The Development of a Sample Controlled Differential Scanning Calorimeter and its Application to the Study of Different Reaction Types

Abstract

A new sample controlled DSC (SC-DSC) system has been developed, which for the first time has enabled the benefits of sample controlled thermal analysis to be extended to the widely used technique of DSC. The system was based on a heat flux DSC cell interfaced to an in-house control and data processing system. Careful optimisation of the instrument parameters during the development stages minimised the potential problem of shifts in the DSC baseline when the temperature programme is changed. This has enabled the rate of heating to be controlled directly from the DSC signal and has also allowed controlled cooling to be incorporated. The difficulty of making baseline corrections in sample controlled experiments has been resolved by the implementation of the facility to replay the temperature programme for an experiment. The potential of the new SC-DSC system was evaluated by studying a wide range of reaction types. The first group consisted of reactions taking place with a change in mass, including endothermic dehydration, dehydroxylation and decomposition reactions and exothermic decomposition and oxidation reactions. The results were compared with those obtained by sample controlled thermogravimetry. Similar profiles were obtained using both techniques and the ability of SC-DSC to provide direct information on reaction mechanisms was demonstrated The second group included both endothermic and exothermic reactions that occurred without any significant mass change and which therefore could not be studied by existing sample controlled techniques. Although it proved difficult to control the rapid fusions of metal and organic DSC standards with the present equipment, promising results were obtained for the fusion of both organic and inorganic phase change materials which occur over a broader temperature range. SC-DSC was found to be successful in preventing the ignition reactions in number of exothermic reactions which could occur under linear heating condition, thus providing a means to investigate the systems in more detail than is possible with conventional thermal analysis techniques. In addition, the ability to control the curing reaction of an epoxy resin should allow the development of temperature profiles to enable samples to be cured at a selected rate