Thermal methods thermogravimetry

The thermal characterisation of elastomers has recently been reviewed by Sircar [28] from which it appears that DSC followed by TG/DTG are the most popular thermal analysis techniques for elastomer applications. The TG/differential thermal gravimetry (DTG) method remains the method of choice for compositional analysis of uncured and cured elastomer compounds. Sircar s comprehensive review [28] was based on single thermal methods (TG, DSC, differential thermal analysis (DTA), thermomechanical analysis (TMA), DMA) and excluded combined (TG-DSC, TG-DTA) and simultaneous (TG-fourier transform infrared (TG-FTIR), TG-mass spectroscopy (TG-MS)) techniques. In this chapter the emphasis is on those multiple and hyphenated thermogravimetric analysis techniques which have had an impact on the characterisation of elastomers. The review is based mainly on Chemical Abstracts records corresponding to the keywords elastomers, thermogravimetry, differential scanning calorimetry, differential thermal analysis, infrared and mass spectrometry over the period 1979-1999. Table 1.1 contains the references to the various combined techniques. 

The synthesis of the complex is followed by the most important step of characterization of the complex. The composition and the structural features of both the ligand and complex have to be established before embarking on further studies. There exist many methods by which the composition and structural features of the complexes are studied. Some of the methods are (i) elemental analysis, (ii) X-ray crystallography, (iii) UV-Vis absorption spectra, (iv) infrared spectroscopy, (v) Raman spectroscopy, (vi) thermal methods of analysis such as thermogravimetry, differential thermal analysis, (vii) nuclear magnetic resonance spectroscopy (proton, multinuclear), (viii) electrospray mass spectrometry. Depending upon the complexity of the system, some or all the methods are used in the studies of complexes. 

Thermal methods of analysis discussed in this section are differential scanning calorimetry (DSC), thermogravimetry (TG), and hot-stage microscopy (HSM). All three methods provide information upon heating the sample. Heating can be static or dynamic in nature, depending on the information required. 

In thermal methods of analysis, either temperature change is measured or the temperature is manipulated to produce the measured parameter. Thermogravimetry (TG), differential thermal analysis (DTA), and differential scanning calorimetry (DSC) are the three major methods that use temperature change as the independent variable. Thermometric titration (TT) and direct-injection enthalpimetry (DIE) use temperature as the dependent variable. These five methods will be discussed primarily from an analytical point of view. Each method has its unique characteristics and capabilities for that reason, the major aspects of each method are considered individually. 

A detailed account of polymorphism and its relevance in the pharmaceutical industry is given elsewhere in this volume and in the literature [42,46,47]. This section will focus on the use of vibrational spectroscopy as a technique for solid-state analysis. However, it should be noted that these techniques must be used as an integral part of a multidisciplinary approach to solid-state characterisation since various physical analytical techniques offer complimentary information when compared to each other. The most suitable technique will depend on the compound, and the objectives and requirements of the analysis. Techniques commonly used in solid-state analysis include crystallographic methods (single crystal and powder diffraction), thermal methods (e.g. differential scanning calorimetry, thermogravimetry, solution calorimetry) and stmctural methods (IR, Raman and solid-state NMR spectroscopies). Comprehensive reviews on solid-state analysis using a wide variety of techniques are available in the literature [39,42,47-49]. 

The monograph Thermal Methods in Petroleum Analysis is based mainly on results of more than twelve years research work on the application of thermoanalytical methods to petroleum and its products during the activities of the author at the German Institute for Petroleum Research. It was very interesting to research the application of well defined physical methods, such as thermogravimetry and differential scanning calorimetry, to the multicomponent systems of petroleum and its products, and to understand the limits of those methods on the one hand and the excellent transferability of the results to technical processes on the other. The diversity of possible applications of thermoanalytical methods to various problems in the petroleum laboratory can only be indicated in this monograph. 

The use of thermal methods of analysis for the characterization of coal liquefaction residues can provide much information regarding the physical nature and composition of such coal conversion byproducts. Their thermal and oxidative stabilities are readily assigned from both TG and DSC methods. Heat history effects may be observed from both DSC and WA techniques. Volatile matter content, fixed carbon values, and ash content are readily obtained from thermogravimetry, Calorific values are accurately determined by dynamic DSC studies in flowing air atmospheres. Furthermore, volatilization profiles by TG and combustion profiles by both DSC and DTG may be used as tools for fingerprinting such residues. The use of computerized DSC offers the additional concept of normalized comparisons and subtraction of these profiles versus temperature. A combination of the information obtained from thermal methods of analysis, elemental analysis, microscopic and spectroscopic techniques, and solubility studies may lead to the total characterization of coal conversion by-products. 

Two thermal methods have been extensively studied in recent years, pyrolysis-gas chromatography (Py-GC) - mass spectrometry (MS) and evolved gas analysis involving infrared spectroscopy (IR) - MS, thermogravimetry and differential scanning calorimetry (DSC). 

Since the experimental conditions have a profound effect on the results obtained by thermogravimetry, and also other thermal methods, it is as well to establish a set of rules to follow in order to obtain the most reproducible results, or to recognize why runs differ. 

A. Auroux, Thermal methods calorimetry, differentieil thermal analysis, and thermogravimetry, in Catalyst Characterization Physical Techniques for Solid Materials, ed. by B. Imelik, J.C. Vedrine (Plenum Press, New York, 1994), pp. 611-635... 

Thermal analysis gives information on the fundamental behavior and structure of materials based on their thermochemical and thermophysical properties. Differential thermal analysis (DTA), differential scanning calorimetry (DSC), thermogravimetry (TG), dilatometry, and other related dynamic thermal methods serve as analytical tools for characterizing a wide variety of solid materials. Information obtainable by these methods includes phase relationships, identification and measurement of impurities in high-purity materials, fingerprint identifications, thermal histories of the material, and dissociation pressures. 

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). 

Thermogravimetry (TG) is a measure of the thermally induced weight loss of a material as a function of the applied temperature [39], Thermogravimetric analysis is restricted to studies involving either a mass gain or loss, and it is most commonly used to study desolvation processes and compound decomposition. Thermogravimetric analysis is a very useful method for the quantitative determination of the total volatile content of a solid, and it can be used as an adjunct to Karl Fischer titrations for the determination of moisture. 

The research papers which originated in the last couple of years in different countries in this field indicate that ED and Er are not generally reported and there is an emphasis on the study of comprehensive thermal behavior of explosives as a function of temperature or time by means of different thermal analytical techniques. Most commonly used methods of thermal analysis are differential thermal analysis (DTA), thermogravimetric analysis (TGA) or thermogravimetry and differential scanning calorimetry (DSC). 

In addition to routinely used methods, such as elemental analysis, IR and UV-vis-NIR spectra, thermogravimetry-differential thermal analysis (TG-DTA), single-crystal X-ray diffraction, and gas adsorption, there are some important characterization methods for coordination polymers. 

Spectral subtraction and spectral search aid the identification of evolved gases, which are often a mixture of products. Nevertheless, for unambiguous identification of unknown volatiles more powerful methods are required. Jansen and co-workers [86] have incorporated a parallel mass spectrometer onto the FTIR stage of a thermogravimetry-FTIR (TG-FTIR). The sample is thermally decomposed by TGA and the products collected in a Tenax (absorbent charcoal) trap. After desorption, the products are separated by a GC and the sample split, with 99% going to the IR spectrometer and 1% to the mass spectrometer. 

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