In TGA/DSC (Brand Perkin Elmer, Mettler Toledo), I noticed that there will be always temperature differences between Program Temperature and Sample Temperature for all result. In your opinion, which temperature I need to use? Should I use Sample Temperature for my graph?
In general the sample temperature is to be used as it really correlates with the current weight. If for some reasons your equipment can not follow your programmed temperature your plot would be completely wrong if you just used programmed temperature. In this case you should check whether your equipment is damaged or what is cause of this (big) deviation. Sometimes it is also possible to set heating rates much higher as the values possible with the equipment...
In some cases, when you for example have a strong exothermic reaction in your sample, it might also be usefull to use the temperature difference between desired/programmed temperature and the real sample temperature. In such plots you can observe these effects easier.
Thank you both for answering my question.
The heating rate that I used is 10deg/min.
Because for the other sample, the differences between Program Temperature and Sample Temperature is +-10-15 degree only. But for this sample, the differences is +-50 degree.
Seems like my both instrument are in good condition. Could it be because of the properties of the sample itself. I wonder...
Your heating rate is a typical value and therefore this should be no problem for the equipment.
Is the temperature difference always that high or does it start to become bigger at a certain temperature? Maybe e thermal event in your sample takes place as e.g. evaporation of water or a strong exothermal reaction.
Do you use nitrogen atmosphere or air?
Miss Fareezex The task you are asking about is very interesting. Some times we have an exothermic change. This will raise the temperature of the sample to a bit higher than the programmed temperature and after a while it returns to the programmed temperature profile. The reverse is noticed for endothermic processes. I would prefer the sample temperature. However, to solve this, we need to use very fine particle for the sample and the sample weight to be kept a minimum... Regards
Sample temperature affected by thermal events should not be used. In order to apply kinetic methods to TGA data, temperature should follow a linear rate. This is not necessarily true when strong endo-exo processes take place in the sample.
If calibration is good, sample temperature should approach program temperature and can be used.
Another option is to plot sample temperature against time, and make a linear correlation so you calculate a new sample temperature unaffected by thermal Events.
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