K. Adamkovičová

Enthalpic analysis of melts in the CaO · SiO2 (CS)-CaO · Al2O3 · 2SiO2 (CAS2) -2CaO · Al2O3 · SiO2 (C2AS) system

Abstract Relative enthalpies for melts in the CS-CAS2-C2AS system have been measured by combination of high-temperature drop calorimetry and solution calorimetry of the same sample at 298 K. From the measured values of relative enthalpy and from those determined using the literature data the temperature-composition dependences of relative enthalpy of melts related to 1 mol of mixture of the CS-CAS2-C2AS system and/or C(CaO)-A(Al2O3)-S(SiO2) system were determined. From these dependences the values of enthalpy of mixing in formation of melts of the CS-CAS2-C2AS system either from the melts of CS, CAS2 and C2AS, or from C, A and S, as well as the values of partial molar enthalpies of mixing of C, A and S in this system in the temperature interval 1600–1950 K, were calculated. The analysis has shown that the values of enthalpy of mixing in formation of the equilibrium melts in the CS-CAS2-C2AS system from melts of components CS, CAS2 and C2AS and/or C, A and S are mostly negative. In the region of compositions close to the binary system CAS2-C2AS and in this system itself, the melts in the temperature interval 1600–1950 K within the error range of ΔHmix behave as the athermic solutions. The formation of the athermic solutions in the CAS2-C2AS system shows that new structural particles are not created in mixing of both basic substances. Different structural roles of oxides are also evident.

Experimental determination of the heat of fusion and calculation of the dissociation degree and dissociation enthalpy of K3FMoO4

Abstract The molar enthalpy of fusion Δ fus H m of KF · K 2 MoO 4 at the temperature of fusion, 1025 K, was measured in the high-temperature Setaram HTC 1800K calorimeter as 58 ± 2 kJ mol −1 . This quantity, together with the known phase diagram of the system KFK 2 MoO 4 and the composition dependence of the enthalpy of mixing at 1273 K, enabled both the dissociation enthalpy Δ dis H and the dissociation degree α of the compound KF · K 2 MoO 4 to be calculated at the temperature of its fusion. The Le Chatelier—Shreder equation, derived without taking hypothetical equilibrium states into account, was also used. The most reliable values of the quantities are those obtained by an iterative procedure using a “quasi-athermal” solution model. Their values are Δ dis,+ H (1, 1025 K) = −1.2 kJ mol −1 and α + (KF · K 2 MoO 4 , 1025 K) = 0.51.

Enthalpic analysis of melts in the Ca2MgSi2O7CaSiO3 system

Abstract Relative enthalpies of the Ca 2 MgSi 2 O 7 CaSiO 3 system melts have been measured by combination of high-temperature drop calorimetry and solution calorimetry of the same sample in the temperature interval 1760–1930 K. From these results, the relative enthalpy-temperature-composition relation has been found by regression analysis. The enthalpy of mixing of melts is zero at any composition within the experimental errors of measurement. The heat capacities of melts do not depend on temperature and are a linear function of composition. They are discussed with values calculated employing Stebbins et al.s, Richet and Bottingas, and Lange and Navrotskys models.

Determination of enthalpy of fusion of K3FSO4

Abstract The enthalpy of melting of K3FSO4 at 1148 K has been determined using a hightemperature calorimeter, the Setaram HTC 1800 K. ΔfusHm(K3FSO4 is found to equal 86 ± 3 kJ mol−1. The given error is calculated at the level of reliability (1 - α) = 0.95.

Enthalpic analysis of the CaTiSiO5 system

The relative enthalpy of titanite and enthalpy of CaTiSiO5 melt have been measured using drop calorimetry between 823 K and 1843 K. Enthalpies of solution of titanite and CaTiSiO5 glass have been measured by the use of hydrofluoric acid solution calorimetry at 298 K. Enthalpy of vitrification at 298 K, δvitrH(298 K) = (80.7 ± 3.4) kJ mol−1, and enthalpy of fusion at the temperature of fusion 1656 K, δfusH(1656 K) = (139 ± 3) kJ mol−1, of titanite have been determined from experimental data. The obtained enthalpy of fusion is considerably higher than up to the present published values of this quantity.

Estimation of the heat of fusion of binary compounds and of eutectic using thermodynamic balances

Abstract Relations to calculate estimated enthalpies of fusion of binary compounds and eutectics at their equilibrium temperature in binary systems of inorganic substances, based on entropy or enthalpy balances, are presented. Their simplified forms were applied to estimate the enthalpy of fusion of equimolar compounds and binary eutectics in the Na 2 SO 4 -NaF and K 2 SO 4 -KF systems. Estimated enthalpies of fusion of NaF · Na 2 SO 4 and KF · K 2 SO 4 depend on simplified assumptions used for the calculation and are 7–13% lower than measured values. Relative errors of estimated enthalpies of fusion for eutectics, related to the values of these quantities calculated using experimental heats of fusion of binary compounds and measured enthalpies of mixing at corresponding eutectic composition, are within the limits 0–12% depending on input quantities.

Determination of the enthalpy of fusion of NaMgF3 and KMgF3

Abstract The enthalpy of melting of NaMgF3 and KMgF3 at the dystectic temperature of fusion of these compounds was determined using a high-temperature calorimeter, the Setaram HTC 1800 K. It was found that ΔfusHm(NaMgF3; 1303 K) = (66 ± 4) kJ mol−1 and ΔfusHm(KMgF3; 1343 K) = (96 ± 5) kJ mol−1. The given error is calculated at the level of reliability (1 − α) = 0.95.

Isoplethic enthalpies of heating in the systems CaO · SiO22CaO · Al2O3 · SiO2, CaO · SiO2CaO · Al2O3 · 2SiO2 and 2CaO · Al2O3 · SiO2CaO · Al2O3 · 2SiO2

Abstract Temperature dependences of the isoplethic enthalpy of heating Δ H isop,heat for compositions in the CaO · SiO 2 (CS)2CaO · Al 2 O 3 · SiO 2 (C 2 AS), CaO · SiO 2 CaO · Al 2 O 3 · 2SiO 2 (CAS 2 ) and 2CaO · Al 2 O 3 · SiO 2 CaO · Al 2 O 3 · 2SiO 2 systems were determined. These quantities were determined using the non-isothermal Hess law, relative enthalpies of individual phases and phase diagrams. The resulting plots allow the direct evaluation of Δ H isop,heat values between any two temperatures for a chosen composition. In the CS—C 2 AS and CS—CAS 2 systems, a narrow temperature range around 1800 K is present in which all mixtures with 0–0.4 CS have the same value of Δ H isop,heat of about 450 kJ mol −1 , but with different proportions of the coexisting phases. Within the single-phase melt region, the Δ Hisop,heat value of all three systems varies linearly with temperature.

Integral enthalpies of solution of components in the binary systems 2CaO · Al2O3 · SiO2-CaO · Al2O3 · 2SiO2, CaO · SiO2-CaO · Al2O3 · 2SiO2 and CaO · SiO2-2CaO · Al2O3 · SiO2

Abstract Integral enthalpies of solution for crystalline phases of one component in the melt of the second one were determined in the 2CaO · Al2O3 · SiO2-CaO · Al2O3 · 2SiO2, CaO · SiO2-CaO · Al2O3 · 2SiO2 and CaO · SiO2-2CaO · Al2O3 · SiO2 systems. Determinations were based on the composition and temperature dependences of the enthalpies of mixing for the binary systems, and on the temperature dependences of the heats of fusion for single components. In the CaO · SiO2-CaO · Al2O3 · 2SiO2 and CaO · SiO2-2CaO · Al2O3 · SiO2, systems we found out that the composition dependences of the integral enthalpy of solution go through extrema at low dilutions; this is due to characteristic composition dependences of the enthalpies of mixing.