THERMAL-DECOMPOSITION OF COBALT CARBONYL-COMPLEXES IN VISCOUS MEDIA

The thermal decomposition of Co-2(CO)(8) to Co-4(CO)(12) and further t o metallic cobalt and CO under an inert atmosphere at temperatures <90 degrees C in hydrocarbon solutions and in the solid state have been s tudied and are documented in the literature. The mechanistic aspects o f the solid state decomposition were similar to those found with the s olution decomposition, but the kinetic aspects were quite different, s ince the rate constant, k(obs), found for the solid state reaction, wa s two orders of magnitude lower than the one found for the solution re action. The decomposition reaction of cobalt carbonyls is primarily go verned by diffusion. The diffusion of the cobalt carbonyls through a c ertain medium is strongly dependent on the viscosity of that medium. I n a solution containing st polymeric system, the viscosity is a domina nt property, since it is directly proportional to the concentration of the polymer in the solution. Therefore, the solution and solid state decompositions may be viewed as two extreme cases, in which the only v ariable is the viscosity of the polymeric solution. In the solution ca se, in the absence of polystyrene, the viscosity of the solution is es sentially the viscosity of pure hydrocarbon solvent (toluene), while i n the solid state case, the viscosity of the composite polystyrene fil m (the film containing the cobalt carbonyl complex) may be approximate d as the viscosity of solid polystyrene just before its melting point. There are no studies to date which examine the effect of the viscosit y of the solution of the cobalt carbonyl complexes on their thermal de composition reaction in an inert atmosphere. Therefore, a study of the variation of the rate constants of the decomposition reactions as a f unction of the concentration of the polystyrene component in the cobal t carbonyl toluene solutions was undertaken. The reaction rates decrea sed with increasing polystyrene concentration, but only after a critic al polymer concentration, c, which is the coil overlap concentration, was reached. The data obtained are reported here with conclusions con cerning the mechanism of the thermal decomposition reaction of cobalt carbonyl complexes to produce zero-valent cobalt particles.