Abstract
High density (> 99% TD) and microstructurally controlled alpha-alumina ceramics were produced from seeded nano-size boehmite (gamma-AlOOH) sols with a very fine crystallite size (2-3 nm). A totally wet processing technique comprising vacuum filtering and pressure filtration (PF) was applied in order to increase the solids-loading of the sol and hence form an extrudable paste suitable for plastic forming using extrusion. High packing densities (> 68% TD in the green state) are achieved by PF starting from the slurry state resulting in the formation of a consolidated paste which is further consolidated by extrusion. This combined processing technique was successfully applied, in an attempt to reduce the gamma-Al2O3 formation temperature, and hence lower the theta- to alpha-Al2O3 transition temperature. The microstructure of dense alpha-Al2O3 bodies derived from seeded boehmite sol contains very fine (250 nm) alumina grains after sintering at 1200 degreesC for 2 h. Although the DTA evidence points to a theta- to alpha-Al2O3 transition temperature of 1208 degreesC for a seeded (with 30 mn TiO2) sample, X-ray analysis indicates that a seeded, pressure filtrated and extruded sample is transformed to alpha-Al2O3 phase after sintering at 1100 degreesC for 2 h. (C), 2002 Elsevier Science Ltd. All rights reserved.
Original language | English |
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Pages (from-to) | 1917-1926 |
Number of pages | 10 |
Journal | Journal of the European Ceramic Society |
Volume | 22 |
Issue number | 2002 |
DOIs | |
Publication status | Published - 1 Jan 2002 |
Keywords
- sol-gel processes
- seeding
- pressure filtration
- microstructure
- extrusion
- Al2O3
- AlOOH