The uncertainty in determining the third law entropy by the heat-pulse calorimetric technique

摘要

Low-temperature heat capacities were measured on milligram-sized samples of various mineralogical materials with a heat-pulse calorimeter. The third law entropy was then calculated by fitting and integrating the c_p data. In order to determine the uncertainty of the third law entropy, a Monte Carlo technique was adopted to propagate errors through the integration process. Using single crystals, the relative uncertainty of the third law entropy is smallest and only little mass-dependent and amounts to approx 0.2 percent of the total. Sample powders have a larger uncertainty that increases exponentially with decreasing sample mass. For heat-pulse calorimetric measurements on powders weighing 20 mg, derived standard entropies have a relative uncertainty of 0.9 percent increasing to 4 percent, if only 6 mg powder were used.