Characterization of green ceramics by microwaves and ultrasound

Time-of-flight measurements using ultrasound at 2 MHz and microwaves at 75-100 GHz were performed on samples of green state alumina. Spatially resolved measurements showed an inverse correlation of time-of-flight measured by ultrasound and microwaves. The findings can be explained by a lower compaction density in the center of the sample cylinders. A model assuming small spherical pores does not explain the experiment completely. An uniaxial anisotropy of longitudinal sound velocity was found