Temperature history and microstructure of alumina

Technical Report · Fri May 01 04:00:00 EDT 1992

DOI:https://doi.org/10.2172/7081532· OSTI ID:7081532

Lin, Jiang Tsair

A simple process for the attainment of fully dense and improved microstructure for Al{sub 2}O{sub 3} ceramics has been developed. Pure, narrow size distribution, submicron powder is used. Homogenization heat treatment of Al{sub 2}O{sub 3} powder compacts at 800{degree}C for 50 hours produces more uniform pore structure and higher green strength. Pore size distribution becomes narrower. Near fully dense, fine-grained (< 1.2{mu}m) and uniform grain size-distribution, undoped Al{sub 2}O{sub 3} 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 Al{sub 2}O{sub 3} ceramics homogenized at 800{degree}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 Al{sub 2}O{sub 3} 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 Al{sub 2}O{sub 3} ceramics, homogenization of powder compacts at 800{degree}C for 50 hours produces 0.80{mu}m. 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 Lab., CA (United States)
• Sponsoring Organization: DOE; USDOE, Washington, DC (United States)
• DOE Contract Number: AC03-76SF00098
• OSTI ID: 7081532
• Report Number(s): LBL-32510; ON: DE92041196
• Country of Publication: United States
• Language: English

Related Subjects

36 MATERIALS SCIENCE
360201* -- Ceramics
Cermets
&amp; Refractories-- Preparation &amp; Fabrication
360202 -- Ceramics
Cermets
&amp; Refractories-- Structure &amp; Phase Studies
ALKALINE EARTH METAL COMPOUNDS
ALUMINIUM COMPOUNDS
ALUMINIUM OXIDES
CHALCOGENIDES
COMPACTS
CRYSTAL STRUCTURE
DENSITY
DOPED MATERIALS
ELECTRON MICROSCOPY
FABRICATION
GRAIN SIZE
HEAT TREATMENTS
MAGNESIUM COMPOUNDS
MAGNESIUM OXIDES
MATERIALS
MATERIALS WORKING
MICROSCOPY
MICROSTRUCTURE
OXIDES
OXYGEN COMPOUNDS
PHYSICAL PROPERTIES
POROSITY
POWDERS
PRESSING
PRODUCTION
SCANNING ELECTRON MICROSCOPY
SINTERING
SIZE
TEMPERATURE RANGE
TEMPERATURE RANGE 1000-4000 K