In TGA analysis, is there negative value for the weight loss at higher temperature , as 800 C?
Do you mean weight loss between 700-800 °C? If so the presence of carbonate can be expected. Under this condition carbon dioxide is formed: CaCO3 --> CaO + CO2
http://www.tainstruments.co.jp/application/pdf/Thermal_Library/Thermal_Solutions/TS079.PDF
Are you running the experiment under Oxygen/Air atmosphere?
This can happen if you run the experiment under Oxygen atmosphere, using a pan which already had been used to test a sample under Nitrogen atmosphere!
If a TGA sample pan was used under Nitrogen atmosphere, the combustion would not be complete. So, the produced ash sticks to the pan.
In the next run if you use the same pan to run the TGA under Oxygen atmosphere, besides your sample the stuck ash is also burns. This results in the weight loss due to the stuck ash+your sample, which means weight loss more the sample size!
To overcome the problem either use a burner to clean the pan, or first run the experiment under oxygen atmosphere with the "empty" pan (with out any sample within). This will clean the pan. Then put your sample in the cleaned pan and enjoy the results.
In my case, I see different behavior, the weight decrease with increased temperature after that increase the weight. Anyone have idea about that thermal behavior, please
Dear Mohamed
negative weight loss means gain of weight, might be oxidation, but what atmosphere gas you are using during the TGA analysis?
or it might be due to experimental error
Have a very good day
thanks
Ahmed
M A Morsi...You are practicing a positive TGA signal beyond 800 oC. At such high temperature only metallic and metal oxide may exist. Positive TG signals means that the material is undergoing some reaction with the atmosphere and acquire more oxygen to its composition. We must know what is your sample to decide what sort of a weight gain reaction is taking place. Without such information we may continue to put possibilities.
In general, weight loss in TGA analysis is represented as a positive value, indicating the amount of mass lost during heating. However, it is possible to observe a negative value in certain cases due to the limitations of the TGA instrument or errors in measurement. For example, if there is a delay in the heating rate or an error in the balance calibration, it can result in an apparent negative weight loss value. Additionally, if there is a reaction occurring during the heating process that results in a mass gain, it could also result in a negative weight loss value. It is important to carefully evaluate the experimental conditions and the validity of the measurement to interpret any unexpected results in TGA analysis.
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