Cesium Chromate Photo-Tube Pellets

The following results have been obtained in an exploratory investigation of the cesium chromate pellets used in the manufacture of photo-tubes: (1) hydrogen evolution or titration can be used to measure the yield of cesium with reasonable precision. Each method has limitations. (2) The theoretical yield could be obtained from cesium chromatesilicon pellets. (3) Within limits, the actual yield increases with the rate of heating; the maximum yield is not highly sensitive to composition in the range investigated. (4) No marked advantage was observed when titanium or zirconium was substituted for silicon as reducing agent. (5) An excess of hydrogen above the theoretical was consistently observed with nickel pellet holders, which points to a reaction of water vapor with reactive nickel formed during the heating and flashing of the pellet. The substitution of the less volatile molybdenum for nickel eliminated this difficulty. An excess of hydrogen was formed also when the reducing agent in the pellets was titanium.

It was suggested for purposes of further study that the complex process occurring when such pellets are induction heated be subdivided into two reactions of elementary silicon: (1) a preliminary exothermic reduction of hexavalent chromium, which initiates (2) a rapid reduction of monovalent cesium. The two reactions may proceed concurrently. This picture explains several observations made in the laboratory or in the factory.