Dear all, I am wondering which of the following is the correct way to calculate the total enthalpy change of dehydration in a salt (my case is SrCl2 in hydrated form). The right picture considers the whole area based on the beginning and the end (where sample reaches a stable condition), and the left one divides it into three sections based on the local maximum points. You can also see that the two ways yield different values for total enthalpy change. I would appreciate your comments.
Dear Arvin Sohrabi ,
Even though I am not an expert in this technique, I would suggest the following:
The amount of necessary energy to dehydrate it is shown by a difference of enthalpy between your sample, and a reference sample in DSC (which is represented by an empty DSC pan). Since this is the principle behind the technique, I tend to think that the "correct answer" is the left one, in which each area of each peak should be measured separately, because the baseline of your experiment could be shifted between each one of the "peaks".
What caught my attention is that this dehydration phenomena occurs in 3 different stages according to this. Are you fully sure that all peaks are related only to dehydration? To confirm that, I suggest doing a TGA analysis by using the same conditions as the DSC. If you see a mass weight loss during the same time interval as you observe the three peaks, then you could confirm that all of them are related to water release.
Hope this clarifies a bit more!
Hi, neither of the two methods is precise, they are both only approximate. There is an enthalpic process (dehydration) on top of a non-trivial baseline shift due to the material's changing heat capacity during the dehydration process. We faced the same issue in polymer curing and the results didn't make sense until we switched to modulated DSC (MDSC). Modulating the temperature of the DSC scan can distinguish between reversible and irreversible signal, solving the task with grace.
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