Densification and Characterization of Magnesium Aluminate Spinel from Commercial Grade Reactants: Effect of Milling and Additives

Abstract

Among different refractory materials, magnesium aluminate spinel is of great importance from the industrial point of view, mainly due to its excellent corrosion and thermal shock resistances. Magnesium aluminate spinel (MgAl2O4), the only compound forms in the MgO-Al2O3 system, has the most desirable characteristics for refractory application, along with the environmental friendliness. Other than refractory there are studies for its applications as humidity sensors, transparent ceramic, anode material in aluminum cell, etc. In combination with alumina, spinel is of great importance as the refractory lining material for the steel ladles essential for iron & steel industries due to excellent corrosion and thermal shock resistances. Again in association with magnesia it is important for the burning zones and transition zones of cement rotary kilns. The major reason for this application is its better resistance to thermal shock and alkali materials, which indicates two or three times longer service lives than other basic bricks such as conventional MgO-chrome. Magnesium aluminate spinel has always an environment friendly advantage, so it has received favor from researchers, scientists and industrialists all over world.

Despite all these properties and application, the magnesium aluminate spinel is not commercially successful at per due to its high cost of production. The formation of magnesium aluminate spinel from its reactant is associated with a volume expansion which hinders to obtain dense magnesium aluminate spinel in a single step firing process. The commercial synthesis process involves two stage firing process which increases the cost of production

The present work focused on synthesis of magnesium aluminate spinel from commercial grade oxide using a single step sintering process. The effect of planetary milling, effect of additives like zinc Oxide, zirconium dioxide was studied. The effect of insitu generated magnesia and alumina from nitrate precursor was also studied. The sintering study was done in the temperature range 1200-16000C.The phase and microstructure was studied with varying milling time and additive percentage using X-ray diffraction technique and field emission scattered electron microscopy respectively. The flexural strength and thermal shock behavior was also studied for each batch.

Dense magnesium aluminate spinel was successfully produced. The planetary milling and additive were found to enhance spinellisation process at lower temperature. The density and strength was also found to improve with milling and additive incorporation.