Structural and morphological transformations in cobalt-carbon mixtures during ball milling, annealing and Spark Plasma Sintering

Abstract

In this work, powder mixtures of cobalt and amorphous carbon of the Co-17 wt%C composition were processed by high-energy ball milling and annealing/Spark Plasma Sintering in vacuum to study the morphological transformations associated with graphitization of carbon in the powder and consolidated states of the material. High-energy ball milling led to the hcp-fcc transition in cobalt. During annealing of the milled powder, cobalt nanoparticles were encapsulated in graphitic shells. In the consolidated state, graphitization of carbon resulted in the formation of a 3D graphitized structure. Cobalt remained as the fcc phase in the annealed powders and sintered compacts due to the stabilizing action of graphitic shells and graphitic 3D walls, respectively. Selective dissolution of cobalt allowed obtaining porous graphitic materials composed of platelet-shape crystallites 20 nm thick. The specific surface area of the porous graphitized materials obtained from the compacts sintered at 800–1000 °C was of the order of 100 m2 g−1.