I am using Vyazovkin's advanced isoconversional method to calculate the activation energies of the co-pyrolysis of biomass and waste tyre mixtures. The problem is that after calculating conversion, the resulting lines cross each other, when in theory they should meet only near conversion = 0 and conversion = 1. The end result is that I am getting negative activations energies, which don't make sense. I belive it might be due to errors during the thermogravimetric analyses, but I have been following the ICTAC recommendations and I don't know what else could be causing these issues. Any input is welcome! thank you in advance.
I would say so! There might be something wrong with the TGA. I would check the sample holder or the pan. Probably, some residue from a previous run burns out along with the new running sample.
Do you run the TGA under oxygen atmosphere?
Ali Nematollahzadeh Thank you very much for answering!
The runs are carried out under a nitrogen atmosphere, the sample holder is clean and the pans are cleaned in boiling water, utrasonic bath with a mild detergent and then rinsed thoroughly before being heated up to 1000 °C in a muffle furnace.
Axel Dullak still I would check the empty pan by running a blank TGA with the empty pan and check the TGA thermogram.
Ali Nematollahzadeh I checked and it seems that the balance in the analyzer takes a while to stabilize and minimize the drift. I should get more reliable results now. Thank you very much for your input, it was really helpful!
You are welcome, I am glad to hear that you have solved the problem.