Operational issues in isothermal calorimetry

Isothermal (heat conduction) calorimetry is a general technique to study processes through the thermal power they produce. This paper deals with operational issues concerning isothermal calorimeters. In this paper it is shown that steady-state and pulse calibrations give the same result; that the use of mobile heaters (placed in the reaction ampoule) give more accurate results than fixed heaters (placed in the ampoule holder); and that at least the tested calorimeter had calibration coefficients that were independent of the thermal power level. It is shown that well balanced references are necessary to get low noise and low drifts. It is discussed how baselines should be measured. The influence of temperature and sample size is also discussed and it is shown that large cement paste samples with high thermal powers will show an accelerated reaction. Finally, the thermal dynamics of a heat conduction calorimeter is discussed.