Differential Scanning Calorimetry of Clay Minerals and Their Intercates
The field of thermal analysis covers a wide variety of techniques, each of which looks at specific characteristics of a sample as the temperature is raised or lowered at a controlled rate. This chapter describes many of the events that take place when a clay mineral that has been intercalated by a molecular species, e.g., water or various organic molecules, is heated or cooled. If a clay intercalate is heated, it decomposes (at a given rate) into two phases: the deintercalated clay and a vapor of the intercalated species. The rate of decomposition, the activation energy, and the rate law are all of interest.
Cooling the sample below ambient temperatures allows the heat capacity, Cp, of the intercalated clay to be examined and, by suitable manipulations described below, the Cp of the intercalated phase to be determined, at least approximately. These two heat capacities are of interest in the examination of the interactions of the guest molecules with the adjacent clay mineral surfaces (Lipsicas et al., 1986).
The chief purpose of the following discussion is to describe several thermal analytical techniques that are applicable to clay intercalates, the theory behind these techniques, the mathematical manipulations and calculations that follow the measurements, and, to a limited extent, how the results might be interpreted. This last point will not be stressed, because the present discussion is about methods; the citations in the text, however, allow the reader to consult references in which possible interpretations are outlined extensively.
The experimental techniques discussed