China's Refractories

Abstract: Calcium hexaluminate (CA6) was synthesized by mixing light-weight calcium carbonate and Al2O3 micropowder (calcined α-Al2O3, activated α-Al2O3 orρ-Al2O3) according to the stoichimetric ratio of CA6, and reaction sintering at 1 200, 1 300, 1 400 and 1 500 ℃ for 3 h, respectively. Effects of the three alumina micropowders on the phase composition, microstructure and properties of CA6 were investigated. The results show that: (1) for the three Al2O3 micropowders, the reaction to generate CA6 in specimens basically completes at about 1 500 ℃; CA6 generated in all specimens is planar, but the array modes are slightly different; (2) the specimens prepared from calcined α-Al2O3 or ρ-Al2O3 shrink almost, while the specimens prepared from activated α-Al2O3 expand; (3) the cold crushing strength of the specimen prepared from activated α-Al2O3 is the highest, reaching 42.5 MPa when only CA6 exists (after firing at 1 500 ℃); (4) the specimen prepared fromρ-Al2O3 has the lowest generation temperature of CA6 and the highest apparent porosity, reaching 70.1% when only CA6 exists (after firing at 1 500 ℃); (5) the specimen prepared from calcined α-Al2O3 has the biggest bulk density.

Key words: calcium hexaluminate, activated α-alumina, calcined α-alumina, ρ-alumina, light-weight calcium carbonate, volume shrinkage rate