Charge conversion and mass transfer on surface of Al2O3 nanoparticles in Y2O3-Al2O3 colloidal system

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 Y2O3 via 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.