Multi-frequency sawtooth modulation of a power-compensation differential scanning calorimeter

In this paper experiments with temperature-modulated differential scanning calorimetry (TMDSC) are described in which the modulation consists of multi ple, superimposed frequencies. The harmonics of the Fourier series of the m easured heat-how rate and temperature are deconvoluted to extract data pert aining to the different frequencies. In order to derive 1st, 3rd, 5th, and 7th harmonics of similar amplitudes, a complex, but simple-to-program sawto oth is generated. In TMDSC with sawtooth modulation with a period of less t han about 150 s, a correction by extrapolation to zero frequency is necessa ry. It is shown that the extrapolation of the heat capacity calculated from the amplitudes of the first and higher harmonics of the Fourier-transforms of heat-flow rate and the sample temperature permits this evaluation of th e hear capacity from a single experiment. The method is tested on a power-c ompensation type TMDSC with temperature control close to the calorimeter he ater. The time constant for the response of the calorimeters is less than 3 0 s (tau < 5 s rad(-1)). Instabilities of the calorimeter response are remo ved by smoothing. Published by Elsevier Science B.V.