Charge conversion and mass transfer on surface of Al2O3nanoparticles in Y2O3–Al2O3 colloidal system

Abstract

The mixing process of Al₂O₃ and Y₂O₃ nanopowders in aqueous suspension was studied. Charge conversion on the surface of Al₂O₃ particles in the Y₂O₃–Al₂O₃ colloidal system was observed. Negative charges on the surface of Al₂O₃ particles became positive due to the assembly of Y₂O₃ on the surface of Al₂O₃ nanoparticles in the colloidal system, as shown by zeta potential analysis of Y₂O₃–Al₂O₃ colloidal systems with different Y/Al ratios. Rheological properties of the mixed powders slurries with different Y₂O₃ content were also investigated. XRD peaks of Al₂O₃ shifted towards smaller angles with increasing amounts of Y₂O₃ added, implying the encapsulation of Al₂O₃ by Y₂O₃via mass transport during the mixing process, as confirmed by HRTEM measurement. A mechanism was proposed for the paragenesis of mineral in this binary colloidal system. Hydrated Y₂O₃ with higher K_sp attaches and migrates onto the surface of another hydrated sediment Al₂O₃ with smaller K_sp and opposite surface charge. The mass transfer process between Y₂O₃ and Al₂O₃ nanoparticles in this binary mixture suspension is analogous to the Ostwald ripening process. This new growth phenomenon is important for the science of crystal growth as it helps boost the exploration of new mechanisms for crystal growth in various material systems and provide clear evidence for the diffusion growth of crystalline structure in a binary colloidal system.