I prepared ferrites by glycine method. whenever I do TGA of my samples , it shows a sudden increase in the molecular weight. Can anyone explain the reason for it?
Hi Narayan
It may be helpful if you share a few more details. Do you run it under nitrogen or air? (Is it oxidation you see?). Could you add your thermogram? If it is irregular (the gain you get) it may be time for a TGA service. is the pan centered with respect to the TGA opening? Is your hang down wire straight? Is your pan clean?
We had similar issues and at the end it was a matter of servicing of the aforementioned issues.
Best of luck
As I understand from your write up, this increase happens at the very beginning of the thermogram. As long as it is insignificant with respect to the full thermogram, you need not to worry. But, be careful of your techniques in operating TGA. Such a increase in weight is phenomenal and quite usual, but can be very intense if you load the pan way too much.(Do not go beyond/ too close the weight limit. If the manufacturer says the good range is between 8 - 15 mg, you better load a maximum of 12 mg, likewise) And make sure that you do not put too much pressure on the cantilever while loading the sample. Technically, don't let it shake! and give enough time for the pans to balance its weights (reference and the sample) before you send it in the oven.
But, if your increase is significantly bigger, you will probably have to revise your handling procedures and/or get the instrument serviced as Kasparis suggests.
The ferrite sample may be ferromagnetic; so that it can change between diamagnetic and paramagnetic behaviour by its Curie temperature. Unwanted magnetic interference somehow located nearby the thermobalance (above or below) can then cause a sharp apparent weight change of the sample when the Curie temperature is crossed. Check also for any possible oxidation from substoichiometric oxide to stoichiometric, or still substoichiometric but with lower oxygen deficiency; or yet to some possibly available higher oxidation state ― in case the sample is heated in air or other oxidizing atmosphere. Being that the case, check also for any possible oxidation of organic matter, if somehow included within the sample. Please note also that the TGA instrument should have been calibrated at analogous experimental conditions, namely in terms of selected gas and flow rate. If air is to be selected, its humidity content should be kept constant.
Hi Narayan,
It's not clear what you are asking. There are few circumstances, the weight of the sample in the thermogram get increases.
One option, there can be an issue in your cantilever and the balance system (In this case the weight of the sample get increase than what you put inside the pan in the initial stage).
Second option, Weight will get increase after a particular temperature. (This depends on which environment you are analyzing your sample and what are the components available in your sample).
For example, If you are doing the analysis in the air environment, there can be weight increase in your thermogram due to the oxide formation in your sample (Thermal oxidation of some metals). This type of weight increase can be seen in different temperatures due to different incineration temperature.
For the full understanding you have to elaborate your problem a bit more with some of your observation like, in which temperature you have the weight increase and what is the environment you are doing the analysis.
Anyway, hope you may get some clarifications from all these answers. Good Luck!!!!
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