Specific heat and thermodynamic properties of metallic systems: Instrumentation and analysis

A small-scale adiabatic calorimeter has been constructed as part of a larger project to study nano-particles and to facilitate specific heat measurements on samples where it is difficult to obtain enough material to run on the current large-scale adiabatic apparatus. This calorimeter is designed to measure sample sizes of less than 0.8 cm3 over a temperature range from 13 K to 350 K. Specific heat results on copper, sapphire, and benzoic acid show the accuracy of the measurements to be better than +/-0.4% for temperatures higher than 50 K. The reproducibility of these measurements is generally better than +/-0.25%.; Experimental specific heat data was collected on this new apparatus for synthetic akaganeite, beta-FeOOH, for samples with varying degrees of hydration. Our results yield values for D298.150S°m of 79.94+/-0.20 J·K-1·mol -1 and 85.33+/-0.021 J·K-1·mol -1 for samples of beta-FeOOH·0.551H2O and beta-FeOOH·0.652H 2O, respectively. From this data, we were able to determine the standard molar entropy for bare beta-FeOOH, as D298.150S°m = 53.8+/-3.3 J·K-1·mol-1 , based on subtractions of the estimated contribution of water from the hydrated species.; Additionally, the specific heats of alpha-uranium, titanium diboride, and lithium flouride have been measured on a low-temperature, semi-adiabatic calorimeter down to 0.5 K. For the alpha-uranium, the specific heat of a polycrystalline sample was compared to that of a single crystal, and it was found that there was a significant difference in the specific heats, which has been attributed to microstrain in the polycrystal. The third law entropy for the polycrystal at 298.15 K, D298.150S°m , calculated from these heat capacities is 50.21+/-0.1 J·K -1·mol-1, which is good in agreement with previously published values of polycrystal samples. For the single crystal D298.150S°m , calculated using the thermodynamic microstrain model, is 49.02+/-0.2 J·K-1·mol-1.; The low-temperature specific heats of titanium diboride and lithium fluoride have been measured from 0.5 K to 30 K as part of a larger project in the construction of a neutron spectrometer. For this application, the measured specific heats were used to extrapolate the specific heats down to 0.1 K with lattice, electronic, and Schottky equations for the respective samples. The resultant specific heat values at 0.1 K for TiB2 and 6LiF are 4.08x10 -4+/-0.27x10-4 J·K-1·mol -1 and 9.19x10-9+/-0.15x10 -9 J·K-1·mol-1, respectively.