Use of Alkali Glasses for the Preparation and Pressure Measurement of Alkali Metals, and Cesium Plate-out Levels on Transition Metals

Abstract

We have prepared pure Li, Na, and Cs films in ultrahigh vacuum apparatus by the electrolysis of alkali-oxide-containing glasses. Details of the procedure which enables precise amounts of alkali metal to be metered out are given. The alkali ions electrolyzed out of the glass cannot be replaced and the glass becomes progressively weakened. The construction and use of an electrochemical Cs pressure gauge is described. The gauge is an electrode concentration cell in which the electrodes display the activity differences. The electrolyte is any alkali-oxide-containing glass. When the Cs pressure to be measured is zero the gauge gives a base EMF which is different for each glass electrolyte used. Pyrex glass (4% Na 2O) works better than Cs 2O glass as the electrolyte because the base EMF for Pyrex is high. The EMF-pressure relationship is given by the Nernst equation and Cs pressures down to 10 -17 Torr can be measured. The gauge has been used to assess Cs plate-out levels (i.e., equilibrium amounts deposited) on clean Ni at 0°C from Cs vapor at pressures below 10 -13 Torr. Ni is an effective Cs getter, leaving little Cs in the vapor phase. Alkali-oxide-containing glasses approximate to Ohmic ionic conductors with a limited degree of electronic conduction. The glass characteristics alter with passage of current and some decomposition occurs with the formation of silica.