Oxygen adsorbed tungsten oxide

In fact, the oxidation of metals with very low work functions (alkali metals, alkaline earth metals) proceeds very quickly at room temperatures and more slowly at 83 K. If the work function of the metal has a medium-sized value, it is increased by oxygen, e.g., that of tungsten from 4.53 to 6.27 volts, or by 1.74 volts, according to the measurements of the contact potential by Bosworth and Rideal (12). In this case oxygen is adsorbed in the form of atoms. No oxidation was observed at low tem-... 

Each of the various processes of adsorption may have desorptions of the reverse forms, for example, dissociative adsorption may have as its reverse, associative desorption. However, the process of chemisorption may not be reversible [ 1.2.2(c)]. Desorption may lead to species other than that adsorbed, for example, ethane dissociatively adsorbed on clean nickel gives little or no ethane upon desorption, 1-butene dissociatively adsorbed to methylallyl and H on zinc oxide gives mainly 2-butenes upon desorption, and some W03 may evaporate from tungsten covered with adsorbed oxygen. 

Determination of the amount of gas which adsorbed on the tungsten flash filament, but which did not produce a pressure increase on subsequent flashing of the filament, e. g., oxygen which is removed as an oxide (6). The procedure described above for test (1) was followed until the necessary diffraction data had been obtained. Then, without flashing the filament, nitrogen was admitted to the tube at a pressure of about 10 mm Hg until the filament was saturated. 

The second type of surface is an atomic layer of oxygen strongly bound to a tungsten 110 surface in the form of a 2-D oxide. This surface will not lose oxygen up to a temperature of 1200 K and when cesium is adsorbed on it with proper coverage, a work function near 1.0 ev can be obtained. An example (9) is shown in Figure 14. 

Adsorption. Oxygen is adsorbed on clean tungsten surfaces in a variety of atomic and molecular states. At low temperature (<0 °C), oxygen is adsorbed molecularly, but at room temperature this adsorption is a precursor state to the atomic adsorption. A covered surface shows an ordered oxygen superstructure. If the temperature is increased, a more extensive coverage occurs and oxide-like structures are formed. The surface layer can be described as adsorbed oxide. 

Reaction with water vapor or humid air (60-95% relative humidity) in the temperature range 20-500 °C results in the formation of a WO3 layer. No lower oxides or hydrates could be found by ESCA. The thickness of the oxide layer increases with increasing humidity. The reaction rate depends on temperature and I20]/[H2] partial pressure ratio and is more rapid than with liquid water. Water molecules are adsorbed at the tungsten surface and dissociate. The oxygen atoms difiuse into the tungsten metal, forming at first a solid solution and then the oxide compound, while, hydrogen escapes as element. 

---