Stability of ZrO/sub 2/ phases in ultrafine ZrO/sub 2/-Al/sub 2/O/sub 3/ mixtures

Journal Article · Sat Feb 01 04:00:00 EST 1986 · J. Am. Ceram. Soc.; (United States)

OSTI ID:5831130

Murase, Y; Kato, E; Daimon, K

Mixtures of ultrafine monoclinic zirconia and aluminum hydroxide were prepared by adding NH/sub 4/OH to hydrolyzed zirconia sols containing varied amounts of aluminum sulfate. The mixtures were heat-treated at 500/sup 0/ to 1300/sup 0/C. The relative stability of monoclinic and tetragonal ZrO/sub 2/ in these ultrafine particles was studied by x-ray diffractometry. Growth of ZrO/sub 2/ crystallites at elevated temperatures was strongly inhibited by Al/sub 2/O/sub 3/ derived from aluminum hydroxide. The monoclinic-to-tetragonal phase transformation temperature was lowered to approx. = 500/sup 0/c in the mixture containing 10 vol% Al/sub 2/O/sub 3/, and the tetragonal phase was retained on cooling to room temperature. This behavior may be explained on the basis of Garvie's hypothesis that the surface free energy of tetragonal ZrO/sub 2/ is lower than that of the monoclinic from. With increasing Al/sub 2/O/sub 3/ content, however, the transformation temperature gradually increased, although the growth of ZrO/sub 2/ particles was inhibited; this was found to be affected by water vapor formed from aluminum hydroxide on heating. The presence of atmospheric water vapor elevates the transformation temperature for ultrafine ZrO/sub 2/. The reverse tetragonal-to-monoclinic transformation is promoted by water vapor at lower temperatures. Accordingly, it was concluded that the monoclinic phase in fine ZrO/sub 2/ particles was stabilized by the presence of water vapor, which probably decreases the surface energy.

• Research Organization: Government Industrial Res. Inst., Nagoya, Hirate-Cho, Kita-Ku, Nagoya
• OSTI ID: 5831130
• Journal Information: J. Am. Ceram. Soc.; (United States), Journal Name: J. Am. Ceram. Soc.; (United States) Vol. 69:2; ISSN JACTA
• Country of Publication: United States
• Language: English

Related Subjects

36 MATERIALS SCIENCE
360202* -- Ceramics
Cermets
& Refractories-- Structure & Phase Studies
ALUMINIUM COMPOUNDS
ALUMINIUM HYDROXIDES
ALUMINIUM OXIDES
ALUMINIUM SULFATES
CHALCOGENIDES
CHEMICAL PREPARATION
COHERENT SCATTERING
CRYSTAL GROWTH
DIFFRACTION
DISPERSIONS
ENERGY
FLUIDS
FREE ENERGY
GASES
HEATING
HIGH TEMPERATURE
HYDROGEN COMPOUNDS
HYDROXIDES
MIXTURES
OXIDES
OXYGEN COMPOUNDS
PHASE TRANSFORMATIONS
PHYSICAL PROPERTIES
SCATTERING
STABILITY
SULFATES
SULFUR COMPOUNDS
SURFACE ENERGY
SURFACE PROPERTIES
SYNTHESIS
THERMODYNAMIC PROPERTIES
TRANSITION ELEMENT COMPOUNDS
VAPORS
VERY HIGH TEMPERATURE
WATER VAPOR
X-RAY DIFFRACTION
ZIRCONIUM COMPOUNDS
ZIRCONIUM OXIDES