DISCONTINUITY IN NORMAL SPECTRAL EMISSIVITY OF SOLID AND LIQUID COPPER AT THE MELTING-POINT

Normal spectral emissivities for solid (epsilon(lambda,solid)) and liq uid (epsilon(lambda,liquid)) copper at the melting point have been det ermined, and the discontinuity in epsilon(lambda,liquid) and epsilon(l ambda,solid) at the melting point has been discussed. The spectral emi ssivity was determined by comparing the spectral radiation intensity o f the sample to that of the fixed-point blackbody over the wavelength range 550 to 750 nm. The samples and fixed-point blackbody were heated in the continuous casting type cold crucible. Values of epsilon(lambd a,liquid) and epsilon(lambda,solid) at 650 nm were 0.167 and 0.108, re spectively. The emissivity ratio of epsilon(lambda,liquid)/epsilon(lam bda,solid) increased from approximately 1.2 to 1.8 as the wavelength i ncreased in the range 550 to 750 nm. The discontinuity in epsilon(lamb da,liquid) and epsilon(lambda,solid) at the melting point has been qua litatively explained by the optical absorption mechanism due to the in traband transition.