Chromate, cesium

Vacuum Tubes. In the manufacture of vacuum tubes for use in polarized ion sources, vaporized cesium is used as a getter for residual gaseous impurities in the tube and as a coating to reduce the work function of the tungsten filaments or cathodes of the tube. The cesium vapor is generated by firing, at about 850°C within the sealed and evacuated tube, a cesium chromate pellet and zirconium (12) (see Vacuum technology). 

Cesium chromate [13454-78-9] M 381.8. Crystd from water (1.4ml/g) by partial evapn in a desiccator. 

Cesium chromate [56320-90-2] M 381.8, pKi 0.74, pK 6.49 (for H2Cr04). Crystalhse the chromate from water (1.4mL/g) by partial evaporation in a desiccator. [Boer et al. Z Anorg Allgem Chem 191 113 1930, Hein Herzog in Handbook of Preparative Inorganic Chemistry (Ed. Brauer) Academic Press Vol II p 1389 1963.]... 

Cesium chromate CrCs O, 963 35.3 Gadolinium(III) chloride CljGd 602 40.6... 

According to Bowsher (1987), the reaction between CsOH vapor and stainless steel surfaces is characterized by the formation of both water-soluble and insoluble cesium-based reaction products it proceeds via a fast physisorption process which is followed by a slower diffusion of cesium into the metal oxide. The cesium is predominantly associated with the inner chromite layer of the duplex oxide which covers the stainless steel surface the results of these studies imply that cesium is present as isolated cations in the chromia layer. Beard et al. (1989) reported that the water-soluble fraction of deposited CsOH is progressively converted upon heating to the insoluble form. At temperatures above 1150 K a significant vaporization of cesium took place, identified tentatively as cesium chromate vapor (Cs2Cr04) however, a substantial fraction was retained in the oxide layer on the metal surface and was not vaporized until the steel began to melt. 

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