Enthalpy Increment Measurements Research Articles

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.

Measurement and interpretation of the thermo-physical properties of UO2 at high temperatures: The viral effect of oxygen defects

Values are reported of specific heat, thermal conductivity and thermal diffusivity of UO2 from 1500 K to 2900 K based on laser flash measurements. Experiment is complemented by the development of solid state physics models that aid in the interpretation of the results. Specific heat is shown to exhibit a smooth maximum at 2715 K ± 100 K, consistent with a competition between two processes - oxygen defect interactions (net attraction) and saturation of oxygen interstitial sites. The specific heat model and measurements show, for the first time that a gradual pre-melting transition is consistent with high temperature literature values – enthalpy increment measurements and independently measured high temperature oxygen defect concentrations. Thermal conductivity exhibits a minimum consistent with: 1) an increase in electronic thermal conductivity via polaron production and mobilization and 2) degradation in lattice thermal conductivity due to phonon - phonon scattering and phonon - defect scattering. It is predicted that the high concentration of oxygen defects should contribute significantly to electrical conductivity and thermal expansion at high temperatures.

High-temperature heat content and thermodynamic functions of REEuTi2O7 (RE = Gd, Dy) from calorimetric measurements

Titanates of gadolinium, europium, and dysprosium are considered potential candidate materials for use in the control rods of future nuclear reactors. GdEuTi2O7 and DyEuTi2O7 were synthesized by powder-pellet route and were characterized by using X-ray diffraction technique. Enthalpy increment measurements were carried out on these compounds in temperature range 795–1658 K by inverse drop calorimetric method by using a high-temperature differential calorimeter. Thermodynamic functions such as heat capacity, entropy, and Gibbs energy functions in the temperature range 298–1700 K were computed from the measured enthalpy increments.

Thermodynamic data of U3Ga5 from calorimetric measurements

U3Ga5, an intermetallic compound in the U–Ga system was prepared by arc melting method and characterised using X-ray diffraction technique. Enthalpy increment measurements on this compound were carried out in the temperature range 793–1323 K by inverse drop calorimetric method by using a high-temperature differential calorimeter. From the fitted equation for the measured enthalpy increments, thermodynamic functions such as heat capacity, entropy and Gibbs energy functions were computed in the temperature range 298–1400 K. Using the enthalpy increments and the enthalpy of formation of U3Ga5 at 1287 K derived by high-temperature mass spectrometry (Manikandan et al. in J Nucl Mater 475:87–93, 2016), the enthalpy of formation at 298 K has been deduced. The enthalpy increments and \(\Delta _{\rm f} H_{298}^{^\circ}\) of U3Ga5 are being reported for the first time.

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.

Thermophysical properties of uranium–europium mixed oxides

Uranium–europium mixed oxides (U1-yEuy)O2-x (y = 0.2–0.8) were prepared by the citrate gel combustion technique and characterized by X-ray diffraction (XRD). Single phase fluorite structure was observed in those solid solutions with y ≤ 0.6. The solid solutions with y > 0.6 were found to be biphasic, with the second phase being cubic Eu2O3. Heat capacity and enthalpy increment measurements were carried out by using differential scanning calorimeter (DSC) and drop calorimeter in the temperature range 298–800 K and 800–1800 K, respectively. The Cp,m values at 298 K for (U1-yEuy)O2-x (y = 0.2, 0.4, 0.6) are 64.8, 64.6, and 63.5 J·K−1·mol−1, respectively. An anomalous increase was observed in the heat capacity in all of the solid solutions with the onset temperature around 950 K. This could be attributed to the contribution from Frenkel pair oxygen defects. From the excess heat capacity data, the enthalpy for the formation of these defects was computed and found to be in the range of 2.10±0.02 eV.

Solubility studies and thermophysical properties of uranium–neodymium mixed oxides system

Uranium–neodymium mixed oxides (U1−yNdy)O2±x (y=0.2–0.85) were prepared by citrate gel-combustion and characterized by XRD. Single phase fluorite structure was observed up to y=0.80. For solid solutions with y>0.80 additional lines pertaining to hexagonal neodymium oxide were observed. Lattice thermal expansion of these samples was investigated by using high temperature X-ray diffraction (HTXRD). The coefficients of thermal expansion for (U1−yNdy)O2±x for y=0.2, 0.4, 0.6, and 0.8 in the temperature range 298–1973K were found to be 16.46, 16.64, 16.79, and 16.89×10−6K−1, respectively. Heat capacity and enthalpy increment measurements were carried out by using DSC and drop calorimetry in the temperature range 298–800K and 800–1800K respectively. The Cp,m values at 298K for (U1−yLay)O2±x (y=0.2, 0.4, 0.6, and 0.8) are 63.4, 64.3, 61.8, and 58.9JK−1mol−1 respectively.

Estimation of the heat capacity of individual substances on the basis of experimental enthalpy increments

A method of determination of the high-temperature (T > 298.15 K) heat capacity function of individual substances by differentiation of enthalpy increment measurements with respect to temperature has been suggested. The approach is based on approximation of enthalpy increment measurements by a polynomial without free term, which makes it possible to strictly meet the boundary conditions of differentiation determined by the properties of the enthalpy increment function. In combination with the Shomate method, the approach enables the optimal choice of the form of temperature dependence of heat capacity that is consistent best of all with the concepts of classical thermodynamics and provides the best reproducibility of enthalpy increment measurements. When low-temperature heat capacity measurements for individual substances are not available, i.e., the Shomate method is inapplicable, the suggested strategy makes it possible to obtain the heat capacity change function in the temperature range of enthalpy increment measurements and to estimate the heat capacity of the substance at standard temperature.

Calorimetric investigation of order–disorder transition in Cu0.6Pd0.4 and Cu0.85Pd0.15 alloys

Order–disorder phase transitions in Cu0.6Pd0.4 and Cu0.85Pd0.15 alloys have been investigated using differential scanning calorimetry and drop calorimetry. The differential scanning calorimetry measurements show that the transition in both these alloys are reversible in nature and the enthalpy increment measurements reveal that these transitions are first order in nature. The transition temperature of first-order phase transition in Cu0.6Pd0.4 and Cu0.85Pd0.15 alloys have been evaluated to be 884(±2) and 799(±2) K, respectively, from drop calorimetric measurements. The latent heat of first-order phase transition in Cu0.6Pd0.4 alloy were evaluated to be 31.2(±0.6) and 28.9(±0.5) J g−1, by enthalpy increment and differential scanning calorimetry measurements, respectively. Similarly, the latent heat of first-order phase transition in Cu0.85Pd0.15 alloy were evaluated to be 23.1(±0.6) and 21.3(±0.5) J g−1, by enthalpy increment and differential scanning calorimetry measurements, respectively. The solidus temperatures of Cu0.6Pd0.4 and Cu0.85Pd0.15 alloys were found to be 1,457(±2) and 1,360 K, respectively.

Thermophysical properties of Dy6UO12

Dysprosium uranate (Dy6UO12) was prepared by citrate gel combustion and characterized by X-ray diffraction (XRD). A single phase with a rhombohedral structure was observed (R3¯). The room temperature values of the lattice parameters “a” and “c” were found to be 9.9747 and 9.4370Å, respectively. Heat capacity and enthalpy increment measurements were carried out by using a differential scanning calorimeter (DSC) and inverse drop calorimetry in the temperature range 298–800K and 600–1700K respectively. The thermal expansion characteristics were measured by using High Temperature XRD (HTXRD) in the temperature range 298–1973K. The heat capacity data of Dy6UO12 is being reported for the first time and its value at 298K is 462JK−1mol−1. The coefficient of lattice thermal expansion in the temperature range 298–1973K along “a” and “c” axes are 13.28×10−6 and 9.35×10−6K−1 respectively. These data are being reported for the first time as well.

Heat capacities and thermal conductivities of AmO 2 and AmO 1.5

The thermal diffusivity of AmO 2 was measured from 473 to 773 K and that of AmO 1.5 between 473 and 1373 K using a laser flash method. The enthalpy increment of AmO 2 was measured from 335 to 1081 K and that of AmO 1.5 between 335 and 1086 K using drop calorimetry. The heat capacities of AmO 2 and AmO 1.5 were derived from the enthalpy increment measurements. The thermal conductivity was determined from the measured thermal diffusivity, heat capacity and bulk density. The heat capacities of AmO 2 was found larger than that of AmO 1.5. The thermal conductivities of AmO 2 and AmO 1.5 were found to decrease with increasing temperature in the investigated temperature range. The thermal conductivity of AmO 1.5 with A -type hexagonal structure was smaller than that of AmO 2 with C-type fluorite structure but larger than that of sub-stoichiometric AmO 1.73.

Characterisation of High Temperature Phase Stability and Evaluation of Metallurgical Compatibility with SS 304L, of Indigenously Developed Alternate Shielding Material Ferro- Boron for Fast Reactor Applications

Abstract The high temperature phase stability and metallurgical compatibility of Ferro boron alloy which contain about 15 wt.% boron and some impurity elements like C(0.3),Si (0.29), P(0.006) etc, with 304 L SS have been evaluated using calorimetry and metallography. The X-ray diffraction of ferroboron revealed the presence of major FeB and minor Fe2B constituents, besides a small amount of Fe3(B, C). The thermal stability of this ferroboron alloy has been characterised up to melting by high resolution thermal analysis. In addition, the enthalpy increment measurements and hence specific heat estimates have been also made in the temperature range 400- 1200oC, using drop calorimetry. The high temperature metallurgical interaction between ferroboron and 304L SS clad has been simulated at temperatures 823 – 1073 K (550-800 oC) for reaction times up to 5000 h, using diffusion couples.

Heat capacity measurements and XPS studies on uranium–lanthanum mixed oxides

Heat capacity measurements were carried out on (U 1− y La y )O 2± x ( y = 0.2, 0.4, 0.6, and 0.8) using differential scanning calorimeter (DSC) in the temperature range 298–800 K. Enthalpy increment measurements were carried out on the above solid solutions using high temperature drop calorimetry in the temperature range 800–1800 K. Chemical states of U and La in the solid solutions of mixed oxides were determined using X-ray photoelectron spectroscopy (XPS). Oxygen to metal ratios of (U 1− y La y )O 2± x were estimated from the ratios of different chemical states of U present in the sample. Anomalous increase in the heat capacity is observed for (U 1− y La y )O 2± x ( y = 0.4, 0.6 and 0.8) with onset temperatures in the range of 1000–1200 K. The anomalous increase in the heat capacity is attributed to certain thermal excitation process, namely, Frenkel pair defect of oxygen. The heat capacity value of (U 1− y La y )O 2± x ( y = 0.2, 0.4, 0.6, and 0.8) at 298 K are 65.3, 64.1, 57.7, 51.9 J K −1 mol −1, respectively. From the XPS investigations, it was observed that the O/M ratios at the surface are higher than that in the bulk. In uranium rich mixed oxide samples, the surface O/M ratios are greater than 2 whereas that in La rich mixed oxides, they are less than 2, though the bulk O/M in all the samples are less than 2.

Calorimetric study of melts in the system KCl–K 2TaF 7

Enthalpy increment measurements on melts in the system KCl–K 2TaF 7 were carried out by drop calorimetry at temperatures between 298 and 1053, 1093 and 1133 K and selected compositions. The heat capacities of melted mixtures and enthalpies of mixing were determined using the experimental data. Calorimetric experiments showed nonideality of the melts in several properties. The molar relative enthalpy and molar heat capacity of melts exhibited small negative divergence from additivity. The molar enthalpy of mixing of melts showed exothermic deviation from ideality which increased with increasing temperature. The thermal effect at mixing was assigned predominantly to addition and substitution reactions producing heteroligand complex anions TaF 6Cl 2−. The nonideality was also confirmed by evaluating of activities considering Margules type model for excess Gibbs energy of mixing.

ChemInform Abstract: Calorimetric Studies on Uranium Molybdate

Abstract Enthalpy increment measurements on UMoO6(s) have been carried out using a high-temperature Calvet micro-calorimeter in the temperature range 299 to 1000 K. The enthalpy increments were least squares analyzed using Shomate’s method. The complete thermodynamic information for UMoO6(s) has been computed. The enthalpy increment expression for UMoO6(s) as a function of temperature is given by H o (T)−H o (298.15 K )( J mol −1 )=−53928.8+158.65T( K )+21.443×10 −3 T 2 ( K )+14.077×10 5 /T( K ).

High-temperature heat capacity of Gd-pyrochlore [formula omitted

The heat capacity of gadolinium pyrochlore ( Gd 2 Ti 2 O 7 ) was measured by enthalpy increment measurements in the range of (585 to 1485) K utilizing drop calorimetry on a synthetic Gd-pyrochlore and the high-temperature dependence of the heat capacity has been determined.

The thermodynamic functions of 4f metal trichlorides in the condensed state

The experimental low-temperature heat capacity values obtained for some solid 4f metal trichlorides were used to determine trends in the variable parameters of the equation that described the lattice heat capacity component in the quasi-harmonic approximation for the whole series of LnCl3 compounds (Ln = La,..., Lu). The results were used to describe the temperature dependences of the heat capacities over the temperature range from 0 K to melting point Tm. High-temperature enthalpy increment measurements for GdCl3 were used to determine the correction to quasi-harmonic description at T > ∼ 0.5Tm. Phase transition temperatures and enthalpies were selected. A procedure for estimating the heat capacities of liquid LnF3 and LnCl3 was described. The thermodynamic functions of LnCl3 in the condensed state were calculated over the temperature range 298.15–2000 K. The calculations were performed taking into account excited electronic states whose energies did not exceed 10 000 cm−1.

Enthalpy measurements of La2Te3O9 and La2Te4O11

Enthalpy increment measurements on La2Te3O9(s) and La2Te4O11(s) were carried out using a Calvet micro-calorimeter. The enthalpy values were analyzed using the non-linear curve fitting method. The dependence of enthalpy increments with temperature was given as: H°(T)−H°(298.15K) (Jmol−1)=360.70T+0.00409T2+133.568×105/T−149923 (373⩽T (K)⩽936) for La2Te3O9 and H°(T)−H°(298.15K) (Jmol−1)=331.927T+0.0549T2+29.3623×105/T−114587 (373⩽T (K)⩽936) for La2Te4O11.

High-temperature heat capacity of zirconolite (CaZrTi 2O 7)

Enthalpy increment measurements in the range of (520 to 1570) K were carried out utilizing drop calorimetry on zirconolite (CaZrTi 2O 7). The high-temperature dependence of the heat capacity of zirconolite has been determined from the simultaneous analysis of our enthalpy increment measurements and published low-temperature heat capacity data.

High temperature heat capacity of Nd 2Zr 2O 7 and La 2Zr 2O 7 pyrochlores

The enthalpy increment measurements were performed using drop calorimetry on two lanthanide zirconates Ln 2Zr 2O 7, Ln = La, Nd, with pyrochlore structure. The temperature dependence of heat capacity in the range (298 to 1550) K was derived by simultaneous linear regression of the measured enthalpies combined with the heat capacity data around ambient temperature. The obtained heat capacity C p ∘ ( T ) is compared to the limit of constant volume lattice C v calculated from the analysis of low temperature specific heat data using a combined Debye–Einstein harmonic approximation model.