Low-temperature Adiabatic Calorimetry Research Articles

Study of heat capacity enhancement in some nanostructured materials

Abstract Heat capacity properties of some nanostructured oxides, metals, and zeolites were studied, mainly with the aid of low-temperature adiabatic calorimetry. Obvious enhancement in the heat capacity of nanostructured materials to different degrees was observed as compared with the corresponding coarse-grained materials. The contributions of enhanced heat capacity of nanostructured materials toward properties such as density, thermal expansion, sample purity, surface effect, and size effect are discussed.

Thermodynamic study of compounds of the Nd-Ba-Cu-O system

Standard enthalpies of formation for solid solutions of composition Nd1 + x Ba2 − x Cu3O y (x = 0–0.8, y = 6.65–7.24) from oxides were determined by solution calorimetry. The heat capacity of NdBa2Cu3O6.87 phase was measured in the range 5–320 K by low-temperature adiabatic calorimetry. The absolute entropy S o(T), the difference of enthalpies H o(T)-H o(0 K), and the reduced Gibbs energy Φo(T) = S o(T)–[H o(T)–H o(0)]/T were calculated on the basis of smoothed dependence C p (T) in the 0–320 K range. An assessment was made for the heat capacities and the absolute entropies of solid solutions Nd1+x Ba2−x Cu3O y . The obtained set of thermodynamic parameters can be used for the calculation of phase equilibria in the Nd-Ba-Cu-O system.

Thermodynamic properties of chlorite CCa-2. Heat capacities, heat contents and entropies

The heat capacities of the international reference clay mineral chlorite CCa-2 from Flagstaff Hill, California, were measured by low temperature adiabatic calorimetry and differential scanning calorimetry, from 5 to 520 K (at 1 bar). The studied chlorite is a Fe-bearing trioctahedral chlorite with an intermediary composition between ideal clinochlore (Si 3Al)(Mg 5Al)O 10(OH) 8 and chamosite (Si 3Al)(Fe 5Al)O 10(OH) 8. Only few TiO 2 impurities were detected in the natural chlorite sample CCa-2. Its structural formula, obtained after subtracting the remaining TiO 2 impurities, is (Si 2.633Al 1.367)(Al 1.116 Fe 0.215 3 + Mg 2.952 Fe 1.712 2 + Mn 0.012Ca 0.011)O 10(OH) 8. From the heat capacity results, the entropy, standard entropy of formation and heat content of the chlorite were deduced. At 298.15 K, the heat capacity of the chlorite is 547.02 (±0.27) J mol −1 K −1 and the molar entropy is 469.4 (±2.9) J mol −1 K −1. The standard molar entropy of formation of the clay mineral from the elements is −2169.4 (±4.0) J mol −1 K −1.

The heat capacities and thermodynamic functions of some derivatives of ferrocene

The heat capacities of benzoylferrocene (BOF), C5H5FeC5H4COC6H5, and benzylferrocene (BF), C5H5FeC5H4CH2C6H5, have been measured by the low-temperature adiabatic calorimetry in the temperature range from 6K to 372K. The purity benzylferrocene and thermodynamic properties – the triple point temperature and the enthalpy of fusion have been obtained. The ideal gas thermodynamic functions (changes of the entropy, enthalpy, and Gibbs free energy) of BOF and BF were derived at T=298.15K using the heat capacities and previously determined data on the saturation vapours pressures and the enthalpies of sublimation. The ideal gas enthalpy of formation and absolute entropy of BOF at T=298.15K have been obtained from quantum chemical calculations, where as the thermodynamic properties of BF have been estimated by empirical method of group equations. A good agreement between experimental and theoretical values provides an additional check of the reliability of the experimental data.

Thermodynamic parameters of phase transitions of perfluoro-N-(4-methylcyclohexyl)piperidine

The heat capacity of perfluoro-N-(4-methylcyclohexyl)piperidine (PMCP) was measured by low-temperature adiabatic calorimetry. The purity of the substance (N 1 = 99.66 mol %), triple point temperature (T tp = 293.26 K), and enthalpy of fusion (Δfus H m ° = 8.32 kJ/mol) were determined. The enthalpy of vaporization was measured by calorimetry at 298.15 K (Δvap H m ° (298.15 K) = 56.56 kJ/mol). The temperature dependence of the saturated vapor pressure of PMCP over the pressure range 6.2–101.6 kPa was determined by comparative ebulliometry. The normal boiling point (T n.b. = 460.74 K), ehthalpies of vaporization (at various temperatures), and critical parameters of PMCP were calculated. The calculated and experimental values of Δvap H m ° (298.15 K) agree to within measurement errors, which proves the reliability of these values and pT parameters used in calculations.

Vapor pressure and heat capacities of perfluoro-N-(4-methylcyclohexyl)piperidine

Heat capacities of perfluoro-N-(4-methylcyclohexyl)piperidine (PMCP) have been measured by low-temperature adiabatic calorimetry. The purity of the compound, its triple-point temperature, and its enthalpy and entropy of fusion have been determined. The saturated vapor pressure was determined by comparative ebulliometry as a function of temperature in the 6.2–101.6 kPa pressure range and 374.2–460.9 K temperature range. The calorimetric enthalpy of vaporization at T = 298.15 K has been measured. The following thermodynamic properties were calculated for PMCP: normal boiling temperature, enthalpy of vaporization ΔvapHm0(T) as a function of temperature, and critical parameters. The enthalpies of vaporization at 298.15 K obtained experimentally and by calculation methods match within their error limits, which validates their adequacy and the adequacy of the ΔvapHm0 = f(T) equation as an extrapolation.

Heat capacity and thermodynamic functions of ferrocenemethanol

The heat capacity (C p, m) of ferrocenemethanol (FM) C5H5FeC5H4CH2OH have been measured by the low-temperature adiabatic calorimetry method in the range 6–371 K. The triple point temperature, the enthalpy of fusion, and the purity of the substance under consideration have been determined. The ideal gas thermodynamic functions of FM—absolute entropy S m(g) 0 and change in the enthalpy Δ 0 T H m at 298.15 K—have been derived from the heat capacity data and the known values of the saturation vapor pressure and enthalpy of sublimation. The ideal gas thermodynamic functions C p, m 0 and S m(g) 0 and the enthalpy of formation of FM have been calculated by the empirical difference method at T = 298.15 K. The experimental and calculated values of the thermodynamic functions are consistent within error limits, which proves their reliability.

Thermodynamic properties of anhydrous smectite MX-80, illite IMt-2 and mixed-layer illite–smectite ISCz-1 as determined by calorimetric methods. Part I: Heat capacities, heat contents and entropies

The heat capacities of the anhydrous international reference clay minerals, smectite MX-80, illite IMt-2 and mixed-layer illite–smectite ISCz-1, were measured by low temperature adiabatic calorimetry and differential scanning calorimetry, from 6 to 520 K (at 1 bar). The samples were chemically purified and Na-saturated. Dehydrated clay fractions <2 μm were studied. The structural formulae of the corresponding clay minerals, obtained after subtracting the remaining impurities, are K 0.026 Na 0.435 Ca 0.010 ( Si 3.612 Al 0.388 ) ( Al 1.593 Fe 3 + 0.184 Mg 0.228 Fe 2 + 0.038 Ti 0.011 ) O 10 ( OH ) 2 for smectite MX-80, K 0.762 Na 0.044 ( Si 3.387 Al 0.613 ) ( Al 1.427 Fe 3 + 0.292 Mg 0.241 Fe 2 + 0.084 ) O 10 ( OH ) 2 for illite IMt-2 and K 0.530 Na 0.135 ( Si 3.565 Al 0.435 ) ( Al 1.709 Fe 3 + 0.051 Mg 0.218 Fe 2 + 0.017 Ti 0.005 ) O 10 ( OH ) 2 for mixed-layer ISCz-1. From the heat capacity values, we determined the molar entropies, standard entropies of formation and heat contents of these minerals. The following values were obtained at 298.15 K and 1 bar: C p 0 (J mol −1 K −1) S 0 (J mol −1 K −1) Smectite MX-80 326.13 ± 0.10 280.56 ± 0.16 Illite IMt-2 328.21 ± 0.10 295.05 ± 0.17 Mixed-layer ISCz-1 320.79 ± 0.10 281.62 ± 0.15

Precision and accuracy of the heat-pulse calorimetric technique: lowtemperature heat capacities of milligram-sized synthetic mineral samples

Low-temperature heat capacities (cp) for milligram(mg)-sized samples of corundum, fayalite and sanidine were measured with a recently available commercial calorimeter (the heat capacity option of the Physical Properties Measurement System (PPMS), produced by Quantum Design®, which operates on the basis of a heat-pulse technique. The measurements were performed between 5 and 300 K on synthetic single-crystals and powders. Since cp-data for the above minerals are known from low-temperature adiabatic calorimetry (low-TAC) these data were used to constrain the accuracy of the PPMS-calorimeter in measuring their cp on mg-sized samples. A relative uncertainty (100*σcp/cp), as a measure of precision, of ~0.3% for T > 50 K, increasing to ~0.5% for T 100 K, 2-3% at T < 100 K for 10-20 mg powders, and ~ 5% for 5 mg powders). The accuracy was highest for cp measurements on single-crystals and sintered-powder. For these, PPMS heat capacities were in excellent agreement with comparable low-TAC data (deviating from these by a maximum of 0.5 ± 0.8% in the temperature range 100–300 K). Heat capacity measurements on sealed powders did not achieve such a high degree of accuracy, but were systematically lower than low-TAC data by 1-2%. Reference entropies were reproduced with a relative error of ≤ 0.5% using single-crystal and sintered-powder samples, and were 1-2% too low for sealed-powder samples. Our measurements demonstrate that the PPMS-calorimeter is a promising new tool for obtaining low-temperature cp-data and calorimetrically determined standard entropies for mg-sized mineralogical samples which are only available in limited amounts.

Heat capacity of lazulite, MgAl2(PO4)2(OH)2, from 35 to 298 K and a (S–V) value for P2O5 to estimate phosphate entropy

AbstractThe heat capacity of synthetic lazulite, MgAl2(PO4)2(OH)2, has been measured between 35 and 298 K by means of low-temperature adiabatic calorimetry. A lazulite third-law entropy (S2980) value of 204(3) J K–1 mol–1 was retrieved after extrapolation of the lazulite heat capacity by a cubic temperature function, down to absolute temperature. Identical measurements on α-Al2O3 yielded S2980 = 51.2 J mol–1 K–1 instead of the recommended 50.94 J mol–1 K–1 value. This new lazulite third-law entropy along with other phosphate entropy data either derived from low-temperature adiabatic calorimetry or experimental phase equilibria under pressure and temperature, were computed to retrieve a (S–V)P2O5 value of 57.4(2.9) to predict phosphate entropies from oxide summation. The predicted third-law entropy for trolleite, Al4(PO4)3(OH)3, amounts to 285.4(8.5) J mol–1 K–1 ~13% higher than the previously published value. We propose a new formation enthalpy from the elements of –6504.2 kJ mol–1 and a new third-law entropy of 281.7 J mol–1 K–1 for trolleite, compatible with the predicted entropy from oxide summation as well as with the published brackets on the trolleite = berlinite + corundum + water reaction.

Low-temperature adiabatic calorimetry of salol and benzophenone and microscopic observation of their crystallization: finding of homogeneous-nucleation-based crystallization

An adiabatic calorimetric and direct microscopic observation of crystallization at low temperatures was performed for salol and benzophenone. Both of the materials in the supercooled-liquid phase exhibited a low-temperature crystallization proceeding in the glass-transition temperature ( Tg) region. The crystallization was observed to proceed as the advance of the crystal front into the liquid phase, and stopped suddenly atT= 227 K and T≈ 215 K for salol and benzophenone, respectively. This anomalous temperature dependence of the crystal-growth rate is a characteristic feature of the homogeneous-nucleation-based (HNB) crystallization, which has been reported for o -terphenyl and triphenylethylene, and the presently observed low-temperature crystallization in salol and benzophenone was concluded to be the HNB crystallization, in which the crystal growth is brought about by the coalescence of crystal nuclei to the crystalline phase on the liquid-crystal interface. The substances exhibiting the HNB crystallization were revealed to have almost the same characteristics with respect to configurational entropy, and undergo the HNB crystallization in the same range of temperature normalized by Tg. These results indicate that the HNB crystallization is potentially a universal phenomenon in fragile liquids, and imply that the process is closely related to the liquid structure changing with temperature.

Low Temperature Heat Capacities and Thermal Analysis of &lt;i&gt;N&lt;/i&gt;-(p-methylphenyl)-&lt;i&gt;N&lt;/i&gt;′-(2-pyridyl)urea

Heat capacities of n-(p-methylphenyl)-n'-(2-pyridyl) urea were determined by low temperature adiabatic calorimetry in the temperature range of 80 to 370 k. it is found that there is no heat anomaly in this temperature region. with the experimental heat capacities thermodynamic functions were calculated. to investigate the thermal stability and decomposition characteristics of n-(p-methylphenyl)-n'-(2-pyridyl) urea, dsc and tg experiments were carried out. the results indicated that n-(p-methylphenyl)-n'-(2-pyridyl)urea started to melt at 153 degreesc and the melting peak located at 173.86 degreesc. the melting enthalpy is 204.45 kj (.) mol(-1). the decomposition peak of n-(p-methylphenyl)-n'-(2-pyridyl)urea was found at 226.11 degreesc from dsc curve. this result is similar with that from tg and dtg experiment, in which the weight loss peak was determined as 227.2 degreesc.

Ａｌ‐Ｍｇ‐Ｓｉ系合金におけるクラスタ形成と二段時効挙動

The cluster formation and two–step aging behavior of Al–1.4%Mg2Si and Al–1.4%Mg2Si–0.3%Si alloys were investigated using low-temperature adiabatic calorimetry, hardness measurement, electrical resistivity measurement and transmission electron microscopy. The specific heat changes in the alloys aged at low temperatures clearly demonstrated the existence of two exothermic peaks at temperatures between 273 and 343 K and higher than 343 K. These exothermic peaks were attributed to the formation of two types of pre-precipitates; i.e. Si-rich clusters and GP zones. The formation of these pre-precipitates was also detected by the electrical resistivity and hardness changes. The complicated two-step aging behavior of the present Al–Mg–Si alloys were well understood by taking into account the stability at higher temperatures and the effectiveness on the nucleation sites for the β″ phase of Si-rich clusters and GP zones during the final aging. The Si-rich clusters give a negative effect on the two-step aging phenomena is proposed. As the both pre-precipitates are formed competitively, such heat treatments as to give priority to the GP zone formation are effective to control the negative effect of the two-step aging and to increase age-hardening of Al–Mg–Si alloys.

Thermodynamic properties of iron silicides FeSi andα-FeSi2

The molar heat capacities of FeSi and α- FeSi2have been determined by low-temperature adiabatic calorimetry at temperatures between T= 11 K and T= 400 K. From the heat capacity data the derived thermodynamic functions; standard molar enthalpy Δ0THmo, standard molar entropy Δ0TSmo, and Gibbs energy function Φmo=defΔ0TSmo−Δ0THmo/T were calculated. Standard molar entropies of (45.57 ± 0.50)J · K−1· mol−1and (68.31 ± 0.71)J · K · mol−1at T= 298.15 K for FeSi and α- FeSi2, respectively, have been found. In an optimization procedure, the standard molar enthalpies of formation ΔfHmowere calculated using our measured data and data calculated from (iron + silicon) melts. The values obtained are: for FeSi, ΔfHmo(298.15 K) =−73.89kJ · mol−1and for α- FeSi2, ΔfHmo(298.15 K) =−78.62kJ · mol−1.

Thermodynamic properties of the nickel silicide NiSi between 8 and 400 K

The molar heat capacities of NiSi have been determined by low-temperature adiabatic calorimetry at temperatures between 8 and 400 K. From the heat capacity data the derived thermodynamic functions Δ 0 T H 0 and S 0 were calculated. At T = 298.15 K a molar standard heat capacity of 45.55 ± 0.05 J K −1 mol −1 and a molar standard entropy of 47.58 ± 0.04 J K −1 mol −1 have been found. The entropy of formation for NiSi was calculated to be −1.11 ± 0.08 J K −1 mol −1.

Thermodynamics and molecular dynamics of some ferrocene derivatives

The heat capacities of acetylferrocene, 1,1′-diacetylferrocene, and 1,1′-diethylferrocene were investigated by low-temperature adiabatic calorimetry in the temperature range from 5 to 300 K and their thermodynamic functions were calculated. The enthalpies of combustion of the substances were determined by calorimetry of combustion, and the thermodynamic functions of their formation were calculated by quantum chemistry methods. Inter- and intramolecular interactions of the ferrocene derivatives were also studied by the methods of molecular mechanics and molecular dynamics.

The heat capacity of NdAlO 3 from 0 to 900 K

The heat capacity of neodymium aluminate NdAlO 3 has been measured by low-temperature adiabatic calorimetry from 4 to 420 K, yielding S 0 (298.15 K)=(99.3±0.3) J K −1 mol −1. For temperatures up to 900 K the heat capacity has been derived from enthalpy-increment measurements (520–880 K) using high-temperature drop calorimetry. The two sets of calorimetric data are in excellent agreement and show no transition in the measured temperature range.

Thermochemistry of Hf-Zirconolite, CaHf Ti2O7

AbstractThe formation enthalpy, - 3752.3 ± 4.7 kJ·mol−1, of Hf-zirconolite, CaHfTi2O7, was obtained using high temperature oxide-melt solution calorimetry. Combined with heat capacity data obtained using low temperature adiabatic calorimetry we report the heat capacity (Cp) and the standard molar formation energetics (ΔH°f. elements, Δ S°T, and ΔG°f. elements)for Hf-zirconolite from T = 298.15 K to T = 1500 K. Comparison of Hf-zirconolite with Zr-zirconolite is made.

The heat capacity of Y 3Al 5O 12 from 0 to 900 K

The heat capacity of yttrium aluminium garnet Y 3Al 5O 12 (YAG) has been measured by low-temperature adiabatic calorimetry from 5 to 420 K. For temperatures up to 900 K the heat capacity has been derived from enthalpy-increment measurements (470–880 K) using high-temperature drop calorimetry. The two sets of calorimetric data join smoothly and show no transition in the measured temperature range.

Thermodynamic properties of copper carbonates ? malachite Cu2(OH)2CO3 and azurite Cu3(OH)2(CO3)2

The thermodynamic properties of the copper carbonates malachite and azurite have been studied by adiabatic calorimetry, by heat-flux Calvet Calorimetry, by differential thermal analysis (DTA) and by thermogravimetrie (TGA) analysis. The heat capacities, Cp0of natural malachite and azurite have been measured between 3.8 and 300 K by low-temperature adiabatic calorimetry. The heat capacity of azurite exhibits anomalous behavior at low temperatures. At 298.15 K the molar heat capacities Cp0and the third law entropies S298.150are 228.5±1.4 and 254.4±3.8 J mol−1 K−1 for azurite and 154.3±0.93 and 166.3±2.5 J mol−1 K−1 for malachite. Enthalpies of solution at 973 K in lead borate 2PbO·B2O3 have been measured for heat treated malachite and azurite. The enthalpies of decomposition are 105.1±5.8 for azurite and 66.1±5.0 kJ mol− for malachite. The enthalpies of formation from oxides of azurite and malachite determined by oxide melt solution calorimetry, are −84.7±7.4 and −52.5±5.9 kJ mol−1, respectively. On the basis of the thermodynamic data obtained, phase relations of azurite and malachite in the system Cu2+-H2O-CO2 at 25 and 75 °C have been studied.