Journal of Thermal Analysis, Vol. 49 (1997) 961-970 THERMAL ANALYSIS OF POWDERED ALUMINA MATERIALS Riko Ozao, Hiroshi Ogura, Moyuru Ochiai and Sadao Tsutsumi 1 Department of Electronics and Informatics, North Shore College of SONY Institute, Atsugi, Kanagawa 243 lSchool of Education, Waseda University,Shinjuku, Tokyo 160-50, Japan Abstract How a DSC result is influenced by the particle size distribution of a powder sample is shown, and a simple and optimal method to, be included in a routine DSC analysis (e.g., purity determi- nation) to improve the reliability of the analysis is proposed. In case of r powder, most reliable heat capacity data can be obtained by preparing a powder with a self-similar particle size distribution with a distribution constant of 0.7, and by compressing it under a pressure of 1.5 MPa for a duration of 5 min or longer. Keywords: distribution constant, DSC, powdercompact, Rosin-Rammler particle size distribu- tion, thermal resistance: Introduction Pharmaceuticals and industrial raw materials are often provided in the form of a powder. The determination of the absolute purity of materials by differential scan- ning calorimetry (DSC) is a well known technique in the pharmaceutical and chemical industries since the development of the DSC in the early 1960s [1]. Although dynamic purity determination has been shown to be a rapid and accu- rate technique, it is also known that the results are influenced by the heat conduc- tivity of the sample, packing state of the powder sample in the sample pan, shape of the particles constituting the powder, etc. Furthermore, thermal resistances be- tween the particles increase with increasing sample size. The technique itself re- quires operating at a moderate to low scanning rate on a sample of small size and correcting for thermal resistance between the sample and the sample pan. However, too slow a scanning rate or too small a sample size reduces the signal. This leads to an increase in S/N ratio as to impair the precision of the measurement. Numerous methods for determining the heat conductivity of a sample in the form of a powder compact by means of DSC have been proposed to the early 1980's [2, 3]. The thermal conductivity of porous compacts are also considered both theo- retically and phenomenologically [4, 5]. The present work shows how a DSC result is influenced by the particle size dis- tribution of a powder sample, which assumably influences thermal resistance within 0368--4466/97/$ 5.00 9 1997 Akad~miai Kiad6, Budapest John Wiley & Sons Limited Chicheste r