The temperature calibration on cooling of differential scanning calorimeters

The procedure for the calibration of differential scanning calorimeters (DS C) has been addressed by several authors. Most of the work published on thi s subject dealt mainly with the calibration on heating. For calibration on cooling, Menczel and Leslie suggested the use of thermally stable liquid cr ystals, for which the isotropic to nematic or cholesteric to isotropic tran sitions do not exhibit hysteresis on cooling. In this work, a new method is proposed to calibrate differential scanning calorimeters on cooling. It is suggested that the calibration on heating, with standard metals, may also be used to perform the calibration on cooling. The onset of the nematic to isotropic transition on heating (and vice-versa on cooling) will be used to support the method and to quantify the errors, which are of similar magnit ude to those obtained by Menczel and Leslie with thermally stable high puri ty liquid crystals. Results of the change in the indium and lead crystallis ation onset temperatures with the cooling rate are presented. Using as an e xample the non-isothermal crystallisation of polyethylene, the errors obtai ned with the standard calibration of the DSC and the new calibration on coo ling are discussed. (C) 1999 Elsevier Science B.V. All rights reserved.