The elastic wave propagation in piezoelectric ceramics with pore volume fractions up to 0.6 has been investigated. The samples have been prepared by tape casting starting from lead zirconate-titanate (PZT) powder with mean particle diameter 1.4 mu m. Sample analysis performed by intrusion mercury porosimeter revealed interconnected porosity with narrow size distribution. The samples were cleaned, silver metallized on two opposite surfaces and polarized in a silicon oil bath by applying an electric field of approximately 3 kV/mm at 120 degrees C for 1 h. After polarizing, the samples were thoroughly cleaned in an ultrasonic bath in acetone. The elastic properties of the samples were measured by different techniques: the electrical impedance method and acoustic wave transmission. From these measurements, the elastic wave velocities, elastic moduli and attenuation were obtained as a function of pore volume fraction, p. It has been found that wave velocities decrease continuously with p. Effective medium models predictions fit well only in a low p range; therefore, we addressed the problem through percolation theories developed for high p systems. We find that our samples can be assimilated with percolation systems in the high p range and calculated the critical exponent of the elastic moduli as well as the percolation threshold. The ultrasonic attenuation experiments were performed in the 1-11 MHz frequency range. The attenuation observed in porous samples is much larger than in bulk PZT, implying that the attenuation is not caused by the usual sound absorption mechanisms in PZT, but is probably associated with scattering from geometric disorder. It has been found that the frequency dependence of the attenuation follows a power law, with the measured exponents in the range 1.3-1.8, depending on porosity and on pore size distribution. We believe that the very large attenuations observed in our samples at high frequencies can be associated with a transition to localized vibrational modes in porous media, as predicted for percolating systems at length scales near the percolation correlation lengths. (C) 1998 Elsevier Science B.V.
Elastic wave propagation in porous piezoelectric ceramics
Galassi C;
1998
Abstract
The elastic wave propagation in piezoelectric ceramics with pore volume fractions up to 0.6 has been investigated. The samples have been prepared by tape casting starting from lead zirconate-titanate (PZT) powder with mean particle diameter 1.4 mu m. Sample analysis performed by intrusion mercury porosimeter revealed interconnected porosity with narrow size distribution. The samples were cleaned, silver metallized on two opposite surfaces and polarized in a silicon oil bath by applying an electric field of approximately 3 kV/mm at 120 degrees C for 1 h. After polarizing, the samples were thoroughly cleaned in an ultrasonic bath in acetone. The elastic properties of the samples were measured by different techniques: the electrical impedance method and acoustic wave transmission. From these measurements, the elastic wave velocities, elastic moduli and attenuation were obtained as a function of pore volume fraction, p. It has been found that wave velocities decrease continuously with p. Effective medium models predictions fit well only in a low p range; therefore, we addressed the problem through percolation theories developed for high p systems. We find that our samples can be assimilated with percolation systems in the high p range and calculated the critical exponent of the elastic moduli as well as the percolation threshold. The ultrasonic attenuation experiments were performed in the 1-11 MHz frequency range. The attenuation observed in porous samples is much larger than in bulk PZT, implying that the attenuation is not caused by the usual sound absorption mechanisms in PZT, but is probably associated with scattering from geometric disorder. It has been found that the frequency dependence of the attenuation follows a power law, with the measured exponents in the range 1.3-1.8, depending on porosity and on pore size distribution. We believe that the very large attenuations observed in our samples at high frequencies can be associated with a transition to localized vibrational modes in porous media, as predicted for percolating systems at length scales near the percolation correlation lengths. (C) 1998 Elsevier Science B.V.I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
