Thermal gravimetric analysis limitations

Determination of the thermal decomposition temperature by thermal gravimetric analysis (tga) defines the upper limits of processing. The tga for cellulose triacetate is shown in Figure 11. Comparing the melt temperature (289°C) from the dsc in Figure 10 to the onset of decomposition in Figure 11 defines the processing temperature window at which the material can successfully be melt extmded or blended. 

There are several nonspecific methods available that can determine the total amount of solvent(s) in a sample. Loss on drying (LOD) determines the amount of volatile components that are released from a sample under specific temperature and/or vacuum conditions. Thermal gravimetric analysis (TGA) measures the loss of volatile components from a sample over a temperature gradient. The advantage of these methods is that they give an estimate of the volatile component content of a sample relatively quickly. The disadvantages of these methods are that they do not speciate and cannot account for volatile components that are trapped in the lattice structure of the compound. By accepting the limitations of these methods, a total solvent amount can be... 

With respect to the intended applications, the thermal durability at inert conditions and, in particular, in air is the most crucial feature. Regrettably, often this aspect is discussed in the literature in a confusing manner. Mostly, the onset of mass loss at raising the temperature as determined by Thermo-gravimetric Analysis (TGA), which is a dynamic method, is taken as the limit of structural stability. Structural transformations, usually occurring at lower temperatures, as well as long term stability and the behavior of the material in atmospheres relevant for applications (e.g. air) are frequently neglected. 

Many ILs are claimed to have a relatively high thermal stability, yet decomposition temperatures commonly reported as the onset of decomposition during thermo-gravimetric analysis (TGA), should be handled with caution [24]. Decomposition may already start at lower temperatures than the onset values, for example, if the treatment time is extended to a couple of hours. Hence, the kinetic parameters of decomposition should be measured to quantify the mass loss at a certain temperature within a certain time span, or to determine the limiting operation temperature based on a suitable criterion of, for example, 1% mass loss per year [25-27]. 

Of the various physical techniques that can be used for mineral identification, thermal methods such as weight-loss curves, differential thermal analysis, and differential thermo-gravimetric analysis are the most useful. However, as these methods are only appUcable to minerals that undergo some reaction involving a change in weight, or the evolution or absorption of heat, their use for heavy minerals is limited. A punched card system with differential thermal analysis data for minerals (Mackenzie [1962]) contains information on a number of heavy minerals. 

Most chemists and materials scientists are not aware that an alternative gravimetric technology has been available for decades that provides sensitivities at least 3 orders of magnitude lower than mechanical balances, using a piezoelectric sensor that is rugged, inexpensive, and operates at high frequencies relatively immune to vibrations the quartz crystal microbalance. The purpose of this chapter is to describe the capabilities and limitations of the quartz crystal microbalance and to discuss its uses in thermal analysis and calorimetry. 

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