Other Thermal Characterization Techniques

While TMA refers to a measurement of a static mechanical property, there are also techniques that employ dynamic measurement. In the torsional braid analysis (TEA), a sample is subjected to free torsional oscillation. The natural frequency and the decay of oscillations are measured. This provides information about the viscoelastic behavior of materials. However, these measurements are elaborate and time consuming. In dynamic mechanical analysis (DMA), a sample is exposed to forced oscillations. A large number of useful properties can be measured by this technique see also Section 6.2.6.5. 

In thermal optical analysis (TOA), the conversion of plane-polarized light to ellipti-cally polarized light is measured in semi-crystalline polymers. The intensity of the depolarized light transmitted through a sample is a function of the level of crystallinity. Melting and recrystallization phenomena can be analyzed the technique does not appear to be sensitive to glass transitions [88]. The TOA technique is also referred to as thermal depolarization analysis (TDA) and depolarized light intensity method (DLI). 

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It should be stressed that the valuable features of hot-stage microscopy in the solid-state characterization of pharmaceuticals are much ignored. In order to understand the results obtained by other thermal analytical techniques (e.g. DSC or TGA), it is highly recommended to perform also thermomicroscopic investigations. Visual images are very convincing and contain often much more information than any plotted curve. This may finally save a considerable amount of time and additional experiments, but like most microscopy techniques, TM requires also some experience and patience. 

Microscopic Methods - Morphology Study and Sizing (0.001-200 pm) Microscopic analyses are and have always been indispensable tools in particle studies. For example, in 1827 the English botanist Robert Brown discovered the random thermal motion of flower pollen particles in suspension now known as Brownian motion" using an optical microscope. A simple optical microscope can provide visual observation and inspection of individual particles features and dimensions down to the micron range. Microscopes are also widely used in preparation of samples for other particle characterization techniques to check whether particles have been properly dispersed. 

Several new thermal analytical techniques are potentially valuable for the study of second-order transitions in the characterization of amorphous solids and for the accurate determination of glass transition temperatures. These modem techniques can detect and characterize glass transitions and other second-order transitions that are not detectable by conventional thermal analytical techniques such as DSC, TGA, or TMA. 

Most workers in the pharmaceutical field identify thermal analysis with the melting point, DTA, DSC, and TG methods just described. Growing in interest are other techniques available for the characterization of solid materials, each of which can be particularly useful to deduce certain types of information. Although it is beyond the scope of this chapter to delve into each type of methodology in great detail, it is worth providing short summaries of these. As in all thermal analysis techniques, the observed parameter of interest is obtained as a function of temperature, while the sample is heated at an accurately controlled rate. 

If one were to judge the importance of TSL and TSC relative to other thermal transport methods for trap characterization by number of recently published papers, these techniques appear to far outweigh all others combined, even though about one-third of the publications are concerned with applications in dosimetry and related TSL (TSC) instrumentation. However, the large number of articles on TSL and TSC does not necessarily indicate any advantage in their usefulness as trap-spectroscopy tools over the other methods. What can safely be concluded is that nonisothermal TSR is still, at the present time, a very active field of research. 

In the first half of this introductory chapter the maceral concept has been discussed and the main maceral groups and their important maceral types described. Emphasis has been placed on in situ characterization techniques which rely mostly on microscopy. The rest of this chapter will examine other techniques used for chemical characterization and examine the reactivity of coal macerals in thermal processes. The availability of separated maceral concentrates was a necessary component of the studies which will be described. 

In addition, there are some other characterization techniques that can be used to examine the carbon-Ti02 composites, including Raman spectroscopy [40,123], atomic force microscopy (AFM) [106,123], thermogravimetric and differential thermal analysis (TGA-DTA) [26,125], determination of pHpzc [19,29], and electron paramagnetic resonance (EPR) [126,127],... 

Potential applications of thermal analysis and calorimetry to quality control is not limited in any way to those discussed in this chapter. Once some physical or chemical characteristic of a material or process is known and can be examined and/or characterized by these techniques, it is only the imagination that limits the possibilities for quality control applications. Both traditional techniques (DSC, TG, DMA, isothermal calorimetry, etc.) and non-traditional techniques (temperature modeling, etc.) have been shown to have potential uses for quality control. With the introduction of many new techniques (fast scanning DSC, sample controlled thermal analysis (SCTA), modulated and other temperature programmed techniques, etc.), many more new opportunities will arise for providing quality control tools. 

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