investigation was made of thermionic emission decay due to chemical interaction between the hexaboride and residual gases in a vacuum system. The results of a thermochemical analysis were in good agreement with experimental data on poisoning. It was shown that oxygen poisoning was possible only at a low cathode temperatures (≲1300C) and relatively high gas pressures, but the LaB6 cathode was much more sensitive to carbon poisoning. The carbon poisoning took place at cathode temperatures of up to 1500C and at low gas pressures (10-7torr) if the residual atmosphere contained heavy hydrocarbons or vapours of organic solvents. It was found that carbon poisoning could be offset by increasing the partial pressure of carbon dioxide.

Poisoning of LaB6 Cathodes. Avdienko, A., Malev, M.: Vacuum, 1977, 27[10-11], 583-8