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Discoloration of Fired Kaolinitic Clays (Study of Fe 3+ Coordination by Mössbauer and UV‐ViS‐NIR Spectroscopy)
Author(s) -
Hanzlicek T.,
Niznansky D.,
Dedecek J.,
Steinerova M.,
Straka P.,
Triskova J.
Publication year - 2007
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.1551-2916.2007.01734.x
Subject(s) - ferric , mössbauer spectroscopy , oxidizing agent , chemistry , spectroscopy , hydrous ferric oxides , oxide , ion , iron oxide , inorganic chemistry , ultraviolet visible spectroscopy , coordination complex , coordination number , ceramic , mineralogy , crystallography , adsorption , metal , physics , sorption , organic chemistry , quantum mechanics
The final color of a ceramic body is generally determined by the contents of Fe 3+ ions. The Central European market accepts kaolinitic clays for the production of tableware, electro‐insulators, and wall tiles only if the Fe 2 O 3 in chemical analyses of the kaolin does not exceed 1.0 wt%. The chemical analyses calculate the content of all iron components as if they were in the form of Fe 2 O 3 and then their quantity excludes even good‐quality clay from the ceramic industry of white bodies. We found that oxidizing firing of the samples fired at over 1180°C changes the color in cases where the initial Fe 3+ component is in the form of hydro ferric oxide [FeO(OH)] or if the ferric ions were added to the white kaolin samples in the form of ferric nitrate [Fe(NO 3 ) 3 ·9H 2 O]. The Mössbauer spectroscopy confirms the presence of only diluted Fe 3+ ions. The UV‐ViS‐NIR spectroscopy confirms that even if the concentration of Fe 2 O 3 is above 3.0 wt%, these ions of Fe 3+ in the case of their initial hydro ferric oxide formed in clay are incorporated into the mullitic structure in tetrahedral coordination. The iron‐coloring effect depends on the coordination of Fe 3+ ions with the studied discoloring effect of fired bodies—the very small and well‐distributed particles enter into the formatted mullitic structure.