Thermogravimetry measures the mass of a sample over time as temperature varies, using a precision balance, heat source, and closed reaction chamber. The data forms a curve that relates mass to temperature, providing information about the sample material and its stability. It is used in pharmaceuticals, agriculture, and forensics, and can be used to study polymers. Differential thermogravimetry provides a more informative visualization.
Thermogravimetry (TG) is a thermal analysis technique in which the mass of a sample is measured over time, in a controlled atmosphere, as the temperature varies. The data from this procedure is examined by thermogravimetric analysis (TGA), one of several methods in which a physical property of a sample relating to temperature change is measured. Similar techniques involve the study of heat flux, length and elasticity. Thermogravimetry is often used in the pharmaceutical industry to analyze the stability of drugs and in agriculture to regulate the dehydration process of crops.
The procedure requires a precision balance, a heat source and a closed reaction chamber. As the sample is heated, its weight and temperature are continuously monitored and recorded. A thermocouple, or temperature sensor, is typically placed in direct contact with the sample; thermogravimetry involves absolute mass changes and is independent of the heating rate of the sample. The environment could be a gas or a mixture of gases at any required pressure or a vacuum.
When plotted, the collected data forms a curve that relates the mass of a sample to its temperature. The correlation between temperature and mass change is examined by comparing the points on the graph with the two axis scales. A more informative visualization is derived from data using differential thermogravimetry, where the rate of change of mass versus temperature is plotted. Individual episodes of change not evident in the simpler mapping can be easily distinguished, leading to a more comprehensive and meaningful analysis.
Change in the mass of a sample, as reflected by its weight, as temperature changes can be due to the breakdown of compounds into their constituent elements, the sample reacting with oxygen, or its loss of water content. At what temperature and under what atmospheric conditions these changes occur provide important information about the sample material. Thermogravimetry is often employed to study how these factors will affect the stability and shelf life of a product. Analyzing a sample’s reaction to thermal change can also be used in forensics to help identify unknown materials.
The behavior of related materials at high temperatures in a selected atmosphere is an important consideration in product design and development. Thermogravimetry can also be used to establish the characteristics of a material for use in subsequent identification or quality control. With careful choice of temperature and atmosphere, sample materials can be selectively decomposed into constituent components. This method is often used in the study of polymers, large molecules made up of repeating parts.
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