The particle-size distributions of WWFs with varying mean particle sizes (MZ) are shown in Fig. 1. The MZ of WWF decreased
from 125-mm to 43-mm with the increase in grinding time from 5 min to 20 min. The distribution profile of the 125-mm group was similar to a gaussian distribution in the range from 0 mm to 1000 mm. All the WWF particles in the 96-mm group were smaller than 700 mm, and its profile showed a larger percentage in the range of 0e75 mm compared to the 125-mm group.