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Effect of Magnesia Solute on Surface Diffusion in Sapphire and the Role‐of Magnesia in the Sintering of Alumina
Author(s) -
Bennison Stephen J.,
Harmer Martin P.
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.tb05122.x
Subject(s) - sintering , sapphire , materials science , diffusion , surface diffusion , thermal diffusivity , grain boundary diffusion coefficient , magnesium , metallurgy , grain size , analytical chemistry (journal) , mineralogy , grain boundary , thermodynamics , microstructure , chemistry , optics , laser , physics , adsorption , chromatography
Surface diffusion in sapphire and sintering of Al 2 O 3 have been studied under identical firing conditions (1593°C, N 2 ) as a function of MgO solute additions. The effect of MgO on surface diffusion has been investigated directly using the technique of multiple scratch smoothing on the (1123) surface of sapphire. For these conditions MgO additions enhance the decay of periodic profiles by a factor of 4; that is interpreted as reflecting an increase in the surface diffusivity by the same amount. Measurements of the grain sizedensity trajectory during final stages of sintering of Al 2 O 3 reveal that MgO enhances the densification rate/coarsening rate ratio by a modest factor of 1.8. Since an increase in surface diffusivity alone would decrease the ratio, it is deduced that the primary role of MgO in the sintering of Al 2 O 3 is other than the influence on surface diffusion. These observations in conjunction with independent measurements of the effect of MgO on grain‐boundary mobility confirm that the primary role of MgO is the suppression of grainboundary motion.