2.3. Observation by scanning electron microscopy (SEM)
SEM was employed to observe the surface of whole particles and whole powder. The fracture surface of the board made from whole particles after the internal bonding test was also observed. All specimens were coated with platinum-palladium by ion sputter coater (E1030; Hitachi, Japan). A field emission scanning electron microscope (FE-SEM, S4000; Hitachi, Japan) was employed for
microscopic study.