FABRICATION OF MULLITE-CORDIERITE BASED COMPOSITE POWDERS FROM A SECONDARY SILICA SOURCE.

A stoichiometric cordierite-mullite composite formulation has been prepared by mechanical activation from indigenous kaolin, talc, alumina, aluminium hydroxide and a new secondary silica source (silica gel). Phase formation behaviour of the samples has been studied from the XRD patterns of the sintered samples. The XRD analysis showed mullite and cordierite as phases for samples sintered at 1150oC and 1300oC for a soaking period of 2hrs. A comparison of the peaks formed shows that all the diffraction peaks change after mechanical activation. This reflects the partial amorphization and structural disordering in alumina, magnesium and quartz. It can also be noted that at 2 theta angle of 10.40 where characteristically cordierite peaks are formed, samples CD3a and CD3b show signs of cordierite peaks. SEM studies showed those different milling times as expected resulted in powders with different particle sizes, shapes, and most importantly degrees of agglomeration. [ABSTRACT FROM AUTHOR]