Effect of CoO on the Formation of Mullite Ceramics from Diphasic Al2O3-SiO2 Gel

In this work the effect of CoO additive on the formation of mullite from Al2O3-SiO2 diphasic gel has been studied. The diphasicgel precursor for mullite was synthesized by sol-gel route following aqueous phase colloidal interaction of aluminiumhydroxide and silicic acid. The precursor gel powder was thoroughly characterized by chemical analysis, measurement ofsurface area, bulk density and also by FTIR spectroscopic studies. The gel powder was compacted with the CoO additives indifferent ratios and sintered at three different elevated temperatures. Microstructure of the sintered compacts was analyzedfrom SEM studies and phase analyses were carried out from XRD studies. It has been observed that the morphology ofthe mullite crystals changed significantly in the presence of the additives. As a result of the inclusion of additive maximumexpansion in the b-axis of the mullite crystal took place. With the addition of 3% additive more than 14% mullite formationoccurred after sintering. A significant improvement in the formation of mullite in the sintered masses was also observed inthe presence of CoO additive. More than 10% improvement in density as well as flexural strength and about 5% improvementin fracture toughness of the sintered compacts were observed in the presence of the CoO additive.