QUANTITATIVE ASSESSMENTS OF POWDER CRYSTALLINITY - ESTIMATES OF HEAT AND MASS-TRANSFER TO INTERPRET ISOTHERMAL MICROCALORIMETRY DATA

Isothermal microcalorimetry is used to study small quantities of amorp hous materials in crystalline powders. The aim of this work is to bett er understand the isothermal microcalorimetry measurement with regard to the quantification of amorphous contents of materials. Amorphous la ctose was crystallized in a sealed ampoule in an isothermal microcalor imeter at a range of temperatures (25-60 degrees C) and humidities. Id entical heat changes for crystallization were observed at all humiditi es at 25 degrees C; however, the measured heat varied with humidity at higher temperatures. The heat measured by isothermal microcalorimetry was approximately the difference between the heat of crystallization and the heat of vaporization of the desorbed water. The isothermal mic rocalorimetry output for this process is now better understood and it can be seen that, in order to obtain quantitative data for crystallini ty, it is necessary to have a slow supply of vapor. As the measured he at change is related to the extent of water desorption, care must be t aken when using microcalorimetry to quantify the amorphous content of powders, especially when comparing data generated at different environ mental conditions. (C) 1998 Elsevier Science B.V.