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- Title
Feedback-Controlled Firing of Reaction-Bonded Aluminum Oxide.
- Authors
Watson, Matthew J.; Chan, Helen M.; Harmer, Martin P.; Caram, Hugo S.
- Abstract
The reaction-bonded aluminum oxide (RBAO) process utilizes the oxidation of intensely milled aluminum/alumina powder compacts that are heat treated in air to make alumina-based ceramics. RBAO samples are typically oxidized in a furnace which is heated at 1°C/min to 1100°C. Heat-treating samples with a characteristic dimension ≷1 mm, without adjusting the furnace temperature program, usually results in a cracked ceramic. Cracking is caused by the excessive thermal and chemical stresses that result from steep temperature gradients (≷30°C/mm) and compositional gradients (≷5000 mol . (m3 .mm)-1), which develop under the deleterious ignition and shrinking core reaction regimes. While adjustments to the furnace temperature program based on continuum models have had some success, the use of feedback-controlled firing is investigated as a means to avoid the furnace temperature program design step and to decrease the firing time. Feedback-controlled firing is shown to improve yields and significantly reduce the time required to completely oxidize the aluminum. For example, a 16 g sample with a characteristic dimension of 7.56 mm, which previously took ≷100 h to oxidize completely, was successfully oxidized crack free in 18.3 h using feedback control. Using the typical heat-treatment cycle, a 1 mm sample was fired in 18 h. With feedback-controlled firing, the same sized sample was fired in only 5 h.
- Subjects
ALUMINUM oxide; ALUMINUM; OXIDATION; OXIDES; CHEMISTRY; HEAT treatment of metals
- Publication
Journal of the American Ceramic Society, 2005, Vol 88, Issue 12, p3380
- ISSN
0002-7820
- Publication type
Article
- DOI
10.1111/j.1551-2916.2005.00639.x