Scientific Program:
SCOPE:
| The focus of the meeting will be to bring together people from the fields of chemistry, geology and materials science who are working in the area of high temperature phenomena in solid and liquid materials. |
TOPICS:
| Masaki Azuma |
Japan |
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Talk
Title: HIGH-PRESSURE SYNTHESIS OF FUNCTIONAL
TRANSTION METAL OXDES |
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| Ricardo Castro |
Brazil |
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| Talk Title:
CALORIMETRIC MEASUREMENT OF THE INTERFACE
ENERGY USING NANOPARTICLES Abstract: The knowledge of interface thermodynamics is of key importance in understanding and controlling high-temperature phenomena such as sintering and phase transformation. However, there is limited experimental data available related to solid-solid interfaces (grain boundary) energy, and most available data is based on simulations and time-consuming image analysis using Young's equation or derivations. In this work we present a procedure to determine the interface energy of oxide nanoparticles using a convenient calorimetric method. Differential scanning calorimetry (DSC) at relatively high-temperature was carried out in highly pressed pellets of nanopowders of the studied oxides. Under this condition, the nanoparticles sinter. Pellets shrinkage was accomplished with an exothermic peak that could be quantitatively separated into surface elimination and grain boundary formation/elimination by microstructural analysis. Nanoparticles were indeed needed for the experiments to allow a measurable heat effect during sintering. After analysis of the results, we were able to determine a relationship between the grain boundary and the surface energy of the studied nanopowder. The grain boundary energy of different oxides could be derived and the obtained results were consistent with literature data when available. The method provides reliable data of interface energies since they are obtained during the process of formation and elimination. Since the system is under high temperature during the measurements, the effect of water and volatile contaminants in the interface and surface energy are minimized. |
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| Yingwei Fei |
USA |
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| Talk Title:
MELTING RELATIONS IN THE FE-C-S-O SYSTEM AT
HIGH PRESSURE: IMPLICATIONS FOR PLANETARY CORES Abstract: It is known that the density of the Earth's core constrained from seismic data is significantly lower than that of pure iron measured experimentally at high pressure and temperature. The density deficit in the core (both liquid outer core and solid inner core) led to the conclusion that the Earth's core must contain several wt% of one or more light elements (lighter than iron) in addition to Fe-Ni alloy. Sulfur (S), carbon (C), and oxygen (O) are the prominent candidates among the proposed light elements, because of their high solar abundance and strong chemical affinity for Fe. Determining the effect of pressure on melting relations in the Fe-S, Fe-C, and Fe-O binary systems and multi-component system is crucial for understanding the chemistry and evolution of planetary cores. There has been significant progress in determining the melting relations in the system Fe-FeS at high pressure, using multi-anvil apparatus and laser-heating diamond-anvil cell. These studies have revealed new iron-sulfur compounds (Fe3S2, Fe2S, and Fe3S) stable at high pressures, change of melting relations, and pressure effect on eutectic temperature and composition. The behaviors of the Fe-C and Fe-O systems have also been experimentally investigated recently. Experimental data in the Fe-C-S-O system at high pressure have just emerged. In parallel, there are high-quality data on density measurements of solid and liquid phases at high pressure and temperature. These experimental data provide critical information needed for building thermodynamic models of the system. In this presentation, I will review recent advances in experimental techniques and summarize melting relations in the Fe-C-S-O system. The emphasis will be on the need to develop thermodynamic models by synthesis of thermochemical, thermophysical, and phase equilibrium data. The systematic approach provides a better understanding of the correlation between physical state and composition with different thermal models of the planetary cores. |
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| Susana Fries |
Germany |
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| Talk Title:
NI-BASE SUPERALLOYS: WHEN BASIC KNOWLEDGE
MEETS APPLICATIONS Abstract: Single crystals properties and order-disorder transitions are object of academic investigations since almost one century (e.g. [1]). I wonder, however, that Mr. Ising or Mr. Bragg and Mr. Williams would imagine that large single crystals would pass flying above their heads as part of a turbine blade of an airplane. Maybe, even today, many scientists do not know about it. In this talk I will show how this very special turbine blades are constructed with a material which shows a very high performance at elevated temperatures: the Ni-base superalloys. The development of these alloys were very much facilitated by the already existing theoretical and experimental knowledge relevant for these materials when they started to be created in the early fifties. Ni-base superalloys are constantly under development and more than 10 elements take part in their constitution nowadays. Returning to theoretical approaches it is exactly the quantum mechanics results provided by Density Functional Theory (DFT) [2] that can contribute at its best to the understanding and prediction of their outstanding properties. The phenomenological Calphad method [3] can merge experimental results, thermodynamic trends and DFT results in a very efficient way and it is with the help of all that knowledge that the microstructure of a multicomponent ordered single crystal turbine blade can be nowadays simulated by using a phase-field approach anticipating and supporting alloys development. [1] Ising E. (1925) Z. Phys, 31 253 [2] Mottura A et al. (2008) Acta Mat, 56 2669 [3] Lukas et al., (2007), Computational Thermodynamics, ed. Cambridge University Press, Cambridge, UK [4] Warnken N, D 82 Dissertation (2007) Shaker Verlag, RWTH, Aachen, Germany |
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| Jonathan Stebbins |
USA |
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| Talk Title:
PRESSURE AND TEMPERATURE EFFECTS ON THE STRUCTURE
OF OXIDE MELTS Abstract: Well-known, and often relatively large, changes in heat capacity, thermal expansivity, and compressibility on transition from glass to liquid for molten oxides require that there are significant changes in structure on heating above the glass transition. Such "configurational" terms, when integrated up in temperature to melting points, often make large contributions to bulk thermodynamic properties. In technology, such changes also control the processes of annealing which are essential in fabricating most usable glass objects. Our understanding of the physical nature of this T-dependent disordering process remains limited, but considerable progress has been made in systems such as aluminosilicates, borates, and borosilicates. Structural changes at high pressure are critical to modeling the large density increases between silicate melts at the Earth's surface and its deep interior, which are critical to their behavior in large-scale geological processes. We have only recently begun to be able to quantify changes in cation and anion structural environments with pressure, but now have clear hints as to some of the mechanisms that are important and some of the controlling compositional variables. This presentation will focus on recent progress in these areas, particularly the application of high-resolution NMR and other spectroscopies to glasses that record T and P effects. |
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| Sharon Webb |
Germany |
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| Talk Title:
CONFIGURATIONAL HEAT CAPACITY, VISCOSITY AND
STRUCTURE OF SILICATE MELTS Abstract: Changes in the compositional dependence of physical properties (e.g. viscosity, density) of melts and glasses have long been used to infer changes in structure. Spectroscopic methods are then applied in order to determine the melt and glass structure. In the case of aluminosilicate melts, NMR measurements have shown that in general Si4+ and Al3+ are tetrahedrally co-ordinated, with the Al3+ requiring a charge-balancing cation. In melts in which there are not enough cations to charge-balance all of the Al3+ a new charge-balanced tetrahedrally co-ordinated Al3+ structural unit must exist. Charge-balanced tri-clusters of AlSi2O5 (in which one oxygen is bonded to two Si and one Al tetrahedron) are thought to be the most probable new structure. Although the viscosity data for Na2O-Al2O3-SiO2 melts indicates that tri-clusters are indeed the new structural unit, NMR measurements have not observed tri-clusters in these glasses as the expected peak is calculated to sit under a strong Si-O-Si peak. The configurational heat capacity (cpconf) and entropy at the glass transition (Sconf(Tg)) are both related to viscosity through the Adam-Gibbs equation. Therefore it is to be expected that these thermodynamic parameters should also reflect changes in melt structure with composition. Although there are no clear trend changes in the heat capacity of glasses and melts as a function of composition, there are unambiguous trend changes in cpconf with composition. The Sconf(Tg) determined from the combination of viscosity and cpconf data show general trends as a function of composition, but the errors in the calculated values preclude clear comments about trend changes and expected structural changes. Here, melts in the Na2O-Al2O3-SiO2 and CaO-Al2O3-SiO2 systems are investigated via viscosity and cpconf measurements. A dramatic change in viscosity trend as a function of composition is observed in both systems as a function of MxO/Al2O3 at the condition where all of the Al3+ tetrahedra are charge balanced and there are no non-bridging oxygens left in the melt (i.e. MxO=Al2O3). A minimum is observed in cpconf for Na2O-Al2O3-SiO2 melts at this condition while a maximum is observed in CaO-Al2O3-SiO2 melts. The maximum in cpconf for CaO-Al2O3-SiO2 melts is due to the unexpected minimum which occurs at the condition 2CaO=Al2O3. This is the condition at which the tetrahedrally co-ordinated Al3+ begin to share their charge balancing Ca2+ with other Al3+ tetrahedra. No trend change is observed in viscosity at this composition. Although the trend changes in cpconf occur in the Na2O-Al2O3-SiO2 and CaO-Al2O3-SiO2 systems at compositions for which one can associate a structural change, the compositional variation has included a Si/Al change. Investigation of cpconf in the CaO-SiO2-CaO-Al2O3 melt system shows that indeed the MxO/Al2O3 relationship is related to the maxima and minima observed in cpconf (and viscosity and density), with no changes occurring at the same Si/Al for all melt compositions. Changes in trends are observed in cpconf for compositions at which no changes in viscosity are observed. Thus it would appear that cpconf is a sensitive measure of changes in melt structure. |
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