Preparation And Characterization Of Porous PZT Ceramics

Lead zirconate titanate (PZT), by virtue of its excellent dielectric property, piezoelectricproperty and coupled electromechanical characteristics, is considered to be the key materialfor ultrasonic transducers. However, for their high sound velocity and low hydrostatic figureof merit (HFOM), dense PZT ceramics are not appropriate for these applications. Byintroducing into dense PZT, a second phase, air, in the form of pores, porous PZT ceramicssucceed in lowering density and relative permittivity, and bringing about improved HFOMand coupling with biological tissue or water.By combining the particle-stabilized foams and the gelcasting technique,3-0and3-3type of porous PZT ceramics with high porosity, improved HFOM, low acoustic impedancewere prepared. Process parameters in the preparation were throughly investigated andoptimized, the gel-casting process of particle-stabilized wet foams has been improved tobecome a mature preparation technique in preparing porous PZT ceramics. The resultsshowed that the slurry with0.5wt%Arabic gum as the dispersant had the best stability.Through the rapid electric stirring of short-chain amphiphilic molecules (valericacid)-modified ceramic powders slurry, particle-stabilized foams with high foaming capacitywere prepared. The catalyst (MBAM) and initiator (APS) aqueous solution of the best contentwas0.5vol%and1.0vol wt%(to solvent), respectively.The effect of solid loading of slurry, pH value, concentration of valeric acid and sinteringtemperature on properties of porous PZT ceramics was analyzed. By adjusting experimentparameters, the foaming capacity and porosity could be controlled. The porosity of the porousPZT ceramics changed between27.8%and76.3%, much broader than that of burnableplastic spheres (BURPS) processes. With the increase in the porosity, the open porosity ofporous PZT ceramics increased too, which implies the changing trend from3-0type to3-3type PZT ceramics. Finally, the prepared sample possessed a maximal HFOM value of19520×10-15Pa-1, and a minimum acoustic impedance of1.35Mrayls, which shows highHFOM and coupling with biological tissue or water, making them promising candidates for application of medical ultrasonic imaging or underwater sonar detectors.The3-1type porous PZT ceramics with unidirectional aligned pores were prepared bythe ionic gel process of sodium alginate. By investigating and optimizing process parameters,the ionic gel process of sodium alginate were improved to become a mature preparationtechnique in preparing3-1type porous PZT ceramics. The results showed that the alginatechains could be cross-linked by the calcium ions, the unidirectional diffusion of the calciumions through the sol formed capillaries which are oriented parallel to the diffusion direction.Wet gels were immersed into gluconolactone and HCl solutions for24h respectively toexchanged calcium ions. The drying process could be operated by combining solventexchanging and room temperature drying to make sure the integrity of green bodies.The effect of solid loading of slurry, concentration of calcium solution, concentration ofalginate sodium and sintering temperature on3-1type PZT ceramics was investigated. Byadjusting experiment parameters, the porosity of the3-1type PZT ceramics changed between16.4%and64.8%with pore size increasing from100μm to300μm. Finally, the preparedsample possessed a high sensitivity with HFOM value between448×10-15Pa-1and7554×10-15Pa-1. Furthermore, by virtue of the unidirectional pore structures and introducing in smallamounts of CaO, the3-1type PZT ceramics processed high compressive strength.By utilizing the periodic repeated array of3-1type PZT ceramics, the calculation modelof electric properties were built, and the effect of pore size/wall thickness on the propertieswere also researched. The results showed that the value of εr, d33and d31decreased with theincrease of pore size/wall thickness; the hydrostatic voltage coefficient (gh) values increasedwith the increase of pore size/wall thickness; the value of HFOM increased first and thendecreased with the increase of pore size/wall thickness. Therefore, it is possible to fabricatehigh sensitive porous PZT ceramics with a low level of porosity by controlling the value ofpore size/wall thickness, which insuring the stability of devices.