High-temperature Drop Calorimetry Research Articles

High-temperature investigations of the rare earth NZP phosphates R1/3Zr 2(PO 4) 3 ( R = La, Nd, Eu, Lu) by drop calorimetry

The high-temperature enthalpy increments of the phosphates La 1/3Zr 2(PO 4) 3, Nd 1/3Zr 2(PO 4) 3, Eu 1/3Zr 2(PO 4) 3 and Lu 1/3Zr 2(PO 4) 3 have been measured by high-temperature drop calorimetry in the temperature range 484.5–1090.7 K. From these results the heat capacity of the studied compounds has been derived.

Thermochemistry and high-pressure equilibria of the post-perovskite phase transition in CaIrO3

To study the ambient analog of the deep mantle MgSiO 3 perovskite to post-perovskite phase transition, high-temperature drop calorimetry experiments of perovskite and post-perovskite phases of CaIrO 3 system as well as high-pressure phase equilibrium experiments in the CaIrO 3 system were made. The enthalpies for dissociation of CaIrO 3 (298 K) to CaO + Ir + O2 (1573 K) were 486.7 ± 9.2 kJ/mol for post-perovskite and 454.5 ± 12.5 kJ/mol for perovskite. From the difference between them, the phase transition enthalpy from perovskite to post-perovskite at 298 K is -32.2 ± 15.5 kJ/mol. This gives 2.7 ± 15.6 kJ/mol as formation enthalpy of CaIrO 3 perovskite from CaO + IrO 2 at 298 K. Using the phase transition enthalpy and volume change of .0.48 ± 0.02 cm 3 /mol determined in this study, the phase equilibrium boundary is calculated to be P (GPa) = 0.040 T (K) - 67.1. The strongly positive slope agrees with that obtained in high-pressure experiments. This is consistent with a large positive Clapeyron slope of post-perovskite phase transition in MgSiO 3 recently reported from experimental and theoretical studies.

The magnesium-ytterbium system: A contribution to the thermodynamics of solid alloys

Abstract Magnesium-ytterbium alloys were investigated in order to determine the enthalpy of formation of YbMg2 and to check the phase diagram of the system. The system was investigated by using differential scanning calorimetry, electron microscopy, electron microprobe analysis, and X-ray diffraction analysis. The enthalpy of formation was measured by high temperature drop calorimetry. A value of −13.5 ± 0.5kJ/mol of atoms was obtained for the standard formation enthalpy of YbMg2.

The Binary System In—Ir: A New Investigation of Phase Relationships, Crystal Structures, and Enthalpies of Mixing.

Abstract The In–Ir phase diagram was investigated by means of X-ray diffraction, electron probe microanalysis and thermal analysis. The existence of the two intermetallic compounds In 3 Ir and In 2 Ir was confirmed, and it was found, that In 3 Ir transforms into a low-temperature modification In 3 Ir-LT (CFe 3 -type structure, oP16, Pnma ) at temperatures below about 350 °C. The peritectic decomposition reaction of In 3 Ir and In 2 Ir at 981 °C and 1188 °C, resp., was confirmed. There are no indications of a liquid miscibility gap as suggested earlier in the literature. On the other hand, some of the experimental results point to the existence of a metastable high-temperature phase In 54 Ir 46 . Enthalpies of mixing were determined by high-temperature drop-calorimetry between 1190 and 1390 °C. The minimum in the extrapolated enthalpy of mixing curve is about −18 kJ mol −1 at a composition slightly above x Ir =0.5.

The binary system In–Ir: a new investigation of phase relationships, crystal structures, and enthalpies of mixing

The In–Ir phase diagram was investigated by means of X-ray diffraction, electron probe microanalysis and thermal analysis. The existence of the two intermetallic compounds In 3Ir and In 2Ir was confirmed, and it was found, that In 3Ir transforms into a low-temperature modification In 3Ir-LT (CFe 3-type structure, oP16, Pnma) at temperatures below about 350 °C. The peritectic decomposition reaction of In 3Ir and In 2Ir at 981 °C and 1188 °C, resp., was confirmed. There are no indications of a liquid miscibility gap as suggested earlier in the literature. On the other hand, some of the experimental results point to the existence of a metastable high-temperature phase In 54Ir 46. Enthalpies of mixing were determined by high-temperature drop-calorimetry between 1190 and 1390 °C. The minimum in the extrapolated enthalpy of mixing curve is about −18 kJ mol −1 at a composition slightly above x Ir=0.5.

The thermodynamic properties ofSrBaFe4O8(s)fromT → 0 toT = 1500 K

The low-temperature adiabatic heat capacity of SrBaFe4O8(s) has been measured fromT= 4 K to T= 420 K, yielding for Cop,m and Som at T= 298.15 K, the values ( 288.9 ± 0.3)J · K−1 · mol−1 and ( 338.0 ± 0.3)J · K−1 · mol−1, respectively. The enthalpy increment function for the above ambient temperature has been obtained from high-temperature drop calorimetry measurements over the temperature range 525 K to 882 K. In addition, the standard molar enthalpy of formation has been derived from the standard molar enthalpies of solution in (2.65 mol · dm−3 HCl + 1.76 mol · dm−3 HNO3)(aq) using an isoperibol solution calorimeter. From these measurements and auxiliary data, the following value has been obtained:ΔfHom (298.15 K){ SrBaFe4O8(s) } =−(2888.0 ± 5.0)kJ · mol−1. A table containing the thermodynamic properties at selected temperatures from 298.15 K to 1500 K is given.

The heat capacity of NdAlO 3 from 0 to 900 K

The heat capacity of neodymium aluminate NdAlO 3 has been measured by low-temperature adiabatic calorimetry from 4 to 420 K, yielding S 0 (298.15 K)=(99.3±0.3) J K −1 mol −1. For temperatures up to 900 K the heat capacity has been derived from enthalpy-increment measurements (520–880 K) using high-temperature drop calorimetry. The two sets of calorimetric data are in excellent agreement and show no transition in the measured temperature range.

The heat capacity of Y 3Al 5O 12 from 0 to 900 K

The heat capacity of yttrium aluminium garnet Y 3Al 5O 12 (YAG) has been measured by low-temperature adiabatic calorimetry from 5 to 420 K. For temperatures up to 900 K the heat capacity has been derived from enthalpy-increment measurements (470–880 K) using high-temperature drop calorimetry. The two sets of calorimetric data join smoothly and show no transition in the measured temperature range.

The thermodynamic properties of Sr3MgSi2O8(s) fromT=(0 to 1500) K

The low-temperature adiabatic heat capacity of Sr3MgSi2O8(s) has been measured fromT=(4 to 420) K, yielding forCp° andS° atT=298.15 K the values (257.35±0.60) J·K−1·mol−1and (280.15±0.60) J·K−1·mol−1, respectively. The enthalpy increment function for temperatures above the ambient one has been obtained using high-temperature drop calorimetry measurements fromT=(525 to 910) K. In addition, the standard molar enthalpy of formation has been derived from the standard molar enthalpies of solution in (3.1 mol·dm−3HCl+3.2 mol·dm−3HF)(aq) using an isoperibol solution calorimeter. From these measurements and the auxiliary data, the following value has been obtained: ΔfHm°(298.15 K){Sr3MgSi2O8(s)}=−(4575.3±5.1) kJ·mol−1. A table containing the thermodynamic properties at selected temperatures from (298.15 to 1500) K is provided.

Melting enthalpies of mantle peridotite: calorimetric determinations in the system CaO-MgO-Al 2O 3-SiO 2 and application to magma generation

High-temperature drop calorimetry in the temperature range of 1398–1785 K was performed for the samples of mixtures of synthetic anorthite (An), diopside (Di), enstatite (En) and forsterite (Fo) with the same compositions as those of primary melts generated at 1.1, 3 and 4 GPa at most 10° above the solidus of anhydrous mantle peridotite in the CaO-MgO-Al 2O 3-SiO 2 system. From the differences between the heat contents ( H T-H 298 ) of liquid and that of crystal mixture at the liquidus temperature, melting enthalpies of the samples of 1.1, 3 and 4 GPa-primary melt compositions were determined at 1 atm to be 531 ± 39 J · g −1 at 1583 K, 604 ± 21 J · g −1 at 1703 K, 646 ± 21 J · g −1 at 1753 K, respectively. These heat of fusion values suggest that mixing enthalpy of the melt in the An-Di-En-Fo system is approximately zero within the experimental errors when we use the heat of fusion of Fo by Richet et al. (P. Richet, F. Leclerc, L. Benoist, Melting of forsterite and spinel, with implications for the glass transition of Mg 2SiO 4 liquid, Geophys. Res. Lett. 20 (1993) 1675–1678). The measured enthalpies of melting at 1 atm were converted into those for melting reactions which occur under high pressures by correcting enthalpy changes associated with solid-state mineral reactions. Correcting the effects of pressure, temperature and FeO and Na 2O components on the melting enthalpies at 1 atm, heat of fusion values of a representative mantle peridotite just above the solidus under high pressure were estimated to be 590 J at 1.1 GPa and 1523 K, 692 J at 3 GPa and 1773 K, and 807 J at 4 GPa and 1923 K for melting reactions producing liquid of 1 g, with uncertainties of 50 J. By applying these melting enthalpies to a mantle diapir model which generates present MORBs, a potential mantle temperature of 1533 K has been estimated, assuming an eruption temperature of magma of 1473 K.

Enthalpic analysis of melts in the Ca 2MgSi 2O 7CaSiO 3 system

Relative enthalpies of the Ca 2MgSi 2O 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 Bottinga's, and Lange and Navrotsky's models.

Standard enthalpy of formation of Cu 3As and heats of mixing in the liquid systems CuAs and FeAs by direct combination high temperature drop calorimetry

The standard enthalpy of formation of the congruent melting compound Cu 3As (m.p. 1000 K) was determined by high temperature direct synthesis drop calorimetry in fused silica capsules at 1113 K. We found ΔH f o (298 K) = −14.6 ± 3.8 kJ mol −1. Using our measured values of the heats of reaction of the process aAs(s)+ bCu(s) → cCu 1− x As x (1) at 1113 K, we calculated the liquid-liquid enthalpies of mixing for three alloy compositions in Cu 1− x As x : x=0.235, 0.26 and 0.375. We carried out similar measurements at 1123 K for the eutectic alloy Fe 1− x As x (1) at x = 0.24. The calorimetric results for the solid and liquid alloys are compared with predicted values from Miedema's semiempirical model.

Superconducting, structural and thermochemical properties of La 2CuO 4+δ prepared by KMnO 4 oxidation

La 2CuO 4+δ having various δ values was prepared by the KMnO 4 oxidation method in aqueous solutions at 333 K. Some samples oxidized in concentrated KMnO 4 solutions underwent spinodal decomposition resulting in products having δ∼0.01 and δ∼0.22. The former showed a superconducting transition at ∼ 14 K, the latter at 40 K. The partial molar enthalpy of excess oxygen up to ∼ -57 kJ/mol O was obtained for La 2CuO 4+δ by high-temperature drop calorimetry. This value suggests that La 2CuO 4+δ is, disregarding the spinodal decomposition, thermodynamically stable in oxygen fugacities less than 1 atm at room temperature.

Enthalpic analysis of melts in the CaO · SiO 2 (CS)-CaO · Al 2O 3 · 2SiO 2 (CAS 2) -2CaO · Al 2O 3 · SiO 2 (C 2AS) system

Relative enthalpies for melts in the CS-CAS 2-C 2AS 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-CAS 2-C 2AS system and/or C(CaO)-A(Al 2O 3)-S(SiO 2) system were determined. From these dependences the values of enthalpy of mixing in formation of melts of the CS-CAS 2-C 2AS system either from the melts of CS, CAS 2 and C 2AS, 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-CAS 2-C 2AS system from melts of components CS, CAS 2 and C 2AS and/or C, A and S are mostly negative. In the region of compositions close to the binary system CAS 2-C 2AS and in this system itself, the melts in the temperature interval 1600–1950 K within the error range of ΔH mix behave as the athermic solutions. The formation of the athermic solutions in the CAS 2-C 2AS system shows that new structural particles are not created in mixing of both basic substances. Different structural roles of oxides are also evident.

Determination of the standard enthalpy of formation of Ni 2.55P by high-temperature drop calorimetry

We have determined ΔfHom(Ni2.55P, cr, 298.15 K) by high-temperature drop calorimetry using two methods. In the first procedure, we measured ΔrHm for 2.55 N i ( c r ) + P ( r e d , a m ) = N i 2.55 P ( m i x ) at 298.15 K by drop calorimetry at a reference temperature of 907 K. The designation “mix” indicates a mixture of Ni3P, Ni2.55P, and Ni12P5 with an overall composition of Ni2.55P. We then used solution drop-calorimetry at a reference temperature of 1181 K to determine ΔrHm for N i 2.55 P ( m i x ) = N i 2.55 P ( c r ) at 298.15 K. These results were combined to give the result for ΔrHm of the reaction: 2.55 N i ( c r ) + P ( r e d , a m ) = N i 2.55 P ( c r ) at 298.15 K of −(188 ± 5) kJ · mol−1. In our second procedure, we used solution drop-calorimetry alone to determine a value for ΔrHm for the reaction: 2.55 N i ( c r ) + P ( r e d , a m ) = N i 2.55 P ( c r ) at 298.15 K of −(181 ± 5) kJ · mol−1. We have taken the mean of these values and applied a correction for ΔfHom(P, red, am, 298.15 K) to obtain a value for ΔfHom(Ni2.55P, cr, 298.15 K) of −(180 ± 8) kJ · mol−1 where the reference state of phosphorus is P(black, orthorhombic).

Thermodynamic properties of glaucophane new data from calorimetric and spectroscopic measurements

New data concerning glaucophane are presented. New high temperature drop calorimetry data from 400 to 800 K are used to constrain the heat capacity at high temperature. Unpublished low temperature calorimetric data are used to estimate entropy up to 900 K. These data, corrected for composition, are fitted for C p and S to the polynomial expressions (J · mol−1 · K−2) for T> 298.15 K: $$\begin{gathered} C_p = 11.4209 * 10^2 - 40.3212 * 10^2 /T^{{1 \mathord{\left/ {\vphantom {1 2}} \right. \kern-\nulldelimiterspace} 2}} - 41.00068 * 10^6 /T^2 \hfill \\ + 52.1113 * 10^8 /T^3 \hfill \\ \end{gathered} $$ $$\begin{gathered} S = 539 + 11.4209 * 10^2 * \left( {\ln T - \ln 298.15} \right) - 80.6424 * 10^2 \hfill \\ * \left( {T^{ - {1 \mathord{\left/ {\vphantom {1 2}} \right. \kern-\nulldelimiterspace} 2}} - 1/\left( {298.15} \right)^{{1 \mathord{\left/ {\vphantom {1 2}} \right. \kern-\nulldelimiterspace} 2}} } \right) + 20.50034 * 10^6 \hfill \\ * \left( {T^{ - 2} - 1/\left( {298.15} \right)^2 } \right) - 17.3704 * 10^8 * \left( {T^{ - 3} - \left( {1/298.15} \right)^3 } \right) \hfill \\ \end{gathered} $$ IR and Raman spectra from 50 to 3600 cm−1 obtained on glaucophane crystals close to the end member composition are also presented. These spectroscopic data are used with other data (thermal expansion, acoustic velocities etc.) in vibrational modelling. This last method provides an independent way for the determination of the thermodynamic properties (Cp and entropy). The agreement between measured and calculated properties is excellent (less than 2% difference between 100 and 1000 K). It is therefore expected that vibrational modelling could be applied to other amphiboles for which spectroscopic data are available. Finally, the enthalpy of formation of glaucophane is calculated.

Heat capacity of some liquid Zintl compounds: Equiatomic alkali–lead alloys

Enthalpies for equiatomic APb (A=Na, Rb, and Cs) have been measured by high-temperature drop calorimetry over a temperature range covering solid and liquid phases. Thermodynamic information on the solid state transitions and the melting process is derived. With the exception of NaPb, the heat capacities of the liquid alloys show a remarkably strong negative temperature dependence above the melting point. It is suggested that this behavior is a consequence of the dissociation of molecular entities present in the liquid state related to the Zintl structures detected in the corresponding solid compounds. Thermodynamic calculations based on the presence of polyvalently charged anions yield valuable information on the temperature dependence of the concentration of these species.

Heat capacity of liquid equiatomic potassium–lead alloy: Anomalous temperature dependence

The temperature dependence of the enthalpy function for the equiatomic K0.5Pb0.5 alloy has been determined using high-temperature drop calorimetry over the temperature range 751–1124 K. Unusually large values for the heat capacity of the liquid equiatomic alloy have been derived in the vicinity of the melting point, which was determined as Tm=862±2 K; also, the temperature coefficient of the heat capacity was found to be anomalously large and negative. Such behavior is consistent with the previously reported compositional dependence of the heat capacity in liquid K–Pb alloys deduced from electromotive force measurements. At relatively high temperatures, the heat capacity drops to values typical of metallic solutions. Possible interpretations of this striking behavior include an order–disorder transition in the liquid and/or the formation of lead clusters, such as Pbm−m.

Standard molar enthalpies of formation of KCdCl 3 and K 4CdCl 6 by high-temperature drop calorimetry

Enthalpies of the synthesis reactions of the two compounds KCdCl 3(cr) and K 4CdCl 6(cr) from KCl(cr) and CdCl 2(cr) have been measured by drop calorimetry of solid samples of KCl, CdCl 2, KCdCl 3, and K 4CdCl 6 into melted mixtures of KCl and CdCl 2. For the two reactions: (1), CdCl 2(cr)+KCl(cr) = KCdCl 3(cr); and (2), CdCl 2(cr)+4KCl(cr) = K 4CdCl 6(cr), the experiments lead to the two standard molar enthalpies of reaction at 298.15 K: Δ 1 H m o = −(21.7±1.0) kJ·mol −1 and Δ 2 H m o = −(39.0±3.8) kJ·mol −1. These values are not in good agreement with those of previous workers.

Thermodynamic properties of tricesium chromium(V) tetroxide (Cs 3CrO 4)

Low-temperature and solution-calorimetric investigations of Cs 3CrO 4 have yielded the following thermodynamic properties at T = 298.15 K: S°=(296.2±1.5)JK -1mol -1, C° p=(179.9±0.5)JK -1mol -1,-{ G°( T- H°(0)}=(169.0±0.8)JK -1mol -1,{ H°(T)- H°(0)}=(37.912±0.114)kJ mol -1 and δ H° f=-(1543.13±2.66)kJ mol -1 An unusual feature of the solution calorimetry was the use of aqueous xenon trioxide, XeO 3(aq). as oxidant. High-temperature drop calorimetry revealed a solid-to-solid (β-to-γ) transition at 774 K with ΔH tr = 1.8 kJ mol −1 and ΔS tr = 2.3 J K −1 mol −1. Below the transition temperature. the enthalpy increment as a function of temperature is best represented by { H°(T)- H°(298.15K)}/J mol -1=-46804.3+135.625( T K )+6.633544×10 -2( T K ) 2+1.777146×10 -5( T K ) 3 ,and, above the transition, by { H°(T)- H°(298.15K)}/J mol -1=-38654.8+155.722( T K )+4.35257×10 -2( T K ) 2 A table of thermodynamic functions to 1000 K is given.