Size ratio induced yttrium aluminum garnet formation characteristics in nano-scaled Y2O3–Al2O3 powder systems via fast firing processes

The formation characteristics of YAG phase synthesized by fast-firing Y2O3 and Al2O3 powder mixtures were examined. Y2O3 powders of 100, 350, and 500 nm in D50 were mixed with α-Al2O3 powder of (D50) 200 nm to obtain starting powders denoted as S0.5, S1.75, and S2.5, respectively. In these mixtures, the two oxides contacted wholly with each other but varied in number of contact points and diffusion length. This study aimed to eliminate the YAM and YAP phases, which normally occur during YAG formation. Examinations were conducted using pressed compacts (bulk density of 0.91 g cm−3) prepared with the three mixtures. After pre-heating at 700 °C for 30 s, the compacts were plunged at temperatures of 1050–1450 °C for 5–60 s and then quenched to room temperature. In the S0.5 system, one-step YAG formation occurred by an interface-controlled mechanism, and intermediates were apparently suppressed. However, YAG formation was divided into two stages in the S1.75 and S2.5 systems. Two stages were defined by the heating duration prior to and after 20 s. The interface-controlled mechanism was dominant in the initial stage, and then the diffusion-controlled mechanism was dominant in the second stage, in which YAG formed sluggishly and substantial amounts of YAM and YAP persisted. However, both stages followed the conversion sequence of YAM to YAP and then to YAG. Accordingly, two YAG formation routes derived from reacted Y2O3 of different sizes are proposed. Finally, a pure YAG phase could be obtained by calcining the S0.5 system at 1200 °C for 60 s.

► This study examined YAG synthesis using Y2O3 and Al2O3 as the starting materials.
► Appropriate size ratios of oxides and fast firing treatments favored YAG synthesis.
► Interface- and diffusion-controlled mechanism can be occurred during YAG formation.
► Finer Y2O3 particles can react to pure YAG rapidly by interface-controlled mechanism.
► In coarser Y2O3 particles, pure YAG attained by two reaction mechanisms in turn.