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Kinetics of the Anatase‐Rutile Transformation
Author(s) -
SHAN ROBERT D.,
PASK JOSEPH A.
Publication year - 1965
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.1151-2916.1965.tb14774.x
Subject(s) - nucleation , anatase , rutile , oxygen , activation energy , materials science , impurity , phase (matter) , transformation (genetics) , titanium , kinetics , hydrogen , chemical engineering , crystallography , chemistry , metallurgy , catalysis , organic chemistry , biochemistry , physics , photocatalysis , quantum mechanics , engineering , gene
Transformation of three commercial anatase powders resulted in sigmoid curves of transformation vs. time, which were interpreted in terms of a nucleation‐growth process. Analysis of these curves by several rate laws led to activation energies for nucleation of 109, 136, and 148 kcal/mole and for growth of 100, 115, and 190 kcal/mole, respectively. The rate of transformation and activation energy are governed by the nature and amount of impurities which determine the defect structure of the TiO 2 , i.e. the concentration of oxygen vacancies or interstitials. It is suggested that, in general, oxygen vacancies accelerate and the interstitials inhibit the transformation. CuO additions and hydrogen atmospheres accelerated the transformation by the introduction of oxygen vacancies and/or by reduction to a second Ti n O 2n−1 Magnéli phase which could act as a nucleating agent. The transformation is retarded in vacuum; this retardation is attributed to the introduction of titanium interstitials.