Evolution of icosahedral copper particles in the process of their growth during electrocrystallization

Abstract

Metal icosahedral microparticles with six fifth-order symmetry axes, a specific faceting and high catalytic activity, open up wide opportunities for their usage as catalysts capable of operating in fluidized bed reactors. In this paper, microparticles of copper of the icosahedral habitus about 15 microns in size in the form of truncated icosahedra have been grown for the first time by electrodeposition from sulfuric acid phate electrolyte. Such icosahedra are faceted by twelve {110} crystallographic planes and twenty {111} planes. Studies of the morphology of the surface of copper truncated icosahedra using metallography and electron microscopy have shown that in the process of growth they transform into perfect icosahedra faceted only by {111} planes. The structure of icosahedral copper particles has been studied in detail. Electron microscopic studies of the cross section of copper icosahedral particles show that they consist of sub-structural volume elements (fragments) that are separated from each other by twin and (or) dislocation boundaries. Often inside the fragments there are broken boundaries, near which extinction contours of dislocation origin are observed. In addition, coherent twin boundaries of the {111} <112> type are observed inside the fragments; they do not create long-range stress fields, twin layers, insertions and dislocations. Pentagonal pits appear on the surface of particles in the process of electrodeposition or etching, which indicate the presence of partial disclinations there. According to the results of experimental data, a scheme for the evolution of truncated icosahedra in the process of copper electrocrystallization into perfect icosahedra is proposed. Using the disclination approach, the density of the total free energy of a truncated and perfect icosahedron has been estimated and it is shown that the transformation of a truncated icosahedron into a perfect one is energetically justified.