Mn-Doped CaBi4Ti4O15/Pb(Zr,Ti)O3 Ultrasonic Transducers for Continuous Monitoring at Elevated Temperatures

Abstract

Continuous ultrasonic in-situ monitoring for industrial applications is difficult owing to the high operating temperatures in industrial fields. It is expected that ultrasonic transducers consisting of a CaBi4Ti4O15(CBT)/Pb(Zr,Ti)O3(PZT) sol-gel composite could be one solution for ultrasonic nondestructive testing (NDT) above 500 °C because no couplant is required and CBT has a high Curie temperature. To verify the high temperature durability, CBT/PZT sol-gel composite films were fabricated on titanium substrates by spray coating, and the CBT/PZT samples were tested in a furnace at various temperatures. Reflected echoes with a high signal-to-noise ratio were observed up to 600 °C. A thermal cycle test was conducted from room temperature to 600 °C, and no significant deterioration was found after the second thermal cycle. To investigate the long-term high-temperature durability, a CBT/PZT ultrasonic transducer was tested in the furnace at 600 °C for 36 h. Ultrasonic responses were recorded every 3 h, and the sensitivity and signal-to-noise ratio were stable throughout the experiment.

CaBi4Ti4O15-based lead-free sol–gel composites for high-temperature application

“…This deterioration could occur mainly owing to silver top electrode deterioration 41) and could be suppressed when the silver top electrode was replaced with the platinum top electrode. 34) The SNR during the thermal cycle is shown to be stable except at 600 °C between 25 and 35 dB in Fig. 12.…”

“…However, the dead-zone length change was smaller than that of CBiT=PZT in the past study, in which even the third reflected echo was hidden at 700 °C. 34) Clear reflected echoes were observed; however, the SNR decreased significantly above 650 °C. To clarify the experimental results, the sensitivity was calculated using Eq.…”

“…Sol-gel composite ultrasonic transducers have been developed to realize piezoelectric ultrasonic transducers for high temperature application. [27][28][29][30][31][32][33][34][35][36][37] In this type of ultrasonic transducer, a broadband characteristic is achieved without a backing material; this probably results from the porosity of the sol-gel composite, and backing material problems at high temperatures are eliminated. In particular, ultrasonic transducers fabricated by a sol-gel spray technique have curved surface suitability such that they could be ideal for industrial application, since many inspection points have curved surfaces.…”

“…In our recent study, ultrasonic transducers fabricated using CaBi 4 Ti 4 O 15 (CBiT)=Pb(Zr,Ti)O 3 (PZT) showed thermal durability at 600 °C. 34) However, Pb has a low melting point and can evaporate above 300 °C when it has small particles such that a lead-free CBiT sol-gel composite is preferred for high temperature application.…”

Polarity effect of corona discharge poling for sol-gel composite-based ultrasonic transducers

“…1,2) The thick porous films made by solgel composite materials have helped realize ultrasonic transducers with variable center frequency (in the range of 2-50 MHz); such transducers are suitable for non-destructive testing (NDT) applications. [3][4][5][6][7][8][9][10][11][12][13][14][15][16][17][18][19][20][21][22] Owing to the porosity of solgel composite films, sol-gel composite-based ultrasonic transducers exhibit high temperature durability, curved surface applicability, reasonable signal strength, and high signalto-noise ratio (SNR), in addition to the suitable frequency range for NDT. 11,20) Therefore, sol-gel composite-based ultrasonic transducers have a good potential for industrial applications.…”