The Temperature Scale, Thermionics, and Thermatomics of Tantalum

The energy cycle $\varphi _0^{}{}_{}{}^{-}+\varphi _0^{}{}_{}{}^{+}=\varphi _0^{}{}_{}{}^0+V$ has been followed experimentally for tantalum. This involved a redetermination of the temperature scale with emissivity varying linearly from ${\epsilon }_{\lambda T}=0.439\mathrm{}$ at $T=1200\mathrm{}$ °K to ${\epsilon }_{\lambda T}=0.384\mathrm{}$ at $T=2400\mathrm{}$ °K for $\lambda =0.669\mathrm{}$μ. Thermionic measurements of the electron work function and of the positive ion work function yielded, respectively, $\varphi _0^{}{}_{}{}^{-}=4.19\mathrm{}$ev and $\varphi _0^{}{}_{}{}^{+}=10.0\mathrm{}$ ev, with an electron emission constant $A^{*}=55\mathrm{}$ amp. ${\mathrm{cm}}^{-2\mathrm{}}$ ${\mathrm{deg}}^{-2\mathrm{}}$. By a gain of weight method the work function of the neutral tantalum atom was found to be $\varphi _0^{}{}_{}{}^0=7.97\mathrm{}$ ev. The ionization potential of tantalum is not known but may be estimated to be about $V=7.3\mathrm{}$ ev. These values fail to close the energy cycle by 1.1 ev which is believed to be outside the experimental uncertainty of the measurements.