Diffusion of oxygen in liquid copper and nickel

Abstract

The diffusivities of oxygen in liquid copper and nickel were determined from 1300°C to 1560°C by a capillary gas-reservoir method. A diffusion cell designed to behave as if of semi-infinite length and consisting of liquid copper or nickel held in an alumina capillary was used. A H2O-H2 gas mixture maintained a constant oxygen potential at the metal-gas interface. A controlled furnace hot zone of 15 cm was obtained with six separate windings of Pt-10%Rh wire. To prevent convection the top of the diffusion cell was adjusted to be hotter than the bottom. The solidified diffusion columns were sectioned and analysed for oxygen by vacuum fusion analysis. Oxygen diffusivities, D, were calculated through use of a solution of Fick's second law. For copper D is 1.52 × 10-8 m2/s at 1295°C and 3.78 × 10-8 m2/s at 1560°C; for nickel D is 3.12 × 10-8 m2/s at 1450°C and 3.39 × 10-8 m2/s at 1580°C. The results for copper can be represented by the Arrhenius relationship ln D equals -19570/RT + 3.21 where E and R are in calories or -81900/RT + 3.21 where E and R are in joules (1350-1560°C) and where the numerator, E, is oxygen diffusion activation energy/mol K and R is the gas constant.