A modulated adiabatic scanning calorimeter (MASC)

The modulated adiabatic scanning calorimeter (MASC) described here is desig ned to work in both the time-domain (adiabatic-like step-scanning) and in t he frequency domain (modulated temperature/power-scanning) operational mode s. The cylindrical form of the cell and the controlled thermal environment in which the sample is located make it possible: (i) to write detailed and reliable equations to describe the heat flow; (ii) to derive analytical rel ations to calculate the energy release from the sample and the real and ima ginary parts of the complex heat capacity at the modulation frequency; (iii ) to study narrow phase transitions using the power modulated scanning mode ; and (iv) to generate adiabatic-like conditions. The thermal environment i s controlled by means of an active thermal shield which is kept at a temper ature close to that of the sample cell in order to minimise the thermal gra dients to which the sample is exposed. The temperature difference between t he shield and the cell is set at the value required to control or cancel he at leakage from the cell. MASC can be used to carry out measurements on a s ingle sample in different operational modes that can be made operative unde r the control of its built-in software. The parameters of interest can be a utomatically calculated by means of a program based on a model of the cell i sample system that will be described in a second paper. To test the performance of the calorimeter, samples of materials which unde rgo a first-order phase transition or a glass transition (indium, ice, and polystyrene) were studied. The specific features of the calorimetric cell, the calibration procedure, and the experimental results an reported and dis cussed, (C) 2000 Elsevier Science B.V. All rights reserved.