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

摘要

In the present invention there is to provided a process for the production of dense magnesia-rich magnesium aluminate spinel useful as refractory aggregates, wherein Al2O3-rich spinel (56 to 66% AI2O3) is densified to a high degree by a single firing process at a relatively low temperature (1600°C). This is done by proper milling, introduction of mixed additives such as incorporation of two additives, ZnO and ZrSiO4, using only single pressing and controlled firing schedule. One of the additives creates lattice strain, while the other additive develops viscous liquid and facilitates liquid phase sintering. The firing schedule is particularly controlled around the spinel formation temperature to lower the rate of expansion due to spinellisation reaction and enhance densification. Sintered magneisa-rich spinel thus produced has a density of 96 to 98% of theoretical density, average grain size 10 to 15 micro-m, hot modulus of rupture at 1300°C is 1300 to 1450 Kg/cm2 and thermal expansion coefficient at 1000°C is in the range of 9.2 to 9.6 x 10-6 °C"1. Spinel is a popular refractory material owing to its excellent high temperature properties. Magnesia-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