Solid‐state sintering of core‐shell ceramic powders fabricated by particle atomic layer deposition

Abstract The properties of technical ceramics are highly dependent on their microstructure, which evolves during sintering. Sintering is the process by which ceramic parts are subjected to high temperatures to activate chemical diffusion and the consumption of porosity. During the initial stage of sintering, interparticle necks between neighboring particles form and subsequently increase in size, consuming porosity as the particle centers move closer together. To experimentally determine how this process depends on particle surface composition, particle atomic layer deposition (ALD) was used to deposit a thin film of amorphous aluminum oxide (Al 2 O 3 ) onto yttria‐stabilized tetragonal zirconia (3YSZ) particles, producing core‐shell structured powders. The uniformity of the Al 2 O 3 film was confirmed with transmission electron microscopy and energy dispersive spectroscopy. Scanning electron microscopy was used to observe microstructural evolution during sintering, and the dihedral angles of Al 2 O 3 and 3YSZ grains were measured to determine the ratio of interfacial energies between the 3YSZ|3YSZ, 3YSZ|Al 2 O 3 , and Al 2 O 3 |Al 2 O 3 interfaces. Analysis of the densification kinetics revealed that the initial stage of densification is dependent on the material at the surface of the particles (ie, the Al 2 O 3 film) and is controlled by the diffusion of Al 3+ cations through Al 2 O 3 . Once the Al 2 O 3 film has coalesced, the sintering behavior is controlled by the densification of the core material (3YSZ). Thus, core‐shell powders fabricated by particle ALD sinter by a two‐step process where the kinetics are dependent on the material present at interparticle contacts.