Abstract
The reaction of tungsten with nitric oxide was studied by static method at tungsten temperatures from 1400 K to 1900 K and nitric oxide pressures from 4×10-3 Pa to 1.3×10-1 Pa. Under the reaction conditions, the tungsten oxide formed by the reaction immediately evaporates and filament surface is kept bright during the reaction. The reaction rate is proportional to the 0.7th power of the nitric oxide pressure and increases with an increase in the tungsten temperature, the apparent activation energy being 206 kJ/mol.
The rate equations for the consumption of nitric oxide and the loss of tungsten are expressed as follows :
DNO=5.8×10-2·P0.7 exp (-206, 000/RT) mol/s·cm2
DW=3.6·P0.7 exp (-206, 000/RT) g/s·cm2
where P is in Pa and R is 8.31 J/mol·K.
The composition of the tungsten oxide produced in the reaction was determined as tungsten trioxide.
Possible reaction mechanism is discussed.
