WORK FUNCTION VARIATION OF TUNGSTEN IN BARIUM PLUS CESIUM AND STRONTIUM PLUS CESIUM VAPOR ENVIRONMENTS

The variation of the electron work function of tungsten in barium, cesium, strontium and their vapor combinations has been experimentally determined in a thermionic diode incorporating independently controlled barium (or strontium) and cesium reservoirs. The data show that in the single vapor cases the work function variation is defined, within experimental error, by Ts/Tv for the regions investigated. For the case of combined vapors, the work function is defined by both ratios, Ts/Tv1 and Ts/Tv2, where Tv1 and Tv2 are the temperatures of the reservoirs generating each vapor, respectively. Furthermore, it is shown that with increasing barium (or strontium) vapor pressure a region of constant φs is established in the φs versus Ts/Tcs plot. For example: at TBa = 700 °K and Ts = 2050 °K, φs is essentially affected by T/Tcs, however, at TBa = 1000°K and Ts = 1800°K, φs is constant at 3.0 eV, for Ts/Tcs equal or greater to 2.8 and decreases for values less than this. The point of department from the constant line for low barium or strontium pressures falls very close to the line of φs versus Ts/Tcs for tungsten when taken in the absence of barium or strontium vapors. However, at high barium or strontium pressures this point crosses over the line of the Cs-on-W system. Data plotted in the form of φs versus Ts/TBa and Ts/Tsr and φs versus Ts/Tcs and other related information are given. © 1969.