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Topotactically Modified Stress in Coatings
Author(s) -
Kalman Zwi H.,
Johnson Lois A.,
Wachtman John B.
Publication year - 1990
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.1151-2916.1990.tb06572.x
Subject(s) - boehmite , materials science , coating , crystallite , tetragonal crystal system , composite material , texture (cosmology) , orthorhombic crystal system , phase (matter) , substrate (aquarium) , fiber , stress (linguistics) , crystallography , metallurgy , crystal structure , chemistry , aluminium , image (mathematics) , oceanography , organic chemistry , artificial intelligence , computer science , geology , linguistics , philosophy
The unexpected occurrence of compressive stresses in solgel‐derived alumina coatings following a densification transformation was found to be related to the topotactic transformation of boehmite (γ‐AlOOH) to γ‐alumina (γ‐Al 2 O 3 ) on heating. The boehmite coating showed a pronounced fiber texture with the [001] crystallographic axis perpendicular to the substrate‐coating interface plane. At about 500°C, the orthorhombic boehmite transformed into tetragonal γ‐alumina with very little, if any, reorientation of the crystallites. Because of the topotactic nature of the transformation, the fiber texture persisted in the γ‐alumina phase. This resulted in an anisotropic change that generated compressive strains in the coating.