The Reaction of Solid Cobalt with Molten Copper (Report 1) : The Dissolution of Solid Cobalt into Liquid Copper

A basic study on the dissolution of solid cobalt into molten copper was undertaken to obtain a fundamental knowledge in cobalt brazing. Cylinders were immersed in molten copper and then rotated under dynamic conditions of peripheral velocities from 19.0 to 61.5 cm/sec in the temperature range 1190°1340°C, the exposure time being from 45 sec to 120 sec. Rapid dissolvingof cobalt into molten copper occurred and the apperarnce of an etched surface after dissolution was observed. The rate of dissolution increased with an increase in temperature and rotational speed. A modified first-order kinetic equation was used to determine the dissolution-rate constants. These varied from 0.55 to 1.61 × 10-2 cm/sec depending on the temperature and the rotational speed, and were increased in proportion to 0.64-0.74 power of peripheral velocity. The activation energy for dissolution of solid cobalt into molten copper was estimated to be about 10.0 Kcal/mole. For a diffusion-controlled dissolution process, activation energy for dissolution is contributed to by the sum of activation energy for diffusion and some fraction of activation energy for viscosity. The dissolution rate of solid cobalt into molten copper is mixed-controlled.