Temperature history and microstructure of alumina

Thesis/Dissertation · Fri May 01 00:00:00 EDT 1992

DOI:https://doi.org/10.2172/10180760· OSTI ID:10180760

Lin, Jiang Tsair ^[1]

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1. Univ. of California, Berkeley, CA (United States)

A simple process for the attainment of fully dense and improved microstructure for Al₂O₃ ceramics has been developed. Pure, narrow size distribution, submicron powder is used. Homogenization heat treatment of Al₂O₃ powder compacts at 800°C for 50 hours produces more uniform pore structure and higher green strength. Pore size distribution becomes narrower. Near fully dense, fine-grained (< 1.2μm) and uniform grain size-distribution, undoped Al₂O₃ ceramics can be produced using a high quality powder, a high-pressure cold isostatic forming method, and a two-step sintering technique. Improvements in the microstructure of Al₂O₃ ceramics homogenized at 800°C/50 h include a smaller pore size and a more uniform pore size distribution. Prevention of differential densification in the early stages and delay of pore channel closure to the later stages of sintering are believed to be the primary mechanisms for the microstructure improvement in two-step sintering. Two-step sintering is an alternate way to improve the microstructure of Al₂O₃ ceramics compared to fast firing or MgO doping. When a homogenization heat treatment and the fast firing are combined, the final density is higher than from fast firing alone. However, the two-step sintering technique is simple and there is no size limit. Generalization of two-step sintering to more systems is needed. For 250 ppM MgO-doped Al₂O₃ ceramics, homogenization of powder compacts at 800°C for 50 hours produces 0.80μm. This improvement is explained by the distribution of MgO becoming more uniform during the homogenization heat treatment, which enhances the effectiveness of MgO doping.

• Research Organization: Lawrence Berkeley National Lab. (LBNL), Berkeley, CA (United States)
• Sponsoring Organization: USDOE
• DOE Contract Number: AC03-76SF00098
• OSTI ID: 10180760
• Report Number(s): LBL-32510; ON: DE92041196
• Resource Relation: Other Information: TH: Thesis (Ph.D.); PBD: May 1992
• Country of Publication: United States
• Language: English

Related Subjects

36 MATERIALS SCIENCE
ALUMINIUM OXIDES
PRODUCTION
SINTERING
POWDERS
HEAT TREATMENTS
MICROSTRUCTURE
POROSITY
MAGNESIUM OXIDES
DOPED MATERIALS
PRESSING
DENSITY
COMPACTS
GRAIN SIZE
SCANNING ELECTRON MICROSCOPY
TEMPERATURE RANGE 1000-4000 K
360201
360202
PREPARATION AND FABRICATION
STRUCTURE AND PHASE STUDIES