ISSN:
1551-2916
Source:
Blackwell Publishing Journal Backfiles 1879-2005
Topics:
Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
,
Physics
Notes:
Nanocrystalline, single-phase undoped ZnO was sintered to 95%–98% of theoretical density at 650°–700°C, using pressureless isothermal sintering. The density increased very rapidly at 500°–600°C, remained constant with sintering temperature until ∼900°C, and then decreased slightly. The estimated activation energy for densification at 600°–700°C (275 kJ/mol) was comparable to grain-growth activation energies previously reported for microcrystalline ZnO but much greater than the grain-growth activation energy measured in the present work. A bimodal microstructure, consisting of nanocrystalline grains within larger ensembles (“supergrains”), was observed, and both modes grew as the sintering temperature increased. The grain-growth activation energy for the nanocrystalline grains was extremely low, ∼20 kJ/mol. The activation energy for the growth of the supergrains depended strongly on temperature but was ∼54 kJ/mol at 〉500°C. The important mechanisms probably are rearrangement of the nanoparticle grains, with simultaneous surface and boundary diffusion, and vapor transport above 900°C.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1111/j.1151-2916.2002.tb00391.x
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