Seeding of the Reaction‐Bonded Aluminum Oxide Process

Abstract

The effect of the initial ␣-Al 2 O 3 particle size in the reactionbonded aluminum oxide (RBAO) process on the phase transformation of aluminum-derived ␥-Al 2 O 3 to ␣-Al 2 O 3 , and subsequently densification, was investigated. It has been demonstrated that if the initial ␣-Al 2 O 3 particles are fine (ϳ0.2 m, i.e., 2.9 ؋ 10 14 ␥-Al 2 O 3 particles/cm 3 ), then they seed the phase transformation. The fine ␣-Al 2 O 3 decreases the transformation temperature to ϳ962°C and results in a finer microstructure. The smaller particle size of the seeded RBAO decreases the sintering temperature to as low as ϳ1135°C. The results confirm that seeding can be utilized to improve phase transformations and densification and subsequently to tailor final microstructures in RBAO-derived ceramics.

On the initial deactivation of MnxOy–Al2O3 sorbents for high temperature removal of H2S from producer gas

“…It was also shown that Fe species can act similarly and induce the alumina transition [38]. It can also be noted the temperature of the alumina transition namely its θ → α transition is lowered by the introduction of α-alumina seeds that act as heterogeneous nucleation sites [39].…”

Water Content and Water Evolution from Reaction‐Bonded Aluminum Oxide (RBAO) Powder Precursors

“…For efficient reaction, the starting powders are milled together in the presence of a liquid to prevent premature reaction. Although considerable research related to the processing of RBAO ceramics has been reported, 4–8 some difficulties still remain with the RBAO process, such as reproducibility, sample cracking, and bloating 7 . Sample bloating occurs when a gaseous species evaporates after the aluminum melts at 660°C.…”

Nanocrystalline Seeding Effect on the Crystallization of Two Leucite Precursors

“…The seeding effect in the preparation of α‐Al 2 O 3 and mullite ceramics has been studied extensively. Nordhal and Messing 23 and Suvaci et al 24 reported that the sintering temperature of γ‐Al 2 O 3 was reduced from 1600°C to 1300°–1400°C by using 1.25 wt%α‐Al 2 O 3 seed particles, and the fine α‐Al 2 O 3 decreased the transformation temperature to approximately 962°C and resulted in a finer microstructure. Kara and Sener 25 found that mullite solid‐state sintering behavior was improved because seeding reduced mullite grain size and prevented the occurrence of fine intragranular pores within mullite grains.…”