Thermo-gravimetric analysis (TGA) is an analytical method that measures the weight of a sample during heating. Modern TGA systems are usually performed with toploading so that the released gases can not pollute the balance.
The principle is simple. The sample is laid on a small dish made of a refractory and inert material, for example platinum or alumina (with a high melting point). It is hung on a weighing arm and an oven is raised around the dish. A thermocouple right next to the dish measures the temperature. The weight in the dish is measured depending on the temperature in the oven. The device
With modern TGA instruments, the temperature is computer controlled and the weight is measured electronically and sent to the computer on a regular basis. Typical temperatures are up to 1000 ° C. The space around the balancing mechanism and around the sample is usually rinsed with pure nitrogen gas to prevent oxidation and rapid burning of the sample. Around the sample, another gas may also be directed, such as helium to improve the heat transfer to the sample, or a reactive gas (e.g. oxygen gas) to effect a reaction. The scale can better stay under nitrogen gas to prevent damage.
The weight of a material can be reduced if, for example, a decomposition reaction takes place with a gaseous product that is flushed away. Even if the sample evaporates, it will reduce weight. In oxidation, the weight may also increase. From the weight gain or decrease, it can often be deduced which substances originated. The temperature taking place is often characteristic of the substance (s) from which the sample exists.
The temperature indicator can be calibrated by programming a magnetic material, for example nickel, by programming its Curie Point in the presence of a magnet. Above the Curio temperature, it loses its magnetism.
An expansion of the technology of TGA is the ability to feed the rinsed gases through a spectrometer, thus identifying the degradation products (solvents, for example).
TGA and DTA (Differential Thermal Analysis) can be performed simultaneously in one measuring instrument. The simultaneous application of thermogravimetry (TGA) and differential thermal analysis (DTA) to a single-sample sample generates more information than the measurement performed in the individual instruments. The thermogram is easier to interpret and a distinction can be made between, for example, phase changes and decomposition between addition and condensation reactions, between pyrolysis, oxidation and combustion reactions. Simultaneous thermal analysis (STA) is available in a temperature range of -150 ° C to 2400 ° C.
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