Simultaneous Thermal Analysis Methods

Simultaneous thermal analysis (STA) refers to the simultaneous application of two or more thermoan-alytical methods on one sample at the same time, such as DTA and thermoconductivity. In practice, however, this term is mostly used for simultaneous measurement of the mass changes and caloric effects on a sample under thermal treatment. The benefits are (i) information on transformation energetics and mass change in one run, under identical conditions (ii) time saving and (Hi) no differences in sample composition for the various thermal measurements - important for non-homogeneous sample materials. Although TG-DSC and TG-DTA are the most widely used of the simultaneous techniques due to 

Short overviews of thermogravimetric analytical techniques (simultaneous, non-simultaneous, (multi)hyphenated) are available [282,283]. 

The advantages of single sample simultaneous TG-DSC (or TG-DTA) have been summarised by Redfern [288] and others (Table 2.12). The technique has recently been reviewed [285,289]. 

Typical applications that are ideal for TG-DSC are temperature stability, decomposition behaviour, drying and firing processes, transition and reaction temperatures, melting and crystallisation processes. Redfern [290] has reviewed single sample simultaneous thermal analysis, i.e. TG-DSC and TG-DTA smdies of polymers, and has reported TG-DSC of an uncured polyimide resin in which a more accurate determination of the quantitative measurement 

Kodama et al. [291] have reported TG-DSC curves for the analysis of the interaction between vulcanisation accelerators (tetramethylthiuram disulfide, dibenzothiazolyl disulfide, diphenyl-guanidine and Af-cyclohexyl-2-benzothiazolylsul-fenamide) and fillers (CB, hard clay and CaCOs). The initial m.p. of the accelerators was largely influenced by the fillers. Emmott et al. [292] have investigated the complex reaction between Sr(N03)2 and the binder Alloprene (a pyrotechnic system) at about 300°C by simultaneous TG-DSC and TG-DTA-MS. The same techniques were used to examine the Ti-NaNOs-Alloprene and Mg-NaNOs-Alloprene systems [293-295]. 

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The extent of dehydration during temperature treatment of tin(IV)oxide powder is Mcertained by thermogravimetry (Simultaneous Thermal Analysis STA 409, Netzsch). Surface are l8 are determined by nitrogen adsorption using a standard volumetric BET apparatus. The tin(IV)oxide content of the loaded crtrriers and the catalysts is quantified gravimetrically. The platinum content of the catalysts is obtained by a spectrophotometric method which has been described elsewhere (11). 

A typical method for thermal analysis is to solve the energy equation in hydrodynamic films and the heat conduction equation in solids, simultaneously, along with the other governing equations. To apply this method to mixed lubrication, however, one has to deal with several problems. In addition to the great computational work required, the discontinuity of the hydrodynamic films due to asperity contacts presents a major difficulty to the application. As an alternative, the method of moving point heat source integration has been introduced to conduct thermal analysis in mixed lubrication. 

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. 

During investigation of a new material it is unlikely that any single thermal analysis technique will provide all the information required to understand its behavior. Complementary information is usually needed, which may be from another simultaneous thermal technique such as thermogravimetric-differential scanning calorimetric-mass spectrometry (TG-DSC-MS), gas chromatography (TG-GC, or DSG-GG), or spectroscopic methods such as IR spectroscopy or X-ray photoelectron spectroscopy (XPS). 

The so-called hyphenated techniques , incorporating thermal methods as one of the combined analytical techniques are sure to play an increasing role in the identification and characterization of crystalline forms of pharmaceutical substances. The combination of TGA with FTIR allows the simultaneous quantitative analysis of weight changes during thermal processes with the IR identification of the decomposition products (e.g. solvent) resulting from those processes (Materazzi 1997). For substances with low volatility, the FTIR analysis may be replaced with mass spectroscopy (Materazzi 1998). 

Tools for the predictive behavior of a design have developed from classical and numerical methods of the past to the current finite element analysis (FEA) utilized by today s engineers and chemists. FEA is a computer-based analytical tool used to perform stress, vibration, and thermal analysis of mechanical systems and structures. A set of simultaneous equations will represent the behavior of a system or structure under load. Because this is a very important tool, some time will be devoted to the discussion of it, but this is not meant to be a comprehensive study. 

The techniques of DTA, and to some extent TG, have long been used by geochemists and others to study the thermal behavior of clays and minerals. Since many simultaneous reactions occur in clays, as well as solid-state reactions that alter the decomposition reaction, the use of other methods such as EGA, X-ray, IR. and so on, are used to supplement conventional thermal analysis techniques. Consequently, there has recently been an unusual amount of interest in the use of EGA (MS) in the study of these compounds. 

Although the principal thermal analysis techniques are thermogravimetry, differential thermal analysis, and differential scanning calorimetry (see Chapter 1), there are a number of other thermal techniques, besides those discussed elsewhere in this book, that are useful for solving chemical and technological problems. Some of these methods are of recent development and hence little used at the present time, but they possess the potential for wider use in the future. Many of these techniques are employed to supplement or complement the three principal techniques of TG. DTA. and DSC, either in the simultaneous (single sample) or concurrent multiple samples) modes. 

Thermoelectrometry has been reviewed in book chapters by Wendlandt (52,53) and Warfield (54), and reviews by Chiu (78), Paulik and Paulik (55), and Wendlandt (56, 98, 99). Since many of the therrooelecirometry studies involve simultaneous methods with other thermal analysis techniques, reference (55) is especially useful. 

It should be noted that, in many cases, the use of only a single thermal analysis technique may not provide sufficient information about a given system. As with many other analytical methods, complementary or supplementary information, as can be furnished by other thermal analysis techniques, may be required. For example, it is fairly common to complement all DTA or DSC data with thermogravimetry. If one or more gaseous products result, evolved gas analysis may prove useful in solving the problem at hand. Simultaneous thermal techniques are helpful in this respect in that several types of data are obtained from the same sample under identical pyrolysis conditions. 

The recent technique of micro-thermal analysis ()U-TA), which now has a variety of measurement modes, is included here because usually two or more measurements are made simultaneously. Micro-TA combines the imaging capabilities of atomic force microscopy (AFM) with a form of localised thermal analysis, and is able to measure thermal transitions on an area of a few microns. A good introduction to the whole family of these methods is available on the internet, from which application studies can... 

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