Science Thread Abstracts

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Structure and properties of Li2O-B2O3-P2O5-GeO2 glasses

P. Mošner*, M. Vorokhta  L. Koudelka

Faculty of Chemical Technology, University of Pardubice, Studentská 573, 532 10 Pardubice, Czech Republic

GeO2 containing glasses are promising materials for IR technologies, nonlinear optics and design of laser devices. Furthermore, the high ionic conductivity of GeO2, makes them interesting candidates for solid electrolyte applications. This work deals with the study of the effect of GeO2 content on the structure and properties of glasses prepared in the series 40Li2O-10B2O3-(50-x)P2O5- xGeO2 with x = 0, 5, 10, 15 and 20 mol% GeO2. Glasses were characterized by the measurements of density, molar volume, chemical durability and refractive index. Thermal properties were investigated by DTA and TD methods. Structure of glasses was studied by Raman spectroscopy and MAS NMR spectroscopy. The obtained Raman, 31P and 11B MAS NMR spectra showed that the structure of starting 40Li2O-10B2O3-50P2O5 glass is formed especially by metaphosphate structural units (Q2) and tetrahedral BO4 (B(OP)4) units. The replacement of tetrahedral PO4 structural units by GeOn units is accompanied by the gradual transformation of Q2 units into Q1 diphosphate units. The incorporation of GeOn units modifies also the coordination of boron atoms, where B(OP)4 units are gradually replaced by B(OP)4-n(OGe)n structural units. Increasing GeO2 content leads also to the partial transformation of tetrahedral BO4 into triangular BO3 structural units. Replacement of P2O5 by GeO2 results in an increase of glass density from 2.4 to 2.8 g/cm3, whereas molar volume decreases within the range of 37.9-29.4 cm3/mol. All GeO2 containing glasses reveal better durability against water corrosion than the parent lithium borophosphate glass, nevertheless with increasing GeO2 content within the concentration region from 5 to 20 mol%, chemical durability of glasses slightly decreases. DTA studies showed that all of glasses crystallize on heating within the temperature region of 550-650°C. Compounds formed by crystallization were LiPO3, Li4P2O7, LiGe2(PO4)3 and BPO4. Glass transition temperature and dilatometric softening temperature increase with increasing GeO2 content, whereas thermal expansion coefficient decreases within the range of 16.9-14.5 ppm/oC. The refractive index has been measured at room temperature at wavelengths 452.9, 532 and 637.3 nm. With the replacement of P2O5 by GeO2, the values of refractive index increase and Abbe number decreases.

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Molecular dynamics modelling of the structure of barium silicate glasses BaO-SiO2

Maha Rai* and Gavin Mountjoy

School of Physical Science, University of Kent, Canterbury, CT2 7NH, UK.

Barium being a heavier element, provides an interest to study BaO-SiO2 glasses for the application of x-ray and thermal shielding. Molecular dynamics modelling techniques were used to make the models of BaO-SiO2 glasses. Models made were for xBaO-(100-x) SiO2 glasses with x=25, 33, 40 and 50. The diffraction from the model for x=33 and 40 were compared with experimental result shows good agreement. The comparisons were done on neutron structure factor S(Q) and x-ray pair distribution function T(r). The Ba-O CN for the glasses ranges from 6.5 to 6.9 with the average bond length R= 2.75 to 2.79 Å. However, the crystal CN for Ba-O of crystal range from 7 to 9.5 with the average bond length from 2.78 to 2.91Å. Model glasses maintained Si-O tetrahedral structure as expected. References: [1] N. Chanthima, J. Kaewkhao, C. Kedkaew, W. Chewpraditkul, A. Pokaipisit, and P. Limsuwan 2011 Prog. Nucl. Sci. Tech. 1 106. [2] C. Lara, M.J. Pascual and A. Durán 2004 J. Non-Cryst. Solids 348 149. [3] E.D. Zanotto, P.F. James and A.F. Craievich 1986 J. Mat. Sci. 21 3050. [4] H. Hasegawa and I. Yasui 1987 J. Non-Cryst. Solids 95-96 201. [5] L. Cormier, P.H. Gaskell and L. Creux 1999 J. Non-Cryst. Solids 248 84. [6] H. Schlenz, A. Kirfel, K. Schulmeister, N. Wartner, W. Mader, W. Raberg, K. Wandelt, C. Oligschleger, S. Bender, R. Franke, J. Hormes, W. Hoffbauer, V. Lansmann, M. Jansen, N. Zotov, C. Marian, H. Putz, J. Neuefeind 2002 J. Non-Cryst. Solids 297 37

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Research into 3D Printed Glass Investment Casting Moulds

Tavs Jorgensen* and Gayle Matthias*

Falmouth University Academy for Innovation and Research (AIR), Penryn Campus, Treliever Road, Penryn, Cornwall, TR10 9EZ , UK +44 (0)1326253689

This paper concerns a research project research undertaken at Falmouth University into the use of emerging 3D printing technology in glass investment casting. This project, which has now been on going for over 4 years, has successfully developed an entirely new method for creating glass investment casting moulds with the aid of 3D printing technology. The method enables glass casting moulds to be created directly from three-dimensional computer files without the need for a physical mould pattern. The method developed is based on Additive Layer Manufacturing (ALM) technology using a three-dimensional printer - a process commonly known as ‘Rapid Tooling’ (RT). The method that has been developed presents a number of significant advantages compared with conventional glass casting techniques. Work is currently underway to explore the usability of the process in various applications. This investigation includes explorations in creative glass practise as well as commercial applications. The latter aspect has so far predominately been focused on the medical sector, in particular exploring the creation of glass moulds for growing human replacement body parts, a technique which have been developed at the Royal Free Hospital, London. A current objective of this stage of the project is to further disseminate the research, and through this process identify other research partners and potential applications for this method.

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Structure and properties of lead borophosphate glasses modified with molybdenum oxide

Ladislav Koudelka*, Ivana Rösslerová, Petr Mošner, Lionel. Montagne, & Bertrand.

Revel Faculty of Chemical Technology, University of Pardubice, Pardubice, Czech Republic UniversiteLille Nord de France, USTL, Villeneuve d'Ascq, France

Borophosphate glasses belong among important classes of glassy materials because they offer better thermal stability and chemical durability than phosphate glasses. The reason for the improvements in the properties of borophosphate glasses is ascribed by the transformation of linear-chain structure of metaphosphate glasses into three-dimensional structure of borophosphate glasses due to the additions of B2O3. Doping of borophosphate glasses by heavy metal oxides like MoO3 and WO3 are interesting due to their semiconducting properties ascribed to the presence of transition metal ions in multivalent states. In this study we prepared glassy samples from the system PbO-P2O5-B2O3-MoO3 in two compositional series (100-x)[0.5PbO-0.4P2O5-0.1B2O3]-xMoO3 and (100-y)[0.5PbO-0.3P2O5-0.2B2O3]-yMoO3 with 0-70 mol% MoO3. Glasses were prepared from analytical grade PbO, MoO3, H3BO3 and H3PO4 using a total batch weight of 30g. The synthesis was carried out in platinum crucibles by heating up to 1000-1200°C. Physical properties of glasses were determined as well as their thermal behaviour. For structural study the 31P and 11B MAS NMR spectroscopy were applied as well as Raman spectroscopy. 31P MAS NMR spectra showed on the depolymerization of phosphate chains with increasing MoO3 content due to the formation of Mo-O-P bonds between octahedral MoO6 structural units and tetrahedral PO4 units. The measurement of 11B MAS NMR spectra of the studied glasses with the NMR spectrometer with a high resolution (magnetic field 18.8T) revealed the formation of several different BO4 structural units containing B-O-P, B-O-B and B-O-W bonds. The decomposition of these spectra brought relative amounts of individual mixed structural units in these glasses.

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Molecular Dynamics simulation of alkali-silicate glasses

Edwin Flikkema*, Zhongfu Zhou, Neville Greaves, Wenlin Chen

Department of Mathematics and Physics, Aberystwyth University, United Kingdom

In this presentation results will be shown on the modelling of alkali disilicate glasses, more specifically Sodium-Potassium-disilicate with various ratios of Sodium and Potassium. Below the glass transition temperature, Sodium-Potassium disilicate can be regarded as consisting of a fixed (modified continuous random) network of silicon and oxygen atoms, with relatively mobile Sodium and Potassium ions, making the glass conductive. The ion conductivity exhibits a minimum close to a 50/50 ratio, replicating the "mixed alkali effect". Parallel effects are found in the intermediate scattering function. Advanced visualisation and virtual reality technology is used to map the available free volume of the alkali ions and to study the cooperative motion of the ions. This will help towards a better understanding of the mechanisms behind the mixed alkali effect.

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Computer simulation and visualization of glass-forming systems (poster)

Wenlin Chen*, Edwin Flikkema

Department of Mathematics and Physics, Aberystwyth University, United Kingdom

Large scale simulation with high performance computing is being used to study glass-forming systems as well as zeolites. These materials can be regarded as consisting of a fixed network of Silicon/Aluminum and Oxygen atoms with relatively mobile Sodium and Potassium ions. Such systems can be modeled using Molecular Dynamics simulation (DLPOLY) and ab initio methods (Gaussian). Glass-forming materials are annealed from high temperature at different cooling rates. Zeolites are simulated at high pressure to study collapse and amorphisation. These processes can be followed in detail by analyzing the Molecular Dynamics trajectory file after simulation. Data such as the radial distribution function, cell parameters, etc. is collected and compared with experimental data. Visualization software such as Avizo and VMD is used to track the motion of ions in a glass and the collapsing of the Silicon/Aluminum-Oxygen framework in zeolites. This will help towards a better understanding of glass-forming systems.

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Unusual Cobalt and Nickel Species in Glasses: Chemical Oxidation, Photoionization and Site Geometry Probed by ESR and UV-Vis Spectroscopy

Doris Möncke*(a), Matthias Müller(a), Mannfred Friedrich(b), Doris Ehrt(a) etal

(a)Otto-Schott-Institute, Friedrich-Schiller-University Jena, Germany

(b)IAAC, Friedrich-Schiller-University Jena, Germany

Cobalt and Nickel are usually present in the divalent state in glasses. Depending on the glass matrix, the coordination changes with increasing optical basicity from octahedral to tetrahedral. In medium basicity glasses occur both ion sites together with a third transitional coordination. This third site is attributed to a fivefold coordination (EXAFS, XANES) or to a pseudo-tetrahedral eightfold coordination in studies relying on magnetic susceptibility and ligand field theory. In a low alkaline borosilicate glass, doping with Co2+ and Ni2+ results in different colours, as the fictive temperature of the glass is varies. In annealed glasses both ions are octahedrally coordinated. In the quenched glasses, coming from the tetrahedral coordination of the melt, the transitional coordination is frozen in. The optical spectra of the quenched glasses obtained in-situ on a heating stage, show that Ni2+ relaxes from the transitional state into the octahedral coordination. However, Co2+ relaxes not into the normally preferred octahedral, but instead into the tetrahedral coordination. From ligand field theory and magnetic suscibility measurements, we assume that the transitional coordination is consistent with an eightfold pseudotetrahedral site geometry. We further present data on high basicity glasses (Cs2O-BaO-SiO2, ~0.7) where Cobalt and Nickel are oxidized chemically to the trivalent state. The glasses have a yellow (Co3+) and violet blue (Ni3+) colour. It is assumed that the ions are tetrahedrally coordinated, since the same optical bands occur upon irradiation of soda lime silicate glass, where Co2+ and Ni2+ are tetrahedrally coordinated and photo-oxidation generates the trivalent (Co2+)+ and (Ni2+)+ species. In phosphate glasses, in which Co2+ are octahedrally coordinated, leads irradiation to extrinsic defects characterized by two bands at 400 and 600 nm, which are assigned to octahedral coordinated (Co2+)+. This defect is very stable and annealing the sample at elevated temperatures does not cause a recombination and recovery of the irradiation induced defects, but instead the transformation of intrinsic hole centre into the photo-oxidized (Co2+)+ species. In contrast to Co2+, upon irradiation Ni2+ is photo-reduced in phosphate glasses. ESR spectroscopy shows distinct signals for (Ni2+)- and (Ni2+)+. .

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SiOx-barrier layers preventing alkali and earth alkaline metal diffusion deposited by Combustion Chemical Vapor Deposition under atmospheric pressure


Paul Rüffer*, Andreas Heft, Bernd Grünler, Arnd Schimanski

INNOVENT e.V. Technology Development, Prüssingstraße 27B, D-07745 Jena

Glass corrosion is a recurring and costly problem all float glass manufacturers in the world have to struggle. It is always associated with water. At the exit of the tin bath float glass leaves the protective gas atmosphere and its surface faces air humidity for the first time. During cooling, storing or transport (different climates, sea air) hazy and foggy films can show up on the glass surface due to diffusion of alkali and alkaline earth metals in water contact. These films are the results of the first steps of glass corrosion. If the pH value of the aqueous solution increases to nine and higher in water deficieny the solubility of the SiO2-network strongly increases, too. The SiO2-network degradates.
The idea of a project at INNOVENT e.V. Technology Development is to prevent the initial reaction of the glass surface by means of the C-CVD process by integrating this technology into a float glass line. Here, under atmospheric pressure SiOx-layers are deposited. It could be shown that this cost efficient procedure can build up powerful thin barrier layers which protect the glass surface from water contact completely.

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Aluminium-free glass ionomer bone cements

Maximilian Fuchs1, Saroash Shahid2, Robert G. Hill2, Delia S. Brauer1,*

Otto Schott Institute of Materials Research, Faculty of Chemistry and Earth Sciences, Friedrich Schiller University, Jena, Germany 2Dental Physical Sciences, Oral Growth and Development, Barts and The London School of Medicine and Dentistry, Queen Mary University of London, UK

Bone cements are used as bone fillers (e.g. in vertebro- or kyphoplasty) or for anchoring implants (e.g. hip implants) into the bone, and current materials include acrylic cements (e.g. poly(methyl methacrylate, PMMA) or calcium phosphate cements. Both have several drawbacks, however, such as exothermic setting reaction (causing damage to surrounding tissue), lack of chemical bonding to bone (adhesion by mechanical interlocking only) and absence of bioactivity (growth of fibrous tissue around the implant rather than formation of a intimate bond with bone) for PMMA, and poor mechanical properties (allowing for use in non-load bearing applications only) for calcium phosphate cements. Glass ionomer cements (GIC), which set by a neutralisation reaction between an acid-degradable glass and a polymeric acid, are routinely used in dentistry, show excellent mechanical properties and form a chemical bond with hard tissue (teeth and bone) or surgical metals. The release of aluminium ions from those cements limits their use in orthopaedics, however, and the development of Al-free alternatives is therefore of great interest for orthopaedic applications. This study investigates the formation of GIC from Al-free glasses (SiO2-CaO-CaF2-MgO with 0, 2.5, 10 or 50% of Ca replaced by Sr on a molar base) and two different polymeric acids, poly(acrylic acid) (PAA) and poly(vinyl phosphonic-co-acrylic acid) (PVPA). Low Sr substitution (up to 10%) did not have a marked influence on cement properties, but the 50% Sr substituted glass showed much shorter working and setting times. This can possibly be explained by a larger cation (Sr2+) replacing a smaller one (Ca2+), resulting in a less compact glass network and, subsequently, a higher solubility of the glass. The glasses formed cements with both polymers, but only PVPA cements were stable in the presence of water, while PAA cements turned rubbery. The results suggest that PVPA, owing to a larger number of functional (carboxylate) groups per monomer unit, is suitable for obtaining mechanically stable GIC using aluminium-free glasses.

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The Rigidity of Vitreous Networks: An Alternative Viewpoint

Adrian C. Wright

J.J. Thomson Physical Laboratory, University of Reading,

An alternative, and much more intuitive, approach is proposed to the rigidity of (relatively) strain-free oxide glass networks, based on effectively rigid basic structural units and the true degrees of freedom that allow the formation of such networks; viz. bond torsion angles plus the bond angle at the bridging oxygen atoms. These ideas are extended to borate networks that include rigid superstructural units with no internal degrees of freedom in the form of variable bond and torsion angles, and it is shown that, for an isostatic network, the average (super)structural unit connectivity is equal to 4. The role of network rigidity in determining glass formation is discussed, together with the effects of steric hindrance, and a comparison with conventional constraints theory is presented for vitreous SiO2 and B2O3. Finally, it is argued that the so-called intermediate phase is merely an extended rigidity transition range, due to the chemical nanoheterogeneity that characterises the structure of glasses having more than one component, and that, in the case of Ge-Se glasses, the bonding in the interfacial regions between the Se and GeSe2 regions exhibits significant metalloid character.

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Factors that affect yellow phase formation during vitrification of highly active wastes

Michelle Cowley & Adrian Gate*

Sellafield Ltd, Seascale, Cumbria, CA20 1PG *National Nuclear Laboratory, Sellafield, Seascale, Cumbria, CA20 1PG

The post operational clean out (POCO) of the highly active storage tanks (HASTs) at Sellafield site will require the removal and immobilisation of residual solids from the heel of the tanks. These solids have accumulated over a number of years of nuclear fuel reprocessing on the site and have been identified as predominantly barium-strontium nitrate, zirconium molybdate (ZM) and caesium phosphomolybdate (CPM). Molybdenum compounds are known to have limited solubility in borosilicate glasses and when present in quantities that exceed the level of solubility form a secondary phase termed 'yellow phase'. Yellow phase is known to be corrosive to some stainless steels and partially water soluble. Therefore, formation of yellow phase in glasses containing nuclear waste destined for geological disposal is undesirable. A laboratory based study has been carried out to identify factors that affect yellow phase formation in glasses containing both molybdenum solids and highly active waste from nuclear reprocessing operations. A number of compositional and operational parameters which affect yellow phase formation in nuclear glasses have been identified.

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EFFECT OF TRANSITION METAL IONS ON ELECTRICAL CONDUCTIVITY OF ZINC PHOSPHATE GLASSES

Anirudh Yadav
Physics Department
M.D.University,Rohtak-124001
INDIA

The d .c .electrical conductivity of 50ZnO.50P2O5 glasses containing ( 9 V2O5. 9-X CuO) where X=0,3,4.5,6 &9 have been studied at different temperatures. It is found that conductivity of the glasses containing 9 mol% V2O5 is greater than the conductivity of the glass containing 9 mol% of CuO. The conductivity of these glasses decreases when V2O5 is replaced by CuO. Density of these glasses has also been measured and it is found that density of the glass decreases when V2O5 is replaced by CuO.                                       

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Increasing the Sodium Content of UK Vitrified High Level Waste

Mike Harrison* 1 and Carl Steele 2

1 National Nuclear Laboratory, Sellafield, Cumbria, UK, CA20 1PG

2 Sellafield Ltd, Sellafield, Cumbria, UK, CA20 IPG

Sodium carbonate is currently being considered as a wash-out reagent for the unagitated Highly Active Liquor (HAL) storage tanks at Sellafield. This will result in a feed to the Waste Vitrification Plant (WVP) containing high concentrations of sodium as well as the high molybdenum expected to present in any settled tank solids. In an initial study, three approaches for the vitrification of high-Na and -Mo WVP feeds were considered, i.e. the addition of extra soda to a 'Ca/Zn'-based glasses, the replacement of Li with Na in a 'Ca/Zn' base glass, and the development of new borosilicate glass compositions. In each case, the maximum sodium that could be incorporated without the formation of significant yellow phase was determined for a representative high-Mo waste composition at a range of incorporations. The compositions that were at the limits of Na and Mo content then underwent a more detailed product characterisation, with the majority of the properties measured being within the ranges expected for standard MW-based Magnox and Blend products. However, the results from this initial study showed that at high MoO3 incorporations (~10 wt%) in both the 'Ca/Zn' and new borosilicate glass compositions, there was very little tolerance for significantly higher concentrations of sodium. This severely limits the maximum total volume of sodium carbonate that could be used as a tank wash-out reagent. Hence, a different approach is required, e.g. reducing the waste (MoO3) loading in the glass, developing a radically different non-borosilicate base glass, or blending the wash-out waste with existing HAL to dilute the sodium.

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Effect of Zn2+ and Cu2+-bearing salts on the dissolution of silicate and borosilicate glasses

Odile Majérus*, Victor de Seauve, Aurélie Tournié, Patrice Lehuédé, Isabelle Biron Daniel Caurant

Institut de Recherche de Chimie Paris, CNRS-Chimie Paristech, CNRS UMR 8243, Ecole Nationale Supérieure de Chimie de Paris, 11 rue Pierre et Marie Curie, 75005, Paris, France Centre de Recherche et Restauration des Musées de France (C2RMF), Palais du Louvre, 14 quai François Miterrand, 75001 Paris, France

Zn2+-bearing salts have been used for a long time to protect the glass surface against corrosion of glassware in dishwashers, as well as against corrosion of flat glass foils during their transport and storage. However, the mechanisms by which Zn2+ ions added in the corroding water diminish the extent of glass corrosion are not known. To describe more precisely the effect of Zn2+ ions and to get insight into the mechanisms involved, we measured the glass dissolution kinetics in solutions bearing increasing concentrations of ZnCl2, using ICP-AES for solution analysis. Two glass compositions were chosen for this study : a Na-K-lime silicate glass with an incongruent dissolution behaviour, and a sodium borosilicate glass with a congruent dissolution behaviour. When the ZnCl2 concentration reaches 10-4 M, a value close to the solubility of Zn2+ (at pH = 6.5 and T = 80°C), the release of Si from both glasses is reduced to undetectable levels. However, the global effect is different in both cases. In the alkali-lime silicate glass, the alkalis are leached at the same rate whatever the Zn2+ concentration. The Zn2+ ions precipitate, so that the pH is kept at a constant neutral value. When the Zn2+ ions have disappeared from the solution (ie below 10-5 M), the pH increases and “normal” dissolution occurs. In the sodium borosilicate glass, the Na+ and B3+ ions are not released and the Zn2+ concentration stays constant for the first days of experiments, where the glass is definetely “protected”. After this first period, Zn2+ ions precipitate, then the glass dissolution occurs. At the end of the experiments, hemimorphite of composition Zn4Si2O7(OH)2.H2O, was observed in the glass powder. Dissolution experiments were also performed in solutions bearing increasing concentration of CuCl2 salts. They conducted to the same results, although Cu2+ ions do not form insoluble hydroxysilicate analogous to hemimorphite. XPS and TOF-SIMS analysis of corroded glass were carried out to complete the picture. We propose that Zn2+ ions, close to their solubility limit, buffer the pH at the glass-water interface, and by this way protect the silicate network against dissolution. For some compositions, a thin interface layer bearing Si and Zn can build up at the interface and reinforce the protection.

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How to tell if your glass is mixed

G. Mountjoy, M. Rai and L. Swansbury

School of Physical Sciences, University of Kent, Canterbury CT2 7NH, U.K.

This presentation will look at whether cations are homogeneously distributed in the atomic structures of silicate glasses.  This is of relevance to describing glasses using words such as mixed, homogenous or phase separated.  Two different examples will be discussed using results from classical molecular dynamics modelling of silicate glasses.  The xBaO-(100-x)SiO2 glasses are of interest because there is experimental evidence of phase separation at low Ba content, i.e. x<30 [1].  Large models [2] have been used to quantify the homogeneity of the Ba and Si cation distributions and these are compared with statistical distributions.  The xMgO-(50-x)CaO-50SiO2 glasses with 0<x<50 are of interest for studies of the mixed alkaline earth effect [3].  In analogy to the mixed alkali effect, this would predict that some glass properties are non-liner functions of mixing (x).  Models have been used to carefully quantify the short and medium range order around Mg and Ca cations, and these are compared with statistical distributions.
 

  

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New Materials for Optical Fibres: Using NMR to understanding the Effect of Modifier on Tellurite Glass Structure

E.R. Barney1, A.C. Hannon2, D. Holland3, R. Dupree3
1Faculty of Engineering, University Park, University of Nottingham, Nottingham, UK
2ISIS, STFC, Rutherford Appleton Laboratory, Didcot, Oxfordshire UK
3Department of Physics, University of Warwick, Coventry, UK

Tellurite glasses have a range of technologically useful properties including high refractive indices, third-order non-linear optical coefficients, near infra-red transmittance and good chemical durability, all of which make them promising candidates as materials for components in a range of optical devices.  However, to fully exploit the potential of tellurites, it is vital to understand the relationship between glass composition, structure, and their physical and optical properties so that materials can be tailored to meet the requirements of specific applications. 
It has been reported extensively in the literature that the environment of tellurium changes from that of a four coordinated pseudo trigonal bipyramid structure ([TeO4E]) in TeO2 rich glasses, to pseudo-tetrahedral [TeO3E] units as modifier (XnOm) is added to the glass network [1-4] . Our recent work investigating the potassium tellurite glass system using neutron diffraction has demonstrated that, for compositions below ~ 15 mol% modifier, n TeO is roughly constant and significantly less than four (typically 3.65), even for zero % modifier [5].  The presence of [TeO3E] units in amorphous TeO2 necessitates a significant number of non-bridging oxygens in this material and from this information, a model for the interaction between tellurium and potassium modifier has been developed that accurately predicts the variation in coordination number with composition [5]. 
Work is now ongoing to extend this model to more complex glass systems where the average coordination number of not only tellurium, but also the glass modifier cation, can vary with composition.  This talk will report some recent work carried out on the aluminium tellurite glass system, where the modifier is able to adopt environments that are four-, five-, or six-coordinated. 27Al NMR studies, carried out at 20 T, quantify that the relative concentrations of these three sites and show that they vary with composition.  When this information is combined with neutron diffraction data, it is possible to determine the changes in the short range structure of these materials. 27Al MAS DQ NMR spectra will also be presented, providing an insight into the relative proximities of the different aluminium sites and the medium range structure of the glass. 

[1] Y. Himei, A. Osaka, T. Nanba, Y. Miura, J. Non-Cryst. Solids 177 (1994) 164. [2] J.C. McLaughlin, S.L. Tagg, J.W. Zwanziger, J. Phys. Chem. B 105 (2001) 67. [3] U. Hoppe, E. Yousef, C. Russel, J. Neuefeind, A.C. Hannon, Solid State Comm. 123 (2002) 273. [4] A.G. Kalampounias, N.K. Nasikas, G.N. Papatheodorou, J. Phys. Chem. Solids 72 (2011) 1052. [5] E.R. Barney, A.C. Hannon, D. Holland, N. Umesaki, M. Tatsumisago, R.G. Orman, S. Feller, J. Phys. Chem. Lett. 4 (2013) 2312.

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A Study of Rhenium Volatility During Simulated Highly Active Waste Vitrification

Nick R. Gribble1* Tracey Taylor1 & Carl J. Steele2

1 National Nuclear Laboratory, Sellafield, United Kingdom;

2 Sellafield Ltd, Sellafield, United Kingdom

Volatilisation of technetium as caesium pretechnetate during vitrification of highly active waste and subsequent deposition of the condensed solids in the off-gas system has reduced the availability of the Sellafield Waste Vitrification Plant (WVP). The Vitrification Test Rig (VTR), a full scale replica of WVP, has been used to study the behaviour of rhenium as a surrogate for technetium in its non-active simulant to better understand the mechanism and to assess operational and plant design changes intended to minimise the build up of material in the off-gas system. This paper presents a summary of the work to date.

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The isobaric thermal capacity, the crystallization driving force and the Glass forming Ability of Bulk Metallic Glasses

A. Roula
Jijel Univ. ; Fac. Sci. & Technol. ; LIME ; Jijel ; 18000 ; Algeria

 The Glass Forming Ability (GFA) of Bulk Metallic Glasses (BMGs) is discussed with a lot of simple and/or complicated criteria [1, 2] while the Crystallization Driving Force (CDF) [3] (computed from the undercooled liquid as (DG/R.T); where DG and R are values for Gibbs free energy change at the considered T temperature and the gas constant) is the most used criterion in thermodynamics. It is similar to the Sun-Rawson GFA  criterion (intensity of the bond strength between the E(2y/x)+ cation and  oxygen anion in the oxide ExOy : SR = Ed/I.Tm  where Ed, I and Tm are values of the dissociation energy, the coordination number and the melting point of the studied oxide. Authors have successfully amended this criterion with the isobaric thermal capacity Cp and obtained a relative (without measurement units) GFA criterion: ThRGFA = (Ed/I.Tm.Cp) [4, 5].
In this study, author propose the Amended Crystallization Driving Force ACDF = (DG/R.T).(R/Cp) = DG/T.Cp) using the isobaric thermal capacity of the studied metallic alloy instead of the universal gas constant. Some computations on some BMGs compositions reveal that the amended criterion does not invalidate the previous criterion but gives a link with the material nature (its characteristics). Computed values confirm that the GFA of BMGs increase only when ACDF decrease.  
References
[1] A. Inoue & al, Glass-forming ability of alloys, J Non-Cryst Solids, 156/157/158, pp. 473−480, (1993).
[2] M. F de Oliveira, A simple criterion to predict the glass forming ability of bulk metallic glasses, J. Appl. Physics, 11. 023509, (2012).
[3] T. Abe et al., J.  Alloys and Compounds, 434–435, pp. 152–155, (2007).
[4] N. Boubata et al, A nondimensional approach to computing the global relative glass forming ability of oxides, Phys. Chem. Glasses: Eur. J. Glass Sci. Technol. B, 53 (3), pp. 115–120, (2012).
[5] N. Boubata Nouar et al, Thermodynamic and relative approach to compute glass-forming ability of oxides, Bull. Mater. Sci., Vol. 36, (3), pp. 457–460, (2013).