TG Technique

The various methods for the online monitoring of coal composition include the TG technique, which automatically performs a multistep analytical sequence by sequentially drying, burning, and weighing the residue. Figure 3.12 shows the analysis results from an automated TG system. The elapsed time of the proximate analysis program and cooling of the tube back to load temperature totals 30 minutes. 

The light-induced dimer should eventually dissociate to return to the monomers, because no permanent change was observed. It may be reasonable to assume that the dimer dissociates when the photoadduct state of LOV2 goes back to the ground state. We should emphasize that this TG technique for the D measurement in the time domain has been the only one technique that can detect such transient dimer formation. 

Therefore, the signal intensity depends on the polarization of the pump, probe, and signal light. For the thermal detection by the TG technique, usually the polarizations of the two pump beams are set to be parallel because of the tensor symmetry of the thermal component (Section 1I.D). Under this parallel polarization, the TG signal can be understood by a more intuitive picture of intensity grating as follows. 

Aromatic azo compounds are well-known to exhibit trans cis photoisomerization upon photoexcitation [129]. The volume change and AH from the photoisomerization of azobenzene and azobenzene derivatives were recently measured by the time-resolved TG technique discussed in Section III.D [130] (Scheme 9). 

By combining the two-step excitation TG technique with the population grating (Section II.C), the rates and the quantum yield of reactions from higher excited states were determined for dimethyl-s-tetrazine [35] (Scheme 10). 

Rajeshwar I52) determined the kinetics of the thermal decomposition of Green River oil shale kerogen by using direct Arrhenius. Freeman and Carroll, and Coats and Redfern methods. The E, A, and values are given in Table 2.7. Rajeshwar concluded that the ability to resolve multiple processes hinges on the efficacy of the particular kinetic analysis employed and is not an inherent difficulty with nonisothermal TG techniques in general. The direct Arrhenius and Coats and Redfern methods clearly indicate the presence of two reactions with distinctly different kinetic parameters. On the olher hand, the Freeman and Carroll method is handicapped at low fractional... 

The application of thermogravimetry to a particular problem is possible if a mass-change is observed on the application of heat. If no mass-change is observed, then other thermal techniques such as DTA, DSC, TMA, and so on, may have to be employed. If the mass-change is very small (< 1%), then perhaps other techniques such as evolved-gas analysis (EGA) may be more useful. Mass-changes (generally mass-losses) which can be detected by TG techniques are summarized in Figure 4.1. 

The determination of the vapor pressure of various compounds was reviewed by Wiedemann (49). He discussed the determination of vapor pressure by TG techniques based on the Knudsen effusion method. The sample holder that was employed is illustrated in Chapter 3 (Figure 3.6). For some measurements, a Pyrex glass cell having a diameter of about 15 mm was used. Four organic compounds were studied p-chlorophenyl-AT. Af-dimethyl urea (Monuron. a herbicide), p-phenacetin, anthracene, and benzoic acid, in the temperature range of 250-400 K. The vapor-pressure curves of these compounds, in the range from 0 10 Torr, are shown in Figure 4.49. The AHs values calculated were Monuron. 27.4 p-phenacetin 27.6 anthracene, 20.1 and benzoic acid. 20.7 kcalmole. 

The nature of MW-CNT produced for the different catalyst series were characterized by transmission electron microscopy (TEM) and thermo-gravimetric (TG) techniques. 

Characterization of the MW-CNT by TEM and TG techniques indicated that the higher thermal stability and the smaller carbon nanotube diameter are obtained for the samples containing a Co/Co+Fe atomic ratio < 0.35 (Table 1). 

The TG technique is (just like the DSC) very popular in polymer reseach, in particular to study the thermal stability of polymeric systems under application conditions. An example of the straightforward use of this technique for polypropylene (PP) is given in chapter 2.2. A series of TG experiments on PP catalyst systems under special conditions (an oxygen- and moisture-free sample loading procedure) is described in... 

Capon and Maggs [68] used DTA and TG techniques to investigate the effects of metal chlorides on the thermal decomposition of viscose rayon and found that ZnCl2 and CdCl2 impregnations lowered the rapid decomposition temperature and increased the char yield, appearing to promote the initial dehydration reaction at the expense of the depolymerization process [69]. 

Tutas M, Saglam M, Yuksel M, Guler C. Investigation of the thermal decomposition kinetics of polyacrylamide using adynamic TG technique. Thermochim Acta. 1987 111 121-6. Kitahara Y, Okuyama K, Ozawa K, Suga T, Takahashi S, Fujii T. Thermal decomposition of acrylamide from polyacrylamide time-resolved pyrolysis with ion-attachment mass spectrometry. J Therm Anal Calorim. 2012 110 423-9. 

FT-Raman has been used as an alternative to TG techniques to determine filler content in HDPE/ CaC03 composites and provides comparable results [400]. As most pigments (apart Ifom carbon-black) and glass are poor Raman scatterers, in principle Raman spectra are obtainable Ifom these samples without removal of the fillers or difficult sample preparation. Conventional visible Raman spectroscopy has failed in attempting to analyse dyesmffs. Conventional Raman spectra of dyed textiles tend to be dominated by the (fluorescent) spectrum of the dye [401]. Consequently, FT-Raman spectroscopy may be a more useful tool for direct observation of low levels of dyestuffs in polymeric materials. Indeed, by using NIR excitation dramatic improvements in the Raman spectra of these dyes can be achieved [392]. FT-Raman was quite useful for the discrimination of differently dyed cotton-cellulose fabrics with the bifunctional reactive dye Cibacron C, provided that the interpretation was facilitated by chemometrics [402]. Schrader et al. [403] have used FT-Raman spectra to distinguish non-destructively the main dye components in historical textiles. Bourgeois et al. [401] have successfully used FT-Raman in the characterisation of... 

Arii et al. [447] have used an integrated simultaneous TG-DTA/GC-MS system with dynamic rate control (DRC), a form of a high-resolution TG technique. In this DRC method the heating rate is controlled in such a way that the absolute value of a sample s temperature decrease rate is expressed as a monotonous function of the sample s weight decrease or decomposition rate. This feature improves... 

Correa and co-workers [a.272] studied the thermal behaviour of short-fibre-reinforced PU composites by DSC and TG techniques and reported that the thermal resistance of aramid-fibre-reinforced composites was greater than that of carbon-fibre-reinforced composites or the pure matrix polymer. The DTG results are presented in Figure 31. 

DTA-TG techniques have been applied to study calcination kinetics of raw materials, quantification of raw materials, determination of total heat for clinker formation, and prediction of material temperature profile in... 

Table 4. Estimation of Hexagonal and Cubic Phases by TG Technique...

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