| Piezoelectric composites are a type of materials that consist of a piezoelectric ceramic phase as well as a polymer phase in a certain connecting way.This kind of new material has been widely studied and applied since it came into being,because it often collects the advantages of various phase materials.Among many piezoelectric composites,1-3 piezoelectric composites are the most deeply studied and widely used.1-3 piezoelectric composites are two-phase piezoelectric composites consisting of one-dimensional piezoelectric ceramic pillars arranged parallel in three-dimensional connected polymers.1-3 piezoelectric composites have many advantages,such as low acoustic impedance,low dielectric constant,high electromechanical coupling coefficient,etc.They have become ideal materials for piezoelectric ultrasonic transducers.Although there have been many studies on 1-3 composites in the past decades,the research on its temperature stability is limited.So,we expect to develop some high-performance 1-3 piezoelectric composite materials with good temperature stability for the practical applications of ultrasonic transducers.Under the above research background,this paper studied the preparations and the physical properties of 1-3 ceramic/polymer piezoelectric composites.Specific research contents are as follows:1.The preparation technology of 1-3 ceramic/polymer piezoelectric composites was studied.The cut&fill process was explored mainly from two aspects.Firstly,in order to solve the problem of easy collapse of ceramic pillars in cutting process,an improved cutting-filling method is proposed,in which epoxy resin coating can improve the utilization rate of ceramic sheets,and step-by-step cutting and filling can effectively avoid the breaking and collapsing of ceramic pillars.Secondly,freezing powder-grinding&hot-pressing filling is newly proposed for 1-3 ceramic/polymer piezoelectric composites with thermoplastic resins as polymer phases.In this method,polymer particles are first ground into fine powder under liquid nitrogen cooling environment and fine powder is filled into the cut ceramic array slot.Subsequently,the powder resin is further melted and pushed into all the slot by appropriate pressure under high temperature.Then,composite material is finally obtained after cooling.This newly proposed method can greatly enlarge the selection range of polymers.2.Using E51 epoxy resin as polymer phase and PZT5H as ceramic phase,1-3 PZT5H/Epoxy piezoelectric composites were prepared by improved cutting-filling method.The effects of ceramics volume ratio(CVR)and pillar aspect ratio on the piezoelectric properties of 1-3 piezoelectric composites were studied.The results show that the thickness electromechanical coupling coefficient kt of the composites increases and kp decreases when compared with monolithic PZT5H ceramics.The acoustic impedance Z and quality factor Qm of the composites increase with the increase of CVR.The piezoelectric constant d33 increases with the increase of CVR,and reaches 405 pC/N when CVR=25%.The kt of 1-3 type PZT5H/Epoxy piezoelectric composites increases first and then decreases with the decrease of thickness.The optimum properties obtained for a PZT5H/E51-Epoxy piezoelectric composite with CVR?25%are d33?405 pC/N,Mrayl,Z=9.9,kt?0.71,Qm?5.7,?r?656 and tan?=0.04,respectively.Using the Smith's composite theoretical model,the relationship between the various physical properties that are relavent to piezoelectric ultrasonic energy-conversion and CVR in the 1-3 PZT5H/E51-Epoxy piezoelectric composites was studied.The results show that the measured values are in good agreement with the theoretical values.3.Using E51 epoxy resin as polymer phase,PZT43 and PZT51 as ceramic phase,1-3 PZT43/E51-Epoxy and PZT51/E51-Epoxy piezoelectric composites were prepared by improved cutting-filling method.The influences of CVR and aspect ratio of ceramic phase on the physical properties of 1-3 piezoelectric composites were studied.It was found that ?r Z and d33 increase with the increase of CVR.Compared with monolithic PZT43 ceramics,Kt is increased and kp is decreased;?r is decreased,and Qm is decreased by two orders of magnitude.Meanwhile,kt has good temperature stability in the test range of-50?to 150?.Furthermore,kt increases first and then decreases with the increase of the thickness of the composites.The maximum kt is obtained when the aspect ratio is about 3.The CVR and aspect ratio were optimized,and the 1-3 PZT43/Epoxy piezoelectric composites shows optimal physical properties of d33?282 pC/N,kt=0.67,Z?10.8 Mrayl,Qm=4.2,?r?415 and tan?=0.03 when CVR is 32%and aspect ratio is 3.The 1-3 PZT51/Epoxy piezoelectric composites with CVR=32%and aspect ratio of 3 were prepared in a similar way.Their physical properties are d33=417 pC/N,kt?0.67,Z?9.5 Mrayl,Qm=4.4,?r?415 and tan?=0.04,respectively,and show also the good temperature stability.Using the Smith's composite theoretical model,the relationship between the various physical properties that are relavent to piezoelectric ultrasonic energy-conversion and CVR in the 1-3 PZT43(PZT51)/Epoxy piezoelectric composites was studied.The results show that the measured values are in good agreement with the theoretical values.4.1-3 PZT5H/Epothin-Epoxy piezoelectric composites were prepared by cutting-filling method using EpoThinTM 2 low viscosity epoxy resin as polymer phase and PZT5H as ceramic phase.The influences of CVR and aspect ratio of ceramic phase on the properties of 1-3 type piezoelectric composites were systematically studied.By adjusting the slot width and pillar width,we prepared piezoelectric composites with CVR of 19%-51%.The experimental results show that compared with PZT5H ceramics,1-3 composites show increased kt and decreased kp.The ?r increases linearly with the increase of volume ratio,while Z and Qm of increase with the increase of CVR.The d33 increases rapidly with the increase of CVR when CVR is small,and reaches 425 pC/N when CVR is 19%,then increases slowly with the increase of CVR.The kt increases first and then decreases with the increase of the thickness of the composite material.When the aspect ratio is about 3,kt reaches its maximum value.By optimizing the CVR and aspect ratio of composite,we successfully prepared a few novel PZT5H/epoxy piezoelectric composites.The optimum properties were obtained at CVR?25%and aspect ratio=3.Among them,d33=515 pC/N,kt=0.73,Z?9.8 Mrayl,and Qm?3.7.The kt of the prepared piezoelectric composite has a good temperature stability in the test range from-50?to 150?.5.Using EpoThinTM 2 low viscosity epoxy resin as polymer phase,PZT43 and PZT51 as ceramic phase,1-3 piezoelectric composites were prepared.Firstly,1-3 PZT43/Epothin-Epoxy piezoelectric composites were fabricated.The results show that compared to PZT43 ceramics,1-3 composites show increased kt and decreased kp.The?r increases linearly with CVR,while Z and Qm increase with CVR.The d33 increases rapidly with CVR when CVR is small,and reaches 269 pC/N when CVR is 17%,then increases slowly with the increase of CVR.The kt increases first and then decreases with the increase of the thickness of the composite sample,and reaches the maximum at the aspect ratio of about 3.By optimizing the CVR and aspect ratio of composites,we successfully prepared a few novel PZT43/Epothin-Epoxy piezoelectric composites.The composite material has good ultrasonic energy-conversion properties,including d33=305 pC/N,kt=0.70,Z=9.7 Mrayl,Qm=7.3.At the same time,kt has good temperature stability in the test range from-50?to 150 ?.(2)PZT51/Epothin-Epoxy piezoelectric composites with good properties were successfully prepared when PZT51 was used as ceramic phase.The composite has good ultrasonic sensing properties,including d33=464 pC/N,kt=0.68,Z?9.5 Mrayl,Qm?4.4.At the same time,kt has good temperature stability in the test range of-50? to 150?.6.1-3 KNNS/Epoxy piezoelectric composites were prepared by cutting-filling method.The piezoelectric properties of the sample were measured.It was found that the kt was enhanced and the kp was weakened.When the aspect ratio is 3,the physical properties of the composites at room temperature are d33?310 pC/N,kt?0.63,Z?11.3 Mrayl,Qm?4.5,?r?588 and tan??0.05.It was found that kt is very stable between-50? and 40? but decreases rapidly with further increasing the temperature.Thus,in general,the temperature stability of the composites is not good in the whole range between-50? and 150?.7.The 1-3 PZT5H/PMMA and PZT5H/PVDF piezoelectric composites were fabricated innovatively by using a frozen grinding powder-hot pressing filling method.The temperature stability of kt was measured.It was found that kt of the 1-3 PZT5H/PMMA piezoelectric composites has a weak temperature dependence in the temperature range of-50?-150?,thereby showing a very good temperature stability.However,temperature stability of the PZT5H/PVDF piezoelectric composite is very poor.8.Study disclosed an important physical phenomenon that the piezoelectric temperature stability of a 1-3 piezoelectric ceramic/polymer composite is mainly determined by the piezoelectric temperature stability of the corresponding piezoelectric ceramic. |
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