Heat capacity and thermodynamic functions of γ-Al2O3 synthesized from Al(NO3)3

Abstract

Heat capacity measurements provide important insight into the energetics and thermodynamic properties of a material, but they are also sensitive to minor changes in a material. Previous experiments have shown that the heat capacity functions for gamma phase aluminum oxide (Al2O3 or alumina) are significantly different from gamma phases calcined at different temperatures or those of alpha phase aluminum oxide (corundum). Thus, calorimetric measurements of different transitional alumina phases are required despite intensive studies conducted on corundum. In this study, we examine the heat capacities for gamma aluminas synthesized from the inorganic reagent Al(NO3)3⋅9H2O, rather than aluminum alkoxides as has been reported previously. Water forms an important part of the gamma alumina’s porous structure and thus makes a significant but complex contribution to the measured heat capacities. Samples calcined to final temperatures of (300, 600, 900, and 1050) °C have chemical formulae Al2O3·1.528H2O, Al2O3·0.571H2O, Al2O3·0.309H2O, and Al2O3·0.0367H2O respectively. Heat capacity data was collected using a Quantum Design Physical Properties Measurement System (PPMS) and divided into three regions for fitting to mathematical models. These models were then used to generate Cp,m, ΔT̥Sm ͦ, ΔT̥Hm ͦ, and φmͦ values over the range 1.8 K–300 K for all samples.