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Thermogravimetric analysis is a technique used in science and industry to characterize how a solid sample changes as it is gradually warmed. The sample may change due to moisture loss, changes in crystal structure, or molecular changes due to decomposition. This type of analysis is used to characterize polymers and coal samples, to date paintings, and for many other uses.
The analysis of samples is done in a controlled environment in which the sample is weighed continuously while it is heated. An inert gas may be introduced to avoid oxidation during heating. The output consists of a temperature versus weight loss curve. When presented in its differential form, the changes in the curve’s slope become peaks, which make it easier for scientists to discern the point of transformation in the sample.
Gravimetric analysis or analysis in which the final quantity is determined by weighing the sample is usually a very precise analytical technique. Thermogravimetric analysis, on the other hand, is more of a descriptive technique. The peaks can be measured in energy released or taken up by a shift in the sample structure. In some hydrogenated molecules, a peak will occur as heat removes hydration. The heat required to cause such a change is also a measure of the bond strength between the molecule and the water molecule.
Polymers are often described by thermogravimetric analysis. Scientists look at the point of softening and the point of degradation, and they evaluate blend analysis and filler content. Flame-retardant materials may be tested by this method, evaluating the conditions under which combustion occurs.
Organic material such as coal may be characterized using thermogravimetric analysis. This technique has replaced older multiple tests required to rank and value coal between buyers and sellers. The test can evaluate the percent of moisture content, volatiles, fixed carbon, and ash in the coal.
Some kinetic studies, or studies determining the rates of reactions, are performed using thermogravimetric analysis. These studies are sometimes conducted by continuously analyzing the exhaust gases from the sample as it is heated. Kinetic studies may determine the order of the reaction, meaning how many molecular species must combine at each stage of the reaction.
Forensic chemistry has found a home for thermogravimetric analysis. The technique can characterize varnishes and paints. By comparison to known samples, the age of certain art pieces can be determined. Useful information regarding the stability of pharmaceuticals is found by use of this instrument.