Enthalpy Increment Data Research Articles

Enthalpy increment of PbBi12O19(s) and ϕ-Pb5Bi8O17(s) by drop calorimetry

Enthalpy increments of PbBi12O19(s) and ϕ-Pb5Bi8O17(s) were measured by drop calorimetry in the temperature range 463–895 K and 475–757 K, respectively. A Python-based computer program implementing the Shomate method was coded to fit the experimental data. The expressions for enthalpy increment of PbBi12O19(s) and ϕ-Pb5Bi8O17(s) as a function of temperature are:HT0-H2980 < PbBi12O19> (J/mol) = 180.994×T+4939.217×10-4×T2-1746.59×104×T-1-39289 (T: 463 – 895 K)HT0-H2980 < ϕ-Pb5Bi8O17> (J/mol) = 792.256×T-65.626×10-4×T2+1638.68×104×T-1-290589 (T: 475 – 757 K)Entropies and Gibbs energy functions were also derived from the enthalpy increment data.

Experimental measurement and modeling of lattice thermal expansion and specific heat capacity of C15-Cr2Nb Laves phase intermetallic compound

In order to determine the lattice thermal expansion and specific heat capacity (Cp) of the C15-Cr2Nb Laves phase, an experimental investigation and modeling were carried out in the present paper by employing high-temperature X-ray diffraction (HTXRD) and differential scanning calorimetry (DSC). A thorough analytical model was utilized to predict the temperature-dependent variations of enthalpy and specific heat, and the predicted findings were compared to the experimentally measured data. Arc melting was employed to synthesize Cr2Nb samples with distinct hexagonal (C14/C36) and cubic (C15) Laves phase structures, which were then subjected to the appropriate heat treatment. Room temperature XRD patterns, SEM, and EDAX experiments on homogenized samples at 1273 K for 72 h validated the homogeneity and C15 (Fd-3 m) crystal structure of Cr2Nb. Rietveld refinement was used to determine the lattice parameters and relative phase fractions of the constituent phases. The average thermal expansion coefficient was determined to be αai = 0.659 × 10−5 and αVi = 1.977 × 10−5 K−1 respectively. The Cp of the C15-Cr2Nb Laves phase intermetallic compound was measured employing heat flux DSC, utilizing conventional “three-step” procedures, and being reported for the first time. The measured Cp and enthalpy increment data (HT – H298.15) with varying temperatures reported in the present investigation are being correlated utilizing the theoretical model applying the quasi-harmonic Debye Grüneisen model in the temperature range 0–860 K and illustrated different contributions to the total heat capacity i.e., vibrational, anharmonic, and electronic.

Structural investigation and specific heat measurements on borosilicate, uranium and rare earths loaded borosilicate glasses

• Disposal of contaminated sodium in borosilicate glass matrix without evolution of hydrogen. • Increase glass transition temperature and decrease linear thermal expansion of doped glasses without altering Na/Si ratio (1.34) is demonstrated. • The intensity variation in the Raman spectra due to high B2O3 and low Na2O and absence of Q0 band due to low sodium oxide content are addressed. • Enthalpy increments and specific heat capacity of doped BSGs are compared well with pristine BSG. Enthalpy increment data were acquired for borosilicate and doped borosilicate glasses containing oxides of uranium and surrogates of plutonium (CeO 2 , Nd 2 O 3 and Gd 2 O 3 ) using isoperibol drop calorimetry. The specific heat of borosilicate glasses were derived from these data and compared with doped glasses. The specific heat of the pristine glass is nearly similar to that of BSGU and found to show a dissimilar trend for BSGUCe and BSGRE. Internal network connectivity of the base glasses was investigated using micro-Raman spectrometer and compared with the glass containing high and low concentration of modifier (Na 2 O) for better understanding of thermal stability of the glasses. The Raman spectra reveal changes in the network structure with varying concentration of Na 2 O.

Redox energetics and enthalpy increments of GdBaCo2O6-δ

The enthalpy increments for the GdBaCo2O6-δ double perovskite were determined by means of drop calorimetry in air in the temperature range between 365.4 K and 1272.4 K. The heats of orthorhombic I→orthorhombic II phase transition at 347.2 K and orthorhombic II→tetragonal transition at 745.8 K are equal to (2.95 ± 0.07) kJ·mol−1 and (2.40 ± 0.09) kJ·mol−1, respectively, as measured with differential scanning calorimetry for GdBaCo2O6-δ. These calorimetric data were used to determine the heat capacity of GdBaCo2O6-δ and the high-temperature ‘chemical’ contribution to the enthalpy increments, caused by the oxygen exchange. The differentiation of the ‘chemical’ contribution with respect to oxygen nonstoichiometry yielded the partial molar enthalpy of oxygen in the GdBaCo2O6-δ, which agrees well with the previously reported results. The enthalpy increment data of nonstoichiometric oxides have proven itself as a valuable source of redox energetics information.

Implementation of the extended Einstein and two-state liquid models for thermodynamic description of pure SiO2 at 1 atm

Thermodynamic description of pure SiO2 at 1 atm was developed for the whole temperature range including the crystalline, supercooled liquid and amorphous phases. Thermodynamic properties of the crystalline phases were assessed using an extended Einstein model. The thermodynamic modelling was based on the critically assessed experimental heat capacity and enthalpy increment data and on the data on phase transitions. The Planck-Einstein approach was used to evaluate the heat capacity data and obtain a more accurate value for the standard entropy at 298.15 K for α-quartz, α-cristobalite and amorphous∖liquid phases. The value for the standard entropy for the amorphous phase obtained just from the assessment of heat capacity data and did not include non-zero residual entropy at 0 K. The liquid and amorphous phases were thermodynamically described as one phase using the two-state liquid model. It was shown that Gibbs energy expression for amorphous silicon dioxide could be evaluated without inclusion of non-zero entropy at 0 K.

Simultaneous analysis of the enthalpy increment and heat capacity data measurements for updating the IVTANTHERMO database

An analysis of the enthalpy increment and heat capacity data measurements is required for developing thermodynamic databases such as the IVTANTHERMO database created in the Glushko Thermocenter of JIHT RAS. A new CondensedThermoFit code is developed which provides experts with a comprehensive set of analysis tools for working with data on the specific heat and enthalpy increments for substances in the condensed state. These tools include simultaneous approximation of these two types of data. The enthalpy increment data is treated using the Shomate method while the heat capacity data is fitted with a flexible and manually constructible function. Only polynomial-like fitting functions are implemented so far. The final results are ready for exporting into the database with a fixed form of the fitting function such as the IVTANTHERMO database. The code has a cross-platform design, extensible module structure and graphical user interface.

BaO-Fe2O3-P2O5 glasses: Understanding the thermal stability

The effect of barium oxide on the structure of iron phosphate glass was investigated by Raman spectroscopy to understand the better thermal stability of barium loaded iron phosphate glasses compared to iron phosphate glass containing caesium oxide. Glasses with composition (mol %) of 36.1 Fe2O3-54.1 P2O5- 9.8BaO and 32.2 Fe2O3-48.3 P2O5- 19.5BaO revealed the existence of higher concentration of meta phosphate linkage, which could be a reason for their enhanced thermal stability. In addition, the enthalpy increment data were obtained by isoperibol drop calorimetry on these glasses. These data of barium oxide loaded iron phosphate glasses were compared with those of caesium loaded iron phosphate glasses. The specific heat of pristine IPG is always higher than that of IPG containing either BaO or Cs2O, showing the effect of modifiers (Ba2+ or Cs+) in glass. Depending on the concentration of the modifier, the density of the glass changes and higher the density lower was the specific heat of the glass.

Thermodynamic functions of thorium–cerium mixed oxides

Thorium–cerium mixed oxides (Th1−xCex)O2 (x = 0.25, 0.5, 0.75) were prepared by the citrate gel combustion technique. X-ray diffraction investigations of these samples revealed the formation of single-phase (fluorite) solid solutions. Heat capacity and enthalpy increments of these samples were measured by using a differential scanning calorimeter and a drop calorimeter (MHTC 96) in the temperature range 298–800 K and 523–1723 K, respectively. The values of heat capacity in the temperature range 523–1800 K were computed from the enthalpy increment data. With the help of these data, analytical expression for the heat capacity of (Th1−xCex)O2 (x = 0.25, 0.5, 0.75) as well as entropy and Gibb’s energy functions were obtained. The heat capacity values at 298 K pertaining to (Th1−xCex)O2 (x = 0.25, 0.5, 0.75) were found to be 64.92, 64.80, and 64.27 J K−1 mol−1, respectively. The thermodynamic functions are being reported for the first time.

The high-temperature heat capacity of the (Th,U)O2 and (U,Pu)O2 solid solutions

The enthalpy increment data for the (Th,U)O2 and (U,Pu)O2 solid solutions are reviewed and complemented with new experimental data (400–1773 K) and many-body potential model simulations. The results of the review show that from room temperature up to about 2000 K the enthalpy data are in agreement with the additivity rule (Neumann-Kopp) in the whole composition range. Above 2000 K the effect of Oxygen Frenkel Pair (OFP) formation leads to an excess enthalpy (heat capacity) that is modeled using the enthalpy and entropy of OFP formation from the end-members. A good agreement with existing experimental work is observed, and a reasonable agreement with the results of the many-body potential model, which indicate the presence of the diffuse Bredig (superionic) transition that is not found in the experimental enthalpy increment data.

Measurement of high temperature phase stability and thermophysical properties of alloy 740

In the present study, the characterisation of phase stability and measurement of different thermophysical properties of alloy 740 has been carried out. The transformation temperatures including liquidus/solidus and corresponding enthalpy of transformation have been measured for different phase changes up to melting using dynamic calorimetry. Further, the enthalpy increment data have been measured in the temperature range of 473–1473 K to obtain the heat capacity using static calorimetry. The present calorimetric data have been analysed in corroboration with the results obtained using JMatPro and Thermo-Calc simulation. In addition, the temperature dependence of other thermophysical properties such as thermal expansivity, density, thermal diffusivity and thermal conductivity are also measured in the range of 300–1473 K using thermomechanical analyser and laser flash method.

Calorimetric measurements on rare earth titanates: RE2TiO5 (RE = Sm, Gd and Dy)

Titanates of samarium, gadolinium, and dysprosium are considered potential candidate materials for use in the control rods of future nuclear reactors. Sm2TiO5, Gd2TiO5, and Dy2TiO5 were prepared by solid-state route and characterized by XRD technique. Enthalpy increment measurements were carried out on these compounds in the temperature range 750–1660 K by inverse drop method by using a high-temperature differential calorimeter. From the fitted equations for the measured enthalpy increment data, other thermodynamic functions, namely, heat capacity, entropy, and Gibbs energy functions, were computed in the temperature range 298–1800 K. The results are presented and compared with the data available in the literature.

Thermodynamic investigations on barium indate

Barium indate (Ba2In2O5) is an interesting compound with potential applications as oxide-ion conductor, oxygen sensor, separation membrane and electrochemical device material. Information on thermodynamic stability of barium indate is essential for long term use of this compound under reactive chemical environments. The present paper deals with the detailed thermodynamic investigations on barium indate, Ba2In2O5. Standard molar enthalpy of formation of Ba2In2O5(s) at T=298K (ΔfH2980) has been determined employing an isoperibol solution calorimeter. The standard molar heat capacity (Cp0) of barium indate was derived from enthalpy increment data measured employing a high temperature calorimeter and the thermodynamic functions such as HT0-H2980,Cpm0, ST0, HT0,GT0,-(GT0-H2980)/T, ΔfHT0 and ΔfGT0 have been generated.

Gibbs energy modeling of Fe–Ta system by Calphad method assisted by experiments and ab initio calculations

In this work we report the Gibbs energy model parameters of equilibrium phases of Fe–Ta system obtained by the Calphad approach. In order to assist the Gibbs energy modeling new constitutional and enthalpy increment data were obtained by experiments. Further, the energy of formation of intermediate phases and the energy of mixing of bcc solid solution were calculated by ab initio method. These results were combined with selected experimental data from the literature in order to optimize the model parameters of the Gibbs energy functions. Calculated phase diagram and the thermochemical properties are in good agreement with the experimental results.

Thermodynamic modeling of the Fe–Mo system coupled with experiments and ab initio calculations

In this paper we report the Gibbs energy functions for all stable phases in the Fe–Mo system obtained using Calphad method. Newly measured enthalpy increment data, tie-line data and liquidus data for selected compositions are used as input for the Gibbs energy modeling, along with carefully selected thermochemical and phase diagram data from literature. Further, ab initio generated energy of formation at 0K for the intermetallic phases and end-members of the sublattice model for the μ phase and the σ phase are also used in the optimization of model parameters of the Gibbs energy functions. Calculated phase diagram and the thermochemical properties show good agreement with the experimental data.

Thermodynamic investigations of Bi–Ni system – Part I

The Bi–Ni system has two intermetallic compounds, Bi0.75Ni0.25 and Bi0.5Ni0.5, which melt peritectically. Enthalpy increments of these compounds were measured using high temperature calorimeters. The enthalpy increment data near their peritectic temperatures were used for determining enthalpies of their decomposition. The most suitable polynomial equations for least square fit of enthalpy increment data were: Δ298.15KTHmo(Bi0.75Ni0.25)/(J·mol-1)=-8339+29.86(T/K)-0.0104(T/K)2+1.367·10-5(T/K)3,Δ298.15KTHmo(Bi0.5Ni0.5)/(J·mol-1)=-5580+16.04(T/K)+0.0139(T/K)2-130616K/T. The enthalpy of decomposition of Bi0.75Ni0.25 and of Bi0.5Ni0.5 was found to be 3.51kJ·mol−1 at equilibrium temperature 744K, and 9.22kJ·mol−1 at equilibrium temperature 927K, respectively. The heat capacities of the compounds were determined using heat flow DSC and fitted into the following most suitable, polynomial equations: Cp,mo(Bi0.75Ni0.25)/(J·K-1·mol-1)=28.92-0.0145T/K+3.05·10-5(T/K)2,Cp,mo(Bi0.5Ni0.5)/(J·K-1·mol-1)=20.25+0.0208T/K-57660(K/T)2.

Investigation of thermal expansion and specific heat of cesium loaded iron phosphate glasses

High temperature thermal expansion and specific heat measurements were carried out on iron phosphate glass (IPG) and a series of cesium substituted iron phosphate glasses. Thermal expansion of the bare IPG and the effect of cesium loading on expansion behavior were determined by push rod dilatometry in the temperature range of 300–700K in air. Specific heat was also measured in the same temperature range by differential scanning calorimetry (DSC) under flowing argon atmosphere. Enthalpy increment was computed using the specific heat data. The enthalpy increments were also measured using isoperibol drop calorimetry in air in the same temperature range. Specific heat was evaluated from the experimental enthalpy increment data. The experimentally measured enthalpy increment data were compared with those evaluated from DSC data for iron phosphate and cesium loaded iron phosphate glasses.

Enthalpy increment and heat capacity of Pb 3Bi

Enthalpy increments of Pb 0.71Bi 0.29 compound and enthalpy change associated with peritectic decomposition reaction of the compound were determined using high temperature Calvet calorimeter. The heat capacity of the compound was determined in the temperature range 230–440 K using heat flow DSC. The enthalpy increment data was fitted into the following polynomial equations. Δ H 298.15 K T ( J/mol ) = − 6492.2 + 21.2775 T + 0.00919 T 2 − 199,341 T ( 298.15 – 457 K ) The enthalpy of decomposition reaction of the compound at the peritectic temperature, 457 K, was found to be 984 J/mol. The heat capacity of the compound determined using DSC was fitted into the following polynomial equation. C P ( J/mol K ) = 23.486 − 0.01482 T + 97,338.4 T 2 ( 228 – 457 K ) The heat capacity values obtained from DSC were in reasonably good agreement with the values calculated from enthalpy increment equation and both were slightly higher than the heat capacity values calculated using Neumann–Kopp's rule.

Calorimetric Studies on Tl2Th(MoO4)3(s) and Tl2UO2(MoO4)2(s).

Abstract Enthalpy increment measurements on Tl2Th(MoO4)3(s) and Tl2UO2(MoO4)2(s) have been carried out using a high temperature Calvet microcalorimeter. Both compounds have shown transition in the experimental temperature range. The enthalpy increment data were least squares analyzed using Shomate’s method (Ttra>T) and origin programme version 6 (T>Ttra). In the Shomate method, the constraints used are Hom(T)−Hom (298.15 K) is zero at 298.15 K and Cop,m (298.15 K) equal to 364.6 and 269.44 J K−1 mol−1 for Tl2Th(MoO4)3(s) and Tl2UO2(MoO4)2(s), respectively. The resulting expressions are given below: H o m (T)−H o m (298.15 K) (J mol −1 )=−163 137+ 447.26T+19.286 ·10 −3 T 2 +83.669·10 5 /T (Tl 2 Th(MoO 4 ) 3 (s) , 299≤T≤500.6) H o m (T)−H o m (298.15 K) (J mol −1 ) =−86 844+237.13T+96.656·10 −3 T 2 +22.516 ·10 5 /T (Tl 2 UO 2 (MoO 4 ) 2 (s) , 299≤T≤496.5) Hom(T)−Hom (298.15 K) data, above the transition temperatures, were least squares analyzed using the origin program version 6 in which only the experimental Hom(T)−Hom (298.15 K) data points are taken. The corresponding expressions for Tl2Th(MoO4)3(s) and Tl2UO2(MoO4)2(s), respectively, are H o m (T)−H o m (298.15 K) (J mol −1 ) =−189 283+468.232T+19.350·10 −3 T 2 +18.878 ·10 6 /T (Tl 2 Th(MoO 4 ) 3 (s) , 775.5≤T≤828.0) H o m (T)−H o m (298.15 K) (J mol −1 ) =−78 811+235.391T+96.420·10 −3 T 2 +2.742·10 4 /T (Tl 2 UO 2 (MoO 4 ) 2 (s) , 626≤T≤835.4) The first differential of above equations with respect to temperature gives the molar heat capacities, Cop,m(T). The complete thermodynamic functions for the Tl2Th(MoO4)3(s) and Tl2UO2(MoO4)2(s) compounds have been computed for the first time.

Calorimetric studies on Tl 2Th(MoO 4) 3(s) and Tl 2UO 2(MoO 4) 2(s)

Enthalpy increment measurements on Tl 2Th(MoO 4) 3(s) and Tl 2UO 2(MoO 4) 2(s) have been carried out using a high temperature Calvet microcalorimeter. Both compounds have shown transition in the experimental temperature range. The enthalpy increment data were least squares analyzed using Shomate’s method ( T tra> T) and origin programme version 6 ( T> T tra). In the Shomate method, the constraints used are H o m( T)− H o m (298.15 K) is zero at 298.15 K and C o p,m (298.15 K) equal to 364.6 and 269.44 J K −1 mol −1 for Tl 2Th(MoO 4) 3(s) and Tl 2UO 2(MoO 4) 2(s), respectively. The resulting expressions are given below: H o m (T)−H o m (298.15 K) (J mol −1 )=−163 137+ 447.26T+19.286 ·10 −3T 2+83.669·10 5/T (Tl 2Th(MoO 4) 3(s) , 299≤T≤500.6) H o m (T)−H o m (298.15 K) (J mol −1) =−86 844+237.13T+96.656·10 −3T 2 +22.516 ·10 5/T (Tl 2UO 2(MoO 4) 2(s) , 299≤T≤496.5) H o m( T)− H o m (298.15 K) data, above the transition temperatures, were least squares analyzed using the origin program version 6 in which only the experimental H o m( T)− H o m (298.15 K) data points are taken. The corresponding expressions for Tl 2Th(MoO 4) 3(s) and Tl 2UO 2(MoO 4) 2(s), respectively, are H o m (T)−H o m (298.15 K) (J mol −1) =−189 283+468.232T+19.350·10 −3T 2 +18.878 ·10 6/T (Tl 2Th(MoO 4) 3(s) , 775.5≤T≤828.0) H o m (T)−H o m (298.15 K) (J mol −1) =−78 811+235.391T+96.420·10 −3T 2+2.742·10 4/T (Tl 2UO 2(MoO 4) 2(s) , 626≤T≤835.4) The first differential of above equations with respect to temperature gives the molar heat capacities, C o p,m( T). The complete thermodynamic functions for the Tl 2Th(MoO 4) 3(s) and Tl 2UO 2(MoO 4) 2(s) compounds have been computed for the first time.

Enthalpy increments and enthalpies of formation of Cd 0.83Ni 0.17 and Cd 0.5Ni 0.5 intermetallic compounds

Cadmium is expected to be the solvent for pyrochemical processing of the burnt metallic nuclear fuel. Therefore, thermodynamic properties of cadmium with various fuel and clad elements are of interest. In the present paper enthalpy increments and enthalpies of formation of the two intermetallic compounds of Cd–Ni system, Cd 0.83Ni 0.17 and Cd 0.5Ni 0.5, are presented. Enthalpy increment data was acquired in the temperature range 375.15–713.55 K and 375.55–810.25 K, respectively, using a high temperature Calvet calorimeter and the drop technique. The enthalpies of formation of the two compounds at 298.15 K, obtained by tin solution calorimetry, were −8.14 kJ/mol and −18.64 kJ/mol, respectively.