Thermoanalytical analysis

How does thermoanalytical analysis give rise to various types of thermograms that help in characterizing either a single or multicomponent system ... 

Hassel [103] has compared DSC, TG, thermal evolution analysis, TMA and DMA in evaluating flame retardant textiles based on different polyester fibres. Also the thermoanalytical analysis (DSC, TGA) of a sisal reinforced flame retardant poly-ester/(DBDPO, Sb203) formulation has been described [104]. Larcey et al. [105] have reported use of a simultaneous TG-DSC system (STA) to investigate the suitability of using magnesium hydroxide as a flame retardant and smoke suppressant in PP formulations. 

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). 

Thermal analysis helps in measuring the various physical properties of the polymers. In this technique, a polymer sample is subjected to a controlled temperature program in a specific atmosphere and properties are measured as a function of temperature. The controlled temperature program may involve either isothermal or linear rise or fall of temperature. The most common thermoanalytical techniques are (1) differential scanning analysis (DSC), (2) thermomechanical analysis (TMA), and (3) thermogravimetry (TG). 

Thermoanalytical techniques such as differential scanning calorimetry (DSC) and thermogravi-metric analysis (TGA) have also been widely used to study rubber oxidation [24—27]. The oxidative stability of mbbers and the effectiveness of various antioxidants can be evaluated with DSC based on the heat change (oxidation exotherm) during oxidation, the activation energy of oxidation, the isothermal induction time, the onset temperamre of oxidation, and the oxidation peak temperature. 

First-order phase transitions can be detected by various thermoanalytical techniques, such as DSC, thermogravimetric analysis (TGA), and thermomechanical analysis (TMA) [31]. Phase transitions leading to visual changes can be detected by optical methods such as microscopy [3], Solid-solid transitions involving a change in the crystal structure can be detected by X-ray diffraction [32] or infrared spectroscopy [33], A combination of these techniques is usually employed to study the phase transitions in organic solids such as drugs. 

The nature of the material to be studied, which means its degree of crystallinity and perfectness of crystal structure, may have a significant effect on the thermoanalytical behavior. In spite of identical chemical composition of a certain material the variations with respect to structure, imperfections, grain boundaries, etc. are almost infinite. Of course many of these will not show in normal thermogravimetric analysis, with very sensitive apparatus characteristically different TG curves18, 19 may be obtained however. As an example Fig. 26 shows the thermal decomposition of hydrozincite, Zn5(OH)6(003)2, whereby equal amounts of samples from natural origin and synthetic preparations are compared. 

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 ... 

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]. 

Table 3.5 Various thermoanalytical techniques for thermal analysis.

This chapter summarizes results obtained during the past 5 years, on the design, preparation and study of titanium and vanadium compounds as candidate precursors to TiC, TiN, VC, and VN. The study of the precursor molecules was conducted through several steps. After their synthesis, thermoanalytical studies (TG-DTA), coupled to simultaneous mass spectroscopic (MS) analysis of the decomposition gases, were carried out to determine their suitability as precursors. CVD experiments were then conducted and were followed by characterization of the deposits by scanning electron microscopy (SEM) energy dispersive spectroscopy (EDS), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), and electron microprobe analysis with wavelength dispersion spectroscopy (EPMA-WDS). 

Thermoanalytical and single crystal X-ray diffraction analysis of alcohol-... 

Thermoanalytical investigations of sedimented airborne particulates [EINAX and LUDWIG, 1991] confirm experimentally the chemometrically found interpretation that aluminum can serve as an indicator element for lignite combustion. Thermogravimetric analysis of mixed samples of sedimented dusts detect a loss of mass at a temperature of 714°C this can be interpreted as dehydration of aluminosilicates. This loss of mass exhibits a well defined summer minimum and a strong winter maximum. These findings also correspond to the results from factor analysis (see Section 7.2.1.2.4). 

It should be noted in conclusion that a thermoanalytical screening of 35 tetrazoles based on the data of differential scanning calorimetry (DSC), thermogravimetric analysis (TGA), and evolved gas analysis (EGA) has been performed <1999MI168> (cf. Section 6.07.5.2.1). 

Marosi, G., Anna, P., Balogh, I., Bertalan, G., Tohl, A., and Maatoug, M. A. 1997. Thermoanalytical study of nucleating effects in polypropylene composites. 3. Intumescent flame retardant containing polypropylene. Journal of Thermal Analysis 48 717-26. 

H. Levine and L. Slade, Cryostabilisation technology thermoanalytical evaluation of food ingredients and systems, in Thermal Analysis of Foods (V. R. Harwalkar and C. Y. Ma, eds.), Elsevier, London, 1989, pp. 221-305. 

Analytical pyrolysis is considered somehow apart from the other thermoanalytical techniques such as thermometry, calorimetry, thermogravimetry, differential thermal analysis, etc. In contrast to analytical pyrolysis, thermoanalytical techniques are not usually concerned with the chemical nature of the reaction products during heating. Certainly, some overlap exists between analytical pyrolysis and other thermoanalytical techniques. The study of the kinetics of the pyrolysis process, for example, was found to provide useful information about the samples and it is part of a series of pyrolytic studies (e.g. [6-8]). Also, during thermoanalytical measurements, analysis of the decomposition products can be done. This does not transform that particular thermoanalysis into analytical pyrolysis (e.g. [9]). A typical example is the analysis of the gases evolved during a chemical reaction as a function of temperature, known as EGA (evolved gas analysis). 

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