Thermal analytical techniques

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. 

Riga, A.T. and Judovits, L. 2001. Material Characterization by Dynamic and Modulated Thermal Analytical Techniques . American Society for Testing Materials, West Conshohocken, PA. Rockland, L.B. 1987. Introduction. In Water Activity Theory and Application to Foods (L.B. 

Thermal analytical techniques such as thermogravimetry (TG), differential thermal analysis (DTA) and differential scanning calorimetry (DSC) have all been successfully employed in studying the pyrotechnic reactions of energetic materials such as black powder, as well as of binary mixtures of the constituents. 

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). 

TABLE 18.2. Thermal Analytical Techniques for the Determination of Selected Thermal Transitions... 

Thermal Transition Applicable Thermal Analytical Technique... 

Figure 18.15. Demonstrated use of thermal analytical techniques to evaluate structural and thermodynamic properties of macromolecular materials.

Potential as a Tool for Thermal Analysis of NOM. As mentioned above, TMA and DMA represent more sensitive thermal analytical techniques relative to... 

Phase and state transitions of maximally freeze-concentrated materials are complex. However, the same thermal analytical techniques as well as ESR and NMR techniques provide information of transitions of freeze-concentrated sohds and ice melting (Slade et al. 1995 Roos, 1995 Laaksonen et al. 2002 Roudaut et al. 2004). Low molecular weight components, such as sugars, often exhibit clearly observable... 

Riga, A. Patterson, G.H. Oxidative Behavior of Materials by Thermal Analytical Techniques, ASTM Special Technical Publication 1326, 1997, ASTM. 

Bilyeu, B. Brostow, W. Menard, K. Materials Characterization by Dynamic and Modulated Thermal Analytical Techniques, ASTM STP 1402 Riga, A.T., Judovits, L.H., Eds. American Society for Testing and Materials West Consho-hocken, PA, 2001. 

Detection and characterization of polymorphs and/or solvates rely on various experimental techniques. X-ray powder diffraction (XRPD), solid state nuclear magnetic resonance (NMR), solid state infrared (IR) and solid state Raman are useful in demonstrating differences in the solid state. Thermal analytical techniques, including differential thermal analysis (DTA), differential scanning calorimetry (DSC), and thermogravimetry (TG), are also... 

There are a number of interrelated thermal analytical techniques that can be used to characterize the salts and the polymorphs of candidate drugs. The melting point of a salt can be manipulated to produce compounds with desirable physicochemical properties for specific formulation t5q)es. Of the thermal methods available for investigating polymorphism and related phenomena, DSC, TGA, and HSM are the most widely used methods. 

Since different crystal forms have different structures, they can, potentially, exhibit different physical properties and different responses to experimental analytical methods. Some of the more commonly used of these methods have been demonstrated above. A central question for any polymorphic system is the relative stability of the various crystal forms. As noted above, these may be investigated qualitatively by HSM methods, and more quantitatively using thermal analytical techniques. The combined results of these measurements are conveniently summarized on a semi-empirical energy-temperature diagram [31], as shown in Fig. 3.3.16. The thermal... 

Table 7.3 Overview of thermal analytical techniques and methods...

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. 

Thermogravimetric analytical techniques A group of thermal analytical techniques in which the change in mass of a sample undergoing incremental heating is used to identify the mineralogical composition. 

The thermal decomposition characteristics of micron-sized aluminum powder and potassium perchlorate mixtures were studied with thermal analytical techniques by Pourmortazavi and coworkers [108]. The results showed that the reactivity of aluminum powder in air increases as the particle size decreases. Pure aluminum with 5 pm particle size has a fusion temperature of about 647 °C, but for 18 pm powder this temperature is 660 °C. Pure potassixun perchlorate has an endothermic peak at 300 C corresponding to a rhombic-cubic transition, a fiision temperature around 590 °C and decomposes at 592 °C. DTA curves for an AI5/KCIO4 (30 70) mixture show a maximum peak temperature for thermal decomposition at 400 °C. Increasing the particle size of aluminum powder increases the ignition temperature of the mixture. The oxidation temperature is increased by increasing the aluminum content of the mixture. 

A novel thermal analytical technique was developed by Frushour [167,189,190] that utilizes water to depress the melting point of AN copolymers. This allows melting and melt... 

A variety of advanced techniques exists for determining the species composition of the fuel, which is vital to improved predictive methods for coal, and especially ash behavior, in boilers. X-ray diffraction, performed on low-temperature ash, is the most widely used technique for qirahtatively identifying the presence of minerals in their crystalline form in concentrations of a few weight percent or greater. Thermal analytical techniques such as differential thermal analysis (DTA) and thermogravi-metric analysis (TGA) have been used as a signature analysis based on changes in physical properties with temperature. 

In addition, thermal phenomena that produce significant effects on a larger scale may not have been detected in smaller-scale reactions and therefore could be less obvious than toxic and/or environmental hazards. Thermal analytical techniques should be used to determine whether any process modifications are necessary. 

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