In this study, we investigated variations in the thermal properties of tetragonal tetra-n-butyl ammonium bromide (TBAB) + tetra-n-butyl ammonium chloride (TBAC) mixed semiclathrate hydrates by ion chromatography and differential scanning calorimetry; these variations were assessed both in terms of their hydration numbers and the guest mole fraction rates of the hydrates. TBAB mole fraction rates in mixed hydrate crystals (yTBABh) are lower than those in mixed aqueous solutions; therefore, as Cl− has a smaller size difference to a water molecule, it is more easily incorporated into the host frameworks of hydrates than Br−. The melting points of mixed hydrates were observed at 286–289 K, and the maxima are around yTBABh = 0.1–0.3 in each hydration number. The increase in melting points largely depends on decreasing yTBABh rather than increasing hydration numbers. It is suggested that the combinations of TBAB and TBAC optimize the crystal structures, and melting points of TBAB + TBAC mixed hydrates become anomalously higher than those of the pure TBAC hydrates. Dissociation enthalpies per mass increase from 193 J g−1 to 215 J g−1, primarily with decreasing yTBABh, whereas those per guest moles increase from 154 kJ mol−1 to 188 kJ mol−1, primarily with increasing hydration numbers rather than yTBABh.
Thermal properties of tetragonal tetra-n-butyl ammonium bromide + tetra-n-butyl ammonium chloride mixed semiclathrate hydrates based on hydration numbers and guest mole fraction rates
Motoi Oshima, Yusuke Jin, Jiro Nagao; Thermal properties of tetragonal tetra-n-butyl ammonium bromide + tetra-n-butyl ammonium chloride mixed semiclathrate hydrates based on hydration numbers and guest mole fraction rates. J. Appl. Phys. 28 November 2020; 128 (20): 205104. https://doi.org/10.1063/5.0025133
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