THERMODYNAMIC PROPERTIES OF SYNTHETIC SAPPHIRE (ALPHA-AL2O3), STANDARD REFERENCE MATERIAL 720 AND THE EFFECT OF TEMPERATURE-SCALE DIFFERENCES ON THERMODYNAMIC PROPERTIES

Comparison of the National Institute of Standards and Technology's Sta ndard Reference Material 720 certificate values for heat capacity with those obtained from recent experimental determinations indicated the possibility of a systematic error in the certificate values. Selected experimental determinations of enthalpy increments and heat capacities were fitted in order to obtain a representation of the thermodynamic properties of alpha-Al2O3, a sample of which is the standard reference material (SRM720) for calibration of some types of calorimeters, The fitted equation and calculated values of the heat capacity, the relati ve enthalpy, and the entropy are given. The new values are more accura te and result from a better representation of the experimental values than did the 1982 SRM720 certificate values, Additionally, the general problem of the effect of changes in practical temperature scales on t hermodynamic properties is briefly discussed, using the results for al pha-Al2O3. A recent report from the IUPAC Commission on Thermodynamics gave a method for the conversion of thermodynamic properties for chan ges in practical temperature scale. The IUPAC method is shown to be no t generally correct. A better method for estimation of these changes i s given.