A PROCESS FOR THE PRODUCTION OF DENSE ALUMINA-RICH MAGNESIUM ALUMINATE SPINEL USEFUL AS REFRACTORY AGGREGATES

摘要

Spinel has become a popular refractory material owing to its excellent high temperature properties. Alumina rich spinel is extensively used now-a-days as a shaped refractory or a constituent for castables which are used in various secondary refining vessels of steel making. However, densification of spinel by a single firing is a big problem due to volume expansion of 5 to 7 % during spinel formation. The present invention relates to the process by which Al2O3-rich spinel (85 to 95% Al2O3) can be densified to a high degree by a single firing process at a relatively low temperature (less than 1600 deg. C). This can be done by proper milling, incorporation of two additives and controlled firing schedule. One of the additives creates cation vacancy while the other remain in the grain boundary and suppresses grain growth. The firing schedule is particularly controlled around the spinel formation temperature to lower the rate of expansion due to spinelisation reaction and enhance densification. Sintered alumina-rich spinel thus produced has a density of 96 to 98% of theoretical density, average grain size 10 to 15mu m, hot modulus of rupture at 1300deg.C is 1300 to 1450 Kg/cm2 and thermal expansion coefficient at 1000deg. C is in the range of 8.7 to 8.9 x 10-6 C-1.