Grain boundary formation through particle detachment during coarsening of nanoporous metals

Grain boundary formation during coarsening of nanoporous gold (NPG) is investigated wherein a nanocrystalline structure can form by particles detaching and reattaching to the structure. MicroLaue and electron backscatter diffraction measurements demonstrate that an in-grain orientation spread develops as NPG is coarsened. The volume fraction of the NPG sample is near the limit of bicontinuity, at which simulations predict that a bicontinuous structure begins to fragment into independent particles during coarsening. Phase-field simulations of coarsening using a computationally generated structure with a volume fraction near the limit of bicontinuity are used to model particle detachment rates. This model is tested by using the measured NPG structure as an initial condition in the phase-field simulations. We predict that up to ∼5% of the NPG structure detaches as a dealloyed Ag75Au25 sample is annealed at 300 °C for 420 min. The quantity of volume detached is found to be highly dependent on the volume fraction and volume fraction homogeneity of the nanostructure. As the void phase in the experiments cannot support independent particles, they must fall and reattach to the structure, a process that results in the formation of new grain boundaries. This particle reattachment process, along with other classic processes, leads to the formation of grain boundaries during coarsening in nanoporous metals. The formation of grain boundaries can impact a variety of applications, including mechanical strengthening; thus, the consideration and understanding of particle detachment phenomena are essential when studying nanoporous metals.

Carbon Supported Pt-Ni Octahedral Electrocatalysts as a Model to Follow Nickel Corrosion and Particle Detachment

Pt-Ni nanoparticles (NPs) are used as electrocatalysts toward the oxygen reduction reaction due to their high mass activity. However, degradation processes at the high potential in the acidic conditions of...

Particle detachment due to wheel rotation

Particle detachment induced by a rotating wheel was investigated theoretically and experimentally. The developed theoretical models were used to reveal how the particle detaches from a wheel surface to the surrounding air. The corresponding experiments were carried out to validate proposed models. Two groups of spherical particles were considered, i.e. silicon dioxide and aluminium oxide particles. Different forces and force moments acting on individual particles were analysed. The criteria for the rolling detachment of particles were considered. The detachment diameters under various conditions were calculated. The results show that the particle detachment was dominated by the removal and resistant forces acting on particles, including the gravity force, adhesion force, hydrodynamic force and centrifugal force. Different relevant parameters can affect particle detachment through these forces, including surface roughness, wheel speed, particle size and properties. A higher wheel speed, larger particle sizes and higher wheel surface roughness were shown to have a conducive influence on particle detachment. The resistant and removal force moments could be affected by the particle properties at the same time; therefore, the detachment diameters of the aluminium oxide particles are similar to those of silicon dioxide. This study can contribute towards the estimation of particle emissions from vehicles.