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Mechanism of Secondary Expansion of High‐Alumina Refractories Containing Calcined Bauxite
Author(s) -
McGEE THOMAS D.,
DODD C. M.
Publication year - 1961
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.1151-2916.1961.tb15378.x
Subject(s) - mullite , bauxite , calcination , materials science , crystallization , chemical engineering , mineralogy , thermal expansion , diffusion , metallurgy , composite material , chemistry , catalysis , ceramic , thermodynamics , biochemistry , engineering , physics
The use of some calcined bauxites in high‐alumina refractories is limited by unusual and excessive secondary expansion. One such calcined bauxite was compared with pure alpha alumina to determine the crystalline changes responsible for the expansion, to determine the mechanism of the expansion, and to suggest means for control of the expansion. X‐ray diffraction and petrographic techniques were used. The expansion was found to result from crystallization of secondary mullite by the action of impurities in aiding the diffusion of alumina and silica. Secondary mullitization and growth began at 1400°C. and caused as much as 23% expansion at 1600°C. The expansion was caused primarily by the mullite growth rather than by the true density changes associated with mullitization. Small sodium fluoride additions proved to be effective for controlling expansion.