What does thermal lag mean wrt DSC?
What does thermal lag mean wrt DSC?
(OP)
Hi,
I've ran a polymer same on the DSC at 5 different temperature and the intensity and position of the peak has changed as a function of heating rate. I.E The melting point peak is at a higher temperature and more intense at a heating rate of 50C than at 30C or 20C. I've read this is due to "thermal lag" but what is thermal lag?
Any help greatly appreciated!
I've ran a polymer same on the DSC at 5 different temperature and the intensity and position of the peak has changed as a function of heating rate. I.E The melting point peak is at a higher temperature and more intense at a heating rate of 50C than at 30C or 20C. I've read this is due to "thermal lag" but what is thermal lag?
Any help greatly appreciated!





RE: What does thermal lag mean wrt DSC?
It's just like a lag in a control system. Does that help?
p.s. "50C" is a difference, not a heating _rate_. Perhaps you meant "50C/min" or "50C/sec".
Mike Halloran
Pembroke Pines, FL, USA
RE: What does thermal lag mean wrt DSC?
One way to avoid / minimise it is to make a very thin sample and clamp the pan so the polymer is squeezed into contact with the pan. Another way is to add an inert oil (like silicone oil) to help conduct the heat.
There are other things that may cause your peak to shift other than thermal lag.
There is not any memory with less satisfaction than the memory of some temptation we resisted.
- James Branch Cabell
RE: What does thermal lag mean wrt DSC?
Thank you very much for your responses - having no good text book on the subject and no one in the lab to ask I find it difficult to find information!
What other things could cause the peaks to shift?
I'm also finding it difficult to find information on what is meant by "thermal history" I've been told to run a number of cycles to eliminate this but no one has given me a satisfactory explanation what thermal history is.
I've read Thermal/Heat history is the accumulated total thermal energy input into the polymer system but how is it "accumulated"?
Oh, and if anyone could suggest a good textbook on DSC that would be great!
Thank you again for your responses :D
RE: What does thermal lag mean wrt DSC?
A long term or high temperature thermal history suggests thermal degradation will have occurred. This is mostly in the form of oxidation, chain scission and cross linking.
Regards
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