| Compared with conventional monolithic piezoelectric ceramics, piezoelectric ceramic tubes with large length-diameter ratio present not only excellent piezoelectric, dielectric properties and small electric field loss but also fine scales, large deflection and flexibility. Due to these advantages, piezoelectric ceramic tubes with large length-diameter ratio are suitable for the preparation of composite materials, such as macro-fiber composite and power composite. The availability of piezoelectric ceramic tubes with large length-diameter ratio advances the development of synthetic multifunctional composite materials, which motivates researchers to fabricate and optimize piezoelectric ceramic tubes with large length-diameter ratio.Lead zirconate titanate (PZT5) ceramic tubes with large length-diameter ratio were fabricated via the viscous plastic processing-extrusion method by using the PZT5 presintered ceramic powder as raw materials, and sintered under different sintering conditions. The phase composition, microstructure and volume density of the tubes were measured by X-ray diffractometer (XRD), scanning electron microscope (SEM) and drainage. The influences of solid content, sintering temperature, maintaining time and sintering atmosphere on phase composition, microstructure and volume density were investigated. PZT5 ceramic tubes with 0.8 mm inner diameter,1.98 mm outer diameter and 150 mm length were successfully fabricated by viscous plastic processing-extrusion method. The optimum solid content of slurry was about 87%. A typical perovskite phase without ZrO2, pyrochlore or other impurities was obtained for the tubes sintered at 1290℃ for 2 h by using a mixture of ZrO2 and Pb3O4 as burning powder. A homogeneous and compact structure with 2-5μm grain sizes was also observed. The volume density of tube was 7.70 g/cm3.The sintered PZT5 tubes were uniformly coated with nickel electrode on both inner and outer wall surfaces by chemical plating. The coarsening way for the PZT5 tubes was optimized by orthogonal test with the deposition rate and resistivity as indexes. The effects of each roughening factor on the deposition performance were systematically studied by single factor method. The optimum coarsening way for electroless nickel plating on the surface of the PZT5 tubes is determined:20% of the mass fraction of sodium hydroxide,35 min of roughening time,25℃ of roughening temperature, and the concentration of ethylene diamine is 30 mL/L. The deposits obtained are greatly improved with brightness, uniform, density, excellent adhesion, low resistivity.The metal ized PZT5 piezoelectric ceramic tubes with large length-diameter ratio were polarized by vacuum polarization. The resonance frequency (fr), anti-resonance frequency (fa), static capacitance (C) and dielectric loss (tanδ) of PZT5 tubes poled were measured by precision impedance analyzer (Agilent 4294A, Agilent Technologies Co. Ltd., United States). The relative dielectric constant (εr) and electromechanical coupling coefficient (K31) were calculated using the static capacitance and the resonance measurement method, respectively. The effects of poling field, temperature and times on the properties of PZT5 tubes were predominantly discussed. It showed that the PZT5 tubes poled with a DC field of 2.0 kV/mm at 25℃ for 10 min were adequate to reach full polarization.The longitudinal piezoelectric constant (^33) of the PZT5 tube was measured by a d33 measuring instrument (ZJ-6A, Chinese academy of sciences institute of acoustics, China). The resonance frequency (fr), anti-resonance frequency (fa), and impedance (Zmin) of PZT5 tubes poled were measured by precision impedance analyzer. The mechanical quality factor (Qm) was calculated using the resonance measurement method. The longitudinal piezoelectric coefficient (d33) of PZT5 tubes was 579 pC·N-1, the electromechanical coupling coefficient (K31) was 0.49, the relative dielectric constant (er) was 1789, the dielectric loss (tanδ) was 0.026, the mechanical quality factor (Qm) was 11. |
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