The Effect of Hydrogen on the Thermionic Emission from Potassium

Abstract

Effect of surface conditions on the current value at a given temperature.---Observing the current at a given temperature after successive cleansings of a potassium surface by distillation followed by contaminations of the surface by hydrogen it was concluded that the large (gg${10}^{\ensuremath{-}14}$ amperes\ifmmode\cdot\else\textperiodcentered\fi{}${\mathrm{cm}}^{\ensuremath{-}2}$ at 180\ifmmode^\circ\else\textdegree\fi{}C) thermionic currents frequently observed from potassium are due to hydrogen contamination, confirming the results of Fredenhagen.Saturation of currents.---With a uniform field in the present apparatus it was shown that it is possible to saturate the thermionic currents observed from potassium at 150\ifmmode^\circ\else\textdegree\fi{}C to 185\ifmmode^\circ\else\textdegree\fi{}C; failure to saturate in the case of previous observers being probably due to non-uniform field conditions. Furthermore, even at temperatures below 100\ifmmode^\circ\else\textdegree\fi{}C no evidence was found for a more important factor in the prevention of saturation than the non-uniform field.The thermionic work function.---The larger currents were found to obey an equation of the Richardson type over a limited temperature range (150\ifmmode^\circ\else\textdegree\fi{}C-210\ifmmode^\circ\else\textdegree\fi{}C). A value of $\ensuremath{\varphi}$ of about 1.3 volts was characteristic of the potassium surface after hydrogen contamination of a certain type. This value is similar to that found by Richardson and Young in the same temperature range. It was concluded that this value of $\ensuremath{\varphi}$ was due to a layer of KH on the surface of the potassium, and that the emission was probably chemical rather than thermionic in origin, being due to the decomposition of the KH. Values of $\ensuremath{\varphi}$ of 0.26 volts were found at temperatures from 100\ifmmode^\circ\else\textdegree\fi{}C to 110\ifmmode^\circ\else\textdegree\fi{}C which are of the order of Richardson's and Young's values at those temperatures.Effect of hydrogen on conductivity of thin potassium layer.---The conductivity of a thin layer of potassium on a Pyrex insulating tube was greatly decreased by exposure to hydrogen.