Abstract
Mullite has many excellent properties which can produce refractories with high quality. The fast transformation of andalusite into mullite and silica is around 1653K. In this work, quenching method was employed to study the effect of Y2O3 additive on the transformation of andalusite into mullite. The experiment was carried out in a closed tube furnace at 1553K and 1573K. The transformation of andalusite into mullite was studied thermodynamically. Thermodynamic calculation reveals that the temperature of spontaneous mullitization of andalusite was 1180K. Additional Y2O3 of 3.75wt% was added into different sizes of andalusite powders. Some Y2O3 was found to be reacted with SiO2 and formed as Y2Si2O7 phase. The mullite contents after fired at both 1523K and 1573K for 2h have improved markedly when the andalusite powders were with small sizes (d50=4μm and d50=43μm) but little affection on the mullitization of andalusite with large size (d50=143μm) was found. Moreover, with the addition of Y2O3, the andalusite (d50=4μm) was completely transformed into mullite after fired at 1573K for 2h. The mullite content in the sample of small size after fired at 1573K went up by more than 20%. The viscosity value of generated liquid phase is major determinants of transformation of andalusite into mullite.
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