Study On Structure And Properties Of Viscous Polymer Processing Fabricated Piezoelectric Ceramic Friber Composites

The ratio of thickness model electromechanical coupling factor to radial model electromechanical coupling factor of 1-3 piezoelectric composites is much larger the that of similar piezoelectric ceramic.This leads to the anisotropism of the composites, and will raise the transducer's resolution to improve the response time of the pulse. Additionally,the hydrostatic pressure sensitivity of the composites can be improved by changing the fiber volume fraction.So,this kind of material is suitable for transducers with high sensitivity,wide bend and narrow pulse,which have been widely used in medical ultrasonic,nondestructive test and hydrophone.In this article,the development of 1-3 composites was discussed.PZT5 fibers were fabricated by viscous polymer processing(VPP).1-3 piezoelectric composites were prepared by arranging ceramic fibers and casting epoxy resin.Based on its use for transducer,the influences of ceramic composition,solid content,ceramic volume fraction and aspect ratio on piezoelectric properties,dielectric properties,ferroelectric properties and acoustic impedance were studied,and the influence of piezoelectric phase on the properties of 1-3 composites was achieved.Vibration mode of 1-3 piezoelectric composites was built and calculated by finite element method,and the results was consistent with the experimental result.(1) PZT5,PMnS-PZN-PZT and PSN-PZN-PZT ceramic fibers were fabricated by viscous polymer processing(VPP).The procedure of VPP,the formation of piezoelectric ceramic fiber and the solidify of epoxy were studied.The affects of organic and sintering condition on fiber structures and properties were analyzed.The solid content has significant impact on the mechanical and ferroelectric properties,and the green ceramic fiber with good strength and plasticity,was obtained when solid content is 86%.After being sintered at 1190-1280℃for 2-4h,the fiber was dense,the crystal size was uniform(about 2～5μm),and the mechanical and ferroelectric properties of fibers were best.(2) The influences of aspect ratio t/d on properties of 1-3 composites were tremendous, and all the properties parameter reached maximum value at t/d～4.Fiber cross-section shape has significant impact on the stress-strain behavior of the fibers,but no influence on the piezoelectric and dielectric properties.The tensile strength of PMnS-PZN-PZT fiber is 43.5MPa,which is 2 time than that of PZT5 fiber. (3) After cured at a suitable temperature,it was found that the structure of epoxy resin was tight and almost had no pore when the curing agent was methyl tetrahydrophthalic anhydride(THPA),plasticizer was dioctyl phthalate(DOP) and promoter was 2,4,6-c-(dimethyl-amino) -phenol as.With increasing the ceramic volume fraction,the relative permittivity constant rose linear,remnant polarization P_r and coercive field E_c, piezoelectric strain constant d₃₃,electromechanical coupling factors k_p and k_t and acoustic impedance Z gained prominently but the piezoelectric voltage constant g₃₃ decreased.And k_t and g₃₃ of the composites were both higher than those of pure ceramics, but Q_m was smaller.These lead to 1-3 piezoelectric composites has high values of g₃₃/d₃₃ and k_t/k_p,and has great anisotropic property.(4) Aspect ratio has significant impact on the planar-mode,thickness-mode and lateral-mode resonances of the composites.With the aspect ratio decreasing,reducing lateral-mode resonances disturbance and the series and parallel resonant frequency,f_s and f_p, increased at the same time,which expanded the bandwidth.This implied that single resonance mode can be obtained by changing the thickness of the composites.But if the aspect ratio is too small,the d₃₃ value of the composites will be too low for using.When 2≤t/d≤3,the composites has single resonance mode and fine properties.The dielectric constant and loss of the composites varied with the properties of the piezoelectric ceramic, so the properties of composites can be controlled by changing fiber's properties.(5)After designing and building modes,the stress-strain of 1-3 piezoelectric composites under the electric field was analyzed by the FEM simulation.The influences of fiber volume fraction and aspect ratio on dielectric and piezoelectric properties were studied.The simulation results shown that the aspect ratio has significant impact on the resonance modes,small aspect ratio leads to thickness-mode and planar-mode resonances, while large ratio leads to thickness-mode and bend-mode resonances.When t/d=2～4,there is single thickness-mode resonance.The stress and strain on the piezoelectric ceramic fiber are much bigger than those on epoxy and stress focus appeared on the interface between fiber and epoxy.With increasing the ceramic volume fraction,d₃₃ increased until it reaches a saturation value the and relative permittivity constant rose linear.The results of FEM simulation was consistent with the experimental result,which were useful for designing and fabrication of the composites.