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Fabrication of Transparent γ‐Al 2 O 3 from Nanosize Particles
Author(s) -
Gallas Marcia R.,
Hockey Bernard,
Pechenik Alexander,
Piermarini Gasper J.
Publication year - 1994
Publication title -
journal of the american ceramic society
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.9
H-Index - 196
eISSN - 1551-2916
pISSN - 0002-7820
DOI - 10.1111/j.1151-2916.1994.tb07104.x
Subject(s) - materials science , compaction , porosity , indentation hardness , composite material , fabrication , transmission electron microscopy , particle size , void (composites) , particle (ecology) , liquid nitrogen , scanning electron microscope , analytical chemistry (journal) , microstructure , chemical engineering , nanotechnology , chemistry , medicine , alternative medicine , oceanography , pathology , chromatography , geology , engineering , organic chemistry
The compaction and heat‐treatment behavior of nanosize γ‐Al 2 O 3 powder (average diameter = 20 nm) was studied. A diamond anvil high‐pressure cell was used to compact the powder at pressures up to 3 GPa, both in air at room temperature and under liquid nitrogen, followed by pressureless heat treatment at 800°C. For all conditions studied, the fabricated compacts were optically transparent. X‐ray diffraction confirmed retention of the γ‐phase. The compacts were also characterized before and after heat treatment by microhardness measurements and by transmission electron microscopy. For both ambient and cryogenic compaction, sample hardness increased with pressure, and heat treatment resulted in about a 50% increase in hardness independent of the initial green‐state value. Samples compacted in LN 2 were significantly harder (up to 9.6 GPa) than those compacted in air. TEM examination revealed a random‐dense‐packed particle structure and interconnected porosity; interstitial void dimensions, however, were always less than the average particle diameter (20 nm). Observed effects on the increase in hardness could not be explained by microstructural changes normally attributed to increased compaction pressure or heat treatment, most notably densification. Alternative explanations are proposed.