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Conversion of Diaspore to Corundum: A New α‐Alumina Transformation Sequence
Author(s) -
Carim Altaf H.,
Rohrer Gregory S.,
Dando Neal R.,
Tzeng ShihYing,
Rohrer Cathy L.,
Perrotta Anthony J.
Publication year - 1997
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.1151-2916.1997.tb03171.x
Subject(s) - corundum , diaspore (botany) , octahedron , crystallography , monoclinic crystal system , sequence (biology) , transformation (genetics) , materials science , x ray crystallography , diffraction , powder diffraction , chemistry , mineralogy , crystal structure , physics , optics , biological dispersal , population , biochemistry , demography , seed dispersal , sociology , gene
A new two‐step transformation sequence has been identified for the conversion of diaspore (α‐AlOOH) to corundum (alpha‐Al 2 O 3 ). The powder X‐ray diffraction pattern of the intermediate phase, designated alpha'‐Al 2 O 3 , has been indexed to a monoclinic (P2) cell, with a = 9.566(5) Å, b = 5.124(2) Å, c = 9.156(4) Å, and ß= 91.76(3)°. Nuclear magnetic resonance of alpha'‐Al 2 O 3 indicates that 15‐20% of the aluminum is on tetrahedral sites, with the remainder in octahedral coordination. Controlled‐atmosphere high‐temperature X‐ray diffraction shows that water accelerates the second transformation step, alpha'‐Al 2 O 3 →> alpha‐Al 2 O 3 , acting as a mineralizer for the conversion process.