NORMAL SPECTRAL EMITTANCE OF VANADIUM AND TANTALUM FOR DIFFERENT SURFACE CONDITIONS AT TEMPERATURES ABOVE 1000 K

Above 1000 K radiation is the most important mode of heat transfer, and in the vacuum of outer space it is the only mode of heat transfer. It is, therefore, important to study the thermal radiation properties of materials at high temperatures. The normal spectral emittance lambda equals 0. 645 mu was determined for vanadium between 1100 and 1750 K and for tantalum between 1200 and 2600 K, at pressures below 10** minus **6 mm Hg for electrochemically and mechanically polished surfaces. The emittance was found to decrease with increase in temperature. It was also lower for the electrochemically polished surface. An empirical equation was fitted to the experimental data, and it was used to predict the emittances up to the melting points.