High temrareture ultrasonic transducers by CaBi2Ta2O9/Pb(Zr, Ti)O3 sol-gel composite

For new-generation thermal power plants, off-line non-destructive testing is not sufficient and long-term monitoring at high temperature is desired. In the previous study, ultrasonic transducers made by CaBi
₄
Ti
₄
O
₁₅
(CBT)/Pb(Zr, Ti)O
₃
(PZT) were investigated and maximum operation temperature was estimated as ~600°C. Since operation temperature of new-generation thermal power plant will be ~700°C, it is necessary to develop new sol-gel composite. Thus new sol-gel composite, CaBi
₂
Ta
₂
O
₉
(CBTa)/PZT was developed. CBTa was chosen as ferroelectric powder phase material because Curie temperature is sufficiently high such as 923°C, which is higher than that of CBT. PZT was chosen as dielectric sol-gel phase because of high dielectric constant. CBTa/PZT films were fabricated on 3mm thick titanium substrates. One CBTa/PZT sample was placed in an electric furnace and ultrasonic measurement in pulse-echo mode was demonstrated between room temperature and 800°C. Sensitivity and signal-to-noise ratio (SNR) was high enough for thickness measurement even at 800°C. Signal amplitude and SNR were stable throughout the experiment.