Heat capacity measurement by sawtooth modulated standard heat-flux differential scanning calorimetry with sample temperature control

Abstract

The frequency dependence of the apparent heat capacity is analyzed when measuring with a heat-flux type, standard differential scanning calorimetry (DSC), controlled at the sample. A specially constructed, centrosymmetric sawtooth modulation composed of 14 heating and cooling segments was used for the measurements. This complex sawtooth produces four harmonics of the order ν=1,3,5 and 7 with close to equal amplitudes in the Fourier representation. A single measurement should thus be sufficient for the evaluation of the frequency dependence of the measured, apparent heat capacity from the amplitudes of the Fourier series of the differential heat-flow rate ( A HF) and the sample temperature ( A T s ). The frequency independent heat capacity can, however, not be represented by the expression: C p = A HF/( A T s νω)[1+( τνω) 2] 0.5, with a fixed τ, as is possible with a sinusoidal modulation which keeps the DSC in steady state, but τ depends on sample and reference properties, as well instrument parameters such as pan masses and thermal contacts, and may also be influenced by the design of the control and analysis software.