3.2. Porosity and pore morphol ogy
Fig. 3 shows the changes of porosity and bulk density with the
increase of sintering temperature. The porosity decreased as the
sintering temperature increased due to the process of sintering
densification. Meanwhile, the bulk density of the body increased
towards that of dense materials. The density of a piezoelectric
ceramic used for a hydrophone or transducer was very important
in that efficient energy transfer could be achieved only through
excellent impedance matching. The detailed pore morphology
and interconnection in the sintered ceramics are shown in Fig. 4.
From these SEM micrographs, it could be observed that the
grains grew up and the porosity decreased as the sintering
temperature increased from 1150 8C to 1250 8C. These change
trends could be verified by the measured values of grain size and
porosity presented in Table 1. Furthermore, with the increase of
the sintering temperature, there was a tendency for small grains to
be even smaller and large grains to be even larger. In addition, all
samples had homogeneous pore distribution and 3–3 connection
structure with pore size around several microns. Fig. 4(f) shows
the typical connection of grains from which the sintering neck
and the local structure similar to stone arch bridges can be easily
observed. These unique structures made it possible for the bodies
to obtain high mechanical strength, easy to handle during the
fabrication process and more adaptive to the working condition.