Glass-forming Oxides Research Articles

Synthesis and characterization of multi-component borosilicate glass beads for radioactive liquid waste immobilisation

High-level radioactive liquid waste (HLW) is immobilized in a glass matrix through a process called vitrification. In this process, HLW and glass-forming oxides are combined in a pre-determined ratio within a glass melter to produce a vitrified waste form. The properties of this waste form, including its ability to accommodate different radioactive isotopes, depend on the composition of the base glass.In the present study, multi-component amorphous borosilicate-based glasses (SiO2-B2O3-Na2O-TiO2-Fe2O3-CaO-K2O) in bead form (diameter 2–3 mm) were developed. The elemental composition of the glass beads (GBs) was analyzed using an optical emission spectrometer. Additionally, the GBs underwent various physico-chemical analyses, including functional group identification, thermal, electrical, and mechanical properties, as well as viscosity and chemical durability assessments, to identify the optimal glass compositions. The influence of Na2O on the pouring temperature was also examined. Crushing strength and attrition rate measurements were conducted to confirm the suitability of GBs for remote feeding into the melter. The GBs developed in the study are unique, with significant potential for worldwide use in vitrification facilities, particularly in continuous vitrification systems employing Joule Heated Ceramic Melter (JHCM) technology.

Mechanochemical synthesis of Li<sub>2</sub>O–LiI-based solid electrolytes with glass-forming oxides

Mechanochemical synthesis of Li<sub>2</sub>O–LiI-based solid electrolytes with glass-forming oxides

Effect of adding Er3+ on the precipitated crystalline phase of SrF2–ZnO–B2O3 glass and upconversion luminescence

Elucidating the relationship between nucleation and its structure in glasses is essential for the efficient development of new glass-ceramics. In this study, we developed new oxyfluoride nanocrystallized glass-ceramics with potential for upconversion luminescence, phosphor for LEDs, and fiber laser hosts. We investigated the glass-forming region in the SrF2–ZnO–B2O3 system and the crystallization behavior, glass structure, and optical properties of the xSrF2–(50−x)ZnO–50B2O3 system with the lowest quantity of glass-forming oxides. Whereas both the x = 10 and x = 20 samples precipitated more than 100 nm diameter of Zn4B6O13 by heat treatment, the Er3+-doped samples with x = 10 and x = 20 precipitated SrF2 nanocrystals of less than 20 nm. The resulting SrF2 nanocrystallized glass was transparent, and upconversion luminescence was observed by irradiating with a 980-nm LD. We found that the addition of Er3+ ions has a significant impact on crystallization, and the proposed mechanism for this is that the bond selectivity arising from the polarizability forms fluoride-rich domains, and Er3+ further assists the nucleation of SrF2 by serving as a crystal nucleation site. This study is expected to provide a guideline for the development of new transparent nanocrystallized glasses.

Preparation and characterization of binary Mg-silicate glasses via Sol-Gel route

Sol-gel processing allows synthesis of low-energy glasses. In this work, binary magnesium silicate glasses with various MgO contents are synthesized using a modified sol-gel route. TGA and XRD analyses indicate that amorphous glasses with up to 50 mol% MgO can be obtained at 500°C. The reactivity of the glasses is evaluated to assess the use of the sol-gel technique in the large-scale synthesis of alternative cementitious materials. Reactivity tests show that, as MgO content increases, reactivity of glasses increases, reaches an optimum and then declines. This trend doesn't agree with the theoretical one estimated by NBO/T value, which is generally used for the evaluation of glass reactivity. Mg2+ ions play a role as the network modifier when first introduced to silicate glasses. This leads to the depolymerization of the networks, causing an increase in reactivity. Then the magnesium partly behaves as a network former, bonding with oxygens to form MgOx polyhedron when there are insufficient primary glass-forming oxide SiO2, resulting in the polymerization of networks, hence the decrease in reactivity.

Network-forming oxides with non-centrosymmetric structural groups – diffraction results on molybdate and tellurite glasses

The structural units of two types of conditional glass-forming oxides are irregular polyhedra whose distorted shapes result from intrinsic electronic causes. First example: The d0-transition metal cations Mo6+ form an amount of MoO6 in Ag molybdate glasses with the Mo6+ cation displaced towards an octahedral edge. Reverse Monte-Carlo results and comparisons with crystal structures corroborate the earlier diffraction interpretations of three distinct Mo−O distances in the MoO6 units. The post-transitional main group cation Te4+ forms high fractions of TeO5E units in phosphate glasses, where E denotes the lone-pair corner of the structural group. Instead of the regular TeO5E pyramids known for some related crystals, only irregular units are found in the glasses. The bond valences of their longest Te−O bonds are small, requiring the occurrence of three-fold coordinated oxygens.

Exploring the structure of pure germanophospate glasses with different concentrations probed by magic angle spinning NMR spectroscopy.

Phosphate-based glasses such as pure germanophosphate can be achieved at moderately low temperature by means of affordable chemical substances. Nowadays, they become more stimulating because they can be easily doped with alkali, transition metal ions, and rare earth oxides to afford the anticipated physical and/or chemical features for nanoscience applications. Herein, we report an experimental study dealing with the structure of pure germanophosphate glass samples of prepared with different concentrations ranging from 20 up to 70 mole%. 31 P magic angle spinning (MAS) nuclear magnetic resonance (NMR) spectroscopy has been employed to characterize the co-formed glasses by two different glass-forming oxides. The components of the phosphate species ( ) in each sample were determined by analyzing the MAS NMR spectra. Interestingly, 31 P MAS NMR spectrum for each sample was found to be characteristic powder patterns of the middle units Q2 . Q2 unit found herein has one oxygen atom bonded towards one germanium atom (non-bridging) and the other two oxygens are bonding towards two phosphorus atoms (bridging) of phosphate group (PO4 ). The results show that Q2 split into two units, Q2 I and Q2 II, due to different shielding of the phosphorus nucleus provided by the next nearest neighbor atoms. The chemical shift is interpreted in terms of the structure of each building unit of the phosphate group. The results obtained herein shed light on the way how to explore the revealed structure of the prepared glasses for the development of supported catalysts. Indeed, owing to their high chemical/thermal stability, the co-formed germanophosphate glasses obtained may prove as useful substrates for potential nanocatalysts.

A significant enhancement of sodium ion conductivity in phosphate glasses by addition of WO3 and MoO3: the effect of mixed conventional-conditional glass-forming oxides.

Ion conducting oxide glasses are attractive materials for application in various electrochemical devices and an understanding of the structure-transport properties relationship is crucial for their development. An interesting effect of glass structure on the dynamics of mobile ions is the mixed glass-former effect which causes a non-linear change of ionic conductivity when glass-forming oxides get gradually substituted. Here, we report a strong, positive effect of structural changes on the conductivity of sodium ions in two glass systems 40Na2O-xMoO3-(60-x)P2O5 and 40Na2O-xWO3-(60-x)P2O5; x = 0-50 mol% where a conventional glass-forming oxide (P2O5) is gradually replaced by WO3/MoO3 which are conditional ones. In both glass systems, the compositional change in DC conductivity is non-linear, with the maximal increase of four orders of magnitude in the case of WO3 and three orders of magnitude in the case of MoO3. This significant enhancement of ionic conductivity is related to the formation of mixed phosphate-tungstate and phosphate-molybdate units in the glass network. The facilitating effect of these structural units on sodium ion dynamics is also observed in the changes of the shape of frequency-dependent conductivity and in the values of typical spatial extent of diffusion of sodium ions known as the Sidebottom length.

Preparation and Properties of Fused Zircon

Melting of zircon with added glass-forming oxides is reported. The structures of the synthesized materials were baddeleyite and a glassy phase, which determined the operating characteristics of the refractory. Corrosion tests of fused zircon samples in Al-alloy melts showed that they were not wetted and minimally corroded. Treatment of fused zircon with HF solution (10%) produced a material with <2% SiO2. The silica content in the fused zircon decreased by three times with carbothermic melting in an electric arc furnace.

Soret effect in binary glass-forming oxide melts: theory and its verification

Soret effect in binary glass-forming oxide melts: theory and its verification

Alumina–silica glass–ceramic sealants for tubular solid oxide fuel cells

In this work, we synthesized the glasses of the SiO2–Al2O3–CaO–Na2O–MgO–K2O–B2O3–Y2O3 system and investigated their thermal properties under changes in the ratios between the components in both modifying (MgO/CaO) and glass-forming (SiO2/B2O3) oxides. In addition, the effects of crystallization on both the properties of sealants and their behaviour at the boundary with ceramic yttria-stabilized zirconia (YSZ) electrolyte have been studied. X-ray diffraction analysis was used to determine the phase composition of the glasses both after quenching, dilatometric measurements and sealing of the glasses with the YSZ ceramic support. The thermal expansion coefficients (CTEs) found for the glasses and glass–ceramics are shown to be in good agreement with those of other cell components. The sealing temperatures of these materials are found to be lower than the operating temperature limit of the interconnector alloy. It is shown that Mg-rich glasses exhibit higher resistance to interaction with Cr compared to other compositions under study. The scanning electron microscopy and energy dispersive spectroscopy studies have confirmed the formation of gas-tight connections by the sealants under investigation. The glass demonstrating the highest stability in contact with the Crofer22APU alloy has been tested as a sealant for a tubular cell. This material is established to ensure a tight connection without cracks during operation at 850 °C for 250 h. The materials are thus found to be promising candidates for use as sealants for solid oxide fuel cells (SOFCs).

Gamma Rays Interactions with Transition Metal Doped-Soda lime Phosphate Glasses Evaluated by Collective Optical, FTIR Spectral Measurements

MnO2, NiO, CoO and CuO doped in soda lime phosphate host glass were prepared. Combined optical and FTIR spectra were measured for the studied glasses before and after gamma irradiation. Some optical and physical properties such as density, molar volume, optical band gap energy and the width of the band tails (Urbach energy) were measured or calculated for the glass samples before and after irradiation. Optical absorption spectra of the selected TM ions reveal specific absorption bands which are characteristics for each ion in accordance with its configuration, valence or coordination state exhibited by the TM ion in the host phosphate glass. Gamma irradiation causes obvious changes which vary with the type of transition metal ion and in some cases obvious shielding effects are identified towards gamma irradiation. FTIR spectra show vibrational bands which are correlated with specific phosphate groups (mainly Q2 and Q3 units) which are related to the percent of constituting glass-forming component oxide. The measured optical properties confirmed the results of the optical absorption spectroscopy which indicate that copper-doped samples have some shielding behavior towards the irradiation process.

Intrinsic electron trapping in amorphous oxide

We demonstrate that electron trapping at intrinsic precursor sites is endemic in non-glass-forming amorphous oxide films. The energy distributions of trapped electron states in ultra-pure prototype amorphous (a)-HfO2 insulator obtained from exhaustive photo-depopulation experiments demonstrate electron states in the energy range of 2–3 eV below the oxide conduction band. These energy distributions are compared to the results of density functional calculations of a-HfO2 models of realistic density. The experimental results can be explained by the presence of intrinsic charge trapping sites formed by under-coordinated Hf cations and elongated Hf–O bonds in a-HfO2. These charge trapping states can capture up to two electrons, forming polarons and bi-polarons. The corresponding trapping sites are different from the dangling-bond type defects responsible for trapping in glass-forming oxides, such as SiO2, in that the traps are formed without bonds being broken. Furthermore, introduction of hydrogen causes formation of somewhat energetically deeper electron traps when a proton is immobilized next to the trapped electron bi-polaron. The proposed novel mechanism of intrinsic charge trapping in a-HfO2 represents a new paradigm for charge trapping in a broad class of non-glass-forming amorphous insulators.

Beneficial reuse of Brest-Harbor (France)-dredged sediment as alternative material in road building: laboratory investigations

ABSTRACTThe scarcity of natural aggregates promotes waste reuse as secondary raw material in the field of civil engineering. This article focuses on the beneficial reuse of marine-dredged sediments in road building. Thus, mixtures of raw sediments and dredged sand collected from Brest Harbur (Bretagne, France) were treated with road hydraulic binders. Formulation were prepared and characterized as recommended by the French Technical Guidelines for soil treatment with lime and/or hydraulic binders. Mechanical resistance results are quite similar for both the hydraulic binders, suggesting a similar reactivity with the studied sediment sample. However, some discrepancies can be noted on sustainability parameters. Indeed, water resistance after immersion at 40°C is significantly better for the mixtures treated with cement containing more glass-forming oxides (SiO2 + Al2O3) and fluxing (Fe2O3+CaO + MgO + K2O + Na2O). Moreover, the both hydraulic binders can lead to swelling in the road materials as observed in scanning electron microscopy analyses. Indeed, microscopic observations indicated volumetric swelling of treated samples, which is greatly influenced on the one side by ettringite quantity and on the other hand by the presence of water in pores material.

On the crystallization of gel-derived albite (NaAlSi3O8): the most stable oxide glass

Some glass-forming oxides, such as unseeded B2O3 and albite (NaAlSi3O8), exhibit outstandingly high resistance to devitrification and have never been crystallized at ambient pressure. For instance, a classical study reported that an albite glass produced by melting was held at 1025 °C (close to the maximum growth rate predicted by a theoretical model) for 5 years without crystallizing. In this study, we tested the crystallization behavior of gel-derived albite glasses synthesized through two distinct and original routes and compared them with a melt-quenched sample because sol–gel glasses normally crystallize much faster than isochemical melt-derived glasses. Not only the melt-derived glass but also one of the gel samples (which contained much more OH− than its melted counterpart) remained amorphous in a differential scanning calorimetry experiment and after 12 h of heat treatment at 1000 and 1030 °C. The other gel-derived material contained residual carbon partially crystallized during the same thermal treatment at 1000 and 1030 °C. Therefore, in the absence of a suitable nucleating agent, crystallization does not occur, even in gel-derived albite glass with a high OH− content.

Neutron diffraction as a probe of liquid and glass structures under extreme conditions

Neutrons provide a unique tool for probing the structure of liquid and glassy materials, and deliver information that cannot be obtained from other experimental techniques. Advances in neutron diffraction instrumentation and measurement protocols now make it possible to measure the structure of these disordered materials under extremes of high temperatures or high pressures. Here, we consider the use of aerodynamic levitation with laser heating to explore the structure of glass-forming oxide melts at high temperatures, and the use of a Paris Edinburgh press to investigate the mechanisms of density-driven network collapse for glassy materials in the gigapascal (GPa) pressure regime.

Glass transition temperatures and structures of multicomponent borate glasses: Influence of modifier cation field strengths

Glass transition temperatures, Tg, are determined for a series of multicomponent borate glasses with composition xPbO·(33.33−x)Na2O·yAl2O3·1.3ySiO2·(66.67−2.3y)B2O3, (where x and y take values from 0 up to 13.5mol%, and from 0 up to 5.3mol%, respectively). For this purpose, differential scanning calorimetry is used while the structure of these glasses containing two kinds of modifier oxides — Na2O and PbO, is investigated by infrared spectroscopy. A detailed analysis of the infrared spectra reveals that at constant total content of the glass-forming oxides (B2O3, SiO2 and Al2O3) in the glasses investigated, the borate network progressively depolymerizes when Na2O is substituted for PbO. This substitution favors the destruction of the more rigid structural units and the formation at their expense of units with a lower degree of connectivity. The macroscopic manifestation of these structural changes is the steep decrease in the glass transition temperature of the glasses investigated at increasing PbO concentration. This tendency for depolymerization of the borate network is explained by the influence of the Pb2+-cations possessing substantially higher ionic field strength as compared to that of the Na+-cations.

Phase composition identification and microstructure of BaTiO3-containing sodium-aluminoborosilicate glass-ceramics

Bulk glasses with a composition 20.1Na2O/23.1BaO/23.0TiO2/7.6B2O3/17.4SiO2/3Al2O3/5.8Fe2O3 containing less than 30 mol% glass-forming oxides are synthesized. Information on the valency of the glass constituents is obtained by x-ray photoelectron spectroscopy and it is concluded that all species are predominantly present in their oxidized state. Glassy samples are annealed above the glass transition temperature which leads to the crystallization of BaTiO3 for all time-temperature applied schedules. The phase composition of the glass-ceramics is studied by x-ray diffraction and the formation of cubic BaTiO3 is suggested. Temperature-dependent Raman spectroscopy confirms the presence of solely cubic BaTiO3. The microstructures of all annealed samples are similar and consist of globular interconnected particles in which nanosized BaTiO3 crystals grow randomly. The mean size of the spherical formations increases with the increasing annealing time from 200 to 600 nm. Electron microscopy suggests that during the annealing process first phase separation and then crystallization of BaTiO3 occurs.

Structure of amorphous silica–hafnia and silica–zirconia thin-film materials: The role of a metastable equilibrium state in non-glass-forming oxide systems

Amorphous heavy metal oxide thin films have important technological applications, including multi-layer mirror coatings in instruments such as the Laser Interferometric Gravitational Wave Observatory (LIGO). However, the structures of these materials are much less well-known than those of conventional glass-forming oxides. For example, it has not been clear whether films deposited by methods such as ion beam sputtering (IBS) ever pass through a state of local (metastable) thermodynamic equilibrium, and hence could be amenable to modeling by thermodynamic approaches long explored in glass-forming liquid systems. We present new 17O and 29Si NMR data on IBS films and sol–gel equivalents in the silica–hafnia and silica–zirconia binary systems. Similar distributions of local structural groups are obtained by different synthesis routes, suggesting that indeed a transient, possibly liquid-like metastable state is reached during film formation. All oxygen species are well-resolved in the spectra and can be readily quantified. Their concentrations are indeed well-predicted by a simple thermodynamic treatment, similar to that applied for decades to binary metal oxide-silica liquids, based on the reaction of bridging oxygens with added “free” metal oxide ions to form non-bridging oxygens.

Vaporization and Thermodynamics of Glass-Forming Oxide Melts: Mass Spectrometric Study and Modeling

Information on the vaporization processes and thermodynamic properties of glass-forming oxide melts in the systems MgO-B2O3-SiO2, CaO-B2O3-SiO2, SrO-B2O3-SiO2, BaO-B2O3-SiO2, PbO-B2O3-SiO2, CdO-B2O3-SiO2, ZnO-B2O3-SiO2, Bi2O3-B2O3-SiO2 and Bi2O3-GeO2-SiO2 together with the earlier obtained data is discussed. These data were obtained by high-temperature mass spectrometric method. Various types of vapor species were found over oxide systems studied such as the associated, dissociated and polymerized products of vaporization. The regularities of the vaporization of the binary and multicomponent glass-forming oxide melts were illustrated and discussed from the point of view of the acid-base concept. Results on determination of thermodynamic functions in oxide systems were considered taking into account the main requirements for the confirmation of their reliability. The generalized lattice theory of associated solutions was used for the calculation of thermodynamic properties of the ternary silicate melts studied. Using this approach the different levels of deviations from the ideality in the melts under investigation were clarified. The relative numbers of bonds of various types formed in the melts considered were also calculated based on the generalized lattice theory of associated solutions.

P-Tphase diagram and structural transformations of moltenP2O5under pressure

The ${\mathrm{P}}_{2}{\mathrm{O}}_{5}$ compound is an archetypical glass-forming oxide with a record high hygroscopicity, which makes its study extremely difficult. We present the in situ x-ray diffraction study of the pressure-temperature phase diagram of ${\mathrm{P}}_{2}{\mathrm{O}}_{5}$ and, particularly, of the liquid ${\mathrm{P}}_{2}{\mathrm{O}}_{5}$ structure under high pressure up to 10 GPa. Additionally, quenching from the melt has been used to extend the melting curve up to 15 GPa. We found that structural transformation in the liquid ${\mathrm{P}}_{2}{\mathrm{O}}_{5}$ under pressure is unique and includes three stages: first, the disappearance of the intermediate range order of the melt together with a slow increase in the average first-coordination number $\ensuremath{\langle}{N}_{1}\ensuremath{\rangle}$ (P-O and O-P neighbors) up to 4 GPa; second, the ``normal'' compression almost without structural modification at higher pressures up to 8--9 GPa; and, finally, the abrupt change of the short-range order structure of the liquid with the jumplike $\ensuremath{\langle}{N}_{1}\ensuremath{\rangle}$ increase at 9--10 GPa. The last stage correlates with the melting curve maximum (\ensuremath{\approx}1250 \ifmmode^\circ\else\textdegree\fi{}C) at \ensuremath{\approx}10 GPa and can be interpreted as a transformation to the liquid phase with entirely fivefold-coordinated phosphorus and twofold-coordinated oxygen atoms.