Thermal Analysis in Clay Science
Thermal analysis involves the observation of a physical property of a sample and how that property changes in response to a change in temperature. Thus, the essence of this group of techniques includes the measurement of a physical property, e.g. mass, temperature, and volume, and the control of temperature. Inasmuch as heating objects is a very ancient practice, one should not be surprised that the first observations of the response of certain materials to heat were made quite some time ago. Such observations might be considered as a form of thermal analysis (Mackenzie, 1981), but serious investigations required that the temperature be known with reasonable accuracy. Temperature measurements, especially of a solid material that is being heated rapidly, was first ccomplished with a thermocouple. Two events, then, mark the beginning of thermal analysis. The first was the invention of the thermocouple. This led directly to the study of the thermal properties of a group of clay minerals. In fact, thermal analysis, in the modern sense, started with a simple description: “Si I 'on echauffe rapidement unepetite quantite d'argile, il seproduit, au moment de la deshydratation, un relentissement dans l'elevation de temperature...” (if one heats rapidly a small quantity of clay, there is, at the point of dehydration, a slowing in the increase in temperature...) (Le Chatelier, 1887). The temperature at which the dehydration occurred was determined for each of the clay minerals examined by Le Chatelier, and he pointed out that the temperature at which dehydration occurred could be used to distinguish between and to identify different clay minerals.