I am currently doing a comparitive study on the characteristics of rockwool, calcium silicate, aerogel, foam glass and glasswool insulation. I had tested my samples for the thermogravimetric analysis to determine the moisture content, volatile matter and ash content. The conditions that I used was 30˚C to 800˚C with a heating rate of 10˚C /min and used nitrogen gas for the testing.
As far as I know, the TGA results should show a decrease in weight but four out of five of the sample weight increased. I should also mention that all five of my samples did not burn as they have a high boiling point.
Looks like your materials do not react/ or absorb with nitrogen or gas impurity so that your TGA results were supposed to show weight losses.
Except instrument reading errors, here are some possible operator errors, such as taring wrong pans, samples touching furnace wall, flowing gas too fast and unsteady ( buoyancy effects), etc.
True weight gain should only happen if the samples react with the atmosphere, e.g. oxidize. This should not be happening for your samples. I think the problem is in the experiment, i.e. some of the problems suggested by Xu Wang. Have you run a blank, with empty pans? ALWAYS run a blank before making any conclusions about TGA results.
I think your machine needs calibration as mentioned by Mrinmoy Karmakar.
After calibration of your system, if you get same result then you need to check the quality of the nitrogen gas.
The weight gain is due to oxidation of your samples or it may react with nitrogen to form some compounds.
Not every material losses its weight during oxidation test.
However,
Moisture removal is nessasary before conducting any experiment.
Muhammad.... Did you try to run at least one DSC experiment for one of the samples gaining weight. Possibly, we may then give you the answer. Oxidation reactions are accompanied with clear exotherm.... Regards
I would imagine this is due to buoyancy effects seen as an article of the testing. Try to perform a calibration and background 'noise' for cancellation prior to any tests. One potential solution, if it is not above, is to use a different sample holder, such as a mesh rather than an alumina pan?
For the final ash content, you should run the experiment under oxygen atmosphere. The weight increase can be linked to an internal "exposure" or due to not correct calibration. Did you run the same test more than twice and you had the same outcome?
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