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Abstract  

Heat capacity and enthalpy increments of calcium niobates CaNb2O6 and Ca2Nb2O7 were measured by the relaxation time method (2–300 K), DSC (260–360 K) and drop calorimetry (669–1421 K). Temperature dependencies of the molar heat capacity in the form C pm=200.4+0.03432T−3.450·106/T 2 J K−1 mol−1 for CaNb2O6 and C pm=257.2+0.03621T−4.435·106/T 2 J K−1 mol−1 for Ca2Nb2O7 were derived by the least-squares method from the experimental data. The molar entropies at 298.15 K, S m 0(CaNb2O6, 298.15 K)=167.3±0.9 J K−1 mol−1 and S m 0(Ca2Nb2O7, 298.15 K)=212.4±1.2 J K−1 mol−1, were evaluated from the low temperature heat capacity measurements. Standard enthalpies of formation at 298.15 K were derived using published values of Gibbs energy of formation and presented heat capacity and entropy data: Δf H 0(CaNb2O6, 298.15 K)= −2664.52 kJ molt-1 and Δf H 0(Ca2Nb2O7, 298.15 K)= −3346.91 kJ mol−1.

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Journal of Thermal Analysis and Calorimetry
Authors:
V. Roháč
,
M. Fulem
,
H.-G. Schmidt
,
V. Růžička
,
K. Růžička
, and
G. Wolf
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Abstract  

Radionuclide X-ray fluorescence method was used for the determination of Fe and Zn in healing plants (Sage, Peppermint, Stinging, Common Agrimony, Milfoil, Ribwort, Tansy, White Dead-Nettle).238Pu exciting source and Si/Li semiconductor detector were used for the determination.

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Journal of Thermal Analysis and Calorimetry
Authors:
M. Hampl
,
J. Leitner
,
K. Růžička
,
M. Straka
, and
P. Svoboda

Abstract

The heat capacity and the heat content of bismuth niobate BiNb5O14 were measured by the relaxation time method, DSC and drop method, respectively. The temperature dependence of heat capacity in the form C pm=455.84+0.06016T–7.7342·106/T 2 (J K−1mol−1) was derived by the least squares method from the experimental data. Furthermore, the standard molar entropy at 298.15 K S m=397.17 J K−1mol−1 was derived from the low temperature heat capacity measurement.

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Journal of Thermal Analysis and Calorimetry
Authors:
J. Leitner
,
M. Hampl
,
K. Růžička
,
M. Straka
,
D. Sedmidubský
, and
P. Svoboda

Abstract  

The heat capacity and the enthalpy increments of strontium metaniobate SrNb2O6 were measured by the relaxation method (2-276 K), micro DSC calorimetry (260-320 K) and drop calorimetry (723-1472 K). Temperature dependence of the molar heat capacity in the form C pm=(200.47±5.51)+(0.02937±0.0760)T-(3.4728±0.3115)·106/T 2 J K−1 mol−1 (298-1500 K) was derived by the least-squares method from the experimental data. Furthermore, the standard molar entropy at 298.15 K S m 0 (298.15 K)=173.88±0.39 J K−1 mol−1 was evaluated from the low temperature heat capacity measurements. The standard enthalpy of formation Δf H 0 (298.15 K)=-2826.78 kJ mol−1 was derived from total energies obtained by full potential LAPW electronic structure calculations within density functional theory.

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