The low-temperature heat capacity of CaUO4 and SrUO4

The heat capacity of calcium monouranate CaUO₄ and strontium monouranate SrUO₄ have been measured over the temperature range (2 to 300) K. The results are significantly different from earlier measurements, confirming the conclusions from our previous study on BaUO₄. The standard entropy at T = 298.15 K of orthorhombic α-SrUO₄ is consistent with the values for the isostructural BaUO₄ as well as the alkali uranates Na₂UO₄ and Cs₂UO₄. The standard entropy of the rhombohedral CaUO₄ is appreciably different, which is attributed to the different structures of the uranium sublattices.     

The low-temperature heat capacity of alkali and alkaline-earth metal uranoborates

The results of heat capacity measurements for several crystalline uranoborates over the temperature range 0–340 K were discussed and analyzed. Low-temperature heat capacities (T < 50 K) were considered using the Debye theory of the heat capacity of solids and its multifractal generalization. The fractal dimensions of compounds were calculated and the heterodynamic characteristics of their structures determined.     

The thermodynamic characteristics of natural iron-lithium micas

A thermochemical study of natural lithium micas, iron-containing polylithionite and lepidolite, was performed on a high-temperature heat-flux Calvet microcalorimeter (Setaram, France). Melt solution calorimetry was used to measure the enthalpies of mineral formation from the elements Δ_f H°_el (298.15 K), ?5989.3 ± 9.6 and ?5981.3 ± 6.3 kJ/mol, respectively. The drop method was used to determine the enthalpy increments heating of the micas over the temperature interval 444–973 K. The equations for the temperature dependences of the heat capacities and enthalpies of Fe-polylithionite and Fe-lepidolite were obtained. The S° (298.15 K) and Δ_f G°_el (298.15 K) values were estimated. The thermodynamic functions of the micas were calculated over the temperature range 298.15–1000 K.     

Evidence for metal-like electronic contribution in low-temperature heat capacity of polypyrrole

Heat capacity measurements in the temperature range of 0.6 to 12 K have been conducted on doped polypyrrole films. At low temperature, a finite electronic contribution gamma prevails in all samples. The value of gamma for hexafluorophosphate doped polypyrrole PPy(PF6) is 6.31 mJ x K(-2) x mol(-1), but is 2.2 mJ x K(-2) x mol(-1) for p-toluene sulfonate doped polypyrrole PPy(TsO). With use of the free electron model, the corresponding densities of states at the Fermi level N(E(F)) are calculated and compared with those obtained from spin susceptibility data.     

An adiabatic low-temperature calorimeter for heat capacity measurement of small samples

A small sample adiabatic calorimeter for measuring heat capacities in the temperature range 60–350 K using the Nernst method has been constructed. The sample cell of the calorimeter is 6 cm³ in the internal volume, equipped with a miniature platinum thermometer and surrounded by two adiabatic shields. Two sets of 6-junction chromel-copel thermocouples were mounted between the cell and the shields to indicate the temperature differences between them. The adiabatic conditions of the cell were automatically controlled by two sets of temperature controller. A mechanical pump was used to pump out the vapour of liquid nitrogen in the cryostat to solidify N₂ (1), and 60 K or even lower temperature was obtained. The performance of this apparatus was evaluated by heat capacity measurements on α-alumina. The deviations of experimental results from a smoothed curve lie within ±0.2%, while the inaccuracy is within ±0.5% compared with the recommended reference data in the wole temperature range.     

The low-temperature heat capacity and standard entropy of synthetic huttonite ThSiO4

The low-temperature heat capacity of synthetic huttonite ThSiO₄ has been measured from T = (2 to 300) K. The sample was synthesised successfully from SiO₂ and ThO₂ by solid-state reaction at T = 1873 K at atmospheric pressure. From the calorimetric results, the value for the standard entropy $S_{\text{m}}^{°}$ (ThSiO₄, huttonite, 298.15 K) = (104.3 ± 2.0) J · K^?1 · mol^?1 has been obtained. This value indicates that the entropy of reaction from SiO₂ and ThO₂ is negative, giving a positive entropy term (?T · Δ_rS) of the Gibbs free energy of reaction. The implications of this finding are discussed extensively.     

The low-temperature heat capacity and ideal gas thermodynamic properties of isobutyl tert-butyl ether

The heat capacities of isobutyl tert-butyl ether in crystalline, liquid, supercooled liquid, and glassy states were measured by vacuum adiabatic calorimetry over the temperature range from (7.68 to 353.42) K. The purity of the substance, the glass-transition temperature, the triple point and fusion temperatures, and the enthalpy and entropy of fusion were determined. Based on the experimental data, the thermodynamic functions (absolute entropy and changes of the enthalpy and Gibbs free energy) were calculated for the solid and liquid states over the temperature range studied and for the ideal gas state at T = 298.15 K. The ideal gas heat capacity and other thermodynamic functions in wide temperature range were calculated by statistical thermodynamics method using molecular parameters determined from density-functional theory. Empirical correction for coupling of rotating groups was used to calculate the internal rotational contributions to thermodynamic functions. This correction was found by fitting to the calorimetric entropy values.     

New experimental heat capacity and enthalpy of formation of lithium cobalt oxide

The heat capacity of LiCoO₂ (O3-phase), constituent material in cathodes for lithium-ion batteries, was measured using two differential scanning calorimeters over the temperature range from (160 to 953) K (continuous method). As an alternative, the discontinuous method was employed over the temperature range from (493 to 693) K using a third calorimeter. Based on the results obtained, the enthalpy increment of LiCoO₂ was derived from T = 298.15 K up to 974.15 K. Very good agreement was obtained between the derived enthalpy increment and our independent measurements of enthalpy increment using transposed temperature drop calorimetry at 974.15 K. In addition, values of the enthalpy of formation of LiCoO₂ from the constituent oxides and elements were assessed based on measurements of enthalpy of dissolution using high temperature oxide melt drop solution calorimetry. The high temperature values obtained by these measurements are key input data in safety analysis and optimisation of the battery management systems which accounts for possible thermal runaway events.     

The low-temperature heat capacity and saturation vapor pressure of ethyl ester of butanoic acid

The heat capacity, thermodynamic properties of fusion, and purity of the ethyl ester of butanoic acid were determined by adiabatic calorimetry in the temperature range from 8 to 372 K. The pT-parameters of the ester for the equilibrium liquid-vapor were measured by comparative ebulliometry in the “atmospheric” range of pressure from 10.8 to 101.7 kPa. The obtained data were used to derive the normal boiling temperature (T _n.b), the enthalpies of vaporization at T = 298.15 K and T _n.b, and the main thermodynamic functions (changes of S, H, G) in the crystal and liquid states of the temperature interval studied and in the ideal gas state at T = 298.15 K. The experimental vapor pressures of the narrow temperature interval, ΔT = 62 K were extended to the entire range of the liquid, T _cr − T _tp⁰ = 394.3 K, from the triple, T _tp⁰, to the critical, T _cr, temperatures.     

Discrepancy in the low-temperature heat capacity of MgFe2O4 and related problems

Evident discrepancy (by six times) between low-temperature heat capacities of two different samples of magnesioferrite (MgFe₂O₄) with a different thermal history is analogous to that (by four times) for franklinite (ZnFe₂O₄) found 50 years ago. The reason is supposed to be in the different magnetic ordering caused by different cation ordering after quenching–annealing. Magnetic nature of the discrepancy in low-temperature thermodynamic functions of minerals with variable cation ordering is out of quantitative consideration so far. This effect can also be found in all oxide phases of magnetic cations with the inversion parameter.     

Isobaric specific heat capacity of typical lithium chloride liquid desiccants using scanning calorimetry

Three kinds of lithium chloride desiccants were selected, which are considered to be potential and interesting working fluids for a desiccant/dehumidification or absorption refrigeration system, and their isobaric specific heat capacities were determined in this context. Experiments were conducted at a high accuracy twin-cell scanning calorimeter. The temperature accuracy and heat flux resolution of the calorimeter are ±0.05 K and 0.1 μW respectively. The data of lithium chloride + water and lithium chloride + triethylene glycol (TEG)/propylene glycol (PG) + water systems were achieved at temperatures from 308.15 K to 343.15 K and atmospheric pressure. The mass fraction of LiCl ranged from 15% to 45% in the LiCl + H₂O system, and the mass fraction of LiCl and glycol ranged from 10% to 23.3% and 20% to 46.7% in the ternary systems respectively. Based on the experimental heat capacity data, a universal empirical formula was correlated as a function of temperature and solute mass fraction. In the experimental mass fractions and temperatures range, the average absolute deviation (AAD) between experiment results and calculated values is no more than 0.15%, and maximum absolute deviation (MAD) is within 0.38%. These thermodynamic data of lithium chloride solutions can be effectively used for analysis and design of desiccant/dehumidification systems and absorption refrigeration systems in both refrigeration and chemical industry.     

Improving the uptake capacity of natural clays by phosphate and heat treatment

Phosphate treatment of carbonaceous clays increased the uptake capacity for uranium and thorium. Heat treatment up to 400°C improved enormously the uptake property of the treated clay. These treatments failed to improve the uptake quality of argileous clays. Strontium exchanges weakly with clays of high Ca and Mg contents but strongly with a silicoaluminium clay of low Ca and Mg contents. A mixed bed of these two clays was found adequate for decontamination of actinides and fission products.     

Synthesis and study of high-temperature heat capacity of erbium orthovanadate

Orthovanadate ErVO₄ has been prepared by solid-phase synthesis from a stoichiometric mixture of high pure V₂O₅ and chemically pure Er₂O₃ by multistage calcination in air in the temperature range 873–1273 K. The effect of temperature (380–1000 K) on the heat capacity of orthovanadate ErVO₄ was studied by hightemperature calorimetry. Thermodynamic properties of erbium orthovanadate (enthalpy change H°(T)–H°(380 K), entropy change S°(T)–S°(380 K), and reduced Gibbs energy Φ°(T)) have been calculated from the experimental C_p = f(T) data. It has been shown that the specific heat varies in a row of oxides and orthovanadates of Gd-Lu naturally depending on the radius of the R³⁺ ion within the third and fourth tetrads.     

A comparative study of different methods of deter-mining exchangeable cations from clays and micas

A comparative study of the various methods of determining exchangeable cations was made in order to assess their relative applicability It seems that SCHOLLENBERGER'S method, is quite well suited for cation exchange studies as the ammonium thus adsorbed gives a fairly accurate measure of the cation exchange capacity at PH 7     

A thermogravimetric study of lithium tetraalkoxyborates

Properties of lithium tetraalkoxyborates Li[t-C₄H₉OB(OR)₃] (R = n-C₄H₉ to n-C₈H₁₇, n-C₁₂H₂₅) were studied by differential thermogravimetry. The kinetic parameters and heat effects of thermal decomposition of lithium tetraalkoxyborates in air and inert gas atmosphere as functions of the carbon chain length were determined.     

An infrared and Raman spectroscopic study of the uranyl micas

Vibrational spectroscopy using a combination of infrared and Raman spectroscopy has been used to study the uranyl micas also known as the autunite minerals, of general formula M(UO2)2(XO4)2.8-12H2O where M may be Ba, Ca, Cu, Fe2+, Mg, Mn2+ or 1/2(HAl) and X is As or P. Included in these minerals are autunite, metautunite, torbernite, meta-torbernite, meta-zeunerite, saléeite and sabugalite. Compared with the results of infrared spectroscopy, Raman microscopy shows excellent band separation enabling the separation and identification of bands attributed to (UO2)2+ units, PO4 and AsO4 units. Common to all spectra were bands at around 900 and 818 cm(-1), attributed to the antisymmetric and symmetric stretching vibrations of the (UO2)2+ units. Water in autunites is in a highly structured arrangement in the interlayer of the uranyl micas. Water molecules are differentiated according to the strength of the hydrogen bonds formed between the water and the adjacent uranyl-phosphate or uranyl-arsenate surfaces and the hydration sphere of the interlayer cation.     

Low-temperature heat capacity of diglycylglycine

Heat capacity of tripeptide diglycylglycine was measured in a temperature range from 6.5 to 304 K. The results were compared with those for glycine and glycylglycine. Peptide bonding was found not to change C _P(T) virtually above 70 K, where heat capacity does not obey the Debye model. Comparison with literature data allows one to expect a significant difference in the heat capacity for enantiomorph and racemic species of valine and leucine, like it was found recently for D-and DL-serine.     

The heat capacity of polymers

The long path to an understanding of heat capacity is traced from isothermal and adiabatic calorimetries to the most recent three methods of isoperibol, scanning, and temperature-modulated calorimetry (TMDSC). These latter three methods are: the traditional method of scanning thermal analysis; the quasi-isothermal method of finding the maximum amplitude of the periodic heat flow in response to a temperature modulation at a constant base temperature; and the pseudo-isothermal analysis of a temperature-modulated scanning experiment by subtracting the effect due to the underlying constant heating rate. In parallel, the development of the knowledge about phases and molecules is traced from its beginning to present-day nanophases and macromolecules.