Kinetics and mechanism of conversion of low-temperature forms of alumina into. cap alpha. -Al/sub 2/O/sub 3/ in presence of additives

Journal Article · Sun Feb 20 04:00:00 EST 1983 · J. Appl. Chem. USSR (Engl. Transl.); (United States)

OSTI ID:5413121

Vereshchagin, V I; Zelinskii, V Y; Khabas, T A; Kolova, N N

For production of high-alumina and corundum materials it is necessary in most cases to ensure a high content of ..cap alpha..-Al/sub 2/O/sub 3/ in the original alumina while retaining or even improving the sintering activity of the material. The purpose of the present work was to investigate the influence of heterophase additive on phase conversions of aluminum oxide in relation to the crystal-chemical characteristics of added cations. Additives in amounts up to 1 wt.% do not alter the sequence of interconversions of different forms of aluminum oxide in the products of Al(OH)/sub 3/ decomposition. Acceleration or retardation of ..cap alpha..-Al/sub 2/O/sub 3/ formation is accompanied by corresponding destablization or stabilization of the x-Al/sub 2/O/sub 3/ and THETA-Al/sub 2/O/sub 3/ forms preceding it. The character of action of additives on conversion of the x and THETA forms of aluminum oxide into ..cap alpha..-Al/sub 2/O/sub 3/ is determined by their crystal-chemical characteristics (charge, radius). If the difference between the radii of the main and impurity cations is less than 33%, the additive accelerates formation of the denser ..cap alpha..-Al/sub 2/O/sub 3/ from x-Al/sub 2/O/sub 3/ and THETA-Al/sub 2/O/sub 3/, and if the difference between the cation radii is greater than 33% the additive stabilizes the less dense x and THETA forms of Al/sub 2/O/sub 3/. The action of additives of the series Sc/sup 3 +/, Y/sup 3 +/, La/sup 3 +/, deviates from this rule; in this case the positive effect of ..cap alpha..-Al/sub 2/O/sub 3/ formation is observed with larger differences of the cation radii (additions of Y/sup 3/ and La/sup 3 +/). Additives which influence both the intensification of ..cap alpha..-Al/sub 2/O/sub 3/ sintering and the intensification of its formation from low-temperature forms of Al/sub 2/O/sub 3/ (additions of V/sup 5 +/, Mn/sup 3 +/, Y/sup 3 +/, Mg/sup 2 +/) should be chosen for practical use.

• OSTI ID: 5413121
• Journal Information: J. Appl. Chem. USSR (Engl. Transl.); (United States), Journal Name: J. Appl. Chem. USSR (Engl. Transl.); (United States) Vol. 55:9; ISSN JAPUA
• Country of Publication: United States
• Language: English

Related Subjects

36 MATERIALS SCIENCE
360202* -- Ceramics
Cermets
& Refractories-- Structure & Phase Studies
ADDITIVES
ALUMINIUM COMPOUNDS
ALUMINIUM OXIDES
CHALCOGENIDES
CHEMICAL PREPARATION
CORUNDUM
CRYSTAL-PHASE TRANSFORMATIONS
ELEMENTS
FABRICATION
LANTHANUM
MANGANESE
METALS
MINERALS
OXIDE MINERALS
OXIDES
OXYGEN COMPOUNDS
PHASE TRANSFORMATIONS
RARE EARTHS
SCANDIUM
SINTERING
SYNTHESIS
TRANSITION ELEMENTS
VANADIUM
YTTRIUM