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Segregation Isotherms at the Surfaces of Oxides
Author(s) -
Mackrodt William C.,
Tasker Phillip W.
Publication year - 1989
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.1151-2916.1989.tb06284.x
Subject(s) - impurity , thermodynamics , arrhenius equation , surface (topology) , materials science , chemistry , activation energy , physics , geometry , mathematics , organic chemistry
A non‐Arrhenius segregation isotherm is derived which includes the change in the heat of segregation with surface coverage due to impurity—impurity interactions. It is shown that a linear dependence of log ( X s ) on the reciprocal temperature, where X s is the surface atomic ratio, can derive either from a constant heat of segregation, i.e., Arrhenius behavior, or from a heat of segregation that varies as X −1 s . This isotherm is then used to calculate the equilibrium surface coverages of Ca at the {001} surface of MgO 1 Mg at the {0001} surface of α‐Al 2 O 3 , γ at the {1012} and {1120} surfaces of α‐Al 2 O 3 , and Na at the {111} and {110} surfaces of Li 2 O from the calculated heats of segregation. Where possible, comparisons are made with experiment. The more useful operational definition of the heat of segregation, namely, that derived from the measured coverage or that defined atomistically and obtained by calculation, is discussed.