Spectral Emissivities of Tantalum, Platinum, Nickel and Gold as a Function of Temperature, and the Melting Point of Tantalum

Spectral emissivities of $\mathrm{Ta}$ 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 $\mathrm{Ta}$.—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 $\mathrm{Ta}$.—Two determinations by the contact method, using tungsten as the known material yielded 3300°K. This is higher than previously reported values.