Formation and densification of mullite through solid-oxide reaction technique using commercial-grade raw materials

Two different commercially available sources of alumina and silica were used to study the formation and densification behaviour of mullite prepared by solid-oxide reaction technique in a single firing. Phase analysis and densification studies were carried out on the samples sintered between 1200 and $$1600^{{\circ }}\hbox {C}$$ . Effect of addition of 1–6 wt% MgO on the sintered mullite ceramics was also studied. MgO was found to improve the density values for all the compositions till 4 wt% and with higher addition it deteriorated, mainly due to higher extent of liquid phase formation. Mullite formation was found to start below $$1200^{{\circ }}\hbox {C}$$ and constituent oxides were found even at $$1600^{{\circ }}\hbox {C}$$ ; however, addition of 4 wt% MgO was found to complete the mullite formation at $$1600^{{\circ }}\hbox {C}$$ for all the compositions. Microstructural studies showed grain growth in the compositions containing MgO and higher impurities due to formation of greater extent of liquid phase.