Abstract 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 accomplished 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 l'on échauffe rapidement une petite quantité d'argile, il se produit, au moment de la déshydratation, un relentissement dans l'élevation de température …” (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

Abstract 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, C p , 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

Abstract Thermal analysis of clay and other substances at atmospheric pressure has developed into a major analytical method, beginning with the pioneering studies of Le Chatelier (1887) on kaolinite, more than a century ago. Thermal analytical methods differ from chemical or structural methods in that they rely on a phenomenological approach by investigating the response of material with respect to a change in temperature. If a material is investigated at constant pressure, but at different temperatures, the results represent observations using one independent variable (i.e., temperature). If successive experiments are carried out at different pressures as well, a two-dimensional pressure-temperature grid can be created, from which important information may be derived. The advantage of using pressure as an additional variable has not gone un-noticed, and different types of apparatus that allow high-pressure studies to be made have been developed (Wendlandt, 1986). The paucity of thermal analytical research at elevated pressures, however, suggests that these earlier methods are cumbersome. Recently, a relatively convenient high-pressure (≥ 10 kbar) differential thermal analysis method was developed in the authors’ laboratory (Koster van Groos, 1979). Because the apparatus is expensive to build and maintain, a simplified computercontrolled version is being developed for routine studies at moderate pressures < 2 kbar), which should facilitate wider usage of pressure in thermal analyses. Rather than review the literature extensively or describe the technique in detail, the purpose of this chapter is to illustrate that high-pressure differential thermal analysis (HP-DTA) is an important tool in solving geologic problems. One

Abstract Thermogravimetric analysis (TGA), in which the mass of a sample is monitored as a function of temperature, is one of the oldest analytical techniques used in clay mineralogy. One of the first applications to the study of minerals was reported in 1903 by Nernst and Riesenfeld. Since then, TGA has been used to obtain a variety of information on minerals, particularly hydrous phases, such as clays and zeolites. TGA is currently widely used in many other disciplines as well, including polymer chemistry, pharmaceuticals, and inorganic analysis (Wendlandt, 1986). Despite the active interest in TGA in other areas of solid characterization and despite the many studies of clay minerals that have been conducted using TGA, the method has not enjoyed significant popularity in recent years in the mineral sciences. The technique appears to be viewed as somewhat qualitative in a field that is demanding more and more quantitative results. Fortunately, however, as a result of the large amount of research in other fields employing TGA, the application of TGA has grown in recent years from a simple technique often used as a fingerprint or water-analysis method to one that can provide quantitative information on many types of thermal processes in minerals. Data available through TGA include, but are not limited to, the kinetics of dehydration and dehydroxylation reactions, the analysis of solids for non-water volatiles, the determination of equilibrium dehydration behavior of hydrous minerals, the quantitative analysis of multicomponent mixtures, and the separation of overlapping dehydration reactions.

Abstract The combined techniques of vacuum thermogravimetric analysis (TGA) and evolved gas analysis (EGA) by mass spectrometry (MS) can be productive tools for mineral studies. In its simplest configuration, a TGA-EGA system correlates quantitative thermal weight-loss with semiquantitative evolved gas data. Thus, each weight-loss event can be assigned to the volatile species identified in that temperature interval. More sophisticated systems are capable of quantitative EGA data, with volatile abundances determined directly by integration of evolved gas peaks and verified with TGA measurements. Alternatively, the ratio of evolved gases may be used to apportion weight losses. The vacuum TGA-EGA results from cyanotrichite, Cu 4 Al 2 (SO 4 )(OH) 12 .2H 2 O , illustrate the importance and power of the combined technique. Even the small size sample (1.18 mg) used in this experiment produces good thermogravimetric information (Figure 1) because the losses during heating are relatively large. The TGA curve consists of five distinct weight-loss steps plus minor inflections that suggest further complexities. Except for assuming that H 2 O will be lost at a lower temperature than OH, such a curve is impossible to interpret with any certainty without further information. The EGA curves (Figure 1) provide this information. The curves of ionized waterl , H 2 O + , and one of its fragments, O + , which peak at 61°C, indicate that the first weight-loss event is due to the loss of H20. Similarly, the second two events, which peak at 168°C and 308°C, represent the evolution of H 2 O during dehydroxylation of the mineral. The sensitivity of the instrument is demonstrated by the detection

Abstract 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.