The Temperature Scale and the Melting Point of Molybdenum

Abstract

Spectral emissivities and temperature scales of Mo from 300\ifmmode^\circ\else\textdegree\fi{} to 2900\ifmmode^\circ\else\textdegree\fi{}K. A tubular filament of pure Mo was made by winding ribbon in a close helix about 15 mm long and 1 mm in diam. Spectral emissivities were then obtained by observing the ratio of the outer surface brightness to the interior brightness as seen through small holes in the wall. The results were checked by two other methods. At room temperature the spectral reflectivities were determined and found to be independent of previous heat treatment. For $0.665\ensuremath{\mu}$ the emissivities at 300\ifmmode^\circ\else\textdegree\fi{}, 1500\ifmmode^\circ\else\textdegree\fi{} and 2800\ifmmode^\circ\else\textdegree\fi{}K are 0.419, 0.371 and 0.331; for $.475\ensuremath{\mu}$ 0.424, 0.390 and 0.365 each within \ifmmode\pm\else\textpm\fi{}.007. These values are all lower than those reported by others, probably because of the greater purity of the Mo or of the better black body conditions. Hence these are believed more reliable. These emissivities lead to a difference between true temperature and brightness temperature as a function of the brightness temperature of 46\ifmmode^\circ\else\textdegree\fi{} at 1000\ifmmode^\circ\else\textdegree\fi{}, 113\ifmmode^\circ\else\textdegree\fi{} at 1500\ifmmode^\circ\else\textdegree\fi{}, 217\ifmmode^\circ\else\textdegree\fi{} at 2000\ifmmode^\circ\else\textdegree\fi{}, and 370\ifmmode^\circ\else\textdegree\fi{} at 2500\ifmmode^\circ\else\textdegree\fi{}K.Melting point of Mo has been obtained by observing the brightness temperature of a Mo V-filament at melt and applying the correction to true temperature, and by two other methods. The rounded average of 97 readings yields 2895\ifmmode^\circ\else\textdegree\fi{}K\ifmmode\pm\else\textpm\fi{}10 (${c}_{2}=14,330\ensuremath{\mu}$ deg., ${T}_{\mathrm{Au}}=1336$\ifmmode^\circ\else\textdegree\fi{}K). This value is higher than most of the results of others.