Modulated Differential Scanning Calorimetry
The reproducibility and reliability of the TA Instruments Modulated Differential Scanning Calorimeter (MDSC) was tested over a range of conditions. The equipment base line was found to be fairly constant with a very small fluctuation (10 μW), which means a 0.1 % fluctuation on the scale of a normal polymer MDSC curve. The excellent stability of the base line and the reasonable reproducibility of the curves (5%) suggest that frequent calibration is not required.
The heat capacities calculated from the modulated response to the variable temperature depend on the frequency for a given cell constant. The heat capacity cell constant is a unique function of the modulation frequency:k c =K c o p/(p−6.3) wherep is the time of the periodicity expressed in seconds and K c o is the heat capacity cell constant measured on a standard material and reduced to zero frequency. The cell constants depend on the flow rate of the helium according to:K(He)=K o(1.298−0.004424He+1.438·10−5 He 2) whereHe is the flow rate of helium in ml min−1 andK o represents a constant at 100 cm3 min−1. There is a strong dependence of cell constant on the flow rate ranges from 10 to 80 cm3 min−1, while above this rate (up to 135 ml min−1) the cell constant approaches a plateau.
Keywordsfrequency dependence heat capacity MDSC thermal analyses
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- 3.Manual for MDSC, TA Instrument Inc. (1994).Google Scholar
- 5.B. Wunderlich et al., Modulated Differential Scanning Calorimetry; Summary of Eq.s and Derivations Needed for the Understanding of MDSC, For internal use of the ATHAS Group, November 8, 1995.Google Scholar
- 6.T. Ozawa and K. Kanari, Preprints of The Fourth Asian Thermophysical Properties Conference, Tokyo 1995, p. 263.Google Scholar
- 8.Perkin Elmer Co, When is a DSC not a DSC and How Does it Work Anyway, in Thermal Analysis Newsletter, No. 9.Google Scholar
- 9.F. Cser, F. Rasoul and E. Kosior, to be published.Google Scholar
- 10.Handbook of Chemistry and Physics, Ed. D. R. Lide, 76th ed. 1995–96, p. 12.171.Google Scholar