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Silica‐Free Phases with Mullite‐Type Structures
Author(s) -
PERROTTA A. J.,
YOUNG J. E.
Publication year - 1974
Publication title -
journal of the american ceramic society
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.9
H-Index - 196
eISSN - 1551-2916
pISSN - 0002-7820
DOI - 10.1111/j.1151-2916.1974.tb11423.x
Subject(s) - mullite , corundum , crystallization , spinel , phase (matter) , materials science , alkali metal , crystallography , chemical engineering , mineralogy , chemistry , metallurgy , ceramic , organic chemistry , engineering
Silica‐free phases which have a structure similar to that of mullite can be crystallized from gels in the Na 2 O‐Al 2 O 3 and (Na,K) 2 O‐BaO‐Al 2 O 3 systems. A gelation step appears to be necessary, since a solid‐state reaction between Na 2 CO 3 and Al(OH) 3 does not give the mullite‐type phase. Crystallization of this phase requires a high alkali content during formation of the gel. A well‐crystallized phase is formed at 950°C and is stable to at least 1000°C; at higher temperatures (i.e. 1200°C), β‐Al 2 O 3 and corundum are formed. The mullite‐type phase appears to crystallize with an increase in temperature at the expense of a γ‐Al 2 O 3 phase, indicating adsorption of Na on the defect spinel structure, which is then rearranged to give the mullite‐type phases.