Determination of structural, thermodynamic and phase properties in the Na2S–H2O system for application in a chemical heat pump (original) (raw)
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Thermochimica Acta, 2000
In this paper, we present a methodology for the prediction of the crystallization enthalpy of mirabilite (Na 2 SO 4 Á10H 2 O) from supersaturated H 2 O±NaCl±Na 2 SO 4 solutions. Required thermodynamic properties of H 2 O±NaCl±Na 2 SO 4 such as dissolution enthalpies, phase equilibria and heat of hydration of Na 2 SO 4 are represented or determined using Pitzer's ioninteraction model. Measurements of crystallization enthalpies at various temperatures and concentrations were made in a SETARAM C80D calorimeter by mixing H 2 O±Na 2 SO 4 and H 2 O±NaCl±Na 2 SO 4 solutions supersaturated relatively to mirabilite with a seed crystal of Na 2 SO 4 Á10H 2 O once the thermal equilibrium was reached.
Acta Crystallographica Section B Structural Science, 2012
The concept that equates oxidation and pressure has been successfully utilized in explaining the structural changes observed in the M 2S subnets of M 2SO x (x = 3, 4) compounds (M = Na, K) when compared with the structures (room- and high-pressure phases) of their parent M 2S `alloy' [Martínez-Cruz et al. (1994), J. Solid State Chem. 110, 397–398; Vegas (2000), Crystallogr. Rev. 7, 189–286; Vegas et al. (2002), Solid State Sci. 4, 1077–1081]. These structural changes suggest that if M 2SO2 would exist, its cation array might well have an anti-CaF2 structure. On the other hand, in an analysis of the existing thermodynamic data for M 2S, M 2SO3 and M 2SO4 we have identified, and report, a series of unique linear relationships between the known Δf H o and Δf G o values of the alkali metal (M) sulfide (x = 0) and their oxyanion salts M 2SO x (x = 3 and 4), and the similarly between M 2S2 disulfide (x = 0) and disulfur oxyanion salts M 2S2O x (x = 3, 4, 5, 6 and 7) and the number of ...
Conductivity, Thermal Measurements, and Phase Diagram of the Na 2 S 2 O 7 −NaHSO 4 System
The Journal of Physical Chemistry B, 1999
The conductivity of the Na 2 S 2 O 7 -NaHSO 4 binary system has been measured for 15 different compositions in the full composition range, and in the temperature range 400-700 K. Phase transition temperatures were obtained, and the phase diagram was constructed. It is of the simple eutectic type, where the eutectic is found to have the composition X NaHSO 4 ) 0.97, as calculated from the measured thermodynamic properties, and to melt at 179°C. The partial enthalpy and entropy of mixing have been obtained, and the negative entropy points to a structural order of the melt, presumably due to hydrogen bonding, as found earlier for the K 2 S 2 O 7 -KHSO 4 system. For each composition measured of the Na 2 S 2 O 7 -NaHSO 4 system in the molten state, the conductivity has been expressed by equations of the form κ )
Calphad, 2021
The binary subsystems of the quaternary system Na 2 SO 4-K 2 SO 4-MgSO 4-CaSO 4 were thermodynamically assessed using the available experimental information including own thermochemical and structure measurements. Phase equilibria and thermodynamic properties of all six binary systems were properly considered. The modified associate species model was successfully applied for the description of the liquid phase while the mutual solubility between various sulphates in the solid state was treated with appropriate multi-sublattice models. The resulting new databank being compatible with the general oxide database was used for the representation of the thermodynamic properties in the binary systems including phase equilibria, activity and mixing data. The calculations are in good agreement with the experimental data.
The conductivity of the Na 2 S 2 O 7 -NaHSO 4 binary system has been measured for 15 different compositions in the full composition range, and in the temperature range 400-700 K. Phase transition temperatures were obtained, and the phase diagram was constructed. It is of the simple eutectic type, where the eutectic is found to have the composition X NaHSO 4 ) 0.97, as calculated from the measured thermodynamic properties, and to melt at 179°C. The partial enthalpy and entropy of mixing have been obtained, and the negative entropy points to a structural order of the melt, presumably due to hydrogen bonding, as found earlier for the K 2 S 2 O 7 -KHSO 4 system. For each composition measured of the Na 2 S 2 O 7 -NaHSO 4 system in the molten state, the conductivity has been expressed by equations of the form κ )
Journal of Chemical & Engineering Data, 2000
Army European Research Office 223 Old Marylebone Road London, NW1 5TH Approved for public release; distribution unlimited. The U.S. Army is developing supercritical water oxidation for destruction of military toxic materials. The properties of high-temperature aqueous solutions are not, in most cases, well known. Understanding the phase behavior of these solutions will facilitate design and efficient operation of high-temperature water reactors. A U.S. Army workshop held at the Forschungzentrum Karlsruhe in July 1999 assembled experts on phase behavior to develop guidelines that, in the absence of more complete knowledge of solution properties, will aid reactor designers and operators. The experts presented papers on model systems, properties of high-temperature aqueous solutions, and chemistry in high-temperature water. Following these presentations, the experts developed some of the desired rules of thumb and made recommendations for research to develop these guidelines further. This workshop report includes the presentation papers, guidelines, and recommendations for research.
Minerale und Phasenbeziehungen im pseudotern�ren System Tl2SAs2S3Sb2S3 bei tiefen Temperaturen
The experimental determination of phase relations in the pseudoternary system T12S-As2S3-Sb2S 3 below 200 °C is practically impossible, especially so under dry condensed conditions. As thallium sulfosalts are naturally formed at low temperatures equilibrium phase assemblages at 100 and 200 °C were calculated by application of thermochemical approximations for the free enthalpies of formation of the sulfosalts. A comparison of the calculated conode configurations with the results of syntheses under dry condensed conditions at 200 °C yielded good agreement between experiment and calculations.
The Na-S (Sodium-Sulfur) system
Journal of Phase Equilibria, 1997
The Na-S system has been widely investigated for both theoretical (the nature of polysulfides) and practical reasons. Practical interest has centered on Na2S of particular importance in the pulp and paper industry [80War] and on the Na-S system as a basis for high-energy density batteries [83Jan]. Most of the reported data are confined to S-rich compositions.
IOP Conference Series: Materials Science and Engineering, 2018
There is a lag between the demand and supply of energy in today"s global scenario. Apart from that, the world is facing serious environmental challenges like global warming due to increased burning of fossil fuels. To mitigate this, people are focusing towards the renewable based energy technology. But harnessing energy from the renewable sources has its own challenges. They are intermittent sources of energy hence, some energy storage medium is necessary for the continuous supply of energy. The present study aims to evaluate the various characteristics of the phase change materials used as energy storage mediums. Various thermo physical properties like melting temperature, enthalpy values and specific heats capacities are calculated using Differential Scanning Calorimetry technique for high temperature PCM materials. In this study, Sodium nitrate and Potassium nitrate are taken as the PCMs because of their high melting temperature above 300 °C and they are widely used in concentrated solar powerplants as a heat transfer fluids.
Thermodynamic study of MgSO 4 – H 2 O system dehydration at low pressure in view of heat storage
Thermochimica Acta
Study about magnesium sulfatewater vapor equilibrium proved to be very interesting especially on the use of dehydration-hydration reactions for the heat storage application in recent research. Heat is realized by hydration of lower hydrates as this reaction is exothermic. Therefore, reversible reaction, endothermic thermal dehydration of higher hydrates, is used for charging of system and in this state the energy can be stored over long time. Even if magnesium sulfate appears as promising candidate with high theoretical energy density of 2.8 GJ/m-3 , technological process is rather complicated. The main problem that thermodynamic and kinetic data are poorly understood to present. In these study salt hydrates equilibrium of magnesium sulfate was investigated by new approach. It makes possible to understand the dehydration reaction of MgSO 4 •6H 2 O for heat storage application. Dehydration reaction under various water vapor pressures and temperatures were investigated by thermogravimetric analysis. The result showed that water content in the solid phase is a function of temperature for given water vapor pressure. So, we can conclude that this magnesium sulfatewater vapor system is bivariant and some hydrates appear as the non-stoichiometric hydrates.