Louis Schuffenecker

Thermodynamics of crystallization of sodium sulfate decahydrate in H2O–NaCl–Na2SO4: application to Na2SO4·10H2O-based latent heat storage materials

Abstract In this paper, we present a methodology for the prediction of the crystallization enthalpy of mirabilite (Na 2 SO 4 ·10H 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 ion-interaction 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 ·10H 2 O once the thermal equilibrium was reached. Good agreement was obtained between experimental and predicted values of crystallization enthalpies. Furthermore, we have studied the influence of NaCl used as an additive regarding the heat storage capacity of supersaturated H 2 O–Na 2 SO 4 solutions.

Use of Pitzer's model to calculate thermodynamic properties of aqueous electrolyte solutions of Na2SO4 + NaCl between 273.15 and 373.15 K

Abstract Pitzers model has been used to calculate various thermodynamic properties of NaCl–Na2SO4–H2O system. A methodology taking into account enthalpy and solubility data has been proposed. This leads to the proposal of a unique set of parameters allowing simultaneous representation of dissolution enthalpies, activity coefficients and solubility data in binary and ternary systems.

Dissolution of some normal alkanes in ethylbenzene: deduction of the enthalpy of mixing two n-alkanes in the solid state

Abstract Drop calorimetry has been used to measure the heat changes occurring upon the dissolution of some single n -alkanes (octadecane to tetracosane) or their binary mixtures (C 22 H 46 C 24 H 50 and C 23 H 48 C 24 H 50 ), in ethylbenzene, at 311.45 K. The enthalpy changes measured show the even-odd alternation effect known for n -alkanes. The binary mixtures show pronounced non-ideality. Their enthalpies of formation at 293.15 K were deduced from the measurement of their heats of dissolution in ethylbenzene and found to depend on the crystal type. It is shown that these mixtures may consist of several phases of solid solutions.

Dissolution enthalpy of NaCl in water at 25°C, 45°C and 60°C. Determination of the Pitzer's parameters of the {H2ONaCl} system and the molar dissolution enthalpy at infinite dilution of NaCl in water between 25°C and 100°C

The dissolution enthalpy of sodium chloride in water was measured until saturation at 24.4°C, 44.3°C and 59.2°C using a C80D differential calorimeter (SETARAM). The experimental data were fitted using Pitzers ion interaction model and the value of the dissolution enthalpy per mole of salt at infinite dilution was found at each temperature by treating ΔsolH∞ as adjustable parameter. Using these calorimetric measurements, the analytical expression of the variation of Pitzers parameters were established with respect to temperature. The validation of this expression is made by the measurement of vapour equilibrium of binary solution {H2ONaCl} closed to saturation. Excellent agreement between experimental and calculated values of water activity has been found using our Pitzers model parameters.

Diagramme de phases et proprietes thermodynamiques du systeme cadmium—plomb

Abstract A solid—liquid phase equilibrium diagram of cadmium—lead has been obtained by thermal analysis. The eutectic point is observed at TE = 520.9 ± 0.3 K for the mole fraction of lead xPb = 0.716 ± 0.004. The lack of solubility of lead in solid cadmium allows the calculation of the activity of cadmium along the liquidus curve for the mole fraction of lead xPb

Aqueous solution of sodium sulfate : determination of the dissolution enthalpy at 25, 27.5 and 45°C

Abstract The dissolution enthalpy of sodium sulfate in water was measured until saturation at 24.4, 27.5 and 44.3°C using a C80D differential calorimeter (Setaram). The experimental data were fitted using Pitzers ion interaction model and the value of the dissolution enthalpy per mole of salt at infinite dilution was found at each temperature, by treating ( Δ diss H ) ∞ as an adjustable parameter.

Thermodynamic properties of liquid (cadmium + lead)

Measurements of the vapour pressure of cadmium above {(1− x )Pb + x Cd}(1) have given activities of Cd over a large range of composition and of temperature. The results show that the partial molar excess enthalpy and partial molar excess entropy of Cd can be regarded as independent of the temperature. The value of the partial molar excess enthalpy of Cd in pure Pb(l) was also measured by calorimetry: H E (Cd, x → 0) = (9636±170) J mol −1 . All the results, associated with a precise study of solidification equilibria, permitted representation of the thermodynamic properties of Cd and Pb with the help of Margules developments, as functions of x , reliable from solidification to 1000 K: H E ( C d ) / J m o l − 1 = ( 1 − x ) 2 ( 9540 − 2280 x + 40777 x 2 − 86580 x 3 + 76530 x 4 ) , H E ( P b ) / J m o l − 1 = x 2 ( 10680 − 29465 x + 105712 x 2 − 147804 x 3 + 76530 x 4 ) , S E ( C d ) / J K − 1 m o l − 1 = ( 1 − x ) 2 ( 2.280 + 0.722 x + 16.648 x 2 − 52.656 x 3 + 55.605 x 4 ) , S E ( P b ) / J K − 1 m o l − 1 = x 2 ( 1.919 − 10.377 x + 56.140 x 2 − 97.140 x 3 + 55.605 x 4 ) . These expressions serve as evidence for a strong tendency to unmix, the limiting temperature of one-phase stability being very nearly the eutectic temperature.

Calorimetry and equilibrium measurements for the reaction of cadmium on divalent lead oxide between 740 and 1050 K Standard molar enthalpy of formation of cadmium oxide

Abstract The reduction equilibrium of yellow lead oxide by liquid cadmium: Cd(l) + PbO(yellow, s) = Pb(l) + CdO(s), has been studied between 740 and 1050 K by several methods: direct reaction calorimetry and equilibrium measurements. For the latter method, two different techniques were used: firstly, decantation of a (lead + cadmium) alloy, in equilibrium with the oxides, which is analysed; and secondly measurements of the vapor pressure of cadmium over the three-phase mixture. The measurements by the two methods lead to very concordant values of the standard enthalpy of reaction at about 800 K. The mean value is ΔH f o (800 K) = −(39.5 ± 1.0) kJ mol −1 . The equilibrium measurements give ΔG f o (800 K) = −(37.24 ± 0.11) kJ mol −1 . The results, reduced to 298.15 K, are compatible with the tabulated entropies. However, they indicate a more precise value of the standard enthalpy of formation of CdO: ΔH f o (CdO, s, 298.15 K) = −(255.7 ± 1.6) kJ mol −1 . The conditions of reaction of liquid cadmium with lead oxide and those of the oxidation of (lead + cadmium) alloys have been refined.