Adsorption of Oxygen on Tungsten at Temperatures from 300° to 850°K

The adsorption of oxygen has been studied on a polycrystalline tungsten ribbon at temperatures from 300° to 850°K. Two types of tungsten surface structure are distinguishable by their adsorption and desorption behavior. At 300°K, adsorption on either type of surface occurs into a single phase, but, at higher temperatures, to a maximum of ∼765°K, additional adsorption occurs, with an energy of activation of ∼0.25 eV. This process probably involves a reconstruction of the tungsten surface rather than the adsorption into a pre-existing set of sites. Limited measurements at temperatures between 800° and 1000°K are consistent with the model of a solution process restricted to the surface layers of the tungsten. The removal of adsorbed oxygen, in a high-temperature flash, occurs only by oxide evaporation below ∼1650°K and by evaporation of both an oxide and oxygen, above this temperature.