High temperature specific heat measurement using quasi-adiabatic calorimetry

摘要

The measurement of specific heat capacity above ambient temperatures is normally performed using differential scanning calorimeters (DSC's), which typically use small samples (5 mm x 1 mm, up to 5 mm x 15 mm). However, some materials (e.g. graphite, complex alloys, polymers and composites) require a large number of grains, or large volumes, for measurements to be representative of a material's bulk properties. For these types of material DSC measurements are not ideal and traditional modelling (i.e. Kopp-Neumann, method of mixtures) has only limited applications and is not always applicable, especially if phase changes take place, or the sample melts. Low temperature specific heat capacity has been successfully measured using Nernst-type (heat pulse) adiabatic calorimetry. This technique has potentially the best accuracy of available techniques and a large freedom on sample size. Therefore, a high temperature quasi-adiabatic calorimeter was developed. The developed system uses a quasi-adiabatic sample mounting arrangement to measure specific heat, using an integrated temperature sensor and heater arrangement for improved sensitivity. During the development of the measurement system two methods of heat pulse analysis were produced; 1.traditional post-pulse regression/interpolation, and 2. a simplified finite element modelling technique The system and both analysis techniques produced reproducible specific heat capacity data between room temperature and 1000℃ on samples sizes between 2 g to 50 g for graphite, copper, stainless steel, and molybdenum samples. This data compared well with accepted values for these materials.