Fast transformation of andalusite into mullite by addition of yttria

Mullite has many excellent properties which can produce refractories with high quality. The fast transformation of andalusite into mullite and silica is around 1653 K. In this work, quenching method was employed to study the effect of Y 2 O 3 additive on the transformation of andalusite into mullite. The experiment was carried out in a closed tube furnace at 1553 K and 1573 K. The transformation of andalusite into mullite was studied thermodynamically. Thermodynamic calculation reveals that the temperature of spontaneous mullitization of andalusite was 1180 K. Additional Y 2 O 3 of 3.75 wt% was added into different sizes of andalusite powders. Some Y 2 O 3 was found to be reacted with SiO 2 and formed as Y 2 Si 2 O 7 phase. The mullite contents after fired at both 1523 K and 1573 K for 2 h have improved markedly when the andalusite powders were with small sizes ( d 50  = 4 μm and d 50  = 43 μm) but little affection on the mullitization of andalusite with large size ( d 50  = 143 μm) was found. Moreover, with the addition of Y 2 O 3 , the andalusite ( d 50  = 4 μm) was completely transformed into mullite after fired at 1573 K for 2 h. The mullite content in the sample of small size after fired at 1573 K went up by more than 20%. The viscosity value of generated liquid phase is major determinants of transformation of andalusite into mullite.