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Anisotropic Calcium Segregation to the Surface of Al 2 O 3
Author(s) -
BAIK SUNGGI,
WHITE CALVIN L.
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.tb05739.x
Subject(s) - auger electron spectroscopy , materials science , anisotropy , annealing (glass) , prism , sapphire , basal plane , electron diffraction , low energy electron diffraction , analytical chemistry (journal) , spectroscopy , crystallography , diffraction , chemistry , metallurgy , optics , laser , physics , chromatography , nuclear physics , quantum mechanics
The surface enrichment of Ca on various crystalloraphic planes of CaO‐doped sapphire has been measured as a function of annealing temperature using Auger electron spectroscopy (AES). Strong Ca enrichment was found on the (10 1 0) prism plane at ≥1300°C, whereas no evidence or Ca segregation could be observed on the (0001) basal plane up to 1500°C. The surface enrichment factor estimated at 1300°C was at least 3 × 10 3 for the prism plane, while that for the basal plane was below 50, which corresponds to the detectability limit of AES. The Ca segregation to the prism plane was uniform and limited to the surface monolayer; an apparent heat of segregation determined in the range of 1300° to 1500°C was–169 kJ/mol. Low‐energy electron diffraction studies of annealed surfaces revealed that Ca segregation was concurrent with a two‐dimensional surface phase transition. The anisotropic segregation behavior of Ca may explain why CaO is not an effective additive for alumina sintering.