Effects of alumina and zirconia addition on transformation of andalusite to mullite

Andalusite, as a refractory material, transforms to mullite and a silica rich liquid phase at 1100-1600 degrees C. The glassy phase constitutes about 20 wt-% of the reaction products, which is undesirable in refractories. In this research, alumina and zirconia were added to andalusite in order to reduce the amount of the glassy phase. Alumina was introduced by dry and solution mixing, while zirconia was added only by dry mixing method. The effects of MgO on andalusite-mullite and andalusite-zirconia mixes were also studied. MgO was introduced by solution ( precipitation) method on andalusite surface. The samples were fired at 1400, 1500 and 1600 degrees C. X-ray diffraction and SEM results showed that alumina reduces the liquid phase at all of the temperatures, but zirconia was effective only at 1400 and 1500 degrees C. MgO seemed to be capable of reducing in andalusite transformation by 100 degrees C and had positive effect on reaction between alumina and liquid phase; it was not effective on reaction between zirconia and liquid phase.