Nano-α-Al2O3 by liquid-feed flame spray pyrolysis

Richard Laine

R.M. Laine, J.C. Marchal, H.P. Sun, and X.Q. Pan (2006)

Nature Materials, 5:710-2.

Nanometre-sized particles of transition (t)-aluminas are important for the fabrication of high-quality alumina ceramics. Multiple tons are produced each year using a variety of gas-phase processes1,2,3,4. The nanoparticles produced by these methods consist mainly of the undesired δ phase with some γ- and θ-Al2O3. Nano-t-aluminas should provide access to dense nano/submicrometre-grained α-Al2O3 shapes offering significant advantages over micrometre-grained shapes5,6,7,8,9,10,11. Unfortunately, polymorphism coupled with the high activation energy for nucleating α-Al2O3 greatly impedes efforts to process dense α-Al2O3 with controlled grain sizes, especially for submicrometre materials. Typically α-Al2O3 nucleation within t-aluminas is sporadic rather than uniform, leading to exaggerated grain growth and vermicular microstructures without full densification5. Thus, production of quantities of nano-α-Al2O3 from multiple nano-t-aluminas for seeding or direct processing of α-Al2O3 monoliths could greatly change how α-Al2O3 components are processed. We report here that liquid-feed flame spray pyrolysis3 of nano-t-aluminas converts them to dispersible 30–80 nm α-Al2O3 powders (50–85% phase transformed). Surprisingly, the powder surfaces are fully dehydrated. These powders pressureless sinter to more than 99.5% dense α-Al2O3 with final grain sizes ≤500 nm without sintering aids.

flame spray pyrolysis, Nanopowder