Drop Solution Calorimetry Research Articles

Energetics of sodium-calcium exchanged zeolite A.

A series of calcium-exchanged zeolite A samples with different degrees of exchange were prepared. They were characterized by powder X-ray diffraction (XRD) and differential scanning calorimetry (DSC). High temperature oxide melt drop solution calorimetry measured the formation enthalpies of hydrated zeolites CaNa-A from constituent oxides. The water content is a linear function of the degree of exchange, ranging from 20.54% for Na-A to 23.77% for 97.9% CaNa-A. The enthalpies of formation (from oxides) at 25 °C are -74.50 ± 1.21 kJ mol(-1) TO2 for hydrated zeolite Na-A and -30.79 ± 1.64 kJ mol(-1) TO2 for hydrated zeolite 97.9% CaNa-A. Dehydration enthalpies obtained from differential scanning calorimetry are 32.0 kJ mol(-1) H2O for hydrated zeolite Na-A and 20.5 kJ mol(-1) H2O for hydrated zeolite 97.9% CaNa-A. Enthalpies of formation of Ca-exchanged zeolites A are less exothermic than for zeolite Na-A. A linear relationship between the formation enthalpy and the extent of calcium substitution was observed. The energetic effect of Ca-exchange on zeolite A is discussed with an emphasis on the complex interactions between the zeolite framework, cations, and water.

New experimental heat capacity and enthalpy of formation of lithium cobalt oxide

The heat capacity of LiCoO2 (O3-phase), constituent material in cathodes for lithium-ion batteries, was measured using two differential scanning calorimeters over the temperature range from (160 to 953)K (continuous method). As an alternative, the discontinuous method was employed over the temperature range from (493 to 693)K using a third calorimeter. Based on the results obtained, the enthalpy increment of LiCoO2 was derived from T=298.15K up to 974.15K. Very good agreement was obtained between the derived enthalpy increment and our independent measurements of enthalpy increment using transposed temperature drop calorimetry at 974.15K. In addition, values of the enthalpy of formation of LiCoO2 from the constituent oxides and elements were assessed based on measurements of enthalpy of dissolution using high temperature oxide melt drop solution calorimetry. The high temperature values obtained by these measurements are key input data in safety analysis and optimisation of the battery management systems which accounts for possible thermal runaway events.

Energetics of metastudtite and implications for nuclear waste alteration.

Metastudtite, (UO2)O2(H2O)2, is one of two known natural peroxide minerals, but little is established about its thermodynamic stability. In this work, its standard enthalpy of formation, -1,779.6 ± 1.9 kJ/mol, was obtained by high temperature oxide melt drop solution calorimetry. Decomposition of synthetic metastudtite was characterized by thermogravimetry and differential scanning calorimetry (DSC) with ex situ X-ray diffraction analysis. Four decomposition steps were observed in oxygen atmosphere: water loss around 220 °C associated with an endothermic heat effect accompanied by amorphization; another water loss from 400 °C to 530 °C; oxygen loss from amorphous UO3 to crystallize orthorhombic α-UO2.9; and reduction to crystalline U3O8. This detailed characterization allowed calculation of formation enthalpy from heat effects on decomposition measured by DSC and by transposed temperature drop calorimetry, and both these values agree with that from drop solution calorimetry. The data explain the irreversible transformation from studtite to metastudtite, the conditions under which metastudtite may form, and its significant role in the oxidation, corrosion, and dissolution of nuclear fuel in contact with water.

Thermochemistry, Morphology, and Optical Characterization of Germanium Allotropes

A thermochemical study of three germanium allotropes by differential scanning calorimetry (DSC) and oxidative high-temperature drop solution calorimetry with sodium molybdate as the solvent is described. Two allotropes, microcrystalline allo-Ge (m-allo-Ge) and 4H-Ge, have been prepared by topotactic deintercalation of Li7Ge12 with methanol (m-allo-Ge) and subsequent annealing at 250 °C (4H-Ge). Transition enthalpies determined by differential scanning calorimetry amount to 4.96(5) ± 0.59 kJ/mol (m-allo-Ge) and 1.46 ± 0.55 kJ/mol (4H-Ge). From high-temperature drop solution calorimetry, they are energetically less stable by 2.71 ± 2.79 kJ/mol (m-allo-Ge) and 5.76 ± 5.12 kJ/mol (4H-Ge) than α-Ge, which is the stable form of germanium under ambient conditions. These data are in agreement with DSC, as well as with the previous quantum chemical calculations. The morphology of the m-allo-Ge and 4H-Ge crystallites was investigated by a combination of scanning electron microscopy, transmission electron microscopy, and atomic force microscopy. Even though the crystal structures of m-allo-Ge and 4H-Ge cannot be considered as truly layered, these phases retain the crystalline morphology of the layered precursor Li7Ge12. Investigation by diffuse reflectance infrared Fourier transform spectroscopy and UV–vis diffuse reflectance measurements reveal band gaps in agreement with quantum chemical calculations.

Surface and grain boundary energies of tin dioxide at low and high temperatures and effects on densification behavior

Abstract

Surface Energetics of Nanoscale LaMnO3+δ Perovskite

Perovskite type LaMnO3 and related materials are important compounds with many useful and unique physical and chemical properties. There is a lack of experimental thermochemical data on the energetics of LaMnO3 nanoparticles. In this work, a series of LaMnO3+δ samples were synthesized via the citrate method and calcined at 700°C–1050°C. All samples displayed rhombohedral structure (X‐ray diffraction) with similar oxygen stoichiometry 3+δ = 3.16–3.18 (iodometric titration coupled with gravimetric analysis). The BET surface area varied from null for bulk sample to 6.88 ± 0.08 × 103 m2/mol for the sample calcined at 700°C. The water content varied linearly with the surface area with the highest value being 2.34 wt%. The chemisorbed water adsorption enthalpy was −63.0 ± 4.1 kJ/mol with the chemisorbed water coverage of 8 H2O/nm2. High‐temperature oxide melt drop solution calorimetry, performed in sodium molybdate at 702°C, yielded enthalpy of formation from La2O3, Mn2O3, and O2 of bulk LaMnO3.16 of −77.85 ± 1.94 kJ/mol. After correction of drop solution enthalpies of nanometric samples for water content, the calorimetric data were used to calculate the surface energy of LaMnO3+δ. The energy of the anhydrous surface was 2.27 ± 0.29 J/m2, and that of the hydrous surface was 2.02 ± 0.27 J/m2. These values are higher than the surface energies of LaMnO3.00 predicted elsewhere by theoretical methods, probably due to the different oxygen content and possibly more complex surface structure and exposed surface planes. The measured surface energy of LaMnO3+δ lies between the values reported recently for BaTiO3 and PbTiO3 and close to the reported values for MnO2. This suggests that LaMnO3+δ surface is predominantly MnO2‐terminated, in line with the trends predicted by theoretical calculations.

Thermodynamic investigation on β- and γ-Ca3(PO4)2 and the phase equilibria

γ-Ca3(PO4)2, naturally known as tuite, is regarded as an important potential reservoir for rare earth elements and large ion lithophile elements. It is a high-pressure polymorph of β-Ca3(PO4)2 whitlockite and a decomposed product of apatite under high-pressure and temperature. Drop-solution enthalpies of β- and γ-Ca3(PO4)2 were obtained as 298.59±3.02 and 278.74±2.98kJ/mol, respectively, by the drop-solution calorimetry with 2PbO·B2O3 solvent at 978K. Thus the enthalpy of transition from β- to γ-Ca3(PO4)2 at 298K (ΔHtr,298o) was 19.85±4.24kJ/mol. The isobaric heat capacities of β- and γ-Ca3(PO4)2 were measured at temperature range of 300–770K by differential scanning calorimetry, and compared with the results calculated from the Kieffer model. The equilibrium phase boundary between β- and γ-Ca3(PO4)2 was calculated using present measured data combined with other available thermochemical and thermoelastic data. The calculated boundary gave a phase transition boundary with a dP/dT slope of 4.7±0.2MPa/K in the temperature range of 900–2000K. Based on the phase relationship, the occurrences of tuite and whitlockite in meteorites are discussed.

ChemInform Abstract: Energetics of Dysprosia‐Stabilized Bismuth Oxide Electrolytes.

AbstractDysprosia‐stabilized bismuth oxides DyxBi1‐xO1.5 (x = 0.11—0.45) are prepared by solid state reaction of appropriate amounts of BiO1.5 and DyO1.5 (alumina crucible, 850—950 °C, 12 h) and their energetics are characterized by drop solution calorimetry in molten 3Na2O·4MoO3 at 702 °C.

Thermodynamic investigation on phase equilibrium boundary between calcium ferrite-type MgAl2O4 and MgO + α-Al2O3

Calcium ferrite-type MgAl2O4 is an important endmember of the calcium ferrite phase, which is a high-pressure constituent mineral of mid-ocean ridge basalt at lower mantle conditions. Drop-solution enthalpies of the calcium ferrite-type MgAl2O4 and a mixture of MgO and α-Al2O3 with a mol ratio of 1:1 were measured as 109.18±1.10 and 140.41±0.85kJ/mol, respectively, by drop-solution calorimetry with 2PbO·B2O3 solvent at 978K. As determined by differences in the drop-solution enthalpies, the formation enthalpy of calcium ferrite-type MgAl2O4 from oxides at 298K (ΔfH°298) was 31.23±1.39kJ/mol. To thermodynamically calculate the phase boundary between calcium ferrite-type MgAl2O4 and MgO+α-Al2O3, the ΔfH°298 was used together with the other thermochemical and thermoelastic data for calcium ferrite-type MgAl2O4, i.e., heat capacity and entropy estimated by the lattice vibrational calculation, thermal expansivity calculated from the Grüneisen equation, and isothermal bulk modulus and its pressure and temperature derivatives determined by Sueda et al. (2009). The calculated boundary gave a phase transition pressure of 26.6GPa at 1873K with a slope of −0.006GPa/K. This phase boundary is potentially applicable to a high-pressure calibration standard.

Thermodynamics of the magnetite-ulvospinel (Fe3O4-Fe2TiO4) solid solution

The thermodynamics of mixing and its dependence on cation distribution in the Fe3O4–Fe2TiO4 (magnetite-ulvospinel) spinel solid solution were studied using high-temperature oxide melt solution calorimetry and a range of structural and spectroscopic probes. The enthalpies of formation of ilmenite and ulvospinel from the oxides and from the elements were obtained using oxidative drop solution calorimetry at 973 K in molten sodium molybdate. The enthalpy of mixing, determined from the fit to the measured enthalpies of drop solution calorimetry, is endothermic and represented by a quadratic formalism, Δ H mix = (22.60 ± 8.46) x (1 − x ) kJ/mol, where x is the mole fraction of ulvospinel. The entropies of mixing are more complex than those for a regular solution and have been calculated based on average measured and theoretical cation distributions. Calculated free energies of mixing show evidence for a solvus at low temperature in good agreement with that observed experimentally.

Effect of boron on the thermodynamic stability of amorphous polymer-derived Si[sbnd](B[sbnd])C[sbnd]N ceramics

The reason for the higher thermal persistence of amorphous polymer-derived SiBCN ceramics (T∼1700–2000°C) compared to SiCN ones (T∼1500°C) has been a matter of debate for more than a decade. Despite recent experimental results which indicate a major kinetic effect of boron on the thermal persistence of the ceramics, no experimental investigation of the thermodynamic stability of the materials has been reported. In this work, we present measured energetics of a series of the amorphous ceramics with various boron contents (0–8.3at.%) using high-temperature oxidative drop-solution calorimetry. Through measurement of the drop-solution enthalpies in molten sodium molybdate at 811°C, the formation enthalpies of the amorphous ceramics from crystalline components (SiC, BN, Si3N4, C) at 25°C were obtained and found to be between −1.4 and −26.6kJg-atom−1. The determined enthalpy data plus the estimated positive entropy of formation values point to the thermodynamic stability of the amorphous ceramics relative to the crystalline phases, but such stabilization diminishes with increasing boron content. In contrast, the higher boron content increases the temperature of Si3N4 crystallization despite less favorable energetics for the amorphous phase, implying more favorable energetics for crystallization. Thus the so-called “stability” of SiBCN ceramics in terms of persistence against Si3N4 crystallization appears to be controlled by kinetics rather than by thermodynamic stability.

Oxide melt solution calorimetry of Fe2+-bearing oxides and application to the magnetite-maghemite (Fe3O4-Fe8/3O4) system

A consistent methodology for obtaining the enthalpy of formation of Fe2+-containing binary and multicomponent oxides using high-temperature oxide melt solution calorimetry has been developed. The enthalpies of wüstite (FeO) and magnetite (Fe3O4) oxidation to hematite (Fe2O3) were measured using oxidative drop solution calorimetry in which the final product is dissolved ferric oxide. Two methods were applied: drop solution calorimetry at 1073 K in lead borate solvent and at 973 K in sodium molybdate, each under both oxygen flowing over and bubbling through the solvent, giving consistent results in agreement with literature values. The enthalpies of formation of all three iron oxides from the elements were obtained using a thermodynamic cycle involving the directly measured oxidative dissolution enthalpy of iron metal in sodium molybdate at 973 K and gave excellent consistency with literature data.

Fluorite-pyrochlore transformation in Eu2Zr2O7—direct calorimetric measurement of phase transition, formation and surface enthalpies

The energetics of the order-disorder phase transformation in the binary oxide system, Eu2O3–ZrO2, is studied by powder X-ray diffraction and high temperature drop solution calorimetry. The nanocrystalline defect fluorite phase of Eu2Zr2O7 is synthesized on crystallization of an amorphous precursor from aqueous precipitation. The defect fluorite transforms to an ordered pyrochlore above 1200 °C. Aerodynamic levitation combined with laser heating is used to prepare coarse defect fluorite, which is otherwise impossible by conventional synthesis techniques. Formation enthalpies from oxides are −62.4 ± 2.6 and −24.6 ± 3.7 kJ mol−1 for the pyrochlore and defect fluorite phase, respectively. The transformation enthalpy from pyrochlore to defect flourite in the coarse sample is 37.8 ± 3.1 kJ mol−1 at 25 °C. The enthalpy of water vapor adsorption on the surface of the nanocrystalline defect fluorite Eu2Zr2O7 is −75 ± 2.5 kJ mol−1 H2O for coverage of 9.5 ± 0.8 H2O/nm2. The calculated surface enthalpies for the anhydrous and hydrous surfaces of defect fluorite Eu2Zr2O7 are 1.47 ± 0.13 and 1.01 ± 0.15 J m−2, respectively.

Energetics of cation mixing in urania–ceria solid solutions with stoichiometric oxygen concentrations

Cation mixing energetics in urania-ceria solid solutions with stoichiometric oxygen concentrations (U(1-y)Ce(y)O(2)) have been measured by high-temperature oxide-melt drop-solution calorimetry. Measurements have been performed on eight samples with compositions spanning y = 0.119 to y = 0.815. The measured mixing enthalpies (ΔH(mix)) range from -0.6 ± 3.3 to 3.9 ± 3.0 kJ mol(-1). These values are discussed in the context of results from atomistic modeling which take into consideration the possibility of charge transfer between uranium and cerium cations to form solid solutions with mixed charge states. A comparison between measured and calculated results for ΔH(mix) suggests that such charge transfer takes place to a limited extent in the most concentrated mixtures studied.

Thermochemistry of La 0.7Sr 0.3Mn 1− xFe xO 3 solid solutions (0< x

The structure, the energetics and the internal redox reactions of La 0.7Sr 0.3Fe x Mn 1− x O 3 have been studied in the complete solid solution range 0.0< x<1.0. High temperature oxide melt drop solution calorimetry was performed to determine the enthalpies of formation from binary oxides and the enthalpy of mixing. There is a noticeable change in the energetics of the solid solution near x=0.7, which is due to the growing concentration of Fe 4+ at higher Fe/(Fe+Mn) ratio. The balance between different valences of the transition metals, Mn and Fe, is the main factor in determining the energetics of the La 0.70Sr 0.30Fe x Mn 1− x O 3 solid solution.

The Effect of Vacancy and Barium Substitution on the Stability of the Cesium Titanium Silicate Pollucite

Cesium titanium silicate (CsTiSi2O6.5) is a titanium analogue of pollucite CsAlSi2O6 and a possible ceramic form for immobilization of short‐lived fission products in radioactive waste. Through β decay, cesium (Cs) decays to barium. Therefore, not only the stability of Cs‐loaded waste forms, but also that of a potential decay product series is of fundamental importance. Ba‐substituted CsTiSi2O6.5 is a potential β decay product with the pollucite structure. Here, we report the effects of the reaction synthesis condition and the study of the thermodynamic stability of potential intermediates in the decay product series (1) with charge‐balance in pollucite as two Cs ions are replaced by one Ba and a vacancy and (2) with one‐to‐one replacement of Cs by Ba. The enthalpies of formation of Ba‐substituted CsTiSi2O6.5 were obtained from drop solution calorimetry in a molten lead borate solvent at 702°C. The enthalpies of formation, from constituent oxides, are exothermic and it decreases with increasing Ba content. The effect of vacancies in the pollucite structure is a more dominant factor in the energetics than that of Ba replacement. The thermodynamic effects of acetate and/or nitrate precursors and of adding acetic acid during synthesis of single phase Ba‐substituted CsTiSi2O6.5 pollucite are insignificant except for the sample prepared from acetate precursors without acid treatment.

Thermochemistry and Crystallization of Glass‐Forming Y‐Substituted Sr‐Analogues of Fresnoite (Sr2TiSi2O8)

Strontium titanosilicate (Sr2TiSi2O8) is the Sr‐analogue of fresnoite (Ba2TiSi2O8). It may provide useful properties due to the unusual five‐coordinate titanium in its structure. Sr2TiSi2O8 is also a possible oxide form for the immobilization of short‐lived fission products in radioactive waste. Through β decay, strontium decays to yttrium and then to zirconium. Therefore, not only the stability of Sr‐loaded waste forms but also that of a potential decay product series with charge‐balance in a naturally occurring mineral or ceramic is of fundamental importance. To incorporate the reaction 3Sr2+=2Y3++vacancy in the fresnoite composition, Y‐substituted Sr‐analogues of fresnoite, (Sr2−xY2/3x)TiSi2O8 (x=0, 0.5, 0.75, 1, 1.25, and 1.5) were prepared by a high‐temperature synthesis and were found to form glass upon cooling. The Y‐end‐member (Y1.33TiSi2O8, x=2) crystallized to a mixture of Y2TiSiO7, TiO2, and SiO2 upon quenching in air. The enthalpies of formation of Y‐substituted Sr‐fresnoite glasses were obtained from drop solution calorimetry in a molten lead borate (2PbO·B2O3) solvent at 702°C. The enthalpies of formation from constituent oxides were exothermic but become less so with increasing Y content. The enthalpy of vitrification of Sr2TiSi2O8 composition was measured to be 68.5 ± 6.2 kJ/mol. The thermodynamic stability of the Y‐substituted Sr‐analogue of crystalline fresnoite may become marginal with increasing yttrium content. Their ready glass formation, even in the absence of radiation, suggests that amorphous phases may dominate as the Sr‐ and Cs‐containing waste forms decay.

Thermodynamic measurements in the Mg–Zn system

New experimental values of the enthalpies of formation of intermediate phases in the Mg–Zn system at 298 K using drop-solution calorimetry in liquid tin solvent at 665 K are presented and compared with the literature data. The heat content of MgZn 2 is also measured at high temperature in order to deduce the evolution of the enthalpy of formation.

Shape-dependent surface energetics of nanocrystalline TiO2

We report the direct determination of surface enthalpies for nanophase TiO2 anatase with different morphologies derived from drop solution calorimetry in a molten sodium molybdate (3Na2Oŀ4MoO3) solvent at 702 °C. The energetics of surface hydration has been measured using a Calvet microcalorimeter coupled with a gas dosing system. The surface enthalpies of hydrated surfaces for anatase TiO2 nanoparticles, nanowires and sea-urchin-like assemblies are 0.51 ± 0.05, 1.07 ± 0.28, and 1.29 ± 0.16 J m−2, respectively, whereas those of anhydrous surfaces are 0.74 ± 0.04, 1.24 ± 0.28, and 1.41 ± 0.16 J m−2, respectively. The trend in TiO2, which shows higher surface enthalpies for more complex nanostructures, is consistent with that reported in ZnO. The shape-dependent surface enthalpy at the nanoscale level is discussed in terms of exposed surface structures. The enthalpies of hydration appear to be similar for all morphologies.

High-pressure phase relations in the system CaAl 4Si 2O 11–NaAl 3Si 3O 11 with implication for Na-rich CAS phase in shocked Martian meteorites

High-pressure phase relations in the system NaAl 3Si 3O 11–CaAl 4Si 2O 11 were examined at 13–23 GPa and 1600–1900 °C, using a multianvil apparatus. A Ca-aluminosilicate with CaAl 4Si 2O 11 composition, designated CAS phase, is stable above about 13 GPa at 1600 °C. In the system NaAl 3Si 3O 11–CaAl 4Si 2O 11, the CAS phase dissolving NaAl 3Si 3O 11 component coexists with jadeite, corundum and stishovite below 22 GPa, above which the CAS phase coexists with Na-rich calcium ferrite, corundum and stishovite. At 1600 °C, the solubility of NaAl 3Si 3O 11 component in the CAS solid solution increases with increasing pressure up to about 50 mol% at about 22 GPa, above which the solubility decreases with pressure. The maximum solubility of NaAl 3Si 3O 11 component in the CAS phase increases with temperature up to around 70 mol% at 1900 °C at 22 GPa. The dissociation of NaAlSi 2O 6 jadeite to NaAlSiO 4 calcium ferrite plus stishovite occurs at about 22 GPa. Lattice parameters of the CAS phase with the hexagonal Ba-ferrite structure change with increase of the NaAl 3Si 3O 11 component: a-axis decreases and c-axis slightly increases, resulting in decrease of molar volume. Enthalpies of the CAS solid solutions were measured by high-temperature drop-solution calorimetry techniques. The results show that enthalpy of hypothetical NaAl 3Si 3O 11 CAS phase is much higher than the mixture of NaAlSi 2O 6 jadeite, corundum and stishovite and is close to that of the mixture of NaAlSiO 4 calcium ferrite, corundum and stishovite. When we adopt the Na:Ca ratio of 75:25 of the natural Na-rich CAS phase in a shocked Martian meteorite, Zagami, the phase relations determined above suggest that the natural CAS phase crystallized from melt at pressure around 22 GPa and temperature close to or higher than 2000–2200 °C. The inferred P, T conditions are consistent with those estimated using other high-pressure minerals in the shocked meteorite.