Zhi-Cheng Tan

Low Temperature Heat Capacities and Thermodynamic Properties of Zinc L-Threonate Zn(C4H7O5)2(s) by Adiabatic Calorimetry

Abstract Low-temperature heat capacities of the solid compound Zn(C 4 H 7 O 5 ) 2 (s) were measured in a temperature range from 78 to 374 K, with an automated adiabatic calorimeter. A solid-to-solid phase transition occurred in the temperature range of 295—322 K. The peak temperature, the enthalpy, and entropy of the phase transition were determined to be (316.269±1.039) K, (11.194±0.335) kJ·mol -1 , and (35.391±0.654) J·K -1 ·mol -1 , respectively. The experimental values of the molar heat capacities in the temperature regions of 78—295 K and 322—374 K were fitted to two polynomial equations of heat capacities( C p,m ) with reduced temperatures( X ) and [ X = f(T) ], with the help of the least squares method, respectively. The smoothed molar heat capacities and thermodynamic functions of the compound, relative to that of the standard reference temperature 293.15 K, were calculated on the basis of the fitted polynomials and tabulated with an interval of 5 K. In addition, the possible mechanism of thermal decomposition of the compound was inferred by the result of TG-DTG analysis.

Calorimetric study and thermal analysis of [Ho-2(Ala)(4)(H2O)(8)]Cl-6 and [ErY(Ala)(4)(H2O)(8)] (ClO4)(6)

Two solid complexes of rare-earth compounds with alanine, [ho2(ala)(4)(h2o)(8)] cl-6 and [ery(ala)(4)(h2o)(8)] (clo4)(6) (ala = alanine) were synthesized, and a calorimetric study and thermal analysis for the two complexes were performed through adiabatic calorimetry and thermogravimetry. the low-temperature heat capacities of [ho2(ala)(4)(h2o)(8)] cl-6 and [ery(ala)(4)(h2o)(8)] (clo4)(6) were measured with an automated adiabatic precision calorimeter over the temperature range from 78 to 377 k. solid-solid phase transitions were found between 214 k and 255 k with a peak temperature of 235.09 k for [ho2(ala)(4)(h2o)(8)] cl-6, between 99 k and 121 k with a peak temperature of 115. 78 k for [ery (ala)(4) (h2o)(8)] (clo4)(6). the enthalpies and entropies of the phase transitions were determined to be 3.02 kj . mol(-1), 12.83 j . k-1 . mol(-1) for [ho2(ala)(4)(h2o)(8)] cl-6; 1.96 kj . mol(-1), 16.90 j . k-1 . mol(-1) for [ery(ala)(4)(h2o)(8)] (clo4)(6), respectively. thermal decomposition of the two complexes were investigated in the temperature range of 40 similar to 800 degreesc by using the thermogravimetric and differential thermogravimetric (tg/dtg) analysis techniques. the tg/dtg curves showed that the decomposition started from 80 degreesc and ended at 479 degreesc, completed in two steps for [ho2 (ala)(4) (h2o)(8)]cl-6, and started from 120 degreesc and ended at 430 degreesc, completed in three steps for [ery(ala)(4) (h2o)(8)] (clo4)(6), respectively. the possible mechanisms of the thermal decompositions were elucidated.