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Effect of Nature of Surfaces on Wetting of Sapphire by Liquid Aluminum
Author(s) -
BRENNAN JOHN J.,
PASK JOSEPH A.
Publication year - 1968
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.1151-2916.1968.tb13324.x
Subject(s) - sapphire , wetting , contact angle , van der waals force , surface energy , corundum , aluminium , materials science , chemistry , oxide , aluminium oxides , atmospheric temperature range , crystallography , analytical chemistry (journal) , mineralogy , composite material , thermodynamics , molecule , optics , metallurgy , organic chemistry , laser , physics , catalysis
Contact angles of aluminum drops on sapphire measured under vacuum conditions from 660° to 1250°C generally fell into three ranges. Large obtuse contact angles indicating interfacial energies greater than either of the two surface energies were obtained up to about 900°C; van der Waals bonding then existed at a compound interface. In the intermediate range, contact angles were 90° or slightly greater indicating a common interface with an energy, s γ l , greater than s γ g but less than lγ g . Acute contact angles indicating a s γ l less than s γ g and greater than l γ g occurred above about 950°C because of the formation of a high temperature complex surface structure with s γ g > l γ g . A hydroxylated sapphire surface has a lower s γ g which increases with gradual dehydroxylation and conversion to the high temperature surface structure with a corresponding change in contact angle through the three ranges. Chemical bonding existed in the latter two ranges. Reactions occurred between Al and the sapphire surface to form volatile species at contact angles less than 90°. Molten Al normally has an oxide coating the effect of which appears to be removed at about 870° C.