fly ash sample is burnt at high tem.(750 -800) in inert atmosphere,after cleaning pan,burning oxygen again but still showing experimental error,while rest of the sample is showing positive result as well.
In case you refer to a negative percentage value at the TGA plot, you may find helpful to check my answer at this earlier query: https://www.researchgate.net/post/Can_TGA_show_negative_percentage_value
In my opinion the reason for the negative weight is in the mass meter. You may need to test the instrument scale.
TGA value is generally defined in terms of mass loss or weight (%) with the function of temperature/time. If you found –ve value of sample mass then please check with following points;
1. Your TGA equipment is needed to calibrate urgently, this is because of the sensitivity of the TGA sensor can be deteriorated after performing several sample tests.
2. After calibration you have to make a baseline/correction analysis before doing the sample test.
3. Check the types of crucible which are using for analysis; Al, AlO3 (Alumina) or Pt-Rd. Sometime what happens the test material is adsorbed on the inner surface of crucible and not cleaned properly with cleaning solvents. During the next testing condition, this mass can be released on same temperature scale or beyond the level, which results into (–ve) mass loss value.
Good luck
This is situation is very unlikely, yet I also encountered many times the same situation. Every time I repeated the TGA experiment and got positive results. So, I would like to recommend you to repeat the experiment. Before repeating, please ensure that, any particle is not adhering on the outer part of crucible or any where which is in contact with the heating zone, but cannot be sensed by the weighing balance. I think, your problem will be resolved.
Thanking you very much and wish you very good luck.
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