I'm not an expert on TGA, but have you considered there could be a process (like a phase change) that consumes energy before the material keeps degrading and losing mass? that could account for the sudden temp change. Also, could be instrumental error.

I think this could be happen due to the instrumental problem or impurities from used crucible to run the sample. To overcome the problem, platinum crucible should be washed properly and then re-run the sample.

May be due the existence of impurities in the sample or container that might change the phase or the process.

DSC can be more helpful to understand the case over particular temperature range. It's better to record DSC data at slow rate for such case.

The heat involved in the reactions that occur with the sample can also affect the appearance of the TG curves, as it changes the equality that should always exist between the oven and sample temperatures. There are cases in which this lag, which partly depends on the heating rate used, can be in the order of 10 ºC for more, if the reaction is exothermic, and for less, if it is endothermic. This effect can cause considerable errors, especially when it is intended to calculate kinetic constants from the thermogravimetric curves.

This effect can be observed in the TG curves of Sm (III), Eu (III), Dy (III) and Y (III) 4-Methoxybenzoates, shown in the Figure. In all curves there is a return of the TG curve for lower temperatures; as already explained, this is due to the great reaction heat involved in the thermal decomposition (4-methoxybenzoate)

Though there are endothermic reactions which reduces the surrounding temperature, TGA is not sensitive to such temperature change. As the sample is degrading at that temperature, please dont put it in DSC. It will contaminate the DSC chamber.

If you look closely, there is N2 and CDA gas which purges the balance and sample at a constant rate. There is also circulating water (depending on the instrument type). None of these should be tampered (intentionally/unintentionally) when the experiment is running. So repeating the experiments by keeping the above constant at all times should help understand if the behavior is from sample or not. Additionally, something we might overlook is that sample at any point of time should not touch the thermocouple. Such as, does it swell when it melts or degrades etc like an envelope before the gas is released?

I faced this problem too .. IT was an instrumental problem ... I think u can repeat the analysis again ...

If it still exist .. it may be from impurities ..

THANK YOU ALL ( Nihal S. Tabasi Richard Perosa Fernandes Anupama sargur ranganath Shielah Mavengere Mohd Ishtiyak ) FOR HELPFUL SUGGESTIONS

Hi all, I have questions on TGA/DTG analysis.

May i know how do i determine whether the combustion temperature is higher or lower? I have attached two of my results here. Do higher overall weight loss signify higher combustion temperature? and what does higher derivative weight (DTG) means?

Thank you.

Hi @Khai Shenn Lau

You can determine ur combustion temperature from the last loss. In ur charts the weight loss continued to about 450 °C, after that there was no weight loss.

About ur 2nd quest. High loss doesn't give any significant about temperature. It's related to ur material. Every material has its own chart (temperature and loss).

Ur 3rd quest. The high derivative means that the most weight loss or consumption (cracking) of ur material at that temperature (230 °C) ..

Hi Nihal S. Tabasi

Thank you very much for the helpful information!

If we force the temperature to rise, it cannot decrease locally. Oddly, the instrument software did not correct for such a slight drop in temperature. Presumably instrument malfunction.

You should check if the recorded temperature at the TGA plot is taken from the reference pan, rather than from the sample pan. If taken from the sample pan; the temperature can indeed retrocede, for a short time period, due to heat absorption by the sample during an endothermic process ― even if the temperature at the reference pan and at the furnace keeps increasing with elapsed time. The temperature taken from the reference pan is not likely to retrocede while the furnace temperature increases. It may help to check the TGA plot vs. elapsed time.