Evaluation of National Institute of Standards and Technology (NIST) Thermal Conductivity Standard Reference Materials Using a 20-cm Heat Flow Meter Apparatus

The equations developed for NIST (formerly National Bureau of Standards) thermal conductivity Standard Reference Materials (SRM's) were derived from thermal conductivity measurements made on guarded hot plate apparatuses at NIST. These instruments are briefly described in the certificates and more fully described in NIST special publications [1,2] Critical to the conclusions ofthis report is the size of the heat flow meter apparatus used for making measurements on the NIST thermal conductivity standards. This work describes additional variability in the NIST thermal conductivity standards when they are measured on a system which is smaller than the guarded hot plate apparatuses used at NIST