National Standard and New Reference Material for Specific Heat Capacity Measurements

Thermal analysis and calorimetry share a close relationship in the field of thermal research. With regards to the specific heat capacity, researchers have been able to realize absolute measurement techniques by utilizing drop, conduction, and adiabatic methods that are used in calorimetry. Furthermore, it is possible to optimize differential scanning calorimetry, which is a comparative measurement technique for the specific heat capacity used in thermal analysis, by improving the absolute measurement techniques. At the National Metrology Institute of Japan (NMIJ), we developed a new certified reference material (CRM) for comparatively measuring the specific heat capacity, the single-crystalline silicon-NMIJ CRM 5806a, using a new type of cryogenic adiabatic calorimeter equipped with a pulse-tube refrigerator working in the temperature range from 50 to 350 K. This CRM was produced in accordance with the quality specifications of NMIJ, and complies with the ISO/IEC 17025, ISO 17034, and ISO GUIDE 35 standards. This paper reports on the procedure for fabricating this CRM and using it to perform specific heat capacity measurements at low temperatures. The specific heat capacity was measured using a differential scanning calorimeter in the temperature range from 280 to 340 K. NMIJ CRM 5806a was used to calibrate the heat flow. It was found that the uncertainty evaluation became easier because one factor of the uncertainty evaluation could be removed using the CRM. We show that the development of the CRM using the adiabatic calorimeter has led to an improvement in the specific heat capacity measurement results obtained by the differential scanning calorimeter.