The Techniques of Thermal Analysis

Thermal analysis is the analytical technique that establishes the experimental data for the variables of state. Details about the definition of thermal analysis are given in Fig. 2.4. The six most basic thermal analysis techniques which allow the determina- 

The term thermal analysis can be applied to any technique which involves the measurement of a physical quantity while the temperature is changed or maintained in a controlled and measured fashion as expressed in Fig. 2.4. Usually the temperature is, for simplicity, kept constant or increased linearly with time. Recently, it was found advantageous to superimpose a small modulation of the temperature to check for the reversibility of the measurement and to separate the calorimeter response from inadvertent gains or losses that do not occur with this modulation frequency (see Sect. 4.4). The professional organizations of thermal analysis are the International Confederation for Thermal Analysis and Calorimetry, ICTAC, and the North American Thermal Analysis Society, NAT AS, described in some detail in Figs. 2.5 and 2.6, respectively. The most common journals dealing with thermal analysis techniques and results are ThermochimicaActa and the Journal of Thermal Analysis and Calorimetry. 

Thermometry, is the simplest technique of thermal analysis. It becomes even more useful when time is recorded simultaneously. Such thermal analyses are called 

The most basic thermal analysis technique is naturally calorimetry, the measurement of heat. The needed thermal analysis instrument is the calorimeter. Instrumentation, technique, theory and applications of calorimetry are treated in 

North American Thermal Analysis Society (NATAS) 

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Yield-temperature curves, typically obtained from programmed temperature experiments using the techniques of thermal analysis, are illustrated in Chapter 5, after consideration of the effects of temperature on the rates of solid state reactions in Chapter 4. 

The dissociations (reversible) and decompositions (irreversible) of oxides have not been the subject of many reviews, though the properties of these phases have been discussed with reference to allied topics, including the oxidation of metals, catalysis, etc. Dollimore [22] has reviewed the applications of the techniques of thermal analysis to the dissociation of single oxide systems. 

In the nine years since the appearance of Volume 1 in 1998, the techniques of thermal analysis and calorimetry have naturally advanced and the applications have broadened even further. Excellent surveys of these developments are the bi-annual reviews in the journal Analytical Chemistry, originally compiled by the late Connie Murphy and extended by the late David Dollimore and colleagues [D. Dollimore and S. Lerdkanchanapom, Anal. Chem., 70 (12) (1998)27-36 D. Dollimore and P. Phang, Anal. Chem., 72 (12) (2000) 27-36.] and now compiled by Sergey Vyazovkin [S. Vyazovkin, Anal. Chem., 74 (2002) 2749-2762 76 (2004) 3299-3312 78 (2006) 3875-3886.]. 

The techniques of thermal analysis stimulated an interest in the estimation of reaction kinetic parameters from programmed temperature experiments. Some of this background was covered by Brown and Galwey in Chapter 3 of Volume 1 [Vol.l, Ch.3]. A major advance was... 

These techniques for studying phase transitions, although powerful, are time-consuming and difficult. A simple and easily applied technique, called thermal analysis, has been used for more than a century. Phase transitions are characterized by the absorption or emission of a heat of transition. The way in which the heat of transition is involved in the technique of thermal analysis can be illustrated by discussion of a simple experiment. 

With the basic functions heat and temperature clarified, one can now complete this initial discussion of thermal analysis by listing the techniques of thermal analysis, as is done at the bottom of Fig. 1.4. The term thermal analysis is applied to any technique which involves a measurement while the temperature is changed or maintained in a controlled and measured fashion. Usually temperature changes are, for simplicity, linear with time. 

The techniques of thermal analysis are very significant to the whole field of polymers in that they provide essential information relating both to their characterisation and their degradation. Table 2a lists areas where Thermal Analysis (TA) provides information for characterisation while Table 2b lists areas where TA provides information on the degradation processes. 

Clearly, the techniques of thermal analysis may also be used for systems in the gel from when the polymers may be regarded as already hydrated. Since these are effectively dissolved polymers, the thermal scans will be dominated by the endotherm corresponding to the melting of free water. However, other thermal events may be detected to the low temperature side of these major endotherms. These may be due to melting of different classes of water, or even a glass transition, followed by recrystallisation of phase-concentrated water [25]. Differentiation of the events by dielectric spectroscopy has at least allowed partial confirmation of the thermal data [ 130]. 

The requirement of dimensional consistency places a number of constraints on the form of the functional relation between variables in a problem and forms the basis of the technique of dimensional analysis which enables the variables in a problem to be grouped into the form of dimensionless groups. Since the dimensions of the physical quantities may be expressed in terms of a number of fundamentals, usually mass, length, and time, and sometimes temperature and thermal energy, the requirement of dimensional consistency must be satisfied in respect of each of the fundamentals. Dimensional analysis gives no information about the form of the functions, nor does it provide any means of evaluating numerical proportionality constants. 

Pires, J. and A. J. Cruz (2007), Techniques of thermal analysis applied to the study of cultural heritage, /. Thermal Anal, and Calorim. 87(2), 411-415. 

The prospects of DSC, have been reviewed in a special issue of Thermochimica Acta, which includes a collection of articles on advances of thermal analysis in the twentieth century and expected future developments [232,235,236]. This journal and the Journal of Thermal Analysis and Calorimetry, where research articles about DSC and its applications are often published, are very useful sources of information on the technique. Although relatively old, the reviews by McNaughton and Mortimer [237] and by Mortimer [238] contain excellent examples of applications of DSC to molecular thermochemistry studies. The analytical uses of DSC, which are outside the scope of this book, can be surveyed, for example, in biannual reviews that appear in the journal Analytical Chemistry [239],... 

There have been many studies that have attempted to elucidate the chemistry of thermolysis of wood by examining the thermal behaviour of isolated wood components, and much of the early work in this respect has been reviewed (Beall and Eickner, 1970). The use of thermal analysis techniques has shown that the results obtained are quite variable and... 

Foreman, J., Sauerbrunn, S. R., and Marcozzi, C. L. (1995). Thermal analysis rheology Exploring the sensitivity of thermal analysis techniques to the glass transition. TA Instruments, Inc., New Castle, DE. 

The development of thermal analysis methods in materials research has led to a plethora of new methodologies since the elaboration of the first thermal method by by Le Chatelier and Robert-Austen [16,86], Thermal analysis consists of a group of techniques in which a physical property of a material is measured as a function of temperature at the same time when the substance is subjected to a controlled increase, or in some cases, decrease of temperature. Temperature-programmed techniques, such as DTA [87-89], TGA [87], DSC [53,90], TPR [91,92], and TPD [93-96], contribute to perform a more complete characterization of materials. 

The main purpose of this chapter is to review the applications of thermal analysis and calorimetric techniques to the study of catalysts such as oxides, heteropolyanions, hydrotalcites, layered silicates and microporous or mesoporous molecular sieves. A brief summary of studies that made use of calorimetry to characterize crystaUine or amorphous oxides and related materials is also presented. 

Application of difiFerential thermal analysis and thermogravimetric analysis techniques to the pyrolysis of cellulose is obviously complicated by the complexity of the reactions involved, and the corrections and simplifying assumptions that are required in calculating the kinetic parameters. Consequently, these methods provide general information, instead of accurate identification and definition of the individual reactions (and their kinetics), which are traditionally conducted under isothermal conditions. The data obtained by dynamic methods are, however, useful for comparing the efiFects of various conditions or treatments on the pyrolysis of cellulose. In this respect, the application of thermal analysis for investigating the effect of salts (and flame retardants in general) on the combustion of cellulosic materials is of special interest and will be discussed later (see p. 467). 

The use of thermal analysis techniques for pharmaceuticals implies the knowledge of the thermal behavior of the excipients. A great number of publications deal with polymorphic behavior of excipients and especially with the amorphous forms as prerequisite knowledge for freeze drying and milling processes. 

The object of this paper is the application of thermal analysis techniques, such as DTA/TGA, and sintering tests performed in a muffle furnace, in combination with SEM-EDX analysis techniques, to deepen our understanding of the high-teroperattu e of the ash of various solid biofiicls. 

Thermal analysis involves observation of the usually very delicate response of a sample to controlled heat stimuli. The elements of thermal-analysis techniques have been known since 1887 when Le Chatelier used an elementary form of differential thermal analysis to study clays (4), but wide application did not come until the introduction of convenient instrumentation by du Pont, Perkin-Elmer, Mettler and other sources in the 1960 s. Currently, instrumentation and procedures are commercially available for DTA, DSC, TGA, TMA, and a number of so-called hyphenated methods. Several methods are currently under study by ASTM committees for consideration as to their suitability for adoption as ASTM standards. 

The use of thermal analysis techniques has increased rapidly in the past ten years and their field of application is widening continuously. This new book provides an overview of the principal thermal analysis methods and their application in major areas of importance, and will bring the reader up-to-date with the latest advances in the field. Special Publication No. 117 Hardcover viii+296 pages ISBN 0 85186 375 2... 

Perhaps the most important advance in commercial thermal analysis instrumentation during the past 10-12 years has been the use of microprocessors and/or dedicated microcomputers to control the operating parameters of the instrument and to process the collected experimental data. This innovation is by no means unique to thermal analysis instrumentation alone since these techniques have been applied to almost every type of analytical instrument. Unfortunately, the automation of thermal analysis has not become a commercial reality. Complete automation is defined here as automatic sample changing, control of the instrument, and data processing. Such instruments were first described by Wendlandt and co-workers in the early 1970s (See Chapters 3 and 5) although they lacked microprocessor control of the operating conditions. 

The primary goal of this book, as described in the preface to the second edition, is to serve as a general introduction to the field of thermal analysis. Due to the voluminous papers published during the past 10 years, it is not possible to make the book comprehensive for each technique. Indeed, separate volumes could easily be written on each one discussed here. Some degree of critical evaluation has been added, especially in chapters such as those on reaction kinetics, purity determination, and instrumentation. 

Surveys of the types of thermal analysis techniques used and their applications to numerous areas cf research have been published by Wendlandt (6), Liptay (7), and Dunn (8). The most widely used techniques are TG and DTA, followed by DSC and TM A. Inorganic materials are the most widely studied by thermal analysis techniques, followed by high polymers, metals and... 

The number of studies in which adsorption microcalorimetry has been successfully applied to this end has increased in recent years, especially concerning the determination of the acidic function of molecular sieves, and extensive reviews of the systems investigated using this methodology have been published [1,5-14,19,78-81]. In particular, an extensive review [4] summarizes some of the most recently published results concerning applications of microcalorimetry to the study of the acid-base sites of zeolites and mesoporous materials. The efficiency of thermal analysis techniques for the characterization of the acid-base strength of zeolite materials is also discussed, as well as their ability to provide information consistent with catalytic data [4]. 

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