Spectral emissivities of tantalum, platinum, nickel and gold as a function of temperature, and the melting point of tantalum
A. G. Worthing
Spectral emissivities of Ta at 0.665μ and 0.463μ have been determined by (a) the tubular filament, (b) the reflectivity and (c) the comparison at contact methods. For 0.665μ the smoothed values at 300°K, 1500°K, and 2700°K are 0.493, 0.438, and 0.394; for 0.463μ, 0.56, 0.50, and 0.43. While agreeing at 300°K with the results of Wartenberg and of Coblentz, at incandescence the present values are lower than previous values. Probable sources of error in emissivity determinations are such as to indicate that these lower values are the more reliable. Temperature scale for Ta.-For 0.665μ, the above emissivities lead to the following differences between brightness temperature and true temperature as a function of the brightness temperature: 57°at 1200°K, 107°at 1600°K, 179°at 2000°K, 278°at 2400°K, and 406°at 2800°K. Melting point of Ta.-Two determinations by the contact method, using tungsten as the known material yielded 3300°K. This is higher than previously reported values. Spectral emissivity of Pt was found to vary linearly with temperature. For 0.665μ, the emissivities at 1200°K and 1850°K are 0.295 and 0.310; for 0.535μ at 1200°K and 1600°K, 0.325 and 0.335; for 0.460μ at 1600°K and 1850°K, 0.375 and 0.390. The emissivity at 0.665μ combined with an observed brightness temperature of 1842°K checks Hoffman's careful melting-point determination exactly. Spectral emissivity of Ni (98.8% pure) was found not to change with temperature. For 0.665μ, 0.535μ, and 0.460μ, emissivities of 0.375, 0.425, and 0.450 were obtained. Spectral emissivity of Au for 0.665μ was found to increase from 0.062 at 300°K to 0.145 at 1300°K, for 0.535μ to increase from 0.352 at 300°K to 0.450 at 1300°K, for 0.460μ to remain constant at 0.633. © 1926 The American Physical Society.
