Desorption kinetics of carbon and oxygen in liquid niobium

Desorption kinetics of carbon and oxygen in liquid niobium were investigate d, in the temperature range from 2700 to 3000 K, in a CO/Ar stream using an electromagnetic levitation technique. It was found that desorption of both species occurs via CO evolution, especially when the starting metal has an excess of carbon. Desorption of carbon and oxygen in liquid niobium are se cond-order processes with a first-order dependence on C and O concentration s, indicating that the overall reaction rate is controlled by the substep o f recombination of C and O. The rate equations for C and O desorption are f ound to be (dO/dt)(des) = (dC/dt)(des) = 3.80 . 10(4) (A/V) exp (-47,500/T) (C-e O-e - CO), where C and O are the carbon and oxygen concentrations in atomic percent, respectively, A is the surface area of the sample in square centimeters, V is the volume in cubed centimeters, and the subscript e den otes the equilibrium concentration.