Calibration of a fast-scanning DSC – project RHC

During the processing of polymers, the material is often exposed to heating and cooling rates considerably higher than the rates usually used in conventional DSC equipment. With project RHC [1], TA Instruments made an attempt to extend the range of heating and cooling rates conventional DSC systems can reach. In this presentation, the calibration of this fast-scanning DSC will be discussed.
The prototype RHC used in our work can reach heating and cooling rates of 2000 K/min and 1500 K/min, respectively. To reach these high rates while retaining an operation similar as in a conventional DSC, the instrument was roughly scaled down by a tenfold. The RHC cell is of the Tzero(TM) type and is heated through infrared radiation and cooled with a liquid nitrogen cooling system.
As thermal lag effects can be important at high heating rates of for larger sample masses, the thermal lag calibration procedure for the RHC will be discussed. The reproducibility of measurements of the melting temperature and enthalpy was studied. Through an investigation of the effects of sample mass and heating rate on the transformation temperatures and enthalpy, the need for a calibration depending on heating rate and sample mass was investigated [2]. The need for a different calibration in cooling was investigated by studying the symmetry of the thermal lag of transitions in three liquid crystalline materials in cooling and heating. Three transitions that behave symmetrically in heating and cooling could be identified, the RHC is behaving symmetrically in heating and cooling, and the same model can be used for describing the thermal lag in both heating and cooling.
Next to the thermal lag, the enthalpy calibration was evaluated for a wide range of sample masses and heating rates. In addition, the enthalpy calibration was checked over the full temperature scale by measuring the heat capacity of sapphire and polymer reference materials.

[1] R.L. Danley, P.A. Caulfield and S.R. Aubuchon, Am. Lab. , January (2008) 9-11
[2] G. Vanden Poel, A. Sargsyan, V. Mathot, Protocol proposed to the Research and Standardization group on "Temperature Calibration of Fast-Scanning Calorimeters", during the Technical Seminar of NaPolyNet, an FP7 program, see www.napolynet.eu (DIN, Berlin, Oct. 20, 2009).