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Effect of Sol‐Gel Mixing on Mullite Microstructure and Phase Equilibria in the α‐Al 2 O 3 ‐SiO 2 System
Author(s) -
PASK J. A.,
ZHANG X.W.,
TOMSIA A. P.,
YOLDAS B.E.
Publication year - 1987
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.1151-2916.1987.tb04867.x
Subject(s) - mullite , microstructure , materials science , phase (matter) , mixing (physics) , colloid , metastability , liquid phase , chemical engineering , base (topology) , mineralogy , composite material , ceramic , chemistry , thermodynamics , organic chemistry , mathematical analysis , mathematics , physics , quantum mechanics , engineering
Starting powders containing 72 wt% Al 2 O 3 and 28 wt% SiO 2 , were prepared by sol‐gel methods classified as colloidal and polymeric. Compacts fired at 1700°C showed significant differences in microstructure. The specimens formed with the colloidal powder had mullite grains of prismatic shape and a liquid phase; with polymeric powder, mullite grains were granular with no liquid phase present. It is shown that the mullite grains in the first case are higher in AI 2 O 3 content, resulting in an excess of SiO 2 which is the base for the liquid phase. In the second case, the mullite grains have the same Al 2 O 3 content as the starting powders. The presence of a liquid phase in the first case is considered to be metastable, resulting from the nature of the starting materials and processing conditions employed.