Interaction of Oxygen with Hot Tungsten

The reaction of oxygen at a polycrystalline tungsten surface has been studied over a temperature range from 1300° to 2450°K and for oxygen pressures from ∼10−5 to ∼10−8 torr. A mass spectrometer was used to measure the oxygen pressure. In determining absolute pressures care was taken to avoid errors which may arise due to spurious currents in a Bayard—Alpert ion gauge. The efficiency of removal of carbon impurity from tungsten, by heating in oxygen, was determined. After obtaining a low carbon content, the rates of removal of oxygen at the tungsten surface were determined as a function of temperature. At temperatures below ∼2000°K evaporation of oxides of tungsten occurs at predictable rates. At higher temperatures atomic oxygen is produced and the observed rate of removal of oxygen is strongly influenced by the specific surfaces present in the entire system. For example, a silver surface efficiently reacts with oxygen atoms, without apparent saturation, to give a large apparent increase in the pumping speed at a tungsten surface enclosed in a glass system.