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Thermodynamic Properties of Adamantane Revisited

“…The joint processing of this data revealed the only reliable source of sublimation pressures, ref (Figure ). The resulting sublimation pressure equation between T = 254 and 543 K over crI is the following ln false( p / kPa false) = 50.9129 − 8494.5 · false( T / normalK false) − 1 − 4.6395 · ln false( T / normalK false) which is in good agreement with the sublimation enthalpy data. ,,, The authors of ref mentioned that the sublimation enthalpy at T = 298.15 K obtained in that work was less reliable because of a large temperature adjustment. Indeed, it showed a large deviation from the values derived from the sublimation pressure given by eq (Figure ) and, hence, was excluded from the joint data treatment.…”

“…The sublimation pressure and sublimation enthalpy for adamantane were evaluated with the NIST ThermoData Engine 103b software (Thermodynamics Research Center of the National Institute of Standards and Technology, Boulder, CO) − based on joint processing of vapor and sublimation pressures, heat capacity in the crystalline and gaseous phases, enthalpies of fusion and sublimation, and gas densities based on estimated virial coefficients. Experimental values of saturated vapor pressure for solid adamantane ,,,,,− and for liquid adamantane, , as well as of sublimation enthalpy ,,,, and vaporization enthalpy , were involved. Although the vapor and sublimation pressures reported in ref are consistent with the enthalpy of fusion (at T fus = 543.2 K) within the evaluated uncertainty, they proved to be inconsistent with the low-temperature sublimation data and their inclusion did not increase the accuracy or reliability of the evaluation (Figure ).…”

“…Sublimation enthalpy data for adamantane: (⧫) from ref ; (○) from ref ; (◊) from ref ; (△) from ref ; (●) from ref ; () from eq .…”

“…Our results are also in agreement with most other combustion results (Table ), except for the result from ref . For the sake of uniformity, we recalculated the uncertainties reported in the original work, − as well as calculated the uncertainty for our results including repeatability (twice the overall standard deviation of the mean), calibration uncertainty, and uncertainty of the combustion energy of benzoic acid and auxiliary compounds. If any uncertainty contribution was not presented in a reference, an estimate was made based on the previous work of the corresponding authors.…”

“…The experimental data for the enthalpy of formation of adamantane are much more ambiguous. The scatter of 9 kJ·mol –1 in the values available from the literature − is unacceptably large for this key property, and new reliable measurements are required. Sublimation and vaporization enthalpies reported in refs , , and − and vapor pressures reported in refs , , , , , , and − also require critical evaluation because of significant discrepancies (up to 10 kJ·mol –1 in Δ sub(vap) H m o and up to 30% in p sat ).…”