HEAT-CAPACITY OF THE REFERENCE MATERIAL SYNTHETIC SAPPHIRE (ALPHA-AL2O3) AT TEMPERATURES FROM 298.15 K TO 1000 K BY ADIABATIC CALORIMETRY -INCREASED ACCURACY AND PRECISION THROUGH IMPROVED INSTRUMENTATION ANDCOMPUTER CONTROL

The heat capacity of synthetic sapphire is determined by adiabatic shi eld calorimetry at temperatures from 298.15 K to 1000 K. The calorimet ric procedures are discussed in detail. Special attention is given to temperature calibration, and to transformation of temperatures measure d on IPTS-48 and IPTS-68 to ITS-90. The accuracy of the present temper ature determination is considered to be within 0.02 K to T = 903 K and within 0.10 K up to T = 1000 K. The effect of the temperature scale c hanges on the measured heat capacities is within +/-0.03 per cent up t o T = 800 K. Above this temperature, adjustment of the heat capacities might be warranted, but it depends on the thermometer used. The prese nt directly determined heat capacities for synthetic sapphire are pres umably the most accurate so far covering the range from T = 300 K to T = 1000 K. The standard deviation of a fit of the experimental heat ca pacity determinations with a smoothed curve is 0.09 per cent. The resu lting heat capacity values for synthetic sapphire deviate from those r ecommended by Archer by less than 0.05 per cent. They thereby confirm the recommended values, which were based on drop-calorimetric results only at T > 700 K. (C) 1996 Academic Press Limited