Phase transformation in nanometer-sized γ-alumina by mechanical milling

Nanocrystalline γ-alumina powders of 50-nm size were milled by high-energy ball milling. It was found that the pure γ-alumina phase showed great stability and did not transform to any other phase even after a long milling time. On the other hand, γ-alumina, which contained a small amount of the α7-alumina phase, showed a gradual phase transformation from γ- to α-alumina on milling. The phase transformation mechanism during milling appears to be nucleation and growth type and promoted by the α-alumina seed.