Measurement of Thermal Diffusivity of Pyroceram 9606 by the Laser Flash Method

Abstract

Up to date, neither Certified Reference Materials (CRM) nor Standard Reference Materials (SRM) has been available for thermal diffusivity values in the range around 10-2cm2/s, which would be useful to advanced ceramics research. Therefore, a round robin test of Pyroceram glass ceramics Corning 9606 for one of the SRMs has been arranged by the subcommittee C-14.91 in National Institute of Standards and Technology (NIST)/ASTM. The results of thermal diffusivity measurement of the Corning 9606 have been described toward the international collaboration to certify Standard Reference Material. The surface of a disc sample was coated by carbon spray. The apparent thermal diffusivity of an identical sample increased with the number of laser beam flashing because the irradiation of a laser beam burns the carbon coating: (1) a small low temperature rise caused by lower absorption ratio of damaged coating substance increases the apparent thermal diffusivity associated with the negative temperature dependence of thermal diifusivity of Corning 9606 and (2) a burned carbon coating permits the penetration of the laser beam to the sample, which caused fast temperature rise of back surface. For reducing the irradiation damage of carbon coating, a glass cell filled with a CuSO4 solution was inserted in the laser beam path as a variable attenuator. Ninety percent attenuation for the sample 0.97mm thick was found to be favorable to determine the thermal diffusivity value with sufficient reproducibility. The effect of transparency of the sample on the measured thermal diffusivity was also estimated by the theoretical calculation and this clearly confirmed the usefulness of carbon coating. Based on these careful preliminary examinations, the thermal diffusivity values of Corning 9606 in a temperature range between room temperature and 976K were independently determined using two different apparatuses and good agreement was found.