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Topic: DSC/TGA data analysis  (Read 5216 times)

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Offline lalapsycho

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DSC/TGA data analysis
« on: October 14, 2012, 05:28:30 PM »
I am currently trying to figure out the data for my DSC and TGA experiment. DSC being differential calorimetry scanning and TGA being theromgravimetric analysis. I understand the concept of the instruments, what they are measuring. The DSC is measuring the change in heat flow to each of the sample holders and in the end determining if the process was exothermic or endothermic. The TGA measuring the difference of mass in terms of temperature to determine phase transitions.

But, I look at the readouts and graphs and I just don't understand what to do with them. For the DSC the graph has a lot of peaks, the information it includes are the onset and end of the peak (which are temps), the area (in mJ), the delta H (in J/g) and the peak height (in mW). The axis of the graph are Temperature (x) x Heat flow (mW) (y). What do I do with this data and how do I determine if it is endo-or exo-thermic??

For the TGA, it is basically a descending line with a slight slope. The information given in this graph is onset, inflection point (degrees C) and the delta Y (mg), how do I determine the water loss?

If anyone could help, it would be greatly appreciated. This lab is really confusing me.

Offline lalapsycho

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Re: DSC/TGA data analysis
« Reply #1 on: October 14, 2012, 05:40:37 PM »
I forgot to mention that it is magnesium sulfate heptahydrate that I am analyzing.

Offline Stepan

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Re: DSC/TGA data analysis
« Reply #2 on: October 16, 2012, 06:46:43 AM »
To understand you TGA results, just imagine that you are drying the salt in the oven. As it looses the first molecule of water, you see 7.3% in weight reduction. Thus you can expect up to 7 steps on our TGA chart (one for each water). TGA is a low resolution technique, some steps can be overlapped.  Now match the TGA spectra with DSC chart. Let say you first molecule of water was lost at 105 C. The energy adsorbed at 105 C on DSC - corresponds to heat of reaction (can be recalculated into enthalpy) of transition from heptahydrate into hexahydrate   

Offline lalapsycho

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Re: DSC/TGA data analysis
« Reply #3 on: October 18, 2012, 04:52:51 AM »
Thank you! Much appreciated!

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