Details

Autor(en) / Beteiligte

• Taylor, Nathan J
• Pottebaum, Andrew J
• Uz, Veli
• Laine, Richard M

Titel

The Bottom Up Approach is Not Always the Best Processing Method: Dense [alpha]-Al sub(2)O sub(3)/NiAl sub(2)O sub(4) Composites

Ist Teil von

• Advanced functional materials, 2014-06, Vol.24 (22), p.3392-3398

Erscheinungsjahr

2014

Quelle

Wiley Online Library

Beschreibungen/Notizen

• The bottom up approach suggests that atomic scale mixing should permit optimal control of processing for many types of materials in terms of densification rates, final and average grain sizes; and, thereafter, global properties thereby minimizing processing conditions, capital equipment requirements, and energy consumption. The literature indicates that, to date, this axiom has not been tested although numerous researchers have whole-heartedly adopted the concept. Liquid-feed flame spray pyrolysis (LF-FSP) provides atomically mixed NiO.3Al sub(2)O sub(3) nanopowders(30-40 nm average particle size, APS) that are a single phase, spinel solid solution. Sintering 56 plus or minus 1 wt% CIPped pellets to 95 plus or minus 1% theoretical density using two different heating schedules produces [alpha]-Al sub(2)O sub(3)/NiAl sub(2)O sub(4) composites with grain sizes of 0.9 plus or minus 0.2 mu m. For comparative purposes, ball milled Al sub(2)O sub(3) are synthesized from both highly atomically-mixed single phase metastable spinel nanopowders and NiAl sub(2)O sub(4) 30-40 nm APS pellets of the same composition with a submicro-meter length scale mixing and similar green densities are also sintered to 95 plus or minus 2% TD. In both instances, the same microstructures are realized despite the great difference in length scale of mixing. This contrasts greatly with the expectation that the atomically mixed materials would give finer grain sizes at the same densities and with faster sintering times, suggesting that the bottom up approach is not always valid. Dense NiAl sub(2)O sub(4)/[alpha]-Al sub(2)O sub(3) composites are synthesized from both highly atomically-mixed single phase metastable spinel nanopowders and from submicrometer mixed NiAl sub(2)O sub(4) and Al sub(2)O sub(3) nanopowders to study bottom-up synthesis from the nanoscale to bulk materials. Surprisingly, both composites sinter to similar densities with similar microstructural properties and grain sizes, suggesting that the bottom-up approach may not be the best choice for bulk synthesis.