Passivation-driven speciation, dealloying and purification

Thin passivating surface oxide layers on metal alloys form a dissipation horizon between dissimilar phases, hence harbour an inherent free energy and composition gradient. We exploit this gradient to drive order and selective surface separation (speciation), enabling redox-driven enrichment of the core by selective conversion of low standard reduction potential (E degrees) components into oxides. Coupling this oxide growth to volumetric changes during solidification allows us to create oxide crystallites trapped in ametal ('ship-in-a-bottle') or extrusion of metal fingerlings on the heavily oxidized particle. We confirm the underlying mechanism through high temperature X-ray diffraction and characterization of solidification-trapped particle states. We demonstrate that engineering the passivating surface oxide can lead to purification via selective dealloying with concomitant enrichment of the core, leading to disparate particle morphologies.

Automated summary

The thin passivating surface oxide layers on metal alloys create a dissipation horizon, allowing for the enrichment of the core through selective conversion of low standard reduction potential components into oxides. By engineering the passivating surface oxide, purification can be achieved through selective dealloying, leading to the formation of disparate particle morphologies.