Drop Solution Calorimetry Research Articles

Revisiting the thermodynamic properties of the ZrCr2 Laves phases by combined approach using experimental and simulation methods

A comprehensive study of ZrCr2 Laves phases is important for both fundamental research and technological applications. The ZrCr2 compound is a typical precipitate observed in Zr-based alloys including the newly developed Cr-coated Zr cladding known as Accident Tolerant Fuel cladding. The brittle behavior of the Laves phases and the low melting point at the interface zone between the precipitates and the Zr matrix are considered as governing the thermomechanical behaviors of these newly developed nuclear fuel claddings for normal operating conditions but more dramatically in case of Loss Of Coolant Accident (LOCA) conditions. The aim of the present study is to investigate the various ZrCr2 Laves polymorphs and their thermodynamic features particularly where conflicts exist in the literature. Based on diffraction experiments of annealed samples, it has been established that the transformation from the C14 high-temperature form to the C15 low-temperature form is of displacive nature without the C36 polymorph forming as an intermediate phase. The stable and metastable domains of C14 and C15 and their thermodynamic properties have been determined. The specific heat of both C14 and C15 types was measured over a wide range of temperatures from 2 to 1063 K by coupling relaxation calorimetry and DSC. The experimental data were fitted using a modified Einstein model. The room temperature entropies of the C14 and C15 phases were evaluated. The enthalpy of formation was measured for the first time using drop solution calorimetry in liquid Al at 1173 K in a Tian–Calvet calorimeter. The experimental value is in good agreement with Density Functional Theory (DFT) calculations. Finally, all these new results are discussed regarding the abundant literature on the ZrCr2 Laves phases.

Novelty detection in the design of synthesis of garnet-structured solid electrolytes

Recent decades have shown arising growth-on-demand fusion of machine learning into all of the areas of chemistry and materials science. In this study, we examine one aspect of using these technologies to gain an advantage in the search for new knowledge in increased amounts of experimental data. The novelty detection approaches are aimed to identify the data artefacts. The analysis of such artefacts, “outliers”, in details of synthesis of garnet-structured solid electrolytes was chosen as an example of the practical application of this methodology. Particular attention was paid to the choice of the precursors. The thermodynamic data such as the heat of formation from the pure oxides as well as the results of drop solution calorimetry for simple oxides were involved as the descriptors for the studied systems. The overall performance of novelty/outlier detection of “outliers” was characterized using the AUC (area under the curve) value and assessed to be 0.71 – 0.72 varying the complexity of data description. It was found that all “outlier” due to the precursors choice compounds were successfully identified. The regression analysis was performed to analyze the impact of outlier/novelty detection on model predictive performance as well as to elucidate the relationship with the data diversity and the complexity of data description.

An experimental investigation of the formation enthalpies of intermetallic phases in the TM(Co,Fe)-REM(Tb,Ho,Er) systems

While the phase diagrams data for the Co-REM (Tb,Ho,Er) and Fe-Ho systems have been recently evaluated, the data on the enthalpy of formation data for the intermetallic compounds is still quite scarce. The enthalpies of formation of the intermetallic compounds Co17Tb2, Co17.12Ho1.88, Co17.25Er1.75, Co7Tb2 and Fe3Ho were determined using the drop-solution calorimetry. The following values for the formation enthalpies have been obtained in the current work: ∆H°f (Tb2Co17)= -6.3 ± 2.0 kJ/mol/atom, ∆H°f(Ho1.88Co17.12)=-7.2 ± 1.7 kJ/mol/atom, ∆H°f(Er1.75Co17.25)=-10.8 ± 1.8 kJ/mol/atom, ∆H°f(Tb2Co7)=-20.7 ± 2.1 kJ/mol/atom, ∆H°f(HoFe3)=-12.0 ± 1.9 kJ/mol/atom. The dependencies of the formation enthalpies and melting temperatures from the atomic number of REM have been analysed for Co-REM compounds.

Investigation of the hardness and enthalpy of formation of the Sigma phase and the phase equilibria in the Cr-Co-Mn system

Phase transformations of the Cr-Co-Mn system have been studied using DTA, X-ray diffraction (XRD), scanning electron microscopy (SEM) and electron probe microanalysis (EPMA). Liquidus and solidus projections, a melting diagram and Scheil reaction scheme in the whole concentration range have been constructed. Enthalpy of formation of equimolar σ phase was obtained using drop-solution calorimetry. Composition dependency of microhardness for single-phase σ alloys was obtained.

Energetics of oxidation and formation of uranium monocarbide

To enable better implementation of uranium monocarbide (UC) as an advanced nuclear fuel for future high-temperature reactors, it is essential to have a thorough knowledge of its thermal and thermodynamic properties under reactor operational conditions. In this work, we studied thermal bulk oxidation of UC by simultaneous thermal analysis consisting of thermogravimetric analysis – differential scanning calorimetry coupled with evolved gas mass spectrometry (TGA-DSC-MS), and we examined the thermodynamic stability of UC using high temperature oxide melt drop solution calorimetry. In air, our studied UC sample (which contains ∼5 mol% UO2) was found to undergo a step-wise thermal oxidation process consisting of consecutive oxidations and thermal decomposition reactions: 0.95UC·0.05UO2→ UO3·0.29(CxOy) + 0.66CO2 → UO3·0.20(CxOy) + 0.09CO2 → UO3·0.03(CxOy) + 0.17CO2 → U3O8 + 0.03CO2 + 0.166O2. DSC was further used to determine the enthalpies of reactions associated with this series of oxidation reactions. Synchrotron X-ray diffraction (XRD) and extended X-ray absorption spectroscopy (EXAFS) were performed to characterize both the long- and short-range structures of UC. The standard enthalpy of formation (ΔH°f) of UC was determined to be –50.7 ± 10.8 kJ/mol·atom, in good agreement with previous values measured by bomb calorimetry. Lastly, the enthalpic landscape of U-C compounds, including UC, U2C3, and α-UC1.94, were established based on the enthalpy normalized per mole atom, which suggests that U-C phases are thermodynamically stable at lower C/U ratios.

Thermodynamic properties of selected glasses in the CaO–Al2O3–TiO2 system

The thermodynamic properties of a Ca12Al14O33 (C12A7) binary glass and the impact of titania additions (+5 and 7 wt%) were studied for the first time using three different calorimetric techniques: low-temperature adiabatic, high-temperature drop solution and transposed temperature drop calorimetry. The enthalpy of formation from oxides at 298.15 K of the Ca12Al14O33 and Ca12Al14O33+7 wt% TiO2 glass samples (16.0±1.8 and 14.5±2.4 kJ/mol, respectively) and the enthalpy of dissolution of TiO2 (rut) at 1073.15 K were obtained by drop solution calorimetry in a 2PbO–B2O3 solvent. A close value (11.9±2.3 kJ/mol) was obtained for the same C12A7 glass by transposed temperature drop calorimetry. The investigation of the impact of TiO2 additions on the thermodynamic properties of glasses shows that there is no influence on heat capacity of C12A7 up to 7 wt% of TiO2. In contrast, a negative deviation of the enthalpy of formation from oxides at 298.15 K from the ideal-mixing straight line was observed.

Solubility and Thermodynamic Investigation of Meta-Autunite Group Uranyl Arsenate Solids with Monovalent Cations Na and K.

We investigated the aqueous solubility and thermodynamic properties of two meta-autunite group uranyl arsenate solids (UAs). The measured solubility products (log Ksp) obtained in dissolution and precipitation experiments at equilibrium pH 2 and 3 for NaUAs and KUAs ranged from -23.50 to -22.96 and -23.87 to -23.38, respectively. The secondary phases (UO2)(H2AsO4)2(H2O)(s) and trögerite, (UO2)3(AsO4)2·12H2O(s), were identified by powder X-ray diffraction in the reacted solids of KUA precipitation experiments (pH 2) and NaUAs dissolution and precipitation experiments (pH 3), respectively. The identification of these secondary phases in reacted solids suggest that H3O+ co-occurring with Na or K in the interlayer region can influence the solubilities of uranyl arsenate solids. The standard-state enthalpy of formation from the elements (ΔHf-el) of NaUAs is -3025 ± 22 kJ mol-1 and for KUAs is -3000 ± 28 kJ mol-1 derived from measurements by drop solution calorimetry, consistent with values reported in other studies for uranyl phosphate solids. This work provides novel thermodynamic information for reactive transport models to interpret and predict the influence of uranyl arsenate solids on soluble concentrations of U and As in contaminated waters affected by mining legacy and other anthropogenic activities.

Enthalpy, heat capacity and thermal expansivity measurements of MgSiO3 akimotoite: Reassessment of its self-consistent thermodynamic data set

Enthalpy, isobaric heat capacity (CP) and thermal expansivity (α) of MgSiO3 akimotoite were re-determined by drop-solution calorimetry, differential scanning calorimetry and high-temperature powder X-ray diffraction measurement, respectively. From the obtained α, thermal Grüneisen parameter of MgSiO3 akimotoite was constrained to be 1.3. Using isochoric heat capacity by lattice vibrational model calculation and the Grüneisen relation equation, α and CP above maximum measurement temperature and the temperature derivative of isothermal bulk modulus were optimized by the least squares fitting to an existing P–V–T dataset which makes these parameters self-consistent. The obtained thermodynamic data set for MgSiO3 akimotoite was used to calculate the akimotoite–bridgmanite phase equilibrium boundary in MgSiO3 and high-pressure phase relations in Mg2SiO4. The result shows the stability field of the phase assemblage of MgSiO3 akimotoite + MgO below about 1400 K and around 23 GPa, suggesting the phase transition from ringwoodite to bridgmanite + ferropericlase via akimotoite + ferropericlase in cold subducted slabs.

Energetics of oxidation and formation of uranium mononitride

Uranium mononitride (UN) is an advanced nuclear fuel currently being considered for use in several generation IV fast and thermal neutron spectrum core designs, with additional applications to thermal and electric nuclear propulsion reactors. To better understand the thermal behavior and thermodynamic stability of UN, we investigated the bulk thermal oxidation process and thermochemical reactions, including the enthalpy of oxidation and standard enthalpy of formation, by conducting thermalgravimetric analysis – differential scanning calorimetry coupled with mass spectrometry (TGA-DSC-MS), and high temperature transposed temperature drop and oxide melt drop solution calorimetry. The bulk oxidation of UN (containing a small amount of α-UN1.5+x) in air was found to follow a step-wise process characterized by consecutive oxidative reactions UN-UN1.5+x-UO2 → UO2-UO3Nk → UO3Nk → UO3 → U3O8. TGA results support that the UO2 – U2N3+x passivating layer delays the onset of rapid bulk oxidation of UN in air up to 662 K. Synchrotron X-ray diffraction (XRD) and extended X-ray absorption fine structure (EXAFS) analyses were performed to characterize UN and its final oxidized product. The standard enthalpy of formation (ΔH°f) of UN was determined to be –144.4 ± 5.9 kJ/mol·atom, in good agreement with previously determined values from Pt encapsulation and bomb calorimetric experiments. Lastly, a negative linear correlation between ΔH°f and the N/U molar ratio was established based on the thermochemical data obtained in this work and previously reported enthalpies of formations of β-UN1.5-x and α-UN1.5+x.

Thermodynamic characterization of synthetic lead-arsenate apatites with different halogen substitutions

AbstractThermodynamic parameters have been measured for synthetic analogs of the mimetite-group minerals Pb5(AsO4)3X (X = OH, Cl, Br, I) belonging to the apatite supergroup. Phases precipitated from aqueous solutions under ambient conditions with well characterized structures and compositions were studied. For each phase, dissolution enthalpy was experimentally determined by oxide melt drop solution calorimetry in a molten solvent of sodium molybdate (3Na2O·4MoO3) at 976 K. The enthalpy of formation from the elements ΔHf,elo was calculated using thermochemical cycles and was −3030.6 ± 11.5, −3026.6 ± 15.8, −2967.6 ± 25.0, and −2993.1 ± 12.2 kJ/mol for Pb5.00(AsO4)3.00OH0.86(CO3)0.07, Pb5.00(AsO4)3.00Cl0.80(CO3)0.10, Pb5.00(AsO4)3.00Br0.80(CO3)0.10, and Pb5.00(AsO4)3.00I0.45OH0.35(CO3)0.10, respectively. These ΔHf,elo values exhibit typical trends for apatites: they increased (were less negative) with the increasing molar mass and ionic radius of X and decreased with the electronegativity and ionization energy of X. The compilation and comparison of data for Ca-, Pb-, P-, and As-apatites revealed correlations indicating that thermodynamic enthalpic stability is largely influenced by chemical factors (e.g., differences in electronegativities of the elements, ionization energy, or ionic characteristics of the bonds) and to a lesser extent by physical and geometric parameters in the crystal structure related to the mass and size of the X anion. Using the correlations, it was possible to estimate the value of hitherto unknown ΔHf,elo for Pb5(AsO4)3F, −3144.3 ± 66.5 kJ/mol. The observed relationships apply to the entire apatite supergroup and can be used to predict the values of ΔHf,elo for phases that have not been studied experimentally. The new data on environmentally significant phases will contribute to the modeling of mineral-water interactions, particularly for potential use in the remediation of soils and wastes contaminated with Pb and As and in the immobilization of radioactive waste containing I-129.

Energetics of hydroxylbastnäsite solid solutions, La1−xNdxCO3OH

Bastnäsites (LnCO3(F,OH)) are a group of common rare earth elements (REE)-bearing minerals and are one of the primary global sources of REE. Due to the chemical similarities among REE, bastnӓsites tend to occur as solid solutions instead of end members in REE containing ores. To better understand the processes and the mechanisms of formation of such deposits, it is essential to determine the thermodynamic properties of bastnӓsites, including hydroxylbastnӓsite (LnCO3OH) solid solutions. In this work, we performed detailed structural and calorimetric investigations on synthetic hexagonal La–Nd hydroxylbastnӓsite (La1–xNdxCO3OH, x = 0, 0.25, 0.5, 0.75, 1) solid solutions. X-ray diffraction confirms the crystal structure of the solid solution series in the P6¯ space group, and pair distribution function (PDF) analysis reveals local bonding environments characterized by three different types of 9-coordinated metal-oxygen polyhedra. Unit cell parameters of La1–xNdxCO3OH exhibit a nearly linear relation with the Nd content x, suggesting a random distribution of La and Nd in the structure. Their standard enthalpies of formation (ΔH°f) were determined by high temperature oxide melt drop solution calorimetry, from which the enthalpies of mixing (ΔHmix) were derived. The ΔHmix can be fitted by a regular solution model with an interaction parameter of 12.58 ± 0.16 kJ/mol, suggesting enthalpic metastability of La1–xNdxCO3OH relative to the two endmembers. Combining entropy and enthalpy, we further estimated the Gibbs free energies of mixing (ΔGmix) at relevant temperatures, revealing favorable temperatures under which the intermediate La1–xNdxCO3OH phases can be stabilized. Such entropy-driven stabilization, as is consistent with our geochemical modeling results, may explain the enhancement of thermal stability of the solid solutions in nature. Additionally, the temperature range constrained from this study may be used to estimate the thermal history of REE bastnӓsite deposit.

Thermodynamics of BaCa(1 + y)/3Nb(2 − y)/3O3 − δ·xH2O proton-conducting perovskites

Complex perovskites BaCa(1 + y)/3Nb(2 − y)/3O3 − δ (y = 0, 0.18 and 0.5) with 1:1-ordered structure ( $$ Fm\bar{3}m $$ space group) were synthesized by standard ceramic technique. The enthalpy increments for these oxides were measured in the temperature range of (295–1273) K by drop calorimetry, and experimental points were fitted with an integral of a single Einstein term. The hydration enthalpies for BaCa(1.18)/3Nb(1.82)/3O2.91 (BCN18), directly measured by calorimetry, were found to be equal to (− 86.7 ± 4.2) kJ (mol H2O)−1 and (− 88.8 ± 4.0) kJ (mol H2O)−1 at (673.8 ± 0.8) K and (872.8 ± 1.1) K, respectively. The calorimetrically determined enthalpies of hydration were found to be in agreement with those calculated using water vapor pressure–temperature–composition data. The increase in the off-stoichiometry index y in BaCa(1 + y)/3Nb(2 − y)/3O3 − δ leads to more exothermic hydration heats. The enthalpies of formation from elements, determined by drop solution calorimetry for dehydrated BaCa(1 + y)/3Nb(2 − y)/3O3 − δ with y = 0, 0.18 and 0.5, become less exothermic with increasing calcium content, and are equal to (− 1577.5 ± 14.5) kJ mol−1, (− 1533.6 ± 14.8) kJ mol−1 and (− 1492.2 ± 14.6) kJ mol−1, respectively. The thermodynamic data obtained allow calculating the enthalpies of formation and enthalpy increments for BaCa(1 + y)/3Nb(2 − y)/3O3 − δ with arbitrary water content.

Thermochemical studies of X(NpO2)(PO4)(H2O)3 (X = K+, Rb+), neptunium analogs of the autunite/meta-autunite group

Actinide phosphate materials with autunite or meta-autunite type sheets consisting of vertex-sharing actinyl square bipyramids and phosphate tetrahedra have low aqueous solubility and potential applications for actinide immobilization in the environment. Neptunyl phosphates, X(NpO2)(PO4)(H2O)3, X ​= ​K+ and Rb+, have been synthesized by hydrothermal reactions and characterized for their structures and purities. Direct thermochemical studies were performed using high temperature oxide melt drop solution calorimetry. After correcting for the presence of residual fluorapatite from the synthesis, the formation enthalpies of K(NpO2)(PO4)(H2O)3 and Rb(NpO2)(PO4)(H2O)3 are determined to be −3235 ​± ​21 ​kJ/mol and −3270 ​± ​11 ​kJ/mol, respectively. The thermodynamic data presented here may be important for understanding neptunium mobility after disposal of nuclear waste in a geological repository.

The structure and thermochemistry of K2CO3–MgCO3 glass

Abstract

A Novel Family of Np(VI) Oxysalts: Crystal Structures, Calorimetry, Thermal Behavior, and Comparison with U(VI) Compounds

Phase formation in the mixed sulfate–selenate Np(VI)-bearing aqueous system has been investigated. The obtained crystalline compounds, Cs2[(NpO2)2(TO4)3] (T = S, Se), crystallize in the tetragonal system, space group P421m, with a = 9.5737(3)–9.817(3) A, c = 8.0824(4)–8.111(3) A, and V = 740.79(6)–781.8(6) A3, and have been chemically characterized. Single-crystal X-ray diffraction experiments at various temperatures were used to define the thermal behavior of the crystal structures relative to the S/Se ratio. The thermal behavior of mixed sulfate–selenate and pure selenate compounds is anisotropic, with the highest thermal expansion in the direction perpendicular to the sheets of Np-bearing polyhedra, while the structure of the pure sulfate compound experiences almost isotropic thermal expansion with slightly higher expansion within the layer, which is explained by the influence of stronger Cs–O bonding. High-temperature drop solution calorimetry was used to derive the enthalpies of formation of the Cs+...

Energetic Trends in Monomer Building Blocks for Uranyl Peroxide Clusters.

The uranyl triperoxide anionic monomer is a fundamental building block for uranyl peroxide polyoxometalate capsules. The reaction pathway from the monomer to the capsule can be greatly altered by the counterion: both the reaction rate and the resulting capsule structure. We synthesized and characterized uranyl triperoxides Mg2UO2(O2)3·13H2O (MgUT), Ca2UO2(O2)3·9H2O (CaUT), Sr2UO2(O2)3·9H2O (SrUT), and K4UO2(O2)3·3H2O (KUT) and compared their thermodynamic stabilities. The enthalpies of formation from oxides and elements of these compounds were calculated by thermochemical cycles from measurements by high temperature oxide melt drop solution calorimetry. Their formation enthalpies from oxides become more negative linearly as a function of the increasing basicity of the respective oxides on the Smith scale. This relationship holds for previously Li and Na analogues. Further affirming the trend, Δ Hf,ox of MgUT departs from linearity, due to the distinct bonding environment of Mg2+, as compared to the other alkalis and alkaline earths in the series.

Thermodynamics and Stability of Rhabdophanes, Hydrated Rare Earth Phosphates REPO4 · n H2O.

Rare earth phosphates comprise a large family of compounds proposed as possible nuclear waste disposal forms. We report structural and thermodynamic properties of a series of rare earth rhabdophanes and monazites. The water content of the rhabdophanes, including both adsorbed and structural water, decreases linearly with increase in ionic radius of the rare earth. The energetics of the transformation of rhabdophane to monazite plus water and the enthalpy of formation of rhabdophane from the constituent oxides was determined by high temperature drop solution calorimetry. The former varies linearly with the ionic radius of the lanthanide, except for cerium. By combining the enthalpy of formation determined by high temperature drop solution calorimetry and the free energy of formation determined previously by solubility experiments, a complete set of thermodynamic data was derived for the rhabdophanes. They are thermodynamically metastable with respect to the corresponding monazites plus water at all temperatures under ambient pressure conditions. This conclusion strengthens the case for monazites being an excellent nuclear waste form.

The enthalpies of formation for various Cu–Li–Sb compounds

The system Cu–Li–Sb has recently gained much attention with regard to Cu–Sb alloys being used as electrode materials for lithium ion batteries. Only few data exists however on the thermodynamics governing the lithiation of such electrode materials. A theoretical model of the corresponding phase diagrams, as provided by the CALPHAD approach, would give tremendous insights, not only into the thermodynamics but also to certain kinetic aspects governing these materials. However in order to develop a reliable model, fundamental experimental data is necessary. Especially the Gibbs energies and enthalpies of formation for the encountered intermetallic phases are essential building blocks for modeling of the system.In this work, the enthalpies of formation of four ternary compounds, i.e. CuLi2−xSb, Cu2−xLi1−xSb, Cu1.5−xLi1+xSb, Cu4+xLi1−xSb2 (i.e. T1–T4), were determined by two different experimental methods. Drop solution calorimetry using a tin bath was used to derive the enthalpies of formation from the limiting partial molar enthalpies of solution of the different ternary compounds as well as of their constituent components. Emf measurements at temperatures ranging from 642 K to 754 K were applied to calculate the enthalpies of formation from the integrated partial enthalpies of reaction with respect to liquid lithium. An electrochemical cell which can be represented as W|”Al, LiAl”|LiCl–KCl|CuxLiySbz|W was used for these measurements.

Understanding the Stability of Salt-Inclusion Phases for Nuclear Waste-forms through Volume-based Thermodynamics

Formation enthalpies and Gibbs energies of actinide and rare-earth containing SIMs with silicate and germanate frameworks are reported. Volume-based thermodynamics (VBT) techniques complemented by density functional theory (DFT) were adapted and applied to these complex structures. VBT and DFT results were in closest agreement for the smaller framework silicate structure, whereas DFT in general predicts less negative enthalpies across all SIMs, regardless of framework type. Both methods predict the rare-earth silicates to be the most stable of the comparable structures calculated, with VBT results being in good agreement with the limited experimental values available from drop solution calorimetry.

Charge Density Influence on Enthalpy of Formation of Uranyl Peroxide Cage Cluster Salts.

More than 60 unique uranyl peroxide cage clusters have been reported that contain as many as 124 uranyl ions and that have overall diameters extending to 4 nm. They self-assemble in water under ambient conditions, are models for understanding structure-size-property relations as well as testing computational models for actinides, and have potential applications in nuclear fuel cycles. High-temperature drop solution calorimetry has been used to derive the enthalpies of formation of the salts of seven topologically diverse uranyl peroxide cage clusters containing from 22 to 28 uranyl ions that are bridged by various combinations of peroxide, pyrophosphate, and phosphite. The enthalpies of formation of these seven salts, as well as three salts of other uranyl peroxide clusters reported earlier, are dominated by the interactions of the alkali countercations with the clusters. There is an approximately linear relationship between the enthalpies of formation of the cluster salts and the charge density of the corresponding uranyl peroxide cluster, wherein salts containing clusters with higher charge densities have more negative enthalpies of formation.