Dear Friends,
This is in contineoutaion with my last question on "Unusual weight gain / loss in the TG thermogram of the same sample on different TG systems - any thoughts?"
First let me express my gratitude to all of you who have share their invaluable experience and expertise with me in understanding the problem at hand. I am highly obliged to all of you.
I would also like to convey my sincere apologies for not responding to your queries / suggestions earlier. The delay was caused because we are running several experiments in our lab, which were based on the suggestions that I have received from all of you. What I have understood from these experiments is that the design of the balance (Top or horizontal) and environment (amount of flow) plays major role as bouncy effects are different in both these circumstances.
As the change is mass, which I need to measure is very small, what I found is precise cancellation of background signal is very very important. To understand this, we put Al2O3 of equal mass as reference and sample, measured its base line first and then in the sample pan Al2O3 was replaced by sample. In that case I found similar trend of data obtained on Netzsch and Perkin system.
But still I am not satisfied with the result. We have make measurements both in the heating and cooling cycling from RT – 800 deg C in Air atmosphere with a heating rate of 5 K/min in Pt-Rh crucibles. During heating cycle, it shows a weight loss (due to loss of water of crystallization) till 350 deg C followed by gain due to oxidation (see attachment). This is expected. But during the cooling cycle, it continues to accumulate further weight, which in my opinion not possible or should not have occurred.
I feel that still base line is not fully compensated for cooling cycle. The base line trend and sample trend during the cooling cycle is exactly the same while such was not the case during the heating cycle. I want your suggestions / guidance on the following aspect, which I feel that would be help me in understanding this mysterious results.
Under what circumstances I would obtain an ideal TG base line. Especially during the cooling cycle do I need to take any special care or need to make any changes in the experimental conditions ?
Note: Please see the attachment for TG and DSC curves.
Hi,
1) what is the specimen material? did dummy Al2O3 sample has the same volume (not the mass! - buoyancy fore depend on volume as well)
2) was the baseline properly subtracted from the specimen curve? Was is really the baseline on empty cricible or with Al2O3 specimen? can you made both (empty and dummy) as well and see whetehr dummy specimen makes a difference?
3) was gas humidity controlled? Where gas is purged to (exhaust), and how outside T/P/RH conditions vary (sometimes sunshine or heavy rain outside make a lot of trouble) - are your tests reproducible?
4) did you try static gas (only balance purge)? how it affect the results?
- Badges
- Science topic
- Similar topics
- Chemistry