| Abstract Scope |
Nanocrystalline ceramics with <100 nm grain sizes and superior properties are of great interest. Much has been discussed about ultrafine grain sizes, but little is known about ultra-uniformity, defined as grain size distribution narrower than predicted by the classical theory of Hillert. Here we provide a generalized growth theory unifying the textbook knowledge of Ostwald ripening and normal grain growth. For curvature driven grain growth, we find a steady-state size distribution that is analytically solvable for growth exponent n > 1 and the distribution narrows with increasing n. Experimental validation of this prediction is found in porous alumina. When coupled with two-step sintering, it creates dense alumina nanoceramics with 34 nm average grain size and an extremely uniform microstructure. Improved bending strength has been demonstrated for two-step sintered ceramics using colloidal processed commercial powders, reaching 1.04 GPa for Al2O3 and 440 MPa for MgAl2O4. |