Barium, on tungsten

Muller first noted field desorption for layers of barium on tungsten (1). He concluded correctly that tunneling could hardly be responsible for the ionization of heavy particles and assumed that the potential curve for the ad-atom substrate complex was deformed to the point where activated desorption over the barrier could take place. This view was supported by the fact that he found that the field necessary for the desorption of thorium was quite temperature dependent, changing from the (remarkably low) value of 6.7 X 10 v./cm. at room temperature to 3.5 X 10 v./cm. at 1500°K (1). Similar results were found by him for barium... 

The adsorptions of sodium, barium and thorium on tungsten and molybdenum have been studied along similar lines. Sodium on tungsten and molybdenum and barium on molybdenum are preferably adsorbed on 211 faces 292) barium on tungsten on 111 faces thorium, however, is preferably adsorbed on 111 faces but not on 110 faces 292). It seems as if other factors are operative besides the work function. 

Langmuir showed that for caosium-on-tungsten occurs when d = 0 67, so that the second assumption is not always true, while Becker (4i) found for barium-on-tungsten that Langmuir s relation was better replaced by... 

So great is the effect of surface concentration upon mobility, however, that errors in estimating the concentration could cause the observed trends. Monovalent metals are more mobile than bivalent metals and bivalent metals than tetravalent metals. Thus mobility in alkali metal monolayers on tungsten can be observed at 300° K. barium migrates measurably only at 1000° K. and thorium at 1500° K. The trend shown in both in respect to surface concentration and valency, is reflected in corresponding trends in the heats of sorption AH (Table 89). 

At room temperature, sulfur unites readily with copper, silver, and mercury and vigorously with sodium, potassium, calcium, strontium, and barium to form sulfides. Iron, chromium, tungsten, nickel, and cobalt react much less readily. In a finely divided state, zinc, tin, iron, and aluminum react with sulfur on heating (19). 

Cesium was first produced ia the metallic state by electrolysis of a molten mixture of cesium and barium cyanides (2). Subsequentiy the more common thermochemical—reduction techniques were developed (3,4). There were essentially no iadustrial uses for cesium until 1926, when it was used for a few years as a getter and as an effective agent ia reduciag the electron work function on coated tungsten filaments ia radio tubes. Development of photoelectric cells a few years later resulted ia a small but steady consumption of cesium and other appHcations for cesium ia photosensing elements followed. 

Effect of Varying Both the Zinc Stearate and Barium Chromate Content on the Burning Rate and Temperature Coefficient of a Tungsten Delay Composition... 

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