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Report Title: Normal Spectral Emittance Measurements (600–2000 nm) of Polycrystalline Alumina (PCA) at High Temperatures

Author(s) L. Bigio, of the Component Ceramics Laboratory
GE Report Number: 99CRD128

Date: November 1999
Number of Pages: 8

Key Words: spectral emittance, 600-2000 nm, polycrystalline alumina, PCA, high temperatures, fiber optic radiance probe

“A novel method is shown for measuring the spectral emittance of polycrystalline alumina (PCA) in the temperature range ~1100-1400 C, from 600-2000 nm. The method utilizes a CO2 laser at 10.6 microns to heat a ~4 mm size spot on a small sample (~6×4 mm) from one side, while the temperature and emission are measured optically from the other side. A fiber optic radiance probe focuses on a 2 mm spot in the middle of the larger heated region, and directs the collected emission to a spectrometersystem. Radiance measurements are conducted relative to a blackbody at 1000 C. The temperature is measured at the same location viewed by the radiance probe using a thermal imaging pyrometer with a narrow bandpass at 10.6 microns. Since this is the same wavelength as the laser, care must be taken to avoid the scattered laser radiation that partially overfills the sample. An emittance at 10.6 microns of 0.97 is assumed for the temperature measurements. In this spectral region, the emittance is found to decrease with increasing wavelength and increase with increasing temperature. This method can be used on other ceramic materials as well.”