Reaction Sequence and Structural Changes in Cordierite Refractories

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Abstract
In order to determine temperatures of mullitization and cordierite formation, to outline the reaction sequence by which cordierite is formed, and to determine the effects of prolonged heating on cordierite development and structure, two separate series of experiments were performed. Specimens were fired for 1 hour at temperature intervals between 1000° and 1360°C. and analyzed for cordierite and mullite by X‐ray diffraction for the purpose of correlation with differential thermal analyses. Specimens were also fired at four different temperatures for periods of 1 to 192 hours and analyzed by X‐ray diffraction for cordierite content and structural changes. Mullitization occurred by exothermic reaction at 1267°C. Endothermic peaks at 1238° and 1330°C. are attributed to the formation of cordierite. Prolonged‐heating studies indicated that a progressive change takes place in cordierite by which a metastable hexagonal form is converted with time, through all intermediate stages, to the orthorhombic form which is stable at that temperature. Temperature was apparently the critical factor in cordierite development, time being of greater importance at lower temperatures.

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