Novel Processing of 1-3 Piezoelectric Ceramic/Polymer Composites for Transducer Applications

Piezoelectric ceramic/polymer composites with 1-3 connectivity were made by weaving sized lead zirconate titanate (PZT) fiber bundles through a honeycomb support. Bundles comprised of fine-scale, 20-50 μm green fibers, made using the viscous suspension spinning process, were sized to increase their manageability. The sizing step comprised of soaking the green PZT fiber bundles in an aqueous solution of poly(vinyl alcohol), then pulling the wet fibers through a steel sizing die. Sizing resulted in dense and flexible fiber bundles, which facilitated composite construction and led to composites with increased volume fractons. Sintering, polymer embedding, and machining produced a composite exhibiting 1-3 connectivity. Composites with 10 vol% PZT yilded d ₃₃ values of 230 pC/N and a dielectric constant of 130.     

Relic Processing of Fine-Scale, Large-Area Piezoelectric Ceramic Fiber/Polymer Composites

Fine-scale, large-area lead zirconate titanate (PZT) ceramic fiber/polymer composites were developed using the relic method. Carbon fabrics were used as a starting template material. These fabrics were soaked in PZT stock solution, stacked, and fired, removing the carbon and resulting in a relic structure identical to that of the original template. The relics were then sintered, backfilled with polymer, polished, and poled, resulting in a piezoelectric ceramic/polymer composite. The processing of the larger-area composites involved scaling up the procedure utilized in the fabrication of the smaller composites. The application of an optimum uniaxial pressure of 580 Pa to the stacks during firing was found to improve the piezoelectric properties and facilitate the increase in sample area. Scale-up to large area was achieved using two approaches: (1) the use of a larger template material, and (2) tiling smaller area relics together in an array configuration. The dielectric and piezoelectric properties of relic composites of 2.5 × 2.5 cm² area with ∼37 vol% PZT were K = 150 ± 8, d₃₃= 180 ± 11 pC/N, d_h= 85 ± 7 pC/N, and d _hg_h= 5525 × 10⁻¹⁵m²/N. The properties of large-area composites were comparable with those of small area.     

Piezoelectric Lead Zirconate Titanate Ceramic Fiber/Polymer Composites

Piezoelectric lead zirconate titanate (PZT) ceramic fiber/polymer composites were fabricated by a novel technique referred to as "relic" processing. Basically, this involved impregnating a woven carbon-fiber template material with PZT precursor by soaking the template in a PZT stock solution. Careful heat treatment pyrolized the carbon, resulting in a PZT ceramic relic that retained the fibrous template form. After sintering, the densified relic was backfilled with polymer to form a composite. Optimized relic processing consisted of soaking activated carbon-fiber fabric twice in an intermediate concentration (405-mg PZT/(1-g solution)) alkoxide PZT solution and sintering at 1285°C for 2 h. A series of piezoelectric composites encompassing a wide range of dielectric and piezoelectric properties was prepared by varying the PZT-fiber orientation and polymer-matrix material. In PZT/Eccogel polymer composites with PZT fibers orientated parallel to the electrodes, K = 75, d ₃₃= 145 pC/N, d _h= 45 ± 5 pC/N, and d _hg_h= 3150 × 10⁻¹⁵ m²/N were measured. Furthermore, in composites with a number of PZT fibers arranged perpendicular to the electroded surfaces, K = 190, d ₃₃= 250 pC/N, d _h= 65 ± 2 pC/N, and d _h g_h= 2600 × 10⁻¹⁵ m²/N.     

Overview of Fine-Scale Piezoelectric Ceramic/Polymer Composite Processing

In the past two decades, piezoelectric ceramic/polymer composites with different connectivities have been developed for transducer applications such as hydrophones, biomedical imaging, nondestructive testing, and air imaging. Recently, much attention has been given to fine-scale piezoelectric ceramic/polymer composites. These composites allow higher operating frequencies, and thus increased resolution, in medical imaging transducers. In this review, methods for processing fine-scale piezoelectric ceramic/polymer composites are discussed. The current capabilities, strengths, and weaknesses of each method are compared. The importance of spatial scale in composite performance is also reviewed. Several of the processing methods have demonstrated composites with fine-scale ceramic phases (<50 μm), and others have potential to form composites with a ceramic scale of under 20 μm.     

1–3型铌酸钾钠基陶瓷/环氧树脂无铅压电复合材料的超微细化制备与性能

利用放电等离子烧结高致密度的铌酸钾钠基无铅压电作为陶瓷相,通过改进后的切割-浇注法复合基体相环氧树脂,制备得到陶瓷柱宽40μm、间隙40μm、纵横比>5的超微细化结构的1-3型铌酸钾钠基陶瓷/环氧树脂无铅压电复合材料(1-3 connective lead-free piezoelectric composites,1-3CLFPC)。1-3CLFPC薄膜的电学性能显示出其作为超声换能器工作的优势:压电电压常数g33达到247×10-3 m2/C,厚度机电耦合系数kt为40.7%。超微细化结构设计也使得1-3CLFPC薄膜的工作频率提高到5 MHz以上,可满足高频医疗超声诊断领域的需求。     

Cement-Based 0-3 Piezoelectric Composites

To meet the requirements of development for smart or intelligent structures in civil engineering, new functional materials that have good compatibility with civil engineering structural materials are needed. In this study, for the first time in the field of piezoelectric materials, cement-based 0-3 piezoelectric (PZT) composites were fabricated by the normal mixing and spreading method. The new materials have very good compatibility with portland cement concrete. The cement-based 0-3 piezoelectric composites were shown to have a slightly higher piezoelectric factor and electromechanical coefficient than those of 0-3 PZT/polymer composites with a similar content of PZT particles; thus, they are adequate for sensor application. There is potential for the application of cement-based 0-3 PZT composites in civil engineering because of their better piezoelectric properties and good compatibility with portland cement concrete.     

Low-Temperature Processing of Ceramic Woven Fabric/Ceramic Matrix Composites

Two-dimensional Al₂O₃ and SiC woven laminate composites, and oxide and nonoxide monolithic ceramics with 5 to 10 wt% of polycarbosilane binder, were consolidated up to 75% of TD (theoretical density) at 1150°C by the multiple impregnations of a polycarbosilane solution. The processing conditions were optimized without causing fiber damage. The near-net-shape composite fabricated by this process showed high reproducibility in terms of relative density and flexural strength. The mechanical properties were characterized by flexural testing with strain gauges. All of the woven laminate composites exhibited good composite-type fracture behavior, e.g., load-carrying capacity following maximum load. The room-temperature flexural strength and first-matrix cracking stress of SiC fabric/SiC composite with 73% TD were about 300 and 77 MPa, respectively.     

Colloidal Processing for Improved Piezoelectric Properties of Flexible 0–3 Ceramic–Polymer Composites

Ceramic-polymer composites with 0–3 connectivity were prepared from (Pb_0.5, Bi_0.5) (Ti_0.5, (Fe_{1- x} Mn _x )_0.5)O₃ ( x = 0.00 to 0.02) ceramic powder and epoxy polymer. Epoxy was dissolved in a methanol solution and the ceramic powder was added to form a suspension. Powder-polymer coacervates were precipitated from the suspension by the addition of water. Colloidal filtration followed by cold-pressing consolidated the coacervates to form composites with uniform microstructure. Composites fabricated in this manner could be poled with higher electric fields than could be sustained by the conventionally prepared composites. The values of piezoelectric coefficients, d ₃₃, d _h, and g _h were as high as 65, 41 pC/N, and 145 mV · m/N, respectively.     

Tough Alumina/Polymer Layered Composites with High Ceramic Content

Ceramic composites found in nature, such as bone, nacre, and sponge spicule, often provide an effective resolution to a well‐known conflict between materials' strength and toughness. This arises, on the one hand, from their high ceramic content that ensures high strength of the material. On the other hand, various pathways are provided for stress dissipation, and thus toughness, due to their intricate hierarchical architectures. Such pathways include crack bridging, crack deflection, and delamination in the case of layered structures. On the basis of these inspiring ideas, we attempted here to create simultaneously strong and tough laminated alumina composite with high ceramic content. Composites were prepared from high‐grade commercial alumina with spin‐coated interlayers of ductile polymers (PMMA and PVA). The specimens' ultimate properties (strength, fracture toughness, and work of fracture) were measured by a four‐point bending method. In some cases, fracture toughness of the composites was increased by up to an order of magnitude, reminiscent of the natural layered composites. It is proposed that this increase may be attributed to an interlocking mechanism, often encountered in biological composites. The significance of sample architecture and the role of the interfacial and bulk properties of the interlayer material are discussed.     

Fine‐Scaled Piezoelectric Ceramic/Polymer 2‐2 Composites for High‐Frequency Transducer

A novel technique was utilized to fabricate fine‐scaled piezoelectric ceramic/polymer 2‐2 composites for high‐frequency ultrasonic transducers. Lead zirconate titanate (PZT) was used as raw material. Tape‐casted acetylene black tapes were used to define kerfs after sintering. A one‐directional supporter was utilized to avoid distortion of PZT elements. PZT elements with 20 ± 2 μm width exhibited good consistency in longitudinal direction. A resonant method was utilized to evaluate the piezoelectric and dielectric properties of the composites. A 72‐μm‐thick composite with an aspect ratio of ~3.6 exhibited a k_t of 0.61 with satisfied piezoelectric and dielectric properties. A prototype high‐frequency ultrasonic transducer was fabricated and evaluated by an underwater pulse‐echo test. The center frequency was found to be 23.75 MHz, with ?6 dB bandwidth of 5.5 MHz.     

陶瓷粉体粒度对PZN—PZT／PVDF压电复合材料性能的影响

将铌锌锆钛酸铅（PZN—PZT）压电陶瓷粉体分散于聚偏二氟乙烯（PVDF）基体中,制备出0-3型PZN—PZT／PVDF压电复合材料。文中研究了PZN—PZT陶瓷不同粒度对复合材料的压电性、介电性、铁电性的影响。结果表明,当陶瓷粒度为100～150目时,压电复合材料的综合性能最佳,压电常数d33达到23．10pC／N,剩余极化强度Pr达到5．131μC·era2,矫顽场Ec为45．7lkV·cm^-1,介电常数ε。为192．86,介电损耗tanδ为0．10。     

Fabrication of Piezoelectric Ceramic/Polymer Composite Transducers Using Fused Deposition of Ceramics

The fused deposition of ceramics (FDC) technique was used to fabricate piezoelectric ceramic skeletons for the development of piezoelectric composite transducers with 2–2 connectivity for medical imaging. The green parts were designed to have 30 vol% lead zirconate titanate ceramic (PZT-5H) in the final composites. Physical characterization of the sintered samples revealed that 96% of the theoretical density was achieved. Optical microscopy showed that defects due to the FDC mode of deposition, such as small roads and bubbles, were eliminated, because of improvements in powder processing. The electromechanical properties of the final composites were similar to the properties that were obtained for conventionally made composites. A matching layer and a backing layer, as well as wires and an inductor, were added to each FDC composite to fabricate a functional medical imaging transducer. The devices were tested in water using a steel target 3.5 cm thick. Echoes from the target could be detected with all the transducers that were fabricated using FDC. The sensitivities of the transducers were similar to that of a commercial transducer. However, the ringing was much longer than that for a commercial transducer, because the backing layer was not optimized in the transducers that were fabricated using FDC.     

Method for Processing Metal-Reinforced Ceramic Composites

A new process is developed to form a ceramic containing a three-dimensional network of metal reinforcement. The process involves four steps: (1) forming a powder compact containing a continuous network of either organic or carbon material by pressure filtration, (2) pyrolyzing the network to form channels within the powder compact, (3) densifying the powder while retaining the channel network, and (4) intruding metal into the channel network by squeeze casting. Pressure filtration is used to form the powder compact containing the pyrolyzable network either by mixing slurries of powder with chopped fiber or by packing powder within pyrolyzable preforms. When pressure is removed after filtration, the differential strain recovery of the powder matrix relative to the organic material can cause damage. Such damage is prevalent for a powder matrix formed from flocced slurries. However, this problem is avoided by using dispersed slurries which produce consolidated bodies that alleviate stresses arising from differential strain recovery by viscous flow. Metal-reinforced ceramic composites with different reinforcement architectures, volume fractions, and sizes can be produced with this technique.     

Thermoplastic Green Machining for the Fabrication of a Piezoelectric Ceramic/Polymer Composite with 2-2 Connectivity

A piezoelectric ceramic/polymer composite with 2-2 connectivity was fabricated by thermoplastic green machining. A thermoplastic body, consisting of 60 vol% lead zirconate titanate ceramic particles (PZT) and 40 vol% thermoplastic binders, was computer numeric controlled-machined, creating periodic channels in the green PZT body. Following thermal treatment (binder burnout and sintering), a 25 vol% array of 147 μm thin PZT slabs with an aspect ratio of seven separated by 442 μm channels was fabricated. The channels were infiltrated with epoxy resin, in order to fabricate the PZT/epoxy composite with 2-2 connectivity. This novel process was evaluated in terms of the machinability and sinterability of the thermoplastic PZT compound. Also, the electromechanical properties of the PZT/epoxy composite were measured.     

压电陶瓷颗粒增韧陶瓷基复合材料研究进展

本文综述了压电陶瓷颗粒增韧陶瓷基复合材料的研究进展,重点讨论了增韧机理、极化及不同工艺对增韧效果的影响.分析认为,研究一种低成本、烧结性能较好且能够与基体稳定共存的压电材料,以及能够获得最佳性能的合适的制备工艺是目前的研究趋势,具有广阔的发展前景.     

Processing and Properties of Intermetallic/Ceramic Composites with Interpenetrating Microstructure

Intermetallic/ceramic composites represent an interesting class of materials for high-temperature structural and functional applications. These materials can be prepared via high-energy milling of pure metals with Al₂O₃ as well as of aluminum with metal oxides. During subsequent compaction via pressureless sintering, the components react to form dense composites that consist of interpenetrating networks of the ceramic and intermetallic phases. Microstructural investigations, mechanical properties, and resistivity and wear resistance measurements of selected composites are presented. Improved fracture toughness and bending strength, with respect to monolithic Al₂O₃, have been achieved.     

Piezoelectric Multilayer Ceramic/Polymer Composite Transducer with 2–2 Connectivity

A multilayer piezoelectric ceramic/polymer composite with 2–2 connectivity was fabricated by thermoplastic green machining after co-extrusion. The multilayer ceramic body was composed of piezoelectrically active lead zirconate titanate (PZN)–lead zinc niobate (PZN)-lead zirconate titanate (PZT) layers and electrically conducting PZN–PZT/Ag layers. After co-extruding the thermoplastic body, which consisted of five piezoelectric layers interspersed with four conducting layers, it was computer numeric-controlled machined to create periodic channels within it. Following binder burnout and sintering, an 18 vol% array of 190 μm thin PZT slabs with a channel size of 880 μm was fabricated. The channels were filled with epoxy in order to fabricate a PZN–PZT/epoxy composite with 2–2 connectivity. The piezoelectric coefficient (effective d ₃₃) and hydrostatic figure of merit ( d _h× g _h) of the PZN–PZT/epoxy composite were 1200 pC/N and 20 130 × 10⁻¹⁵ m²/N, respectively. These excellent piezoelectric characteristics as well as the relatively simple fabrication procedure will contribute in widening the application range of the piezoelectric transducers.     

Low Dielectric Loss Polytetrafluoroethylene/TeO2 Polymer Ceramic Composites

TeO₂ particle-filled PTFE composites were prepared by the powder processing technique. The structure and microstructure of the composites were investigated by X-ray diffraction and scanning electron microscopic methods. The effect of the ceramic content (0–0.6 volume fraction) of TeO₂ on the dielectric properties of the composites was studied at 1 MHz and 7 GHz. The dielectric constant and dielectric loss increased with an increase in the TeO₂ content. For 60 vol% of TeO₂, the composite has a dielectric constant of 5.4 and a loss tangent of 0.006 at 7 GHz. The measured dielectric constant (ɛ_r) is compared with the effective dielectric constant calculated using different theoretical models. The observed dielectric constants are in agreement with that calculated using effective medium theory. The coefficient of thermal expansion of the composites decreases with the TeO₂ content, reaching a minimum of 32 ppm/°C for 60 vol% loading.     

Piezoelectric Properties of a Pioneering 3‐1 Type PZT/Epoxy Composites Based on Freeze‐Casting Processing

Lead zirconate titanate (PbZr_1 ? xTi_xO₃, PZT)/epoxy composites with one‐ dimensional epoxy in PZT matrix (called 3‐1 type piezocomposites) have been fabricated by tert‐butyl alcohol (TBA)‐based directional freeze casting of PZT matrix and afterward infiltration of epoxy. The composites with PZT volume fraction ranging from 0.36 to 0.69 were obtained by adjusting initial solid loading in freeze‐casting slurry. The effect of poling voltage on piezoelectric properties of the composites was studied for various volume fraction of PZT phase. With the increasing of PZT volume fraction, relative permittivity (ε_r) increased linearly and piezoelectric coefficient (d₃₃ and d₃₁) increased step by step. The resultant composites with 0.57 PZT volume fraction possessed the highest hydrostatic piezoelectric strain coefficient (d_h) value (184 pC/N), voltage coefficient (g_h) value (13.6 × 10^?3 V/m Pa), and hydrostatic figure of merit (HFOM) value (2168 × 10^?15 Pa^?1).     

铁电陶瓷颗粒填充压电复合材料的微结构与性能

采用模塑工艺制备了含铁电陶瓷PZT颗粒填充的PZT／P（VDF－TrFE）压电复合材料,用差热分析研究并确定了复合材料的固化工艺参数,测试并研究了压电复合材料的电性能和显微结构,结果表明,随着PZT质量百分比的增加,电性能参数逐渐增大,当PZT的质量百分比达到85％时,介电常数ε和压电常数d33值最大,铁电陶瓷颗粒分布均匀,当PZT含量较低时,两相材料界面结合良好,而当PZT含量达到90％时,气孔则明显增多,这就是导致复合材料的介电常数和压电常数在PZT高含量区下降的主要原因。