【作者】 刘炜；

【导师】 徐宏； 杨金龙；

【作者基本信息】 中北大学 ， 机械设计及理论， 2014， 博士

【摘要】 锆钛酸铅（PZT）压电陶瓷具有优良的介电、压电性能和可靠性，是高灵敏度水声传感器和医用超声换能器的首选材料。研究发现，烧结致密的PZT压电陶瓷静水压品质因数HFOM较低、声阻抗较大，用于水声传感器领域时和医用超声换能器领域时，会降低器件的灵敏度和医用超声换能器成像的分辨率。多孔PZT压电陶瓷通过在压电陶瓷相中引入具有低密度、低介电性和无压电性的空气相，可以显著提高材料的HFOM值，降低声阻抗，增加了材料的灵敏度和材料与媒介的声学匹配。论文主要结论如下：通过直接发泡法与凝胶注模工艺相结合，制备具有高孔隙率、高静水压品质因数和低声阻抗的3-0与3-3型的泡沫PZT压电陶瓷。通过优化工艺参数，使该工艺适用于制备泡沫PZT压电陶瓷。经过研究，加入0.5wt%（相对于粉体重量）阿拉伯树胶分散剂的浆料流变性能较好；采用机械搅拌的方式使陶瓷浆料发泡，通过短链的两亲分子戊酸修饰PZT陶瓷颗粒，可以使浆料具有更高的发泡率；催化剂（MBAM）和引发剂（APS）水溶液最佳含量分别为0.5vol%和1.0vol%（相对于溶剂）。系统研究了浆料的固相体积分数、浆料pH值、戊酸浓度和烧结温度对直接发泡法制备泡沫PZT压电陶瓷性能的影响规律。通过调控陶瓷浆料的发泡率和多孔PZT压电陶瓷的孔隙率，泡沫PZT压电陶瓷的孔隙率在27.8%至76.3%之间，其变化范围远高于传统的造孔剂燃烧工艺。并且，随着孔隙率的增大，泡沫PZT压电陶瓷的开孔气孔率相应增高，由3-0型向3-3型压电陶瓷转变。多孔PZT压电陶瓷的HFOM最大值可至19520×10-15Pa-1，声阻抗最小值为1.35Mrayls，具有非常高的灵敏度和低的声阻抗，适用于高灵敏度水声传感器和医用超声换能器。利用海藻酸钠离子凝胶反应工艺制备具有定向通孔结构的3-1型蜂窝压电陶瓷。系统深入研究了Ca2+作为固化剂，在1mol/L葡萄糖酸内酯溶液和1mol/L HCl溶液中依次各浸泡24h的方式置换阳离子，得到湿坯后通过溶剂置换与空气中室温干燥相结合，成功避免了坯体开裂，制备了孔径分布均匀，具有定向通孔结构的蜂窝陶瓷坯体。研究了浆料的固含量、阳离子溶液浓度、海藻酸钠溶液浓度和烧结温度对海藻酸钠离子凝胶反应工艺制备3-1型PZT压电陶瓷性能的影响规律。通过调节工艺参数，3-1型PZT陶瓷的孔隙率在16.4%-64.8%之间，孔径在100-300μm之间，HFOM值在448-7554×10-15Pa-1之间，具备较高的灵敏度。并且，鉴于3-1型PZT陶瓷蜂窝状的孔结构，以及在制备工艺中引入了CaO掺杂物，其机械性能得到了大幅度提升。利用3-1型PZT陶瓷压电相和非压电相周期性排列的特征，建立3-1型PZT陶瓷电学计算模型，研究了孔径尺寸/壁厚对多孔PZT陶瓷电学性能的影响规律。研究发现：3-1型PZT陶瓷的相对介电常数εr、纵向压电应变常数d33和横向压电应变常数d31都随着孔径尺寸/孔壁厚度比的增大而减小；3-1型PZT陶瓷的静水压压电电压常数gh随着孔径尺寸/孔壁厚度比的增大而增大；3-1型PZT陶瓷的静水压品质因数HFOM则随着孔径尺寸/孔壁厚度比值的增大而呈现先增大后减小的趋势。因此，可以在较低孔隙率下通过控制孔径尺寸/孔壁厚比值使多孔压电陶瓷达到较高的灵敏度，并且使材料具备较高的相对介电常数，增强了器件的稳定性。更多还原

【Abstract】 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.更多还原