Thermoanalytical methods

The procedures of measuring changes in some physical or mechanical property as a sample is heated, or alternatively as it is held at constant temperature, constitute the family of thermoanalytical methods of characterisation. A partial list of these procedures is differential thermal analysis, differential scanning calorimetry, dilatometry, thermogravimetry. A detailed overview of these and several related techniques is by Gallagher (1992). 

Difl erential thermal analysis (DTA) and differential scanning calorimetry (DSC) are the other mainline thermal techniques. These are methods to identify temperatures at which specific heat changes suddenly or a latent heat is evolved or absorbed by the specimen. DTA is an early technique, invented by Le Chatelier in France in 1887 and improved at the turn of the century by Roberts-Austen (Section 4.2.2). A 

This approach is an alternative to quantitative metallography and in the hands of a master gives even more accurate results than the rival method. A more recent development (Chen and Spaepen 1991) is the analysis of the isothermal curve when a material which may be properly amorphous or else nanocrystalline (e.g., a bismuth film vapour-deposited at low temperature) is annealed. The form of the isotherm allows one to distinguish nucleation and growth of a crystalline phase, from the growth of a preexisting nanocrystalline structure. 

The measurement of mechanical properties is a major part of the domain of characterisation. The tensile test is the key procedure, and this in turn is linked with the various tests to measure fracture toughness... crudely speaking, the capacity to withstand the weakening effects of defects. Elaborate test procedures have been developed to examine resistance to high-speed impact of projectiles, a property of civil (birdstrike on aircraft) as well as military importance. Another kind of lest is needed to measure the elastic moduli in different directions of an anisotropic crystal this is, for instance, vital for the proper exploitation of quartz crystal slices in quartz watches. 

There is space here for a brief account of only one technique, that is, hardness measurement. The idea of pressing a hard object, of steel or diamond, into a smooth surface under a known load and measuring the size of the indent, as a simple and 

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Thermoanalytical methods (tga, dta) often enable definite identification of the type of asbestos fibers (Fig. 7). For example, the strong exotherm observed with chrysotile at 830°C can be used as a routine indicator for determining the chrysotile content of talc (4,10). Thermal methods are also usefiil for determining certain mineral contaminants of asbestos fibers, for example bmcite and calcite in chrysotile. 

Thermoanalytical method is one of the widespread methods of physical and chemical reseai ches. Considerably broadens its possibilities combination with methods differential-thermal (DTA), differential-thermogravimetric (DTG), thermogravimetric (TG) analyses. 

P.D. Gam, Thermoanalytical Methods of Investigation, Academic Press, New York, 1965. 

Thermoanalytical methods comprise a series of techniques in which a property is determined at different temperatures or as the temperature changes continuously. The property measured may include the mass of the sample (TGA), the heat flow to the sample (DSC), the magnetic character of the sample (TMA), or some other property such as dimensional changes. Each of these types of measurements gives information on some change undergone by the sample, and if the change is followed over time, it is possible to derive kinetic information about the transformation. 

The effects of stepwise heating29 in shifting the reaction to lower temperatures and in decreasing the interval AT as compared to linear heating is shown schematically in Fig. 32. By such special heating techniques it is possible to obtain thermodynamic data also by thermoanalytical methods. This has been demonstrated recently for the... 

These measurements on the oxidation of palladium prove that it is possible to obtain thermodynamic data also by dynamic, thermoanalytical methods. The values... 

The theoretical background of various thermoanalytical methods is now well established. An important contribution to the quantitative evaluation of the results was made by the use of standard reference materials. These allow not only the calibration of the instrument but also the comparison and correlation of results which were obtained with different instruments. 

The possibilities for combining thermoanalytical methods like TG with other techniques and to carry out such measurements in certain cases simultaneously are increasing. This is of great significance for the easier and sometimes unambiguous interpretation of results. 

Thermoanalytical methods, including thermogravimetry, have been used originally in the earth sciences and in chemistry. With todays multifunctional and highly sensitive instruments, these methods are becoming important for many other, new fields of science and technology. 

Gam, P. D. Thermoanalytical methods of investigation. London-New York Academic Press 1965... 

Thermoanalytical methods essentially encompass such techniques that are based entirely on the concept of heating a sample followed by well-defned modified procedures, such as gravimetric analysis, differential analysis and titrimetric analysis. In usual practice, data are generated as a result of continuously recorded curves that may be considered as thermal spectra . These thermal spectra also termed as thermograms, often characterize a single or multicomponent system in terms of ... 

Broadly speaking the thermoanalytical methods are normally classified into the following three categories, namely ... 

As described in Section 3.3.2.1 on heat sensitivity, thermoanalytical methods are sufficiently sensitive as an early indication of incipient chemical decomposition or chemical reaction, that is, stability and incompatibility. Some research papers discuss the use of differential thermal analysis (DTA) and differential scanning calorimetry (DSC) for this purpose [20-22]. 

A catalyst surface may be assumed to be characterized by specific poisoning if the number of adsorption sites, the strength (or the strength distribution) of the adsorbate-catalyst interaction, and the nature of this interaction as well as the chemical nature of the adsorbed species can be determined. All three properties are equally important to characterize fully, i. e., qualitatively and quantitatively, a catalyst surface. The number of adsorption sites may be determined from the adsorbed amount of poison as measured by conventional techniques, whereas thermoanalytical methods have to be applied for a quantitative characterization of the adsorption bond strength. Spectroscopic methods will be most suitable for studies of the chemical nature of the adsorbed species and the nature of the adsorbate-surface interaction. 

Wright, D. J. 1984. Thermoanalytical methods in food research. In, Biophysical Methods in Food Research (H.W.-S. Chan, ed.), pp. 1-36, Blackwell Scientific Publications, Oxford. 

Kuhnert-Brandstatter, M. (1996). Thermoanalytical methods and their pharmaceutical applications. Pharmazie, 51,443-57. [105, 250]... 

Crighton, J., Findon, W., Happey, F., Application of Thermoanalytical Methods in the Study of Keratin and Related Proteins, in Proceedings of the Fourth International Wool Textile Research Conference, Part II, p. 847, L. Rebenfeld, Ed., Interscience, New York, 1971. 

Epple, E. Cammenga, H.K. Temperature resolved x-ray diffractometry as a thermoanalytical method a powerful tool for determining solid state reaction kinetics. J.Therm. Anal. 1992, 38, 619-626. 

For these methods the problems inherent in calorimetry arc added to those which were described previously as being typical for dynamic thermoanalytical methods. 

Titanium(il).—Standard enthalpies of solution have been determined for the molten systems of TiCl3-TiCl2-NaCl and TiCl3-TiCl2. The system VCl3-TiCl2-KCI has been studied by thermoanalytical methods. ... 

Ti has been detected by e.p.r. spectroscopy in electrochemically reduced solutions of TiCU, and the standard enthalpies of solution have been determined for the systems TiClj-NaChTiClj-TiClj-NaCl, and TiCla-TiClj. The system VCI3-TiClj-KCl has been studied by thermoanalytical methods. TiCla reacts with alkaline K2Hgl4 to form a compound with the stoicheiometry K2[Hgl4],4TiCl3,18H20 which liberates Hgl2 when heated. ... 

An interesting property of many polymers is their ability to undergo a temperature dependent transition from a primarily liquidlike state (sol) to a gel possessing elasticity. The temperature at which this transition occurs is termed the sol-gel transition. Given the relevance of this transition to both the clinical and nonclinical performance of pharmaceutical systems, various authors have examined this phenomenon using thermoanalytical methods, including thermal oscillatory analysis. Examples of these are now presented. 

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