A Method for Evaluating and Correlating Thermodynamic Da ta

Shomate, C. Howard

doi:10.1021/j150514a018

Cited by 150 publications

(68 citation statements)

References 3 publications

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“…These functions are generally polynomials such as those used by SGTE [1] or the Shomate equation [57] used by the NIST Chemistry Webbook [58]. Unlike SGTE, where the functions cover the temperature range from 298 to 6000 K, the Shomate equations from the NIST Chemistry Webbook are only valid above the melting point.…”

Section: Single-state Modelsmentioning

confidence: 99%

Thermodynamic modelling of liquids: CALPHAD approaches and contributions from statistical physics

Becker

Ågren

Baricco

et al. 2013

Physica Status Solidi (b)

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We describe current approaches to thermodynamic modelling of liquids for the CALPHAD method, the use of available experimental methods and results in this type of modelling, and considerations in the use of atomic-scale simulation methods to inform a CALPHAD approach. We begin with an overview of the formalism currently used in CALPHAD to describe the temperature dependence of the liquid Gibbs free energy and outline opportunities for improvement by reviewing the current physical understanding of the liquid. Brief descriptions of experimental methods for extracting high-temperature data on liquids and the preparation of undercooled liquid samples are presented.Properties of a well-determined substance, B 2 O 3 , including the glass transition, are then discussed in detail to emphasize specific modelling requirements for the liquid. We then examine the two-state model proposed for CALPHAD in detail and compare results with experiment and theory, where available. We further examine the contributions of atomic-scale methods to the understanding of liquids and their potential for supplementing available data. We discuss molecular dynamics (MD) and Monte Carlo methods that employ atomic interactions from classical interatomic potentials, as well as contributions from ab initio MD. We conclude with a summary of our findings.1 Introduction Although few inorganic materials are used in their liquid state, liquids play an important role in the manufacture of many materials. This can be either because they are processed from the liquid or, for fulfilling performance criteria, the formation of the liquid phase must be avoided. Additionally, there are now a number of commercially available amorphous solids, both in the form of oxides and metallic glasses, and accurate descriptions of these sys-tems are necessary over a wide range of temperatures. How-ever, liquid phases of many inorganic substances are only sta-ble at high temperatures where the experimental determination of their properties is more challenging than at lower tem-peratures. Many amorphous phases are, at best, metastable and their properties can be difficult to measure. In addition, the data from glassy phases cannot be directly applied to modelling liquids because they have gone through the glass transition, with the attendant sharp drop in heat capacity. As a result, the experimental data for generating and evaluating models of liquids and glasses are fairly sparse. This has a significant impact on the development and refinement of models that strongly depend on the availability of thermodynamic data, such as those needed in CALPHAD modelling.CALPHAD is one of the major ways to model the thermodynamics of liquids. However, for many systems, especially the unaries (elements and sometimes compounds), the data necessary to develop, parameterize and validate models are limited. Theoretical approaches, e.g. first-principles or classical atomistic simulation, can help provide data

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Section: Single-state Modelsmentioning

confidence: 99%

Thermodynamic modelling of liquids: CALPHAD approaches and contributions from statistical physics

Becker

Ågren

Baricco

et al. 2013

Physica Status Solidi (b)

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“…42 A number of assumptions were necessary to calculate the energy of reaction 5. The heat capacities of NaTcO 4 and TcO 2 were assumed to be the same as those of NaReO 4 and ReO 2 , and the heat capacity of Re was assumed to be the same as W since the heat capacity of Re at high temperature was not available.…”

Section: -40mentioning

confidence: 99%

Dissimilar Behavior of Technetium and Rhenium in Borosilicate Waste Glass as Determined by X-ray Absorption Spectroscopy

et al. 2007

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ABSTRACT. Technetium-99 is an abundant, long-lived ( 1/2 = 213,000 yr) fission product that creates challenges for the safe, long-term disposal of nuclear waste. While 99 Tc receives attention largely due to its high environmental mobility, it also causes problems during its incorporation into nuclear waste glass due to the volatility of Tc(VII) compounds. This volatility decreases the amount of 99 Tc stabilized in the waste glass and causes contamination of the waste glass melter and off-gas system. The approach to decrease the volatility of 99 Tc that has received the most attention is reduction of the volatile Tc(VII) species to less volatile Tc(IV) species in the glass melt. On engineering scale experiments, rhenium is often used as a non-radioactive surrogate for 99Tc to avoid the radioactive contamination problems caused by volatile 99 Tc compounds.However, Re(VII) is more stable towards reduction than Tc(VII), so more reducing conditions would be required in the glass melt to produce Re(IV). To better understand the redox behavior of Tc and Re in nuclear waste glass, a series of glasses were prepared under different redox conditions. The speciation of Tc and Re in the resulting glasses was determined by X-ray absorption fine structure spectroscopy. Surprisingly, Re and Tc do not behave similarly in the glass melt. Although Tc(0), Tc(IV), and Tc(VII) were observed in these samples, only Re(0) and Re(VII) were found. In no case was Re(IV) (or Re(VI)) observed.

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“…Here, " 5 is the specific heat at a constant pressure which is found using the Shomate equation [18] with the parameters and form necessary for nitrogen at the temperatures present in the UHTS heat pump [19]. " 6 , the specific heat at a constant volume is found using Equation 13 where 7 is the gas constant (297 J/kg K for nitrogen).…”

Section: Equation 12mentioning

confidence: 99%

Ultra-high temperature thermal energy storage. part 1: concepts

Robinson

2017

Journal of Energy Storage

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Renewable energy sourced from the sun, wind, waves or tides is clean and secure. Unfortunately, the energy that can be extracted from renewables and the demand for it varies both temporally and spatially. Therefore, energy storage is required to match generation with use. To date grid-scale energy storage has been limited by low energy densities, long-term performance degradation, low round-trip efficiencies or limited deployment locations. Although thermal storage has found uses these have been restricted to lower temperatures by thermal losses resulting in low energy densities and uneconomical electricity generation efficiency. In this paper an ultra-high temperature (1800K) storage system is proposed where heat losses are minimised and recovered to make a higher storage temperature attractive, thus unlocking greater energy densities and efficiencies. Radiation dominates heat losses at ultra-high temperatures but can be minimised through the design of the storage medium container. However, even after energy is lost from storage, heat pumps in the store and charge cycles in addition to preheating during the extraction cycle can be used to recover a significant amount of heat. Collectively loss reduction and recovery techniques can lead to a storage system with a performance and utility that exceeds other energy storage methods. Here the feasibility of the novel storage technique is demonstrated through thermodynamic and thermal analysis in each of the three key states of operation: charge, store and generation. KeywordsThermal grid energy storage electric heat pump co-generation IntroductionCommon renewable generation methods rely on the sun, wind or waves, which vary temporally or spatially and do not follow demand. Grid-scale energy storage will be necessary to fully enable the operation of electricity networks with high penetrations of distributed renewable energy generation and realise targets for CO2 reduction. However, existing energy storage technologies are limited in their uptake and usefulness by low energy densities, long term performance degradation, low round-trip efficiencies or limited deployment locations [1].Thermal storage is a fully reversible process that does not have any of the by-products and degradation over multiple cycles seen in electrochemical storage approaches [2,3]. Until now thermal energy storage has been limited to a temperature of around 800 K [4], making it uncompetitive in terms of energy density and round-trip efficiency from heat to electricity. Consequently, thermal energy storage has only seen widespread deployment to collect heat for later re-use. By storing energy as heat at ultra-high temperatures (>1100K), it is possible to raise energy density and round-trip efficiency to the point where grid-scale thermal storage becomes technically and economically feasible.

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A Method for Evaluating and Correlating Thermodynamic Da ta

Cited by 150 publications

References 3 publications

Thermodynamic modelling of liquids: CALPHAD approaches and contributions from statistical physics

Thermodynamic modelling of liquids: CALPHAD approaches and contributions from statistical physics

Dissimilar Behavior of Technetium and Rhenium in Borosilicate Waste Glass as Determined by X-ray Absorption Spectroscopy

Ultra-high temperature thermal energy storage. part 1: concepts

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