Martin Wilding
University of Bath, Department of Physics, Department Member
- Current research In collaboration with Dr Chris Benmore, Dr Rick Weber and Prof John Parise, a research programme ha... moreCurrent research
In collaboration with Dr Chris Benmore, Dr Rick Weber and Prof John Parise, a research programme has been developed at the Advanced Photon Source (APS), Argonne National Laboratory to study the structure of stable and supercooled oxide liquids. This involves a combination of high energy X-ray diffraction and containerless techniques, including aerodynamic levitation for the study of refractory oxide liquids and, more recently, acoustic levitation for the study of organic glass-forming liquids.
My research at extreme conditions, including high temperatures and pressures, includes studies of amorphous materials at high pressures including magnesium silicates and network-forming glasses such as silica and vitreous boron oxide. I collaborate with groups at the ISIS neutron source (Dr Matt Tucker and Dr Craig Bull), at the University of Bath (Prof. Phil Salmon and Dr. Anita Zeidler) and at the spallation source in the US (SNS) (Dr Chris Tulk and Dr. Jamie Molaison). These technically challenging experiments are directed at ultimately evaluating liquid structures at high pressure and temperature.
My research has focused has been the understanding of changes in liquid structure that accompany polyamorphic liquid transitions, apparent first order transitions between liquids of different density and reported for liquids close to YAG (Y3Al5O12).The study of polyamorphic liquids forms part of a broader, continuing collaboration with Professor Paul McMillan (UCL) and Dr Mark Wilson (Oxford). More recently, by developing fast data acquisition systems we have been able to monitor the evolution of structure of liquids as they are quenched to form a glass.
Combined neutron and X-ray diffraction studies can be used to evaluate the mid-range order of oxide glasses. I have been working with groups at Argonne National Laboratory to develop this approach over the past ten years. This technique uses high energy X-rays to achieve a real space resolution comparable to that obtained by elastic neutron diffraction.
A future goal of this research is the combined diffraction studies of liquids at high temperature and pressure, allied to extreme conditions research, polyamorphism and fundamental interpretations of the liquid and amorphous states.
Most recently, combined high energy X-ray diffraction and aerodynamic levitation of iron- and other transition-metal-bearing liquids has been undertaken using controlled atmosphere (changes in CO/CO2 ratios). It is evident that the influence on structure of mixed valance state elements is complicated and requires detailed analysis and modelling. A collaboration is being established (together with Mark Wilson and the collaborators at Argonne) to explore composition, temperature and fO2. This work is closely allied with the UK-China steel research forum and has direct application to steel production as well as being a fundamental study of liquid structure.edit
Molten carbonates are highly inviscid liquids characterized by low melting points and high solubility of rare earth elements and volatile molecules. An understanding of the structure and related properties of these intriguing liquids has... more
Molten carbonates are highly inviscid liquids characterized by low melting points and high solubility of rare earth elements and volatile molecules. An understanding of the structure and related properties of these intriguing liquids has been limited to date. We report the results of a study of molten sodium carbonate (Na 2 CO 3) which combines high energy X-ray diffraction, containerless techniques and computer simulation to provide insight into the liquid structure. Total structure factors (F x (Q)) are collected on the laser-heated carbonate spheres suspended in flowing gases of varying composition in an aerodynamic levitation furnace. The respective partial structure factor contributions to F x (Q) are obtained by performing molecular dynamics simulations treating the carbonate anions as flexible entities. The carbonate liquid structure is found to be heavily temperature-dependent. At low temperatures a low-dimensional carbonate chain network forms, at T = 1100 K for example ~55% of the C atoms form part of a chain. The mean chain lengths decrease as temperature is increased and as the chains become shorter the rotation of the carbonate anions becomes more rapid enhancing the diffusion of Na + ions. Carbonatites are rarely occurring igneous liquids whose formation is dominated by molten carbonates derived from the Earth's mantle. Although their occurrence is currently restricted to a single active volcano, Ol Doinyo Lengai in Tanzania, it is believed that this type of volcanism has occurred throughout geological history 1–4. As recently observed eruptions confirm, these carbonatite liquids have low viscosity and low eruption temperatures and are believed to play a significant role in the geological evolution of other terrestrial planets 5. The low viscosity, the high solubility of key elements such as P and the light rare earth elements and ability to dissolve volatile elements makes carbonatite liquids important agents for geochemical enrichment in the Earth's mantle and they are closely linked to kimberlite genesis and diamond formation 6,7. Economically, carbonatites are important as sources of rare metals including niobium, tantalum and uranium 2,3 while molten carbonates are important in development of molten carbonate fuel cells and as battery electrolytes 8. Despite their recognised importance the structure of these liquids is not well-known. The traditional view is that they are similar to molten salts with car-bonate groups − (CO) 3 2 acting as anions and combining with metal cations 9–11. This contrasts strongly with the silicate liquids which form the majority of terrestrial igneous liquids and are considered to be dominated by polymerised Si n O m networks 12. An early X-ray diffraction (XRD) study provided estimates of the CO , CC and O-O distances for the car-bonate anion and M-O, M-C and MM distances in molten alkali (M +) carbonate liquids 13. These X-ray data were interpreted in terms of the contact distances between the oxygen atoms in carbonate anions and the metal cati-ons. The number of sites in contact with a single oxygen was found to increase systematically from Li + to K + and correlated with an increase in free volume allowing free rotation of anions. Vibrational spectroscopy performed on carbonate systems that form glasses hints at two populations of carbonate species, resembling those observed in crystalline configurations and those forming part of a network with the cations 14,15 , making their structures more complex than a typical molten salt. Simulations of carbonates which assume rigid anions with cations in interstices do not reflect the distortions suggested by spectroscopy 15,16 .
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Structure factor changes in supercooled yttria‐alumina. [AIP Conference Proceedings 1092, 98 (2009)]. Martin C. Wilding, G. Neville Greaves, Quang Vu Van, Odile Majérus, Louis Hennet. Abstract. Changes in the structure factor ...
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Research Interests: Materials Engineering, Molecular Dynamics Simulation, Monte Carlo Simulation, Nuclear Magnetic Resonance, Glass, and 14 moreRaman Spectroscopy, Neutron Diffraction, Monte Carlo Simulations, Transport, Text, Nearest Neighbor, Non crystalline solids, First-Order Logic, Impurities, Chemical Bonds, Scattering, Amorphous solids, Coordination number, and Raman Spectra
Alkali silicate glasses containing lanthanum oxide are useful model systems for understanding the structural role of rare earth cations in optical and other types of materials. We report 29Si and Raman spectra of sodium and potassium... more
Alkali silicate glasses containing lanthanum oxide are useful model systems for understanding the structural role of rare earth cations in optical and other types of materials. We report 29Si and Raman spectra of sodium and potassium silicate glasses, both with added La2O3 and with La2O3 substituted for Na2O or K2O on an equal-oxygen basis. In the former series, silicate speciation changes show the formation of more non-bridging oxygens (NBO) as more of the network-modifying La2O3 is added. In the latter series, however, in which the nominal ratio of NBO to Si is constant, silicate speciation changes indicate that the actual ratio decreases significantly as La is substituted for 3 Na or K. The simplest explanation of this finding is that up to several percent of the oxygen in the La-rich glasses is not bonded to any Si, but instead forms `free oxide' ions that are part of La-rich domains. Although the size of these domains remains unconstrained, the lack of evidence for phase separation and continuity of trends in structure with composition suggests that the metastable liquid structure at the glass transition contains substantial intermediate-range heterogeneity.
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The behaviour of amorphous materials under pressure is a rich and, as yet, poorly-explored area of research in condensed-matter physics and Earth and Materials Science. The MgO-SiO2 system has particular geophysical significance since... more
The behaviour of amorphous materials under pressure is a rich and, as yet, poorly-explored area of research in condensed-matter physics and Earth and Materials Science. The MgO-SiO2 system has particular geophysical significance since liquids in this system are good approximations of primitive melts formed within the Deep Earth. Previous diffraction studies of MgO-SiO2 glasses formed at ambient pressure have demonstrated a jump in Mg-O coordination number (CN) as a function of composition. These changes coincide with changes in the rheological properties and configurational entropy. It can be argued that these structural changes mean the glasses with low SiO2 content and increased Mg-O coordination are "high pressure like" and that similar behaviour might be expected as more SiO2-rich liquids are compressed. To test this hypothesis neutron and X-ray diffraction data have been collected in situ on a low silica MgO-SiO2 glass compressed to 8 Gpa. The diffraction data and the...
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A 2-megawatt TRIGA reactor, now owned and operated by UC Davis as a research facility, was especially designed and built by the USAF with a large L/D for neutron-beam radiography of aircraft parts. More recent efforts in computed... more
A 2-megawatt TRIGA reactor, now owned and operated by UC Davis as a research facility, was especially designed and built by the USAF with a large L/D for neutron-beam radiography of aircraft parts. More recent efforts in computed tomography (CT) have established capabilities of 3-D imaging of a broad range of geological materials, including textured igneous rocks up to 10's cm in size. Neutron-beam imaging is complementary to X-ray CT, especially because of the high neutron cross-sections for many light elements that are not easily detected by X-rays. Our goal is to optimize neutron-beam CT techniques for quantitative studies of igneous textures and mineralogy. To this end, we have made improvements in both image acquisition and data processing. Specifically, we have measured the attenuation coefficient for diabase for beam-hardening corrections. We have characterized the dark charge contribution and developed new strategies for flat field corrections. We have increased our samp...
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As for x-rays, neutron radiography is a noninvasive imaging technique based on the attenuation of thermal neutrons by the object in question, described by BeerAfAøAøâ_sA¬Aøâ_zAøs law. However, neutron imaging is complementary to x-rays,... more
As for x-rays, neutron radiography is a noninvasive imaging technique based on the attenuation of thermal neutrons by the object in question, described by BeerAfAøAøâ_sA¬Aøâ_zAøs law. However, neutron imaging is complementary to x-rays, as it is especially well suited for materials containing hydrogen atoms and mostly other low atomic weight attenuating materials. Although neutron attenuation techniques are routinely used in
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ABSTRACT Aluminates form in binary systems with alkali, alkaline earth or rare-earth oxides and share the high melting point and resistance to chemical attack of the pure Al2O3 end-member. This means that these ceramics have a variety of... more
ABSTRACT Aluminates form in binary systems with alkali, alkaline earth or rare-earth oxides and share the high melting point and resistance to chemical attack of the pure Al2O3 end-member. This means that these ceramics have a variety of applications as cements, castable ceramics, bioceramics, and electroceramics. Calcium aluminate cements are used for example in specialist applications as diverse as lining sewers and as dental restoratives. Ceramics in aluminate systems are usually formed from cubic crystal systems and this includes spinel and garnet. Rare earth aluminate garnets include the phase YAG (yttrium aluminium garnet), which is an important laser host when doped with Nd(III) and more recently Yb(III). Associated applications include applications as scintillators and phosphors. Aluminate glasses are transparent in the infrared region and these too have specialist applications, although the glass-forming ability is poor. Recently, rare earth aluminate glasses have been developed commercially in optical applications as alternatives to sapphire for use in, for example, infrared windows. Aluminates are refractory materials and their synthesis often simply involves solid-state growth of mixtures of purified oxides. Alternative synthesis routes are also used in specialist applications, for example in production of materials with controlled porosity and these invariably involve sol–gel methods. For glasses, one notable, commercially important method of production is container-less synthesis, which is necessary because of the non-Arrhenius (fragile) viscosity of aluminate liquids.
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Research Interests: Materials Engineering, Molecular Dynamics Simulation, Monte Carlo Simulation, Nuclear Magnetic Resonance, Glass, and 14 moreRaman Spectroscopy, Neutron Diffraction, Monte Carlo Simulations, Transport, Text, Nearest Neighbor, Non crystalline solids, First-Order Logic, Impurities, Chemical Bonds, Scattering, Amorphous solids, Coordination number, and Raman Spectra
... Martin C. Wilding 1 and Alexandra Navrotsky Corresponding Author Contact Information , E-mail The Corresponding Author. ... The heat effect measured during the calorimetric experiment, the heat of drop solution, ΔH drop-sol consists... more
... Martin C. Wilding 1 and Alexandra Navrotsky Corresponding Author Contact Information , E-mail The Corresponding Author. ... The heat effect measured during the calorimetric experiment, the heat of drop solution, ΔH drop-sol consists of two components, the heat content of the ...
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A negative correlation exists between advanced maternal age and reproduction. Current data suggest that this correlation is due to a decline in oocyte quality with respect to female age. Since a new individual is derived from the fusion... more
A negative correlation exists between advanced maternal age and reproduction. Current data suggest that this correlation is due to a decline in oocyte quality with respect to female age. Since a new individual is derived from the fusion of a single sperm and egg, we tested whether the quality of this material could influence the long-term physiological health of offspring, by examining whether a link between parental age and lifespan of offspring exists. We requested a search from the Swedish demographic database POPUM 3 maintained by the University of Umeå, Sweden between years 1700 and 1900. Parameters requested included mothers' and fathers' age at gestation, the lifespan of the children, cause of death of children and the region of birth. Complete data was obtained for 30,512 children born to 12,725 mothers and fathers. Kaplan-Meier estimators demonstrated a strong relationship between mother's age at gestation and the longevity of offspring. Extrinsic factors such as century of birth also had an effect on the data. The forward stepwise procedure on Cox's model of proportional hazards suggested that most significant intrinsic factors were mother's lifespan and mother's age at gestation. These data demonstrate that intrinsic and extrinsic factors influence the lifespan of children. Among intrinsic factors, mother's lifespan and age at gestation had a significant influence on the data. The influence of intrinsic factors remained significant despite a strong extrinsic influence. We suggest that the influence of the mother on the lifespan of offspring is due to extra-genomic factors.
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Research Interests: Genetics, Treatment Outcome, Infertility, Prospective studies, Pregnancy, and 15 moreHumans, Female, Intracytoplasmic Sperm Injection, Assisted Reproduction, Male, Male Infertility, Randomized Trial, Adult, Semen, Spermatozoa, Embryos, Pregnancy Rate, Assisted, Computer Assisted Sperm Analysis, and DNA fragmentation
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In this preliminary report, we describe a new technique involving the same-day transfer of activated oocytes to the uterus after intracytoplasmatic sperm injection (ICSI). The technique, termed activated oocyte transfer (AOT), offered to... more
In this preliminary report, we describe a new technique involving the same-day transfer of activated oocytes to the uterus after intracytoplasmatic sperm injection (ICSI). The technique, termed activated oocyte transfer (AOT), offered to 19 couples, yielded a pregnancy rate per cycle of about 30%, equivalent to traditional in-vitro fertilization (IVF) and ICSI in a laboratory setting. AOT is performed 4 h after oocyte retrieval, permitting the patient to undergo treatment as an out-patient procedure.
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Enthalpy relaxation of a reheated natural tektite glass has been used to determine the coolingrate of the glass in nature. The relaxation parameters for the tektite samples were obtained by internal calibration through a series of thermal... more
Enthalpy relaxation of a reheated natural tektite glass has been used to determine the coolingrate of the glass in nature. The relaxation parameters for the tektite samples were obtained by internal calibration through a series of thermal treatments applied to the sample following the first ...
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This paper will describe the results of in situ high-energy X-ray measurements performed on stable and supercooled oxide liquids using containerless techniques. As will be discussed in the companion paper (Weber et al.), the use of an... more
This paper will describe the results of in situ high-energy X-ray measurements performed on stable and supercooled oxide liquids using containerless techniques. As will be discussed in the companion paper (Weber et al.), the use of an aerodynamic levitator furnace with laser heating allows the structures of refractory oxide liquids to be probed. Because of the contactless nature of this sample environment liquids can be deeply supercooled, and this provides opportunities to study the metastable structures of supercooled liquids. Of particular interest are the so-called fragile liquids that depart from Arrhenius-law viscosity behaviour and that, by definition, have temperature-dependent structures. The focus of this paper is the study of two oxide systems, MgO–SiO2 and Al2O3–SiO2. These two liquids have highly disordered stable liquid structures that differ substantially from the structures of the equivalent glasses. We present data showing how these structures change when supercoole...
Liquids in the Y2O3-Al2O3 system exhibit liquid state 'polyamorphism' with a transition occurring between two liquid phases (in the supercooled state) with the same chemical composition but different density and structure.... more
Liquids in the Y2O3-Al2O3 system exhibit liquid state 'polyamorphism' with a transition occurring between two liquid phases (in the supercooled state) with the same chemical composition but different density and structure. Differential scanning and high temperature solution calorimetry experiments were performed on Y2O3-Al2O3 glasses quenched from polyamorphic liquids to establish the thermodynamic properties of the high and low density amorphous phases (HDA, LDA) and the energetic factors that drive the liquid-liquid phase transition. Glasses produced from the high density, high temperature liquid by rapid quenching show the onset of a glass transition for the HDA form at 1120-1150 K. The HDA liquid is highly 'fragile' with a non-Arrhenian temperature dependence consistent with its large configurational entropy.The HDA-LDA transition occurs at 1450-1575 K, depending upon the composition, during quenching experiments. The HDAform can be recovered metastably to ambien...
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ABSTRACT Containerless techniques (levitation) completely eliminate contact with the sample. This unique sample environment allows deep supercooling of many liquids and avoids contamination of high-temperature melts. Recent experiments at... more
ABSTRACT Containerless techniques (levitation) completely eliminate contact with the sample. This unique sample environment allows deep supercooling of many liquids and avoids contamination of high-temperature melts. Recent experiments at the Advanced Photon Source (APS) high-energy beamline 11 ID-C used aerodynamic levitation with laser beam heating and acoustic levitation with cryogenic cooling. By using these two methods, liquids were studied over much of the temperature range from −40 to +2500°C. This paper briefly describes the instrumentation and its use and is illustrated with examples of measurements on molten oxides and low-temperature liquids.
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Glass fragments from three different hyaloclastites have been used to evaluate the range of cooling rates experienced by undersea volcanic deposits. We found that the glass fragments retain structures with a range of apparent quench rates... more
Glass fragments from three different hyaloclastites have been used to evaluate the range of cooling rates experienced by undersea volcanic deposits. We found that the glass fragments retain structures with a range of apparent quench rates from 25 to 0.15 K min–1. The most rapid cooling rates are interpreted to be those resulting from cooling of the lava near the water interface. Simple conductive cooling models produce a range of quench rates comparable to those of the more rapidly cooled samples. The very slow apparent quench rates are unlikely to result from simple linear cooling through the glass transition, because of the onset of crystallization; instead, they are indicators of a more complex thermal history that involves the annealing of glasses at temperatures within the glass transition interval for a dwell time sufficient to allow the relaxation of the glass to lower temperature structures. The thermal history recorded in these samples illustrates the complexity of eruptive processes and demonstrates that quench rates for natural glasses retain information relevant to more complex cooling models.
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Understanding the structure of magnesium silicate liquids is important for interpreting the behavior of liquids produced by melting processes in the Earth and Lunar mantles. Glasses produced from MgO-SiO2 liquids ranging in composition... more
Understanding the structure of magnesium silicate liquids is important for interpreting the behavior of liquids produced by melting processes in the Earth and Lunar mantles. Glasses produced from MgO-SiO2 liquids ranging in composition from forsterite to enstatite have been studied by combined neutron and X-ray diffraction to constrain their structure and related transport and thermodynamic properties. Neutron diffraction measurements were made on the Glass and Amorphous Materials Diffractometer at the Intense Pulsed Neutron Source, Argonne National Laboratory (ANL). The collected data yield real space pair correlation functions which show the coordination environments for the main structural units in these glasses. The neutron diffraction data are dominated by the scattering from oxygen so complementary high energy X-ray diffraction data was collected at the 11-ID-C beamline at the Advanced Photon Source at ANL. The X-ray and neutron diffraction data can be combined to eliminate th...
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ABSTRACT Liquids in the MgO-SiO2 system provide a good approximation for the liquids that are produced when the mantle minerals from planetary interiors melt, however because of their refractory nature, direct study of liquid structures... more
ABSTRACT Liquids in the MgO-SiO2 system provide a good approximation for the liquids that are produced when the mantle minerals from planetary interiors melt, however because of their refractory nature, direct study of liquid structures is logistically difficult. Magnesium silicates do not form glasses particularly easily and specialised synthesis techniques are required to provide vitreous forms. Combined neutron and high energy X-ray diffraction studies for a range of magnesium silicate glasses has however shown a change in structure between 38 and 33 % SiO2. This is an increase in coordination number from 4.5 to 5.0 and a limit to the formation of a polymerised silicate network. These changes coincide with a change in the rheology and similar changes might be anticipated at high pressure in more silica-rich compositions. Diffraction studies at high pressure and temperature provide a direct measure of the changing structure of liquids and amorphous materials that result in changes in their density and bulk thermodynamic properties. In this presentation the results of neutron and X-ray scattering experiments on magnesium silicate liquids and glasses are presented. Neutron diffraction studies on a single composition magnesium silicate glass from ambient pressure to 8.7 GPa show changes in the amorphous structure. There is a change in the oxygen environment consistent with a collapse of a relatively open silicate framework. Between 5.7 and 8.6 GPa changes in the local environment of magnesium is identified consistent with a change from a low pressure glass structure with a sparse silicate network to a higher pressure structure in which connected magnesium-oxygen polyhedra adopt the network-forming role. Further insight into this high pressure behaviour is provided by ambient pressure diffraction measurements of liquid magnesium silicates are high temperature. These measurements using high energy X-rays and levitation techniques show changes in the local environment surrounding magnesium and changes in structure when the liquids are cooled to form glasses. Intriguingly, the glass structures are not necessarily direct representatives of the liquid. Although both the high temperate and high pressure experiments are challenging, these in-situ studies reveal a wealth of structural complexity in geophysically important liquids. As new facilities become commissioned and new techniques are developed, studies of these and similar liquids at elevated pressures and temperatures will soon be achievable.
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Silicate melts form glasses in a variety of geological environments. The relaxation (equilibration) of the frozen glass structure provides a means of investigating the quench rates of natural glasses, and this cooling history provides an... more
Silicate melts form glasses in a variety of geological environments. The relaxation (equilibration) of the frozen glass structure provides a means of investigating the quench rates of natural glasses, and this cooling history provides an important constraint for models of melt dynamics. Phonolite glasses from the central volcanic edifice of Tenerife, Canary Islands indicate a range of five orders of
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Glass formation, and associated potential polyamorphism are investigated for the key ceramic Y2O3-Al2O3 using a combination of experimental and theoretical techniques. Liquid samples are rapidly cooled by drop quenching and high and low... more
Glass formation, and associated potential polyamorphism are investigated for the key ceramic Y2O3-Al2O3 using a combination of experimental and theoretical techniques. Liquid samples are rapidly cooled by drop quenching and high and low density amorphous regions (LDA and HDA respectively) are identified using reflected light microscopy. Raman spectra are obtained to low frequency focussed on regions identified as pure LDA or HDA. The respective compositions of these regions are confirmed by electron microprobe analysis. These spectra are used to extract the vibrational densities of states and these are compared with those generated for the liquid oxide using polarizable-ion molecular dynamics simulations. The experimental and simulated spectra are used to determine the low temperature heat capacities. The low frequency regions of the spectra display an excess of states (boson peaks) which are different for the two glasses. Thermodynamic modelling is used to demonstrate how samples o...
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Containerless high energy X-ray diffraction measurements have been performed on molten Al(2)O(3)-SiO(2) as a function of composition. The data show a strong distortion of the SiO(4) tetrahedral units and a breakdown of intermediate range... more
Containerless high energy X-ray diffraction measurements have been performed on molten Al(2)O(3)-SiO(2) as a function of composition. The data show a strong distortion of the SiO(4) tetrahedral units and a breakdown of intermediate range order as alumina is added. For silica-rich compositions, the X-ray pair distribution functions are consistent with the presence of 4-fold oxygen triclusters predicted by molecular dynamics simulations, where these liquids exhibit relatively high viscosities compared to other binary silicates. For higher alumina content liquids, the average cation-oxygen coordination number gradually increases with increasing Al(2)O(3) content, but the pair distribution functions change very little with composition, suggesting the increased presence of disordered AlO(n) (n = 4,5,6) polyhedra are associated with low viscosity melts. A comparison of the liquid and glassy X-ray pair distributions functions at the alumina-rich mullite composition indicate a significant distortion of the polyhedra in the melt, suggesting structural changes are temperature dependent.