Heating rate dependence of melting peak temperature examined by DSC of heat flux type

Abstract

Crystal melting behavior of indium and isotactic polypropylene has been examined by differential scanning calorimetry of heat flux type in terms of the heating rate, $$\beta $$ , dependence. The melting shows the dependence characterized by a power, $$z$$ , of the shift in peak temperature in proportion to $$\beta ^{\text{z}}$$ . The power, $$z$$ , differentiates the melting with and without superheating. For polymer crystal melting, intrinsic nature of the broad melting region with a fractional power, $$z\,\le\,1/2$$ , due to superheating of melting kinetics has been reconfirmed experimentally. On the other hand, the crystal melting of indium, which is supposed to proceed with negligible superheating, showed the shift in peak temperature with the power in the range of $$1/2\,\le\,z \le\,1$$ , depending on sample mass, which is due to instrumental thermal lag predicted by the Mraw’s model consisting of lumped elements. The $$\beta $$ dependence is influenced by the thermal lag determined by the thermal contact resistance between the sample pan and the stage, the effect of which has been examined in terms of the dependence on sample mass and the application of silicone grease between the sample pan and the stage. The influence of two different types of the definition of heat flow has also been examined; the simplified one without the time derivative of temperature difference showed an apparent shift in peak temperature at faster scan rates in a similar way as that of thermal lag.