]/[SiO2], though glasses notably remained heterogeneous. The collective results suggest that radiation and composition can both be used as design tools to modulate the domain size and distribution of separated phases in heterogeneous glasses

Characterisation of immiscibility in calcium borosilicates used for the immobilisation of Mo 6+ under Au‐irradiation

The aim of this paper was to assess factors affecting primary and secondary phase separation in simplified calcium borosilicate glasses studied for nuclear waste applications. Several glasses with varying [MoO3] and [B2O3] were synthesised and exposed to Au‐irradiation to examine compositional effects on the glass structure and domain size of separated phases induced by accumulated radiation damage resulting from α‐decay over a ~1000 year timeframe. The produced glasses fell within the immiscibility dome of CaO−SiO2−B2O3 and showed a unique microstructure of embedded immiscibility with three identifiable amorphous phases according to electron microscopy, Raman spectroscopy and diffraction. These glasses were then bombarded with 7 MeV Au3+ ions to a dose of 3×1014 ions/cm2 creating an estimated ~1 dpa of damage. Several changes to the morphology, spatial distribution and size of secondary phases were observed, indicative of significant structural reorganisation and changes to the chemical composition of each phase. A general mechanism of coalescence to form larger particles was observed for [MoO3] < 2.5mol%, while segregation to form smaller more evenly distributed particles was seen for [B2O3] ≤ 15mol% and [MoO3] ≥ 2.5mol%. These microscopic changes were concurrent to surface‐bulk diffusion of Ca and/or Mo ions, where the direction of diffusion was dependent on [B2O3] with a barrier identified at ~20mol%, as well as cross phase diffusion of said ions. These modifications occurred in part through the formation of distorted ring structures within the borosilicate network, which enabled the increased dissolution of isolated (MoO4)2‐ units. Au‐irradiation was therefore able to increase the solubility of molybdenum and alter the structure and composition of secondary phases with the extent of modification varying with [MoO3] and [B2O3]/[SiO2], though glasses notably remained heterogeneous. The collective results suggest that radiation and composition can both be used as design tools to modulate the domain size and distribution of separated phases in heterogeneous glasses

Phase Transitions in Zeolitic Imidazolate Framework 7: The Importance of Framework Flexibility and Guest-Induced Instability

A study of the phase transitions in ZIF-7 (zeolitic imidazolate frameworks- (Zn(PhIm)2, PhIm = benzimidazolate)) as a function of guest occupancy and temperature was reported. Raman spectra of an as-synthesized sample were collected in air between 297 and 421 K. The major contributions of the spectra come from the vibrational modes of the benzimidazolate ligand. Upon heating, most of the Raman bands remain similar and keep the same frequencies until 357 K, indicating that the structure of ZIF-7 seems to be stable in this temperature range. Above 357 K, strong modifications are observed in the regions corresponding to the lattice modes. The formation of ZIF-7-II is attributed to the loss of dimethylformamide (DMF) solvent molecules from the ZIF-7-I framework. This can be confirmed by the differential scanning calorimetry and thermogravimetric analysis traces of ZIF-7-I. The highly-distorted and locally-strained nature of ZIF-7-II leads to its poor crystallinity, reflected by X-ray powder diffraction and scanning electron microscope

Discovery of a maximum damage structure for Xe-irradiated borosilicate glass ceramics containing powellite

In order to increase the waste loading efficiency in nuclear waste glasses, alternate glass ceramic (GC) materials are sought that trap problematic molybdenum in a water-durable CaMoO4 phase within a borosilicate glass matrix. In order to test the radiation resistance of these candidate wasteforms, accelerated external radiation can be employed to replicate long-term damage. In this study, several glasses and GCs were synthesized with up to 10 mol% MoO3 and subjected to 92 MeV Xe ions with fluences ranging between 5 × 1012 to 1.8 × 1014 ions/cm2. The main mechanisms of modification following irradiation involve: (i) thermal and defect-assisted diffusion, (ii) relaxation from the ion's added energy, (iii) localized damage recovery from overlapping ion tracks, and (iv) the accumulation of point defects or the formation of voids that created significant strain and led to longer-range modifications. Most significantly, a saturation in alteration could be detected for fluences greater than 4 × 1013 ions/cm2, which represents an average structure that is representative of the maximum damage state from these competing mechanisms. The results from this study can therefore be used for long-term structural projections in the development of more complex GCs for nuclear waste applications

Study of incorporation mechanisms of ethanol in ice and influence of its presence on ice homogeneous nucleation

Ce travail de thèse porte sur l’étude des mécanismes d’incorporation de l’éthanol dans la glace et de l’influence de la présence de ce composé sur la nucléation homogène de la glace. Nous nous sommes d’abord intéressés à la nucléation homogène de la glace dans l’eau pure et les solutions aqueuses d’éthanol par cryomicroscopie. Les taux de nucléation homogène de la glace dans des microgouttelettes d’eau pure et de solutions aqueuses d’éthanol préparées en émulsions ont été mesurés et leurs évolutions sur une large gamme de température ont été déterminées à l’aide de considérations théoriques. A l’aide de la théorie basée sur l’activité de l’eau et du diagramme de phase du système eau-éthanol, nous avons montré que le solide qui nuclée lors du refroidissement de microgouttelettes de solutions aqueuses d’éthanol de concentrations ([Chi]EtOH)L = 0 – 2.62 mol% est la glace tandis que pour les concentrations ([Chi]EtOH)L = 5.30 – 20 mol%, le solide qui nuclée est un hydrate d’éthanol de composition E · (2 ± 0.2) H2O. Ceci est conforté par les caractéristiques du spectre Raman de l’hydrate. Nous avons ensuite réalisé une étude Raman in situ de solutions aqueuses d’éthanol gelées. Ces solutions présentent des comportements différents lors du refroidissement et du recuit suivant leur concentration initiale. Ainsi, à haute concentration (25.4 mol%), la cristallisation d’un hydrate d’éthanol est observée à 212 K lors du refroidissement. Lors du recuit, un réarrangement structurel prend place entre 143 et 173 K menant à la formation d’un second hydrate. A faible concentration (3.61 mol%), la cristallisation de la glace hexagonale intervient à 248 K. Celle-ci coexiste avec une solution aqueuse se surconcentrant lors du refroidissement. Une partie de cette solution cristallise sous la forme d’un hydrate d’éthanol vers 208 K et une autre reste sous forme d’éthanol pur liquide avant de cristalliser sous la forme d’éthanol pur solide vers 149 K. Les fontes de ces trois structures sont observées lors du recuit. Enfin, une analyse Raman in situ couplée à une étude en diffraction de rayons X a été réalisée sur des films minces obtenus par co-condensation de mélanges gazeux eau-éthanol. Un premier hydrate d’éthanol de composition E · (4.75 – 5) H2O, stable entre ([Chi]EtOH)S = 10.9 et 18.8 mol% est ainsi reporté. Un hydrate distinct, de composition E (2 ± 0.2) H2O est observé aux concentrations ([Chi]EtOH)S ≥ 22 mol%. Les mesures effectuées en diffraction de rayons X pour cet hydrate indiquent une structure tétragonale de groupe d’espace P4/mmm. Enfin, à basse concentration (([Chi]EtOH)S = 0.3 mol%), les spectres Raman révèlent l’existence d’une structure composée de molécules d’éthanol extrêmement diluées dans la glace (solution solide). Ce régime peut être transposé aux conditions troposphériques.This thesis focuses on studying the incorporation mechanisms of ethanol in ice and the influence of its presence on the homogeneous ice nucleation. We are primarily interested in the homogeneous ice nucleation in pure water and ethanol aqueous solutions using cryomicroscopy. The homogeneous nucleation rate of ice in droplets of pure water and ethanol aqueous solutions prepared in emulsions were measured and their evolutions over a wide temperature range were determined using theoretical considerations. Using the water-activity-based ice nucleation theory and the ethanol-water phase diagram, we have shown that the solid that nucleates during the cooling of microdroplets of ethanol aqueous solutions of concentrations ([Chi]EtOH)L = 0 – 2.62 mol% is ice whereas for concentrations ([Chi]EtOH)L = 5.30 – 20 mol%, the solid that nucleates is an ethanol hydrate of composition E · (2 ± 0.2) H2O. This is confirmed by the spectroscopic features of the hydrate Raman spectrum. We have then conducted an in situ Raman study on frozen ethanol aqueous solutions. These solutions show different behavior during cooling and annealing according to their initial concentration. Thus, at high concentration (25.4 mol%), the crystallization of an ethanol hydrate is observed at 212 K during cooling. During annealing, a structural rearrangement takes place between 143 and 173 K leading to the formation of a second hydrate. At low concentration (3.61 mol%), the crystallization of hexagonal ice occurs at 248 K. It coexists with an aqueous solution that overconcentrating during cooling. A part of this solution crystallizes as an ethanol hydrate around 208 K and another one remains as liquid pure ethanol before crystallizing in the form of solid pure ethanol around 149 K. The melting of these three structures is observed during annealing. Finally, an in situ Raman analysis coupled with an X-ray diffraction study was performed on thin films obtained by co-condensation of water-ethanol mixtures. A first ethanol hydrate of composition E · (4.75 – 5) H2O, stable between ([Chi]EtOH)S = 10.9 and 18.8 mol% is thus reported. A distinct hydrate of composition E · (2 ± 0.2) H2O is observed at concentrations ([Chi]EtOH)S ≥ 22 mol%. The X-ray diffraction results obtained for this hydrate indicate a tetragonal structure with a space group P4/mmm. Finally, at low concentrations (([Chi]EtOH)S = 0.3 mol%), the Raman spectra reveal the existence of a structure of ethanol molecules extremely diluted in ice (solid solution). This regime can be transposed to tropospheric conditions

Study of incorporation mechanisms of ethanol in ice and influence of its presence on ice homogeneous nucleation

Ce travail de thèse porte sur l’étude des mécanismes d’incorporation de l’éthanol dans la glace et de l’influence de la présence de ce composé sur la nucléation homogène de la glace. Nous nous sommes d’abord intéressés à la nucléation homogène de la glace dans l’eau pure et les solutions aqueuses d’éthanol par cryomicroscopie. Les taux de nucléation homogène de la glace dans des microgouttelettes d’eau pure et de solutions aqueuses d’éthanol préparées en émulsions ont été mesurés et leurs évolutions sur une large gamme de température ont été déterminées à l’aide de considérations théoriques. A l’aide de la théorie basée sur l’activité de l’eau et du diagramme de phase du système eau-éthanol, nous avons montré que le solide qui nuclée lors du refroidissement de microgouttelettes de solutions aqueuses d’éthanol de concentrations ([Chi]EtOH)L = 0 – 2.62 mol% est la glace tandis que pour les concentrations ([Chi]EtOH)L = 5.30 – 20 mol%, le solide qui nuclée est un hydrate d’éthanol de composition E · (2 ± 0.2) H2O. Ceci est conforté par les caractéristiques du spectre Raman de l’hydrate. Nous avons ensuite réalisé une étude Raman in situ de solutions aqueuses d’éthanol gelées. Ces solutions présentent des comportements différents lors du refroidissement et du recuit suivant leur concentration initiale. Ainsi, à haute concentration (25.4 mol%), la cristallisation d’un hydrate d’éthanol est observée à 212 K lors du refroidissement. Lors du recuit, un réarrangement structurel prend place entre 143 et 173 K menant à la formation d’un second hydrate. A faible concentration (3.61 mol%), la cristallisation de la glace hexagonale intervient à 248 K. Celle-ci coexiste avec une solution aqueuse se surconcentrant lors du refroidissement. Une partie de cette solution cristallise sous la forme d’un hydrate d’éthanol vers 208 K et une autre reste sous forme d’éthanol pur liquide avant de cristalliser sous la forme d’éthanol pur solide vers 149 K. Les fontes de ces trois structures sont observées lors du recuit. Enfin, une analyse Raman in situ couplée à une étude en diffraction de rayons X a été réalisée sur des films minces obtenus par co-condensation de mélanges gazeux eau-éthanol. Un premier hydrate d’éthanol de composition E · (4.75 – 5) H2O, stable entre ([Chi]EtOH)S = 10.9 et 18.8 mol% est ainsi reporté. Un hydrate distinct, de composition E (2 ± 0.2) H2O est observé aux concentrations ([Chi]EtOH)S ≥ 22 mol%. Les mesures effectuées en diffraction de rayons X pour cet hydrate indiquent une structure tétragonale de groupe d’espace P4/mmm. Enfin, à basse concentration (([Chi]EtOH)S = 0.3 mol%), les spectres Raman révèlent l’existence d’une structure composée de molécules d’éthanol extrêmement diluées dans la glace (solution solide). Ce régime peut être transposé aux conditions troposphériques.This thesis focuses on studying the incorporation mechanisms of ethanol in ice and the influence of its presence on the homogeneous ice nucleation. We are primarily interested in the homogeneous ice nucleation in pure water and ethanol aqueous solutions using cryomicroscopy. The homogeneous nucleation rate of ice in droplets of pure water and ethanol aqueous solutions prepared in emulsions were measured and their evolutions over a wide temperature range were determined using theoretical considerations. Using the water-activity-based ice nucleation theory and the ethanol-water phase diagram, we have shown that the solid that nucleates during the cooling of microdroplets of ethanol aqueous solutions of concentrations ([Chi]EtOH)L = 0 – 2.62 mol% is ice whereas for concentrations ([Chi]EtOH)L = 5.30 – 20 mol%, the solid that nucleates is an ethanol hydrate of composition E · (2 ± 0.2) H2O. This is confirmed by the spectroscopic features of the hydrate Raman spectrum. We have then conducted an in situ Raman study on frozen ethanol aqueous solutions. These solutions show different behavior during cooling and annealing according to their initial concentration. Thus, at high concentration (25.4 mol%), the crystallization of an ethanol hydrate is observed at 212 K during cooling. During annealing, a structural rearrangement takes place between 143 and 173 K leading to the formation of a second hydrate. At low concentration (3.61 mol%), the crystallization of hexagonal ice occurs at 248 K. It coexists with an aqueous solution that overconcentrating during cooling. A part of this solution crystallizes as an ethanol hydrate around 208 K and another one remains as liquid pure ethanol before crystallizing in the form of solid pure ethanol around 149 K. The melting of these three structures is observed during annealing. Finally, an in situ Raman analysis coupled with an X-ray diffraction study was performed on thin films obtained by co-condensation of water-ethanol mixtures. A first ethanol hydrate of composition E · (4.75 – 5) H2O, stable between ([Chi]EtOH)S = 10.9 and 18.8 mol% is thus reported. A distinct hydrate of composition E · (2 ± 0.2) H2O is observed at concentrations ([Chi]EtOH)S ≥ 22 mol%. The X-ray diffraction results obtained for this hydrate indicate a tetragonal structure with a space group P4/mmm. Finally, at low concentrations (([Chi]EtOH)S = 0.3 mol%), the Raman spectra reveal the existence of a structure of ethanol molecules extremely diluted in ice (solid solution). This regime can be transposed to tropospheric conditions

Raman modes of carbonate minerals as pressure and temperature gauges up to 6 GPa and 500°C

Diamond anvil cell (DAC) experiments focusing on the solubility of carbonates and aqueous carbon speciation at subduction zones require pressure monitoring with sensitive, chemically inert sensors. Commonly used pressure indicators are either too insensitive or prone to contaminate pressure-transmitting media due to their increased solubility at high pressure and/or temperature (P/T). Here, the P- and T-induced frequency shifts of the Raman vibrational modes of natural crystalline carbonate minerals aragonite, calcite, dolomite, magnesite, rhodochrosite, and siderite have been calibrated for application as Raman spectroscopic P and T sensors in DACs up to 500°C and 6 GPa. The shifts of all modes are quasi-constant over the observed P and T ranges and are generally less prominent for internal modes than for external modes. Our method provides a sensitive and robust alternative to traditional pressure calibrants, and has three principal advantages: (1) higher sensitivity (for particular Raman vibrational modes), (2) monitoring P/T -induced shifts of several modes allows even more accurate P/T determination, and (3) no contamination of pressure-transmitting media by foreign materials can occur. Additionally, the isobaric and isothermal equivalent of the Grüneisen parameter and the anharmonic parameter for each of the traced modes have been determined

Characterization of immiscibility in calcium borosilicates used for the immobilization of Mo 6+ under Au‐irradiation

Funder: FfWGFunder: Cambridge Philosophical SocietyAbstract: The aim of this paper was to assess factors affecting primary and secondary phase separation in simplified calcium borosilicate glasses studied for nuclear waste applications. Several glasses with varying [MoO3] and [B2O3] were synthesized and exposed to Au‐irradiation to examine compositional effects on glass structure and domain size of separated phases induced by accumulated radiation damage resulting from α‐decay over a ~1000 year timeframe. The produced glasses fell within the immiscibility dome of CaO−SiO2−B2O3 and showed a unique microstructure of embedded immiscibility with three identifiable amorphous phases according to electron microscopy, Raman spectroscopy, and diffraction. These glasses were then bombarded with 7 MeV Au3+ ions to a dose of 3 × 1014 ions/cm2 creating an estimated ~1 dpa of damage. Several changes to the morphology, spatial distribution, and size of secondary phases were observed, indicative of significant structural reorganization and changes to the chemical composition of each phase. A general mechanism of coalescence to form larger particles was observed for [MoO3] < 2.5 mol%, whereas segregation to form smaller more evenly distributed particles was seen for [B2O3] ≤ 15 mol% and [MoO3] ≥ 2.5 mol%. These microscopic changes were concurrent to surface‐bulk diffusion of Ca and/or Mo ions, where the direction of diffusion was dependent on [B2O3] with a barrier identified at ~20 mol%, as well as cross‐phase diffusion of said ions. These modifications occurred in part through the formation of distorted ring structures within the borosilicate network, which enabled the increased dissolution of isolated (MoO4)2− units. Au‐irradiation was therefore able to increase the solubility of molybdenum and alter the structure and composition of secondary phases with the extent of modification varying with [MoO3] and [B2O3]/[SiO2], though glasses notably remained heterogeneous. The collective results suggest that radiation and composition can both be used as design tools to modulate the domain size and distribution of separated phases in heterogeneous glasses

In situ Raman study and thermodynamic model of aqueous carbonate speciation in equilibrium with aragonite under subduction zone conditions

International audienc