High Temperature Heat Content Research Articles

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.

Comparing the UK Met Office Climate Prediction System DePreSys with idealized predictability in the HadCM3 model

AbstractThe initial condition effect on climate prediction skill over a 2‐year hindcast time‐scale has been assessed from ensemble HadCM3 climate model runs using anomaly initialization over the period 1990–2001, and making comparisons with runs without initialization (equivalent to climatological conditions), and to anomaly persistence. It is shown that the assimilation improves the prediction skill in the first year globally, and in a number of limited areas out into the second year. Skill in hindcasting surface air temperature anomalies is most marked over ocean areas, and is coincident with areas of high sea surface temperature and ocean heat content skill. Skill improvement over land areas is much more limited but is still detectable in some cases. We found little difference in the skill of hindcasts using three different sets of ocean initial conditions, and we obtained the best results by combining these to form a grand ensemble hindcast set.Results are also compared with the idealized predictability studies of Collins (Clim. Dynam. 2002; 19: 671–692), which used the same model. The maximum lead time for which initialization gives enhanced skill over runs without initialization varies in different regions but is very similar to lead times found in the idealized studies, therefore strongly supporting the process representation in the model as well as its use for operational predictions. The limited 12‐year period of the study, however, means that the regional details of model skill should probably be further assessed under a wider range of observational conditions. Copyright © 2011 Royal Meteorological Society and British Crown Copyright, the Met Office

Measurement of High Temperature Heat Content by Drop Calorimetry

Measurement of High Temperature Heat Content by Drop Calorimetry

Thermodynamic investigation of the Cu–Zr system

High temperature heat contents of the Cu–Zr system alloys were measured over temperature range from 880 to 1470 K using a drop calorimeter. The enthalpies of fusion of some solid compounds were determined by the heat content—temperature plots and the entropies of fusion were calculated. Enthalpies of mixing in the liquid Cu–Zr system were measured by high temperature reaction calorimetry in the concentration range of x Zr = 0.182–0.667 at 1443 K. This system has negative enthalpies of mixing over the measured concentration range. The standard enthalpies of formation at 298.15 K of Cu 9Zr 2, Cu 51Zr 14, Cu 8Zr 3, Cu 10Zr 7 and CuZr 2 compounds were determined from the obtained data for the heat contents and enthalpies of mixing. Based on the experimental data, published thermodynamic and phase diagram data, the Cu–Zr binary system was analyzed using Redlich–Kister polynomial equation. The thermodynamic properties and the phase diagram calculated from the optimized parameters agree well with the experimental data.

Measurement of high temperature heat content of silicon by drop calorimetry

Heat content of silicon has been measured in a temperature range of 700-1820 K using a drop calorimeter. Boron nitride was used as a sample crucible. The enthalpy of fusion and the melting point of silicon determined from the heat content-temperature plots are 48.31±0.18 kJ mol-1 and 1687±5 K, respectively. The heat content and heat capacity equations were derived using the Shomate function for the solid region and the least square method for the liquid region, respectively, and compared with the literature values.

The heat capacity of MgCr2O4, FeCr2O4, and Cr2O3at low temperatures and derived thermodynamic properties

The heat capacity of synthetic eskolaite, Cr 2 O 3 , and of the synthetic spinels magnesiochromite, MgCr 2 O 4 , and chromite, FeCr 2 O 4 were measured from 1.5 K to 340 K. For MgCr 2 O 4 , a substantial magnetic contribution to the entropy is revealed by a sharp peak in the heat capacity curve at 12.55 ± 0.05 K, which indicates the transition to antiferromagnetic long-range order. Integration of the heat capacity curve yields a value of 118.3 ± 1.2 J/(mol·K) for the standard entropy at 298.15 K, which is in excellent agreement with that calculated from phase equilibria studies on the reaction MgCr 2 O 4 + SiO 2 = Cr 2 O 3 + MgSiO 3 . The new calorimetric results for Cr 2 O 3 indicate a standard entropy at 298.15 K of 82.8 ± 0.8 J/(mol·K). The measurements for FeCr 2 O 4 show three distinct heat capacity anomalies, one of which (peaking at 36.5 ± 0.2 K) was missed by previous low temperature heat capacity measurements, which only extend down to 53 K. Integration of the heat capacity curve yields a value for the standard entropy at 298.15 K of 152.2 ± 3.0 J/(mol·K) for FeCrO 4 , some 6 J/ (mol·K) greater than the previous calorimetric value. These low-temperature heat capacity data were combined with high-temperature heat content measurements from the literature to derive heat capacity equations for all three phases to 1800 K. The resulting heat capacity equations were then used to extract revised recommended values of the standard enthalpies of formation and entropies of MgCr 2 O 4 and Cr 2 O 3 from phase equilibrium data. For FeCr 2 O 4 , the phase equilibrium data are of dubious accuracy, the enthalpy of formation is only approximate

Some simple thermodynamic approaches to superionic disorder in fluorite-type crystals: Application to SrCl 2 and K 2S

Some simple phenomenological models of superionic disorder (both those allowing and not allowing for the interaction between defects) have been analysed using potassium sulphide and strontium chloride as examples, with reference to the quantitative description of the gradual transition of AB 2 fluorite (antifluorite) type compounds to the highly-conducting state. The approach as a whole is based on the use of the excess values of enthalpy ( H E ), entropy ( S E ) and free energy ( G E ). Their temperature dependence in the region of the diffuse transition has been determined based on available experimental data for the high-temperature heat content of these compounds. It is established that the change in defect concentration vs temperature in the superionic region is characterized by deviations from an Arrheniustype dependence, and is consistent with the analogous behaviour of ionic conduction. At the melting points the degree of disorder is still limited, being about 10–20% for SrCl 2 and 20–40% for K 2S of the maximum possible value. The excess entropy S E includes a significant fraction due to a vibrational component. However, neither of the models considered describes exactly all the peculiarities of the superionic transition in fluorites.

Measurements of High Temperature Heat Content of the II–VI and IV–VI (II: Zn, Cd IV: Sn, Pb VI: Se, Te) Compounds

High temperature heat contents of the II–VI and IV–VI compounds (II: Zn, Cd IV: Sn, Pb VI: Se, Te) were measured over the temperature range of 700–1550 K using a drop calorimeter. The heat of α-β transformation of SnSe was 1.1±0.1 kJ/mol at 788±2 K, and the heat of fusion of CdSe, CdTe, SnSe, PbSe, SnTe and PbTe were 44.8±0.2, 43.5±0.3, 35.5±0.4, 42.3±0.4, 39.5±0.3 and 47.6±0.4 kJ/mol, respectively, at the corresponding melting points of 1521±3, 1373±3, 1149±2, 1351±2, 1080±3 and 1209±2 K. The heat contents and heat capacity equations were derived using the Shomate function for the solid compounds and the least square method for liquid phases. Based on the third law method, the Gibbs free energies of formation were determined from the obtained heat capacity data.

An internally consistent model for the thermodynamic properties of Fe-Mg-titanomagnetite-aluminate spinels

A model is developed for the thermodynamic properties of Fe2+−Mg2+-aluminate-titanate-ferrite spinels of space group Fd3m. The model incorporates an expression for the configurational entropy of mixing which accounts for long-range order over tetrahedral and octahedral sites. Short-range order or departures from cubic symmetry are not considered. The non-configurational Gibbs energy is formulated as a second degree Taylor expansion in six linearly independent composition and ordering variables. The model parameters are calibrated to reproduce miscibility gap constraints, order-disorder phenomena in MgAl2O4 and MgFe2O4, and Fe2+−Mg2+ partitioning data between olivine and: (1) aluminate spinels; (2) ferrite spinels; (3) titanate spinels; (4) mixed aluminate-ferrite spinels. This calibration is achieved without invoking non-configurational excess entropies of mixing. The model predicts that the ordering state of FeAl2O4 is more normal than that of MgAl2O4. It also successfully accounts for heat of solution measurements and activity-composition relations in the constituent binaries. Phase equilibrium constraints require that the structure of Fe3O4 is more inverse than random at all temperatures and that Mg2+ has a strong tetrahedral site preference with respect to that of Fe2+. The analysis suggests that in the titanates short range order on octahedral sites may be significant at temperatures as high as 1300° C. Constraints developed from calibrating the thermodynamic properties of Fe2+−Mg2+-aluminatetitanate-ferrite spinel solid solutions permit extension of the database of Berman (1988) to include estimates of the end-member properties of hercynite (FeAl2O4), ulvospinel (Fe2TiO4), MgFe2O4 and cubic Mg2TiO4. In constructing these estimates, provision is made for low-temperature magnetic entropy contributions and the energetic consequences of disordering the aluminates and the ferrites. These estimates are consistent with all of the available low-temperature adiabatic calorimetry, high-temperature heat content, and heat of solution measurements on the end-members. The analysis implies that there is a substantial heat capacity anomaly in the range 300°–900° C associated with disordering of the MgAl2O4 structure while that in FeAl2O4 becomes significant at temperatures above 700° C. The same heat capacity response in the ferrites indicates that the order/disorder transformation is coupled to the antiferromagnetic-paramagnetic transition in MgFe2O4 but takes place well above the ferrimagnetic-paramagnetic transition in magnetite. The proposed model is internally consistent with solution theory reported elsewhere for Fe2+−Mg2+ olivines and orthopyroxenes (Sack and Ghiorso 1989), rhombohedral oxides (Ghiorso 1990a) and the remaining end-member properties of Berman (1988).

High temperature heat contents of III-V semiconductor systems

As part of calorimetric studies on metals and alloys at high temperature, heat contents of the III-V compounds of AlN, GaN, AlP, GaP, InP, AlAs, GaAs, InAs, AlSb, GaSb and InSb were measured over the temperature range 650 to 1550K using a drop calorimeter. The heat content and the heat capacity equations for the solid compounds were derived by the use of the Shomate function. Heat contents of the Ga-As, In-As, Ga-P and In-P binary alloys were also measured to derive the thermodynamic quantities of these liquid alloys by the use of a therniodynamic analysis method, and the vapour pressure-temperature-composition diagrams were constructed.

III-V族化合物の高温含熱量測定

III-V族化合物の高温含熱量測定

High Temperature Heat Content Measurements of Cu–RE (RE=Y, La, Ce, Pr, Nd) Binary Systems

High Temperature Heat Content Measurements of Cu–RE (RE=Y, La, Ce, Pr, Nd) Binary Systems

High-temperature heat contents, thermal diffusivities, densities, and thermal conductivities of n-type SiGe(GaP), p-type SiGe(GaP), and p-type SiGe alloys

The high-temperature heat contents of n-type SiGe(GaP), p-type SiGe(GaP), and p-type SiGe alloys were measured from 400 to 1400 K by using a copper block drop calorimeter. The heat capacity and related thermodynamic functions were calculated. Smoothed values of H0T−H0298.15, Cp, S0T−S0298.15, and −(F0T−H0298.15)T−1 were tabulated at 100-K intervals. Thermal diffusivities were measured by using a laser technique. Thermal conductivities were calculated from the heat capacity, thermal diffusivity, and density.

High-temperature thermodynamic properties of alpha and gamma lanthanum sesquisulfides and related compounds

The high-temperature heat contents of La2S3(α), La2S3(γ), La3S4, and La2.65Eu0.35S4 were measured from 400 to 1800 K by using a copper block drop calorimeter. The heat and entropy of transition of the α-to-γ transformation of La2S3 was determined. Equations for the thermodynamic functions H0T−H0298.15, Cp, S0T−S0298.15 and −(F0T−H0298.15)/T were derived in terms of the least-squares fit parameters of the heat content data.

High temperature heat contents and heat capacities of liquids and glasses in the system NaAlSi3O8-CaAl2Si2O8

Enthalpies and heat capacities of glasses and of stable liquids in the system NaAlSi3O8-CaAl2Si2O8 have been measured by drop and differential scanning calorimetry. Within experimental error, values of C p and of H T 300 of three intermediate compositions fall on straight line interpolations between the end members for both liquids and glasses, indicating that excesses in true and in mean heat capacities [(H T −H 300)/(T−300)] are small or absent. A value for the heat capacity of the An100 liquid component can therefore be derived, and is probably a better estimate than that based on measurements on the pure substance alone. On the assumption of zero excess heat capacity in this system, heats of mixing in the stable liquids are equal to those measured in the glasses by solution calorimetry, and can be as negative as -2 kcal mol−1. Heat capacities of solids and glasses in the Ab-An system are similar and do not vary greatly with composition. The C P's of the liquids, however, increase strongly with An content, suggesting major structural changes take place across the binary.

The high temperature heat content and heat capacity of liquid cerium-copper alloys by levitation calorimetry

The electromagnetic method of heating was used to determine the heat contents of liquid-cerium-copper alloys over the complete range of alloy composition. The temperatures of the levitated samples were determined pyrometrically utilizing the normal spectral emissivity data measured in an earlier work. The heat capacity was derived from analytic expression for heat contents. The composition dependence of the heat capacity goes through a maximum at 67 at. pct Cu. This behavior is ascribed to the effect of a Ce-Cu2-type atomic clustering in the liquid phase.

High-temperature properties of silicate liquids: applications to the equilibration and ascent of basic magma

High-temperature heat content measurements have been made on a series of silicate liquids, which in conjunction with published data, are used to derive partial molar heat capacities of SiO2, TiO2, Al2O3, Fe2O3, FeO, MgO, CaO, Na2O and K2O in the temperature range 1200-1650 K. Only Fe2O3appears to be compositionally dependent, and the best evidence suggests that there is no excess heat capacity (CPi i = C°). In combination with calorimetric data and the effect of pressure on the fusion temperature of solid compounds, a consistent set of enthalpy, entropy and volume data have been derived for the liquid compounds CaMgSi2O6, NaAlSi3O8, KAlSi3O8, Fe2SiO4and TiO2. By using activities (relative to a liquid standard state) calculated at 1 bar for a range of lavas, the equilibration pressures and temperatures of lavas with a lherzolitic source material are calculated, and for basanites indicate 22-26 kbar and 1310-1360 °G. The regular solution formulation used in these calculations gives an estimated error of 40 °G and 5.7 kbar when compared to experimental equilibria. It is suggested that one of the thermal responses of ascending alkali basalt magma to engulfing cooler lherzolitic nodules could be the precipitation of megacrysts, and the calculated equilibration pressures and temperatures of the megacryst assemblage (16-20 kbar, 1220-1240 °G) is in accord with this. The importance of viewing volcanic eruptions as the last stage in a sequence of chemical and thermomechanical instabilities is pointed out. Equations expressing the conservation of energy, mass and momentum on a macroscopic scale are given. The high Rayleigh numbers appropriate for even the relatively small magma volumes of erupted alkali basalts indicate turbulent flow-regimes with characteristic thermal convection velocities of the same order as nodule settling velocities. There is a significant partial melting effect in the mantle surrounding an ascending diapir if buoyancy is a significant force acting to drive the magma upwards. The effect of latent heat and convective heat losses on the thermal budget of a rising diapir has been calculated and shows the assumption of adiabaticity is often unwarranted - even for rapidly ascending magma. Finally, mass transfer rates due to convective diffusion have been calculated for all the major components in a basic silicate liquid. Integral mass exchange depends inversely on the ascent rate and is quite small for the rapidly ascending alkalic basalts.

High temperature heat content and heat capacity of silicate glasses; experimental determination and a model for calculation

High temperature heat content and heat capacity of silicate glasses; experimental determination and a model for calculation

High temperature heat content and diffuse transition of lead fluoride

The high temperature heat content of crystalline PbF 2 increases rapidly between 625 and 750 K, with an antropy incre ase of 16.5 JK -1 mol -1. The region of rapid heat content increase correlates with a large increase in ionic conductivity and is associated with fluoride ion disorder.

Liquid praseodymium heat content by levitation calorimetry

The high-temperature heat content of liquid praseodymium was measured experimentally by the levitation calorimetry technique. The samples, ranging in size from 0.5 to 1.5 g, were simultaneously levitated and heated by a radiofrequency generator in an argon-helium mixture prior to being dropped into a conventional copper block drop calorimeter. Corrections were made for the convection and radiation losses during the fall of the sample from the levitation chamber into the calorimeter. The praseodymium data, from 1460 to 2289K, were fitted by the following equation where the indicated errors represent the average deviation of the experimental value from the value predicted by the equation: H/sub T/ - H/sub 298/./sub 15/ = (41.57 +- 0.29) (T - 1208) + (41733 +- 197) J/mol. (auth)