SPECTRAL ABSORPTION-COEFFICIENT OF MOLTEN ALUMINUM-OXIDE FROM 0.385-MU-M TO 0.780-MU-M

The spectral extinction coefficient, k(lambda), and the absorption coe fficient, alpha(lambda), of liquid aluminum oxide were determined from emission measurements on partially molten single-crystal sapphire fil aments. Measurements were made at wavelengths from 0.385 to 0.780 mu m in both argon and oxygen atmospheres and at 0.650 mu m in a 10% H-2-9 0 % N-2 mixture, The values of alpha(lambda) were found to vary with t he time for which the specimen had been molten and achieved different steady-state values in the three processing atmospheres, A decrease in alpha(lambda) with wavelength (Urbach tail) was observed from 0.385 m u m to about 0.420 mu m in argon and 0.490 mu m in oxygen, and approxi mately constant values were obtained at longer wavelengths. Steady-sta te values of alpha(lambda) at the optical pyrometer wavelength of 0.65 0 mu m were 9 +/- 2 cm(-1) in argon, 41 +/- 8 cm(-1) in oxygen, and 14 +/- 2 cm(-1) in the 10% hydrogen-90% nitrogen gas mixture.