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Neutron diffraction with magnesium isotope substitution, high energy x-ray diffraction, and 29Si, 27Al, and 25Mg solid-state nuclear magnetic resonance (NMR) spectroscopy were used to measure the structure of glassy diopside (CaMgSi2O6), enstatite (MgSiO3), and four (MgO) x(Al2O3) y(SiO2)1−x−y glasses, with x = 0.375 or 0.25 along the 50 mol. % silica tie-line (1 − x − y = 0.5) or with x = 0.3 or 0.2 along the 60 mol. % silica tie-line (1 − x − y = 0.6). The bound coherent neutron scattering length of the isotope 25Mg was remeasured, and the value of 3.720(12) fm was obtained from a Rietveld refinement of the powder diffraction patterns measured for crystalline 25MgO. The diffraction results for the glasses show a broad asymmetric distribution of Mg–O nearest-neighbors with a coordination number of 4.40(4) and 4.46(4) for the diopside and enstatite glasses, respectively. As magnesia is replaced by alumina along a tie-line with 50 or 60 mol. % silica, the Mg–O coordination number increases with the weighted bond distance as less Mg2+ ions adopt a network-modifying role and more of these ions adopt a predominantly charge-compensating role. 25Mg magic angle spinning (MAS) NMR results could not resolve the different coordination environments of Mg2+ under the employed field strength (14.1 T) and spinning rate (20 kHz). The results emphasize the power of neutron diffraction with isotope substitution to provide unambiguous site-specific information on the coordination environment of magnesium in disordered materials.

L’étendue et la nature de l’interface liant l’argile cuite du corps céramique et la matière vitrifiée de la glaçure jouent un rôle essentiel sur les propriétés physico-chimiques de l’objet fini. Ce chapitre résume l’étendue des connaissances pour les glaçures riches en plomb.

Li2O-Al2O3-SiO2 (LAS) glass-ceramics have important industrial applications and bulk nucleation is usually achieved by using nucleating agents. In particular, P2O5 is an efficient agent in glasses containing a low level of Al2O3 but its role in the first stages of nucleation is not well established. In this study, we combine structural investigations from local to mesoscales to describe the structural evolution during crystallization of LAS glass-ceramics. Local environment is probed using 29Si and 31P MAS-NMR, indicating organization of P in poorly crystallized Li3PO4 species prior any crystallization. To better understand the detailed nanoscale changes of the glass structure, 31P-31P DQ-DRENAR homo-nuclear correlation experiments have been carried out, revealing the gradual segregation of P atoms associated with the formation of disordered Li3PO4. Small-angle neutron scattering data also show the apparition of nanoscale heterogeneities associated with Li3PO4 species upon heating treatments and allow the determination of their average sizes. These new structural information enhance our understanding of the P role in nucleation mechanisms. Nucleation is initiated by gradual change in P environment implying P segregation upon heating treatments, forming disordered Li3PO4 heterogeneities. The segregation of P atoms enables the precipitation of meta-and di-silicate phases.

International audience; In this work, a structural characterization of sputtered silica films was carried out using Raman spectroscopy. Due to the low cross-section and the thinness of the silica layer, its Raman signature is dwarfed by that of the glass substrate and is therefore difficult to extract. Overcoming these limitations represents an experimental challenge and requires the development of specific analysis strategies. For this purpose, an integrated approach for extracting and interpreting the Raman signature of amorphous silica films deposited on a soda-lime glass substrate was developed, based on three distinct methods: delamination of the sputtered silica film, creating a reflective mask substrate by depositing a metallic silver coating on the glass substrate and applying a numerical signal analysis (Non-negative matrix factorization) to the multidimensional dataset acquired through depth profile acquisitions on silica films directly deposited on a glass substrate. The reliability of each proposed method is demonstrated for the extraction of the silica thin film Raman spectra. These various methods can be easily extended to other materials, either crystalline or amorphous. Furthermore, we discuss the advantages and the limits of each approach.Applying this methodology allowed us to highlight the structural differences between sputtered silica thin film and bulk vitreous silica glass (v-SiO2). Magnetron sputtering film deposition is shown to form dense silica glass layers, with an estimated densification ratio, measured by x-ray reflectivity, equal to 7%. At the medium distance range, the network connectivity change in v-SiO2 is expressed by an unusually high population of three-membered rings leading to a more compact structure. The short-range order transformation was also studied by deriving the intertetrahedral angle decrease. The present results could be a step towards advanced investigation to gain insights into the structure of films at the atomic level.

Un décor de porcelaine est obtenu à l’aide de mélanges de pigments et de composants incolores qui, en se vitrifiant, fixent l’émail à la surface de l’objet et révèlent ainsi la couleu. Cet article s’intéresse à la stabilité d’un pigment de type spinelle au cours de la cuisson du décor. La caractérisation d’un grain de ce pigment par microscopie électronique, spectroscopie optique et absorption des rayons X, a permis de montrer que le changement de couleur parfois observé après cuisson résulte d’un enrichissement en chrome de la périphérie des grains de spinelle.

Ni:MgAl2O4 spinel shows a reversible random Ni2+ site redistribution with increasing temperature. With the aim of determining the influence of the structure evolution induced by heat-treatment on the nature of luminescence centers in NiO-doped spinel-based magnesium aluminosilicate glass-ceramics nucleated by a mixture of TiO2 and ZrO2, the detailed spectroscopic study of the initial glass during its heat-treatments at increasing and decreasing temperatures has been performed and accompanied by an XRD analysis and Raman spectroscopy. The initial glass was X-ray amorphous. Its optical spectrum is mainly formed by absorption of [5]Ni2+ sites with a small amount of [4]Ni2+ ones. Crystals of the nucleating catalyst, ZrTiO4, about 4 nm in size, appear during heat-treatment at 800 °C, while the absorption spectrum of Ni2+ ions remains near unchanged. At 850 °C, spinel crystals with size of about 6 nm precipitate, which is accompanied by a broadband luminescence in the near-IR centered at 1330 nm with a bandwidth of 380 nm. At 950 °C, there is a slight reduction in intensity of absorption bands attributed to [6]Ni2+, which can be explained by a tendency toward random Ni2+ site redistribution with increasing temperature. A decrease in the amount of the [6]Ni2+ luminescent centers is not accompanied by a decrease in the luminescence intensity because of the increased size of spinel crystals. Additional low-temperature heat-treatment does not lead to a redistribution between [6]Ni2+ and [4]Ni2+ sites in spinel crystals in favor of [6]Ni2+ ones. An increase of the luminescence intensity after low-temperature heat-treatment is associated with additional spinel crystallization.

International audience; This paper deals with the structural investigation of a new class of glasses belonging to the Ga-Sb-Se system. Neutron diffraction and 77 Se NMR were performed on the Ga 8 Sb 27 Se 65 glass composition to understand the structural network in this unconventional system. The experimental data were confronted to molecular dynamics simulations and show a good agreement. Detailed analyses are consistent with Ga and Se coordination numbers (CN) of 4 and 2, respectively, as usually obtained in chalcogenide glasses. This study also highlights a variable CN of Sb, ranging from 3 up to 5, allowing to better understand the formation of glasses in a such complex system.

International audience; A multiedge study of the local structure of lithium borate glasses and melts has been carried out using X-ray Raman scattering (XRS) as a function of temperature. Thanks to a wide range of compositions, from pure B2O3 up to the metaborate composition, we are able to finely interpret the modifications of the local environment of both the boron and oxygen atoms in terms of boron coordination number, formation of nonbridging oxygens (NBOs), and polymerization degree of the borate framework as a function of temperature and composition. A temperature-induced [4]B to [3]B conversion is observed above the glass transition temperature (Tg) from the glass to the melt from the triborate composition up to the metaborate composition. Two distinct melt structures are reported: a well-polymerized borate network—with few NBOs—below the triborate composition and a depolymerized borate network above the diborate composition with a rapid increase of the number of NBOs when Li2O is added. These two structurally distinct melts allow explaining the two dynamic regimes observed for lithium ion diffusion.

International audience; The glass formation, crystallization behavior and structure were investigated in the ZnO-Al2O3-SiO2 system. The boundaries of the glass forming region are defined, indicating the absence of glasses along the ZnO-SiO2 binary and the role of Al to improve glass formation. The crystallization behavior has been clarified for representative glass compositions showing first crystallization of willemite near the ZnO-SiO2 binary and a metastable zinc aluminosilicate solid solution for higher Al2O3/SiO2 content. Gahnite appears as a second phase and is mainly present near the center of the tectosilicate join. Glass structure was studied using 27 Al NMR spectroscopy, neutron and X-ray diffraction and molecular dynamics simulation. Both Al and Zn are shown to be distributed between four-fold and five-fold sites. The proportion of [4] Al is more important near the ZnAl2O4-SiO2 join. A remarkable similar behavior is revealed for the glass forming ability and structural properties between MgO and ZnO aluminosilicate systems.; La formation du verre, le comportement en cristallisation et la structure ont été étudiés dans le système ZnO-Al2O3-SiO2. Les limites de la région de formation du verre sont définies, indiquant l’absence de verres le long du binaire ZnO-SiO2 et le rôle d’Al pour améliorer la formation du verre. Le comportement en cristallisation a été clarifié pour des compositions de verre représentatives montrant la première cristallisation de willemite près du binaire ZnO-SiO2 et une solution solide d’aluminosilicate de zinc métastable pour une teneur plus élevée en Al2O3/SiO2. La gahnite apparaît comme une deuxième phase et est principalement présente près du centre du joint tectosilicate. La structure du verre a été étudiée en utilisant la spectroscopie 27Al RMN, la diffraction des neutrons et des rayons X et la simulation par dynamique moléculaire. Il est démontré que Al et Zn sont répartis entre des sites de coordinence quatre et cinq La proportion de [4]Al est plus importante près du joint ZnAl2O4-SiO2. Un comportement similaire est révélé pour la capacité de formation du verre et les propriétés structurelles entre les systèmes d'aluminosilicate de MgO et de ZnO.

International audience; The presence of titanium in Ground Granulated Blast-furnace Slags (GGBS) has been suspected to modify cement properties. This study provides the first evidence of a relation between the TiO 2 content of slags and the mechanical properties of mortars based on slag cements. It is observed that only the slags containing less than 1%TiO 2 show a compressive strength at 28 days that remains within the 52.5 MPa norm with CEM III cements complying with the European Standard NF EN 197-1. The structural origin of this chemical dependence of the performance of cements is investigated by determining directly the titanium speciation in various European slags by spectroscopic methods. Electron Paramagnetic Resonance indicates that about 76% of Ti in slag occurs as Ti 4+. The atomic structure around Ti was determined by Ti K-edge X-ray Absorption Near Edge Spectroscopy, which shows that Ti is mainly 5-fold coordinated in square-based pyramid geometry. Five coordinated Ti acts as network-stabilizer of the silicate network as it increases the polymerization. Requiring Ca 2+ for charge-compensation of the titanyl bond, it reduces the availability of Ca 2+ during glass alteration in a modified random model of glass structure, where Ca 2+ atoms are clustered in percolating cationic domains. As a consequence, the presence of 5-coordinated Ti results in a slower dissolution of the slag. These peculiar structural properties of titanium may explain the detrimental role of Ti above a 1% concentration, for many physical and chemical slag properties. This work provides a scientific ground for the technological acceptability of the upper limit of the Ti-content of GGBS.

International audience; Aluminosilicate glasses are widely used and investigated materials with current and promising technological applications such as high-power laser gain media, flat-panel displays, solid oxide fuel cells, sealing materials, glass-fiber composites and long-term immobilization of wastes, to name a few. They are also abundant in nature and relevant for geological processes as they are chemically close to the natural magmatic compositions of the Earth mantle. Finally at low SiO 2 content, quenched metallurgical slags are mainly composed of aluminosilicate glasses. Introducing Al 2 O 3 strongly affects many physico-chemical properties. For instance, it improves fracture strength, increases elastic modulus and chemical resistance or hinders the trend to phase separation. Many properties correlate with the nature of non-framework cations present in the glass and to the flexibility for Al to adopt multiple coordination states. Different aspects of the disorder (network connectivity, Si/Al disorder, short range environment) affect the topological and configurational entropies. In this article we address the specificities of the atomic-scale structure in diverse glass models containing alumina with important implications for interpreting and controlling the physico-chemical properties. Commercial Glasses Aluminosilicate (AS) glasses, notably at low-alkali content, have high values of tensile strength, resistance to high temperature and excellence resistance to chemical corrosion (Varshneya and Mauro, 2019). They have found widespread commercial application as fibers to reinforce plastics or concrete. E-glass (a low-alkali Ca-Mg alumino-borosilicate glass with 10-15 mol% Al 2 O 3) is the most common glass fibers. Nowadays, a major application concerns alkali-free aluminosilicates used as thin glass sheets for liquid crystal flat displays. With higher amounts of alkalis, aluminosilicate glasses can be used to obtain high surface strength via an ion exchange process. The chemical exchange (typically Na replaced by K) produces a permanent compressive stress in the glass surface that improves resistance to cracks and scratches. This type of glass is exploited in smartphone screens or aircraft windshields and further applications (for instance in automotive) are foreseen. Alkali or alkaline-earth aluminosilicate systems are also the precursor glasses for most glass-ceramics successfully designed for consumer applications. Al 2 O 3 , The Archetypical Intermediate Oxide Al 2 O 3 itself cannot form a glass as it does not satisfy the rules proposed by Zachariasen (1932) for a network former. However, a specificity of Al 2 O 3 is to be able to form a glass when it is mixed with some modifying cations (typically alkaline earths or rareearths). Sun (1947) has classified Al 2 O 3 as an intermediate oxide acting as network former or modifier according to the composition. Indeed, Al 2 O 3 can be added into the vitreous silicate network by replacing Si 4 þ cations in a tetrahedral environment. In that case, it plays the role of a network former and even small amounts of Al 2 O 3 considerably modify the glass properties. Alternatively, Al can enter into high coordinated sites, playing the role of a modifier.

International audience; We report a detailed structural investigation of Ca-Na aluminosilicate glasses containing 0-20 wt% ZrO2 using X-ray absorption spectroscopy, Raman spectroscopy and 27 Al and 29 Si NMR. The X-ray absorption spectroscopy data reveal that Zr is predominantly present in ZrO6 octahedra but a significant Zr coordination change occurs with increasing ZrO2 content. Though Al and Zr are competing to be surrounded by charge balancing cations, 27 Al NMR data do not show the presence of high-coordinated Al species; thus charge-balancing cations are preferentially localized close to AlO4 tetrahedra rather than Zr polyhedra, explaining the increase in Zr coordination number that ultimately leads to limit Zr solubility in glasses. Raman and 29 Si NMR data indicates that Zr atoms are linked to the silicate network with a trend for higher degree of network connectivity at high zirconia content. Change in network connectivity and in Zr environment provide insights to understand chemical durability or crystallization in glasses.

International audience; Over the past decades, glass-ceramics doped with transition metals have become promising materials for the development of active and passive optical functional devices, interesting a wide variety of commercial applications due to their unique properties. In this Perspective paper, the intrinsic advantages of these composite materials are outlined and we provide an overview of recent and ongoing progress and state-of-the-art knowledges of the main applications: broadband amplifiers, tunable lasers, long persistent phosphors, non-invasive optical temperature sensors, saturable absorbers, high IR emitters and thermal shock-resistant color filters. Finally, the today challenges and future prospects are exposed to provide guidelines for future research.

International audience; High temperature cation mobilities, based on the multicomponent diffusion method, have been coupled with a structural investigation in the Na2O-CaO-Al2O3-SiO2-ZrO2 (NCASZ) system at 1200°C and 1250°C. From structural investigation using X-ray absorption spectroscopy (XANES), zirconium was determined in six-fold coordinated sites in the reduced glass composition range of our study and no significant structural changes have been evidenced compared to a quaternary Na2O-CaO-Al2O3-SiO2 (NCAS) glass with a similar composition. Additionally, the diffusion experiments revealed that adding zirconium in the quaternary melt has no influence on the dominant eigenvectors that correspond to exchange between calcium and sodium. Despite the expected mobility decrease resulting from a viscosity increase upon the addition of zirconium, the dominant eigenvalue calculated in this study is higher when Zr is introduced in the melt structure. This result strongly suggests that the sodium mobility is enhanced by the presence of Zr, which is explained by a change in the structural role of sodium from network modifier associated to Q3(Si) sites in NCAS melts to charge compensator associated with [ZrO6] 2-sites in NCASZ melts. This modification generates lower bond strengths between sodium and other cations in the melt, thus favoring an enhancement in mobility. Moreover, the diffusion matrix was applied to predict diffusion profiles between zirconium-bearing crystals and melts. We observed that even far from the composition field used for the matrix determination, predictions of zirconium diffusion profiles may be relevant and demonstrate the potential of this approach to evaluate crystal/melt dissolution behavior.; Les mobilités de cation à haute température, basées sur la méthode de diffusion multicomposante, ont été couplées à une étude structurale dans le système Na2O-CaO-Al2O3-SiO2-ZrO2 (NCASZ) à 1200°C et 1250°C. À partir d’une étude structurale utilisant la spectroscopie d’absorption des rayons X (XANES), le zirconium a été déterminé dans des sites de ccoordinence 6 dans la gamme de composition réduite de notre étude et aucun changement structurel significatif n’a été démontré par rapport à un verre quaternaire Na2O-CaO-Al2O3-SiO2 (NCAS) avec une composition similaire. En outre, les expériences de diffusion ont révélées que l’ajout de zirconium dans la fonte quaternaire n’a aucune influence sur les vecteurs propres dominants qui correspondent à l’échange entre le calcium et le sodium. Malgré la diminution prévue de la mobilité résultant d’une augmentation de la viscosité lors de l’ajout de zirconium, la valeur propre dominante calculée dans cette étude est plus élevée lorsque Zr est introduit dans la structure du liquide. Ce résultat suggère fortement que la mobilité en sodium est renforcée par la présence de Zr, ce qui s’explique par un changement dans le rôle structurel du sodium depuis un rôle de modificateur de réseau associé aux sites Q3(Si) dans les liquides NCAS vers un rôle de compensateur de charge associé aux sites [ZrO6]2- dans les liquides NCASZ. Cette modification génère des forces de liaison plus faibles entre le sodium et d’autres cations dans le liquide, favorisant ainsi une amélioration de la mobilité. En outre, la matrice de diffusion a été appliquée pour prédire les profils de diffusion entre les cristaux porteurs de zirconium et les liquides. Nous avons observé que même loin du champ de composition utilisé pour la détermination de la matrice de diffusion, les prédictions des profils de diffusion du zirconium peuvent être pertinentes et démontrer le potentiel de cette approche pour évaluer le comportement de dissolution à l'interface cristal/liquide.

Les verres jouent un rôle fondamental dans notre quotidien tant au niveau économique, culturel, sociétal, énergétique que géologique. Les verres géologiques témoignent de l’activité ignée de la Terre et représentent une source importante d’outils et d’objets ornementaux du Paléolithique à nos jours. Désormais, les verres sont utilisés également pour fabriquer des matériaux techniques, tels que des récipients (plats, verres à boire, bocaux, carafes…), des écrans (télévision, ordinateur, smartphone…), des fibres aux multiples applications (renforcement, transport d’information, énergie, santé…), pour assurer le stockage de déchets domestiques ou nucléaires et, plus récemment, des biomatériaux (implants dentaires ou osseux…). Par conséquent, les verres à base de silice sont au cœur de l’histoire de la Terre et de l’humanité. La variation de composition des verres naturels et industriels est vaste mais sa structure repose généralement sur une ossature tétraédrique d’unités SiO4, l’épine dorsale de plus de 90% des verres qui nous entourent dans notre quotidien. Autour de cette ossature de silice, les autres éléments chimiques se répartissent en éléments modificateurs de réseau, compensateur de charge, colorants, volatiles, et l’ensemble constitue un matériau ou une substance chaque fois unique. Cet article propose de passer en revue les liens entre la structure, les propriétés et la composition chimique des verres, essentiellement à base de silicate.

This paper presents a comprehensive investigation at the microscopic scale of various pigments composed of chromium from the French ‘Manufacture de Sevres’ to establish the origin of color in glazes. Electron microscopy coupled with X-ray diffraction allows the determination of the microstructure and composition of the crystalline phases after firing. X-ray absorption spectroscopy reveals subtle changes in the medium-range ordering around Cr with high spatial resolution, in the pigment grain or at the pigment/glass interface. Principal results indicate systematic and common changes whatever the pigment types: (i) Cr-enrichment for the final crystals, that controls the coloration of the glaze, (ii) migration of specific elements such as Al or Zn from the pigments to the amorphous part of the glaze, and (iii) crystallization of anorthite in the near proximity of the altered Cr-bearing crystalline pigments.

International audience; The properties of Na2O-B2O3-SiO2+La2O3 glasses (NBS_La) are not well understood. In particular the influence of the lanthanides on the polymerized network structure and organization are not well known. In this work, we use a Polarizable Ion Model (PIM) that was fitted on electronic structure calculations to simulate a series of NBS_La glasses using molecular dynamics. The simulations account well for the main structural characteristics of NBS_La glasses such as the structure factors and the ionic local environments despite minor discrepancies with experiments about the Si-O distance and the B coordination. In particular, we examine the impact of La2O3 addition to Na2O-B2O3-SiO2 glasses in term of structural changes and in the Na migration paths which become more homogeneous.

International audience; Chromium (Cr) is at the origin of a wide variety of coloration (green, pink and brown) in porcelain glazes from the French Manufacture de Sèvres. This element was introduced for the first time at the factory in 1804, just a few years after its discovery by Louis-Nicolas Vauquelin. Pigments for glazes were developed at the laboratory of the factory, leading to a palette of 76 references. While the synthesis protocol and the nature of the precursors of these pigments are kept in laboratory notebooks, the products have never been characterized. In this work, the pigments composed of Cr were characterized by X-ray diffraction (XRD), UV-visible spectroscopy and X-ray absorption near edge structure spectroscopy (XANES). The analyses reveal the presence of common crystalline phases, and open new perspectives for the synthesis of pigments containing chromium at the Manufacture de Sèvres.

μ-XANES is used to study the modifications in the alkali and alkaline-earth environments induced by the Na+/K+ ion-exchange process in various Na –silicate glasses. The results indicate that the ion-exchange process induces a shortening of the Na O, Ca O and Mg O bond distances. The contraction of the Na O, Ca O and Mg O coordination shell allows a better accommodation of the K+ cations in the glass network and thereby leads to partial relaxation of the stress developed by the Na+/K+ ion-exchange. Nevertheless, despite the stress relaxation process, the K+ environment in the ion-exchanged glass is not equivalent to the one in Na,K–silicate as-melted glasses. Hence, this study clearly shows that the ion swapping forced K+ cations to occupy smaller sites which are not achievable via the melt quench route for glasses with the same K amount.

Epoxies are widely used as adhesives and matrix material for composites in civil infrastructure. As such structures are likely to be exposed to a wide variety of environmental conditions over long service lives, knowledge of their time–temperature sensitivity is desirable. The present study proposes a model describing the evolution of storage modulus for epoxies and their composites subject to forced dynamic excitations over wide temperature and frequency ranges. The model is tested against results for one rubber toughened epoxy and one carbon–epoxy composite. Results show a good agreement between the model and experiments, both in terms of temperature and frequency effects. Moreover, the model is shown to provide an unambiguous definition of the frequency dependent glass transition temperature, which is found to naturally follow the expected Arrhenius relationship with regards to frequency. Activation energies for the glass transition temperature evaluated by the new approach are in good agreement with results from the literature. It is also shown that when accounting for the effect of frequency on the glass transition, the evolution of the time–temperature shift factor is continuous across the glass transition.

Predicting the fatigue performance of composites has proven to be a challenge both conceptually, due to the inherent complexity of the phenomenon, and practically, because of the resource-intensive process of fatigue testing. Moreover, mechanical behaviour of polymer matrix composites exhibits a complicated temperature dependence, making the prediction of fatigue performance under different temperatures even more complex and resource intensive. The objective of this paper is to provide a method for the prediction of fatigue life of glass–polymer composites loaded in the fibre direction at various temperatures with minimal experimental efforts. This is achieved by using a static strength degradation approach to fatigue modelling, where only two parameters (including static strength) are temperature dependent, in conjunction with relationships for these two fatigue model parameters temperature dependence. The method relies on fatigue data at a single temperature and simple static tests at different temperatures to predict the effects of temperature on the material’s fatigue behaviour. The model is validated on experimental data for two unidirectional and one woven glass–epoxy composites and is found to accurately predict the effect of temperature on fatigue life of composites. A method to obtain probabilistic stress-life [Formula: see text] fatigue diagrams including temperature effects is also presented.

We present differential scanning calorimetry (DSC) analyses of seven French stained glasses from the 13th to 16th centuries. These glasses illustrate the dramatic compositional change from the antique soda-rich glasses to potash- and lime-rich compositions, resulting in drastic temperature and viscosity increases. We investigate the influence of chemical composition on glass thermal properties: glass-transition (Tg), crystallization, and melting temperatures. We find that Tg varies from 533°C (soda type) to 638°C±17°C (potash type) to 685°C±5°C (lime type). The viscous slowdown of the melt as a function of the temperature, close to Tg, was modeled using the Vogel-Tammann-Fulcher equation. This enables temperature-viscosity profile calculations, and suggests that recipes have been empirically optimized to reach similar thermoelastic properties suitable for glassmaking despite changing the nature of raw materials.

International audience; We investigated using solid-state NMR spectroscopy the short-range structural features in lithium aluminosilicate glasses with the addition of P2O5 and considering various Al2O3/Li2O ratios. The phosphorus environment is determined quantitatively using P-31 Magic Angle Spinning NMR constrained by results obtained from P-31-Al-27 Multiple-Quantum Coherence-based NMR techniques. Phosphorus is mainly located as orthophosphate and pyrophosphate species in glasses with a low amount of Al2O3. These depolymerized units disappear with increasing Al2O3 content and a strong affinity of PO4 tetrahedra for aluminum is revealed, which reduces phase separation. The local environments of framework (Si and Al) and charge-balancing (Li) cations are also studied through NMR experiments to assess the influence of P2O5 addition. The Si environment is mostly modified by the presence of P2O5 in glasses containing a low amount of Al2O3, with an increase of Q4Si species in relation to phase separation phenomena observed in these compositions. Conversely, P2O5 addition does not have a significant influence on the Al-27 NMR response. Li-7 NMR spectra reflect a change in the structural role of Li when P2O5 or Al2O3 is added. The observed structural changes can be rationalized to improve our knowledge of the structure-property relationships, focusing, in particular, on phase separation and nucleation/crystallization processes that are strongly affected by the presence of P and the evolution of its local environment with composition.

Determining the uranyl(VI) UO22+ reactivity in crystalline and amorphous oxides is necessary to control its mobility. The intrinsic versatility of borate structural units containing both triangular BO3 and tetrahedral BO4 makes them original and rich hosts for uranyl. As part of the effort to determine the uranium stability in borate oxides, we have determined the speciation of uranium(VI) in two lithium borate glasses containing, respectively, 10 mol % and 30 mol % Li2O using a combined structural and spectroscopic approach based on X-ray absorption spectroscopy (XAS). M4- and L3-edge high-resolution XAS demonstrates the speciation of U(VI) as uranyl in both glasses. Comparison of uranyl bond distances obtained by EXAFS with distances found in borate crystals reveals that in the low alkali borate glass, uranyl is present as hexagonal bipyramids with six equatorial oxygen ligands. This local environment was never observed in any other oxide glass. We show that the increase of the lithium content induces t...

International audience; Our understanding of the deep carbon cycle has witnessed amazing advances in the last decade, including the discovery of tetrahedrally coordinated high pressure (P) carbonate phases. However, little is known about the physical properties of their molten counterpart at moderate depths, while their properties at lower mantle conditions remain unexplored. Here, we report the structure and density of FeCO3 melts and glasses from 44 to 110 GPa by means of in situ x-ray synchrotron diffraction, and ex situ Raman and x-ray Raman spectroscopies. Carbon is fully transformed to 4-fold coordination, a bond change recoverable at ambient P. While low P melts react with silica, resulting in the formation of silico-carbonate glasses, high P melts are not contaminated but still quench as glasses. Carbonate melts are therefore polymerized, highly viscous and poorly reacting with silicates in the lower mantle, in stark opposition with their low P properties.

Glass-ceramics are innovative technological materials made up of crystals dispersed in a glass matrix. This dual feature enables the combination of the advantages of glass, mostly ease of shaping/forming, with the specific properties of crystalline phases. Since their discovery in the 1950s, numerous studies have been devoted to glass crystallization mechanisms. Such an understanding is of primary importance to further design glass-ceramics with tailored properties that are closely related to their microstructure. This chapter will thus start with a description of the different nucleation and growth processes. Some practical examples will be provided to illustrate the particular interest of nucleating agents and phase separation in order to master nucleation and growth processes. A brief overview of the complementary characterization techniques used to finely describe the multiscale structure of these glass-ceramic materials will then be presented. Finally, the large range of accessible glass-forming compositions and microstructures will be illustrated by a variety of technological materials combining mechanical, thermal, optical, energetic, and bioactive properties.

This study presents a description of the structure of amorphous slags, with particular attention to the Ca local environment and the medium range arrangement of Ca-sites. Using Ca K-edge X -ray absorption spectroscopy (XANES and EXAFS) and pair distribution function (PDF) as well as numerical modeling combining Molecular Dynamics and Reverse Monte-Carlo, we demonstrate that Ca occurs in a complex environment with a distribution between 6- and 7-coordinated sites. Ca atoms are not distributed randomly within the glass structure: the Ca sites are linked by edges and form a complex percolating sub-network of network-modifying cations. The aluminosilicate network in slags is highly depolymerized with, on average, Q2.06 arrangements for Si, indicating the predominance of chain-like structural units and Q2.67 arrangements for Al in more polymerized units cross-linking the Ca-domains. The Ca percolating sub-network forms clusters that may enhance the early dissolution rate of slags in water.

International audience; The French manufacture of Sèvres, famous for its production of fine porcelain artefacts, has been synthesizing pink pigments mainly composed of the spinel phase ZnAl 2−x Cr x O 4 with x varying from 0.25 to 0.41 since the middle of the 19 th century. This kind of pigment is mixed with an uncolored frit to obtain decorations for porcelain artefacts. However, the pink color of 2 the pigment is altered in a particular uncolored frit and a brownish color appears. The mechanism of this color change was investigated. Observations under a scanning electron microscope revealed the formation of a phase rich in Cr resulting from reactions between the uncolored frit and the pigment during firing. X-Ray Diffraction combined with Rietveld refinements and X-Ray Absorption Near Edge Structure at the Cr K-edge measurements showed that the new formed phase belongs to the same spinel phase ZnAl 2−x Cr x O 4 than the pigment, but with a higher Cr content x. We showed that its formation and thus the stability of the pigment is driven by the Al content in the uncolored frit.

This work aims to discuss on the characterization of Algerian dune sand named Boussaâda sand (SB) and its suitability for glass industry. Based on chemical and mineralogical analyses of SB by XRF and XRD, quartz, kaolinite, calcium carbonates and albite are the main mineralogical phases found. However, Fe2O3 content is relatively low (

Glasses in the Li2O–Al2O3–SiO2 (LAS) system with different Al 2 O 3 Li 2 O ratio and with or without addition of P2O5 have been synthesized and characterized by thermal analysis. The glass structure and the phosphorus environments in the glasses and their evolutions with annealing have been studied by 31P Solid-State Nuclear Magnetic Resonance (NMR) and 27Al{31P} D-HMQC (Dipolar Hetero-nuclear Multiple-Quantum Coherences) NMR correlation technique. The crystallization behavior has been studied by X-ray diffraction, NMR and Raman spectroscopy. The results showed a different role for P2O5 depending on the Al 2 O 3 Li 2 O ratio. For low alumina content, P2O5 plays a nucleating role while it acts as crystallization inhibitor for high alumina content. These different roles are related to different local environments of the phosphorus in the as-cast glasses. Our study emphasizes the importance of POAl complexes in the crystallization of aluminosilicate glasses.

The short and medium range structures of 80GeSe

International audience; Noble gases are used to trace the evolution of the Earth's atmosphere and magmatic processes. However little is known about their solubility mechanisms in silicate melts or glasses, whereas it could be fundamental to interpret these data. We report here the first in situ X-ray absorption spectroscopy data at the Kr K-edge on a feldspathic Kr-bearing glass and melt (0.5 wt% Kr) up to 2.7 GPa and 1086 °C. Kr fitting of the EXAFS signal shows that Kr is surrounded by oxygen atoms. Two Kr-O distances are identified: 2.49 ± 0.1 Å and 3.32 ± 0.1 Å. Results can be interpreted as two Kr populations. Kr surrounded by O atoms at 3.32 ± 0.1 Å suggests a filling of the large cavities available in the silicate network, in agreement with previous studies. On the contrary, Kr surrounded by O atoms at 2.49 ± 0.1 Å, and the observed +0.6 eV shift of the edge position at high pressure, suggest Kr bonding to O atoms and Kr oxidation inside cages formed by the largest aluminosilicate rings (i.e. ~12-membered-rings). Present results show that heavy noble gases incorporation in silicate melts can no longer be considered as a passive filling of the voids.

Effects of cold climate exposure on structures made of composite materials are scarcely documented. As a result, even if exceptional wind conditions prevail in some cold regions, uncertainties related to composite materials durability at low temperatures may hinder development of wind energy projects in those regions. Therefore, as part of the Wind Energy Strategic Network (WESNet) of the Natural Sciences and Engineering Research Council (NSERC) of Canada, efforts were made to evaluate the effects of cold climate exposure on the mechanical properties of glass–epoxy composites. Tensile and compressive quasi-static tests as well as tensile (R = 0.1) and fully reversed (R =− 1) fatigue tests were performed on vacuum-infused [±45]2s glass–epoxy composites at −40°C and 23°C. Results for quasi-static tests show an increase of tensile, compressive and shear strengths and moduli at low temperatures. It is also demonstrated that for the stress range under scrutiny, fatigue performance is improved at −40°C for both the R = 0.1 and R =− 1 loading cases. Moreover, the failure mode for R =− 1 fatigue changed from compressive failure due to buckling of delaminated plies to tensile failure, suggesting a more efficient use of the material. However, if R =− 1 fatigue results at low temperature are extrapolated towards the very low stresses that are also part of wind turbine blades fatigue load spectrum, fatigue life may be degraded compared with that at ambient temperature. Finally, evidence of visco-elastic behaviour leading to changes in s − N curve slope parameter are reported. Copyright © 2015 John Wiley & Sons, Ltd.