Study of the Kinetics of Gas-Metal Reactions

Abstract

The rates of reaction of oxygen with liquid silver have been studied by blowing Ar-O₂ mixtures onto the metal electrically heated both by resistance and by high frequency induction at 1000°C.
Oxygen absorption into liquid silver is a first-order reaction, which is similar to nitrogen absorption into liquid iron, while oxygen desorption into the atmosphere of pure argon is virtually a second-order reaction, which is similar to nitrogen desorption into the same atmosphere.
On the other hand, the rates of absorption and desorption near equilibrium oxygen concentrations are found to be equal. But the apparent first-and second-order reaction rate constants are both dependent on the oxygen partial pressure in the gas phase.
These phenomena are explained by mixed-control model of first-and second-order reactions. The firstand second-order reaction rate constants are 0.022 cm/sec and 0.055 cm/%.sec. It is presumed that the former corresponds to mass transfer in the metal and the latter to surface reaction.
The mixed-control model is applied to the reaction of nitrogen desorption from liquid iron.It is shown that with decrease of the nitrogen partial pressure and nitrogen concentration in the metal the kinetics changes gradually from a first-order to second-order reaction.