Hello everyone, I ran some TGA (coupled with DSC) tests on two barks of two different trees and an invasive grass, because I want to compare the thermal stability calculating the activation energy and other parameters like onset temperature. I used 5 different heating rates (5,10,20,30 and 40 °C/min). For the grass I get relatively coherent curves. Nevertheless for the trees and the 40°C/min heating rate I get a drastic mass loss in the first 2°C of heating. (I attach the image, there are 3 curves because I separated the inner and outer bark for one of the trees). The other heating rates work just fine.
Thank you in advance
Cheers
Please check initial mass of each sample and if the TGA instrument was correctly mass-calibrated, so that the initial mass equals 100% for all samples. I suggest that you check also the absolute mass vs. time plot. Note that the plot drops well below -100% in terms of percentage (lost) of the initial mass.
This could happen due to disturbance of your instrument. Sometimes pieces of samples may be affected by gas flow and disturb the balance. Also, try to run instrument several times without sample to check the stability of balance.
Thank you everyone for your responses. I am not sure about the initial mass and the calibration, because for that same heating rate and other kind of sample (grass) it works just fine, so my equipment is working properly. I also have subtracted the zero curve (made on the same alumina crucible and the same heating rate). As Carlos pointed out, the curve works fine below -100% relative mass change, so I might just correct it with the inital weight and see if it works. What I think is peculiar is that it happened for all the bark samples, not just one.
Cheers
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