In my TGA curves related to liquid polysulfide resin-clay nanocomposites, for neat LPS and LPS/CNPs 1% , a small peak can be seen in higher temperatures as in following fig.
what can be an acceptable explanation for this secondary small shoulder?
in other words, what process can suddenly increase the mass of the sample at the end of the process?
Does the result change when you repeat the experiment in different atmospheres? Ar or N2 or air?
There are two instances that I can think of that increase the mass. Reaktion with oxygen when you change the gas flow. Since you would have probably figued this out urself, its probably a malfunction, for example vibration of the measuring instrument or pressure surge in the gas flow. The image is not very high-resolution, but it looks as if the mass abruptly decreases sharply just before the jump. After that, the curve continues as if nothing happens. Since the blue curve shows an irregularity at the exact same temperature, it looks as if the procedure changes at that temperture.... The "acceptable explanation" would be to point out the procedure change at that temperature or to repeat the experiment.
Iman... have you done the TG experiment under nitrogen? Have you noticed the appearance of the material after the heating experiment? If there is any evidence of melting, your material may suffer reaction with Oxygen and hence weight gain. Gain in weight occur by oxidation of the freshly form middle product. The switching of the reaction atmosphere will clearly show you the nature of the change. However, the absence of the weight gain at the low heating rate suggests such possibility. Even though the best condition for the heating is at 10o /min and nitrogen atmosphere. Regards
Thanks all for your valuable response to this question. I have already repeated the test and this small shoulder does not exist anymore in my new TGA curve.
Only an additional chemical reaction can cause this, for example, oxidation. So the experiment should be conducted in a nitrogen atmosphere. However, such a small peak is presumably an instrument error that the software did not compensate for.
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