Le GDR-Verres et l’USTV : des réseaux pour la réflexion scientifique sur des problématiques verrières académiques et industrielles

International audienceLa communauté scientifique et industrielle du verre est extraordinairement riche en France. Des équipes scientifiques avec une renommée internationale et une R&D verrière industrielle française, très dynamique, ayant besoin d’échanges sur des domaines d’expertise. Le réseau animé par le GDR-Verres et l’USTV crée un lien entre les équipes de recherche fondamentale, celles plus appliquée ou technologiques, et le monde industriel

Phosphorus solubility in basaltic glass: limitations for phosphorus immobilization in glass and glass-ceramics

The composition of sewage sludge from urban wastewater treatment plants is simulated using P-doped basalts. Electron microscopy analyses show that the solubility of P in the basaltic melt is limited by the formation of a liquid-liquid immiscibility in the form of an aluminosilicate phase and a Ca-Mg-Fe-rich phosphate phase. The rheological behavior of these compositions is influenced by both phase separation and nanocrystallization. Upon a thermal treatment, the glasses will crystallize into a mixture of inosilicates and spinel-like phases at low P contents and into Ca-Mg-Fe phosphate at high P contents. Hardness measurements yield values between 5.41 and 7.66 GPa, inside the range of commercial glasses and glass-ceramics. Leaching affects mainly unstable Mg2+-PO43- complexes

Structural characterization of SiO2-Na2O-CaO-B2O3-MoO3 glasses

5 pagesNuclear spent fuel reprocessing generates high level radioactive waste with high Mo concentration that are currently immobilized in borosilicate glass matrices containing both alkali and alkaline-earth elements [1]. Because of its high field strength, Mo6+ ion has a limited solubility in silicate and borosilicate glasses and crystallization of alkali or alkaline-earth molybdates can be observed during melt cooling or heat treatment of glasses [2-4]. Glass composition changes can significantly modify the nature and the relative proportions of molybdate crystals that may form during natural cooling of the melt. For instance, in a previous work we showed that CaMoO4 crystallization tendency increased at the expenses of Na2MoO4 when B2O3 concentration increased in a SiO2-Na2O-CaO-MoO3 glass composition [4]. In this study, we present structural results on two series (Mx, By) of quenched glass samples belonging to this system using 29Si, 11B, 23Na MAS NMR and Raman spectroscopies. The effect of MoO3 on the glassy network structure is studied and its structural role is discussed (Mx series). The evolution of the distribution of Na+ ions within the borosilicate network is followed when B2O3 concentration increased (By series) and is discussed according to the evolution of the crystallization tendency of the melt. For all glasses, ESR was used to investigate the nature and the concentration of paramagnetic species

Erbium environment in glass-ceramics investigated by atom probe tomography

Glass-ceramics (considered here as a glassy host containing crystalline or amorphous nanoparticles) are of interest for luminescent properties as they can combine the sturdiness and low cost of a matrix host with particular spectroscopic behavior that would not appear in this host [1]. Ideally, nanoparticles would fully encapsulate luminescent ions to produce engineered spectroscopic properties. This approach is particularly promising for optical fibers. Indeed, silica is the most common glass used to prepare such waveguides. However, it is necessary to overcome some of its characteristics (high phonon energy, low luminesent ions solubility, ...) which may be detrimental to luminescent properties. As silicate systems have a large phase immiscibility domain when they contain divalent metal oxides (such as Mg), one can take advantage of thermal treatments inherent to the MCVD (Modified Chemical Vapor Deposition) process to obtain nanoparticles through phase separation [2]. By modifying Mg concentration, we have observed modifications of luminescent properties of Er3+ ions [3]. However the question arises of the partition of rare-earth ions in nanoparticles. Qualitative partition of erbium ions in nanoparticles was reported thanks to Secondary Ion Mass Spectrometry analyses [4]. However, the spatial resolution is about the particle size. To go further, we take advantages of recent developments in Atom Probe Tomography (APT) which allowed the extension of such studies to glass-ceramics [5]. Partition of erbium ions is clearly observed in nanoparticles smaller than 10 nm (Figure 1). During this presentation, we will discuss this partition and the most probable nearest neighbors and correlate these results with luminescent properties

Structural study of a rare earth-rich aluminoborosilicate glass containing various alkali and alkaline-earth modifier cations

4 pagesA rare-earth rich aluminoborosilicate glass of composition (given in wt.%): 50.68 SiO2 - 4.25 Al2O3 - 8.50 B2O3 - 12.19 M2O - 4.84 M'O - 3.19 ZrO2 - 16.35 Nd2O3 (where M and M' are respectively an alkali and alkaline earth cation) is currently under study as potential nuclear waste form. In this work, we were interested in the structure of this glass in relation with the modifier cation type. Two different glass series were elaborated by changing separately the nature of the alkaline (M=Li, Na, K, Rb, Cs) and the alkaline-earth (M'=Mg, Ca, Sr, Ba) ions and different structural studies were intended to elucidate the local environment of the rare-earth and the network arrangement. Only slight effect was put in evidence on the covalency degree and the length of Nd-O linkage with a change of M or M', by optical spectroscopy and EXAFS measurements. Raman and MAS NMR (29Si, 27Al, 11B) spectroscopies showed a variation of the polymerization degree of the network with the size of the modifier cation. Finally, the most important feature of this glass composition is related to the AlO4- charge compensation which was proved to be uniquely assured by alkali cations

Effect of network connectivity on behavior of synthetic Broborg Hillfort glasses

There is wide industrial interest in developing robust models of long-term (>100 years) glass durability. Archeological glass analogs, glasses of similar composition, and alteration conditions to those being tested for durability can be used to evaluate and inform such models. Two such analog glasses from a 1500-year-old vitrified hillfort near Uppsala, Sweden have previously been identified as potential analogs for low concentration Fe-bearing aluminosilicate nuclear waste glasses. However, open questions remain regarding the melting environment from which these historic glasses were formed and the effect of these conditions on their chemical durability. A key factor to answering the previous melting and durability questions is the redox state of Fe in the starting and final materials. Past work has shown that the melting conditions of a glass-forming melt may influence the redox ratio value (Fe+3/∑Fe), a measure of a glass's redox state, and both melting conditions and the redox ratio may influence the glass alteration behavior. Synthetic analogs of the hillfort glasses have been produced using either fully oxidized or reduced Fe precursors to address this question. In this study, the melting behavior, glass transition temperature, oxidation state, network structure, and chemical durability of these synthesized glass analogs is presented. Resulting data suggests that the degree of network connectivity as impacted by the oxidation state of iron impacted the behavior of the glass-forming melt but in this case does not affect the chemical durability of the final glass. Glasses with a lower degree of melt connectivity were found to have a lower viscosity, resulting in a lower glass transition temperature and softening temperature, as well as in a lower temperature of foam onset and temperature of foam maximum. This lower degree of network connectivity most likely played a more significant role in accelerating the conversion of batch chemicals into glass than the presence of water vapor in the furnace's atmosphere. Future work will focus on using the results from this work with outcomes from other aspects of this project to evaluate long-term glass alteration models

Ca and Na environments in Na2O–CaO–Al2O3–SiO2 glasses: influence of cation mixing and cation-network interactions.

X-ray absorption spectroscopy at Ca and Na K-edges and Molecular Dynamics (MD) simulations are used to investigate the Ca and Na environment in soda lime aluminosilicate glasses. Both X-ray Absorption Near Edge Structure (XANES) spectra and MD calculations indicate a coordination number of about 7 for Ca and 6 for Na, in a distorted polyhedron. Ca and Na XANES spectra are poorly affected either by the Si/Al substitution or the Ca/Na substitution while MD simulations present some variations in the cationic environment. We show an affinity for non-bridging oxygens (NBOs) to be connected with Ca rather than Na. Evidence of Ca–Na mixing is shown by the MD models and there is a tendency toward forming more regions enriched in (Ca, NBOs) for CaO-rich aluminosilicate glasses. Variations in the cationic mobility upon the Na/Ca substitution are correlated with the observed structural modifications

La spectrométrie Raman, un outil de choix pour étudier les volatils dissous dans un verre ou un silicate fondu : le cas de l’eau

L’eau dissoute dans un verre ou un silicate fondu affecte fortement ses propriétés rhéologiques, thermodynamiques et sa structure. Pour certaines applications des sciences de la Terre ou industrielles, la quantification de cette eau est nécessaire. À l’aide de la nouvelle méthode que nous avons développée, la Spectrométrie Raman permet de le faire sans préparation de l’échantillon, de manière rapide, sans aucun standard, avec une résolution spatiale micrométrique. Cette calibration est, de plus, indépendante de la chimie du verre étudié. Elle offre des perspectives intéressantes pour l’étude de la spéciation et la diffusion de l’eau dans les verres et silicates fondus

Al coordination and speciation in calcium aluminosilicate glasses : effects of composition determined by 27Al MQ-MAS NMR and Raman spectrocospy

The structure and properties of glasses and melts in the CaO–Al2O3–SiO2 (CAS) system play an important role in earth and material sciences. Aluminum has a crucial role in this ternary system, and its environment is still questioned. In this paper, we present new results using Raman spectroscopy and 27Al Nuclear Magnetic Resonance on CAS glasses obtained by classic and rapid quenching methods. We propose an Al/Si tetrahedral distribution in the glass network in different Qn species. In this system, we show that Al and Si are mainly in Q4 species along the join R=CaO/Al2O3=1, and in depolymerized Q2 and Q3 units at high CaO content for other joins (R=1.57 and 3). Five- ([5]Al) and six-fold ([6]Al) coordinated aluminum can be detected in the peraluminous glasses (R1), except for glasses with low silica and high CaO content. The presence of [5]Al is related to viscous flow mechanisms while, in highly depolymerized glasses, the absence of [5]Al may indicate different mechanisms for melts to flow. This systematic study on the CAS system modifies the simple picture of aluminosilicate glasses, and the existence of [5]Al should be included by geochemists, geophysicists and glass scientists to model appropriately the physical properties of aluminosilicate glasses and melts