Research On An Automatic Adiabatic Calorimeter And Development Of Standard Material Of Molar Heat Capacity

Molar heat capacity is a material's property that reflects the ability to absorb and release heat.As a basic thermodynamic property,it has a wide range of applications.Differential scanning calorimetry(DSC)is the common method to measure the molar heat capacity,but the commercial DSC lacks the certified standard reference material to verify and calibrate the equipments.The reliability and traceability of the measurement results can't be guaranteed.In order to solve this problem,an automatic adiabatic calorimeter based on absolute methods was established.This calorimeter consists of a sample cell,an adiabatic control device,an adiabatic control system,a temperature and energy measurement system and a data processing system.The adiabatic property,precision,repeatability and heat exchange coefficient were evaluated by measuring the heat capacity of the empty calorimeter.The precision of the empty calorimeter is less than ±0.05% and the repeatability is less than 0.1% in the temperature range of 300 K to550 K.Several methods of data correction and processing were established and the optimal experimental conditions of empty and full calorimeter were explored.The reliability of the calorimeter was evaluated by measuring the standard material-synthetic sapphire of National Institute of Standards and Technology(NIST).Measurement repeatability of molar heat capacity is less than 0.7% and precision is less than ±0.2%.Compared with the reference value of NIST,the relative deviation of the molar heat capacity is almost less than ±0.25% and the relative deviation of the relative enthalpy is almost less than ±0.5%.The method of measuring the molar heat capacity using DSC was improved.The homogeneity and stability of sapphire and molybdenum reference materials were tested by this method.The molar heat capacity value of sapphire was determined by the adiabatic calorimeter.The molar heat capacity value of molybdenum was determined by DSC compared with sapphire.The results can betraced to the international system unit including current,voltage and temperature.The extended uncertainty of the calorimeter is 0.98%.The extended uncertainty of the sapphire standard material is 1.4%.The extended uncertainty of the molybdenum standard material is 2.77%.