Hi,
I have performed differential scanning calorimetry (DSC) analysis for some biomass derivatives. I found that the peaks are becoming broad with increasing heating rate. So, I just want know that, why these melting peaks are becoming broad with increasing heating rate?. I want scientific reason behind this pattern. Please help and thanks in advance.
The answer is in principle simple: Its the kinetics of the reaction. From a thermodynamical point of view, you have a sharp transition temperature for the reaction you are aiming at. If the heating rate is low, nothing will happen if you are slowly approaching your equilibrium temperature Teq, and if you reach Teq, then, because you stay relatively long at this particular temperature, allmost of the material will react and form the peak in the DSC. If in contrast the heating rate is high, you will initiate the reaction while you fastly scan over Teq, but the reaction may not be complete because you are limited by the kinetics. Thus the peak in the DSC will extend to higher temperatures, and will further broaden for increasing rates. So lower heating rates are generally favored! Hope this helps, Dirk
heat transfer. there is a lag in temperature between the thermocouple used to measure temperature and the temperature of the sample itself which increases with increasing heating rate...further, the temperature gradient across the sample is more pronounced with a faster heating rate meaning the exterior of the sample will react sooner than the interior relatively speaking. This also explains why Tmax is shifted to a higher temp with a faster heating rate. The reaction actually goes to completion more rapidly with the faster heating rate but since you are plotting against the DSC thermocouple temperature, not against run time, the peak will be sharper with a slower heating rate.
Dear Mood Mohan,
The above answers are valid, as far as I can see. The basic point is the rate of the physical or chemical reaction/transformation under study as compared to the set DSC heating/cooling rate. See attached reference.
Article Transformational kinetics in liquid crystal polymers and dif...
I agree with Darrell N. Taulbee and the fact that, there is the issue of transition gradient with respect to heat flow and its attendant effects on material transition.
Is there any general explanation for broadening of peaks in case of sodium salts of organic compounds
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