A comparison of a novel single-pan calorimeter with a conventional heat-flux differential scanning calorimeter

There are a number of problems associated with a conventional heat-flux differential scanning calorimeter. When latent heat is absorbed or evolved, large temperature differences arise in the calorimeter and heat can flow between the reference and sample leading to rate sensitive enthalpy changes. In addition the heat appears to be smeared over a large range of temperatures. The reason for the smearing is discussed and a simple scanning calorimeter has been designed which eliminates the need for de-smearing. The present apparatus uses samples of about 1 cm(3) and can be used from about 300 to 1300 degrees C. The temperature can be scanned at a constant rate or alternatively the heat flux can be fixed and the thermal response recorded. A heat flow analysis is presented which allows enthalpy changes to be calculated. The results for pure aluminium and an aluminium alloy (LM25) are reported. It is concluded that the new calorimeter has a number of advantages. In a pure material, the latent heat appears over a very narrow range of temperature giving an indication of the improved temperature discrimination: the apparent latent heat per unit mass does not depend on specimen size or significantly on rate of heating. In alloys, the calorimeter is more sensitive to the onset of a phase transition because of the better temperature discrimination.