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Low‐Frequency Grain‐Boundary Relaxation in Alumina
Author(s) -
TURNBAUGH JERRY E.,
NORTON F. H.
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.tb15951.x
Subject(s) - relaxation (psychology) , grain boundary , impurity , materials science , diffusion , crystallite , thermal diffusivity , grain boundary diffusion coefficient , debye model , condensed matter physics , debye , internal friction , analytical chemistry (journal) , nuclear magnetic resonance , thermodynamics , mineralogy , chemistry , composite material , microstructure , metallurgy , physics , psychology , social psychology , organic chemistry , chromatography
The internal friction spectrum of polycrystalline, sintered alumina was determined at 15 to 25 cps and 25° to 1550°C. Two relaxation mechanisms appeared to be operative. A high‐temperature relaxation interpreted as stemming from diffusion‐controlled grain‐boundary motion was dominant above 1150°C. Assuming a mean diffusion path of 10 −4 cm gave a diffusivity of D = 5.2 × 10 −2 exp (−52,000/RT) which was independent of impurity content. A lower‐temperature relaxation was observed in specimens of higher impurity content at 900° C. This relaxation reached a maximum but did not behave as a Debye‐type relaxation. Single‐crystal alumina exhibited neither of these relaxations.