FIFTH CANADIAN CONFERENCE ON NONDESTRUCTIVE ... - IAEA

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heating and cooling rates of 450 C/h. Bulk densities were measured in butanol
and distilled water.
Both hot presses and sintered ceramics were sliced into « 6 mm thick discs.
Tfi^ hot-gressed slices were oxidized in a controlled atmosphere for 4-24 hours at
350-1200 C, depending on composition. Both sides of these discs were lapped to
a thickness of 400/urn with optimum flatness and parallelism. Fired silver electrodes
and sputtered gold electrodes were deposited on them. The fired silver
electrodes were polished to M 2/tm on both sides of the piezoelectric discs.
III ELECTRICAL AND ACOUSTIC CHARACTERIZATION
All materials were poled in oil at 80-180°C. The poling temperature, time
and voltage were varied to identify the optimum poling conditions for each
cemposition. All poled specimens were aged for 24 hours, prior to measurement.
The resonant (f ) and antiresonant frequencies (f ) were measured according
to IEEE standards. Following measurement of the ccmpressional and shear
wave velocities, the Poisson's ratio for each cemposition was obtained by calculation.
The piezoelectric constants, the planar coupling factor, k ; the piezoelectric
strain constant, d.,, and the piezoelectric 'voltage' constan? g-., ware thus
obtained and are tabulated in Table I. Capacitance and loss factors were
measured at 1 kHz using an impedance bridge.
The ccmpressional sound wave velocities at 50 MHz ware measured in both
polarized and unpolarized piezoelectric discs. In the polarized materials,
velocity was measured in the polarized direction. The pulse-echo overlap nethod
was employed and velocities were measured to one part in 10 . A low-viscosity
oil was used as a couplant between the 50 MHz transducer and the piezoelectric
discs. The thickness variation of the discs was monitored before and after
polarization and also during the velocity measurements.
The microstructural grain size was determined from photomicrographs (optical
and electron optical) of the test specimens. These were mechanically'polished to
a surface roughness of 0.3A