NDLI: Crystallization mechanism of aluminoferrate glass accompanying a precipitation of nanocrystals of dicalcium ferrite (Ca2Fe2O5) and mayenite (12CaO·7Al2O3)

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Crystallization mechanism of aluminoferrate glass accompanying a precipitation of nanocrystals of dicalcium ferrite (Ca₂Fe₂O₅) and mayenite (12CaO·7Al₂O₃)

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Crystallization mechanism of aluminoferrate glass accompanying a precipitation of nanocrystals of dicalcium ferrite (Ca₂Fe₂O₅) and mayenite (12CaO·7Al₂O₃)

Content Provider	Royal Society of Chemistry (RSC)
Author	Tamaki, Toyomi Kubuki, Shiro Shibata, Morihiro Nishida, Tetsuaki Maeda, Yonezo
Copyright Year	1997
Abstract	Heat treatment of 60CaO·27Al 2 O 3 ·13Fe 2 O 3 glass resulted in a precipitation of antiferromagnetic dicalcium ferrite (Ca 2 Fe 2 O 5 ) and mayenite (12CaO·7Al 2 O 3 ). The effective magnetic moment of the sample decreased from 2.0 to 1.7 µ B owing to the precipitation of antiferromagnetic particles. The Mössbauer spectrum of the heat-treated sample consisted of two sextets (magnetic hyperfine structure) which were superimposed on two quadrupole doublets. The sextets were assigned to Fe 3+ occupying octahedral (O h ) and tetrahedral (T d ) sites in the nanocrystals of dicalcium ferrite with a mean diameter >10 nm. The quadrupole doublets were assigned to Fe 3+ (T d ) occupying Al 3+ sites in mayenite particles and the glassy phase. IR transmittance of the sample showed a gradual decrease along with the heat treatment. A Johnson–Mehl–Avrami (JMA) plot from the IR-transmission method yielded activation energies (E a ) of 4.9±0.4 and 4.3±0.4 eV for 60CaO·27Al 2 O 3 ·13Fe 2 O 3 and 60CaO·35Al 2 O 3 ·5Fe 2 O 3 glasses, respectively. These values are equal to E a obtained from a Kissinger plot by the DTA method, i.e., 4.2±0.3 and 4.6±0.3 eV, and also to the Al–O bond energy (4.4 eV). These results reveal that crystallization of calcium aluminoferrate glass is triggered by cleavage of Al–O bonds at an early stage in order to form mayenite particles containing Fe 3+ . After a prolonged heat treatment, the relative absorption area of sextets in the Mössbauer spectra increased at the expense of two doublets. This change suggests a migration of Fe 3+ (T d ) from mayenite particles and the glassy phase into dicalcium ferrite particles. JMA and Kissinger plots for iron-free 60CaO·40Al 2 O 3 glass yielded E a values of 5.6±0.4 and 6.0±0.3 eV, respectively, equal to the sum of the Al–O (4.4 eV) and Ca–O bond energies (1.4 eV), indicating simultaneous cleavage of Al–O and Ca–O bonds.
Starting Page	1801
Ending Page	1806
Page Count	6
File Format	PDF
ISSN	09599428
Volume Number	7
Issue Number	9
Journal	Journal of Materials Chemistry
DOI	10.1039/a702854g
Language	English
Publisher	Royal Society of Chemistry
Access Restriction	Open
Subject Keyword	JMA DTA Johnson Mehl Kissinger Antiferromagnetism Ferrite core Royal Aircraft Factory F.E.2 Chlormayenite Magnetic moment Hyperfine structure Quadrupole Electronvolt Henry Kissinger Bond energy Calcium Chemical bond
Content Type	Text
Resource Type	Article
Subject	Chemistry Materials Chemistry

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Crystallization mechanism of aluminoferrate glass accompanying a precipitation of nanocrystals of dicalcium ferrite (Ca₂Fe₂O₅) and mayenite (12CaO·7Al₂O₃)