A Study of Calcium Hexaluminate

D. S. Buist
Central Research Laboratories, General Refractories Limited, Worksop, Notts.

Summary: Calcium hexaluminate has recently been confirmed as a stable phase occurring within the system CaO-Ao2O3. In the present investigation, this aluminate has been synthesized from the constituent oxides and its X-ray, optical, and physical (microhardness and reflectivity) properties determined. Similar data have also been obtained on the ferrian phase from the immediate hot-face zone of high-alumina bricks that had been in service in electric arc furnace roofs. An electron-probe microanalysis study revealed that between 12 and 13 % atomic replacement of Al by Fe had occurred in this ferrian calcium hexaluminate. The melting behaviour of the pure compound has been studied by firing pellets in a specially-constructed vacuum furnace. Results show the incongruent melting point to be 1870°C (±10° C), while the liquidus temperature is 1970° C (±10° C). These points were determined by examining polished sections of compacts heated within the range 1820 to 2000° C. A revised phase diagram of the high-alumina portion of the system CaO-Al2O2 is presented.

Mineralogical Magazine; March 1968 v. 36; no. 281; p. 676-686; DOI: 10.1180/minmag.1968.036.281.10
© 1968, The Mineralogical Society
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