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This paper reports a novel way of producing macroporous ceramics with aligned microporous walls by unidirectionally freezing foamed aqueous ceramic suspensions. The stability of the air bubbles introduced by magnetic stirring was improved remarkably using polyvinyl alcohol (PVA) as both a binder and emulsifying agent. Furthermore, the unidirectional freeze casting method could not only trap the air bubbles in the solidified sample successively but also induce the preferential growth of ice dendrites. This endowed the samples with uniform macropores surrounded by aligned microporous alumina walls after freeze drying and sintering. The sample produced with a PVA content of 8 wt% showed a high compressive strength of 4.6 ± 1.6 MPa at a high porosity of 91 vol%. [ABSTRACT FROM AUTHOR]

The strength of a reticulated porous ZrO2 ceramic was improved significantly by applying a novel infiltration technique. In a conventional reticulated porous ZrO2 cellular ceramic, a polymer foam is coated with the ceramic. Heat treatment produces triangularly shaped pore channels within most of the ceramic struts of the reticulated body. These channels are detrimental to mechanical strength. In an infiltration process under vacuum, a ZrO2 slurry was filled partially into the triangular pore channels of the ZrO2 body. Accordingly, the tips of these triangular pore channels became rounded and previously cracked strut walls were mended. As a result, the compressive strength of the reticulated ZrO2 was more than doubled compared with that obtained from specimens not subjected to the infiltration process. [ABSTRACT FROM AUTHOR]

Lead zirconate titanate (PZT) films were deposited on platinized silicon substrates by spin coating using PZT sols containing polyvinylpyrrolidone (PVP) as an additive. PZT films with a 60/40 composition and a thickness of up to 8 μm were fabricated by repeating the deposition process 15 times on highly oriented (100) and (111) seed layers with the same composition. The films grew well in the direction of the seed layers and had a uniform and smooth surface without any cracks. As the thickness of the films increased, the grain size remained almost the same, but the effective d33 value increased steadily. The thickness dependence of the piezoelectric properties was attributed to the residual stress of the films. [ABSTRACT FROM AUTHOR]

This study examined the effects of permanent residual compressive stress on the ferroelectric properties of PbZrxTi1-xO3 (PZT) films that was induced during cooling after annealing. PZT films were deposited on the tensile side of elastically bent silicon substrates by rf magnetron sputtering using a single oxide target. Compressive stress was induced on the film by removing the substrate from the holder immediately after annealing. The compressive stress effectively compensated for the inherent tensile stress that had developed during cooling. The ferroelectric properties were enhanced markedly by the induced stress; the remnant polarization and the saturation polarization increased by 35% and 24%, respectively, while the coercive field did not change much. Contrary to the ferroelectric properties, the dielectric properties decreased slightly by the stress. [ABSTRACT FROM AUTHOR]

Fluoridated hydroxyapatite (FHA) powders were fabricated by a solid-state reaction, and their dense bodies were obtained by sintering at 1350°C. The biological performance of FHAs was evaluated and compared with that of pure hydroxyapatite (HA). The fluoridation of FHAs was confirmed by the changes in their lattice parameters. Human osteoblast-like cells attached and proliferated well on all of the FHAs, including pure FA. The proliferation and differentiation levels of the cells on FHAs were similar to those on pure HA. This finding suggests that the FHAs possess cell viability and activity comparable to pure HA, and thus are potentially applicable as hard tissue substitutes. [ABSTRACT FROM AUTHOR]

A ceramic-ceramic actuator composed of two piezoelectric ceramic layers with opposite poling directions was developed. One layer of the actuator had a high coercive electric field (PZT (Pb(Zr,Ti)O3)-I; Ec = 1.1 kV/mm), while the other had a relatively low coercive electric field (PZT-II; Ec = 0.6 kV/mm). The actuator was fabricated by cofiring a green compact composed of the PZT-I powder on top of the PZT-II powder. When an electric field > 1.1 kV/mm was applied to the sintered body, the whole specimen was poled in one direction. Subsequently, by applying a field between 0.6 and 1.1 kV/mm, only the PZT-II layer was switched to the other direction. When an electric field was applied to this oppositely poled two-layer specimen, one layer of the specimen expanded while the other layer shrank. As a result of these reverse dilations, the actuator was bent into a dome shape, yielding a large axial displacement at the center. The displacement of this actuator with dimensions of 20 mm (diameter) × 1 mm (thickness) was 16 μm at 0.9 kV/mm. [ABSTRACT FROM AUTHOR]

Highly oriented lead zirconate titanate [Pb(Zr,Ti)O3 PZT] thin films were deposited on Pt/Ti/SiO2/Si and glass substrates by the sol-gel method using lanthanum nitrate as a buffer layer. When the lanthanum nitrate buffer layer was annealed at temperatures between 450 and 550 °C, the PZT layer coated onto this buffer layer showed strong (100) orientation. The film deposited on the buffer layer had this orientation, regardless of the other deposition conditions, such as the pyrolysis temperature, pyrolysis time, annealing temperature, and heating rate. The lanthanum nitrate huller layer also acted as a very effective diffusion barrier against Ph-Si interdiffusion, thus allowing for the direct deposition of PZT films on Si, SiO2/Si, and glass substrates. Using this huller layer, highly oriented PZT film was fabricated stably and reproducibly, regardless of substrate material and the coating conditions. The nature of the lanthanum nitrate buffer layer and its role in the growth of the highly (100) oriented PZT films were investigated. [ABSTRACT FROM AUTHOR]

Lead zirconate titanate (PZT) films were deposited on platinized silicon substrates by spin coating using PZT sols containing polyvinylpyrrolidone (PVP) as an additive. Single-layered 1-μm-thick PZT films with 60/40 composition were fabricated using two successive spin coatings followed by a single heat treatment step. The crack formation was effectively suppressed by the presence of nanosized pores which were generated during the heat treatment. The film has a preferred orientation corresponding to the (100) crystallographic direction. The ferroelectric and piezoelectric properties of the specimen were comparable to those of a film with same composition and thickness but prepared by the conventional sol-gel procedure. [ABSTRACT FROM AUTHOR]

To improve the biocompatibility of Ti-based metal implants, a hydroxyapatite (HA) coating layer was formed on the surface by electron-beam deposition. The dissolution rate of the coating layer was strongly dependent on the layer's calcium/ phosphorus (Ca/P) ratio. Layers with a Carp ratio close to that of crystalline HA (Ca/P = 1.67) showed good stability in a physiologic saline solution. When the layer was crystallized by heat treatment in air at temperatures between 400° and 500°C, the stability was enhanced further while maintaining good interracial bonding strength with the substrate. Preliminary in vivo tests on rabbits indicated that heat treatment and the resultant enhancement in stability are beneficial for bone attachment to the implants. [ABSTRACT FROM AUTHOR]

Porous bioceramics, such as hydroxyapatite (HA), tricalcium phosphate (TCP), and biphasic HA/TCP, were fabricated using the polyurethane sponge technique. The porosity of the ceramics was controlled by a multiple coating of the porous body. When a porous body was produced by a single coating, the porosity was ∼90%, and the pores were completely interconnected. When the sintered body was coated five times after the porous network had been made, the porosity decreased to 65%. As the porosity decreased, the strength increased exponentially. The TCP exhibited the highest dissolution rate in a Ringer's solution, and the HA had the lowest rate. The biphasic HA/TCP showed an intermediate dissolution rate. [ABSTRACT FROM AUTHOR]

The oxidation behavior and its effect on the mechanical properties of fibrous monolith Si[sub 3]N[sub 4]/BN after exposure to air at temperatures ranging from 1000° to 1400°C for up to 20 h were investigated. After exposure at 1000°C, only the BN cell boundary was oxidized, forming a B[sub 2]O[sub 3] liquid phase. With increasing exposure temperature, the Si[sub 3]N[sub 4] cells began to oxidize, forming crystalline Y[sub 2]Si[sub 2]O[sub 7], SiO[sub 2], and silicate glass. However, in this case, a weight loss was observed due to extensive vaporization of the B[sub 2]O[sub 3] liquid. After exposure at 1400°C, large Y[sub 2]Si[sub 2]O[sub 7] crystals with a glassy phase formed near the BN cell boundaries. The oxidation behavior significantly affected the mechanical properties of the fibrous monolith. The flexural strength and work-of-fracture decreased with increasing exposure temperature, while the noncatastrophic failure was maintained. [ABSTRACT FROM AUTHOR]

A three-layered composite, composed of a strong outer layer (monolithic S[sub 3]N[sub 4]) and a tough inner layer (fibrous Si[sub 3]N[sub 4]/BN monolith), was fabricated by hot-pressing. For the inner layer, a Si[sub 3]N[sub 4]-polymer fiber made by extrusion was coated by dipping it into a 20 wt% BN-containing slurry. The threelayered composite exhibited excellent mechanical properties, including high strength, work of fracture, and crack resistance, because of the combination of a strong outer layer and a tough inner layer. In other words, the strong outer layer withheld the applied stress, while the tough inner layer promoted crack interactions through the weak BN cell boundaries. Also, the residual thermal stress on the surface due to the anisotropy in the coefficient of thermal expansion of BN affected a median/radial crack generation after indentation. [ABSTRACT FROM AUTHOR]

Examines the reaction sentering and mechanical properties of hydroxyapatite-zirconia composites with calcium fluoride additions. Improvement of flexural strength and fracture toughness of the composites; Observation of microstructure of the specimens by the use of scanning electron microscopy.

Examines the effects of manganese ion diffusion on the microstructure evolution of lead lanthanum zirconate titanate (PLZT) ceramics. Applications of PLZT ceramics to the electrooptic industry; Characteristics of the microstructure of PLZT; Increase in the rate of dentification at the Mn-doped region.

Investigates the effect of Al2O3 addition on the densification behavior of ceramics. Nonoxide ceramics that have been found to be effective as sintering additives; Observation that small amounts of oxides are effective in improving the sinterability of nonoxide ceramics; High hardness and light weight of certain ceramics.

The microstructural evolution and piezoelectric properties of lead-free ceramics (0.98-x)(Na0.5Bi0.5)TiO3-x(Na0.5K0.5)NbO3-0.02BaTiO3 (0 ? x ? 0.98, abbreviated as (0.98-x)NBT-xNKN-0.02BT) were investigated. The effects of the amount of NKN on the crystal structure, microstructural evolution, and piezoelectric properties were examined. The 0.93NBT-0.05NKN-0.02BT ceramics having a lower NKN content gave good performances with piezoelectric properties of d33 = 140 pC/N and kp = 21%, because of the soft additive Nb5+ ions at the B sites. However, a paraelectric cubic phase was observed in the wide range of compositions between x = 0.1 and x = 0.9. At a higher NKN content of x > 0.9, a morphotropic phase boundary (MPB) between the tetragonal and orthorhombic phases was found in the 0.015NBT-0.965NKN-0.02BT ceramics, and the piezoelectric properties were enhanced (d33 = 135 pC/N, kp = 29%). The piezoelectric properties of this system were closely related to its crystal structure. [ABSTRACT FROM AUTHOR]

Thick and crack-free Pb(Zr,Ti)O3 [PZT] films were fabricated on platinized silicon substrates by a multisputtering technique. The PZT films were deposited on the Si substrate by the radio frequency magnetron sputtering method using a single oxide target. As the film became thicker, its grain size increased. Therefore, the microstructure of the film was able to be controlled by repeatedly depositing thin layers. In addition, by using a seed layer with the same composition but a much smaller grain size, it was possible to further reduce the grain size of the film. When the film had a small in-plane grain size and a fibrous columnar structure, it was highly resistant to cracking, presumably because of its enhanced strength and structural stability. By exploiting these phenomena, highly dense, crack-free, and thick PZT films were successfully deposited up to a thickness of about 5 µm. The evolution of the crystallographic orientation of the film as a function of its thickness was also observed and correlated with the total strain energy of the system. [ABSTRACT FROM AUTHOR]

Highly dense and crack-free Pb(Zr,Ti)O3 (PZT) thick films with a controlled microstructure and orientation were deposited on a platinized silicon substrate by the radio frequency magnetron sputtering method using a single oxide target. The microstructure and orientation of the films were adjusted by applying a thin (100) PZT seed layer by the sol-gel method and subsequent repeated sputtering. When a thin layer was deposited on the seed layer, the film had small grains with a columnar structure. However, as the film became thicker, it developed a large and non-columnar grain structure. Therefore, reducing the thickness of the film per deposition allowed the columnar microstructure to be maintained. The (100) orientation of the film was able to be maintained by depositing it on a (100) oriented seed layer. PZT thick films with controlled orientations and microstructures were successfully deposited up to a thickness of about 5 µm, and their ferroelectric and piezoelectric properties were characterized. [ABSTRACT FROM AUTHOR]

Highly (100)- and (111)-oriented lead magnesium niobate-lead zirconate titanate (PMN-PZT) films were deposited on Pt(111)/Ti/SiO2/Si substrates using a sol containing polyvinylpyrrolidone (PVP). The molar ratio of Zr/Ti in the PZT was fixed at 60/40, and the PMN content was changed in the range of 0-30 mol%. The films had a dense and columnar microstructure with a thickness of about 1 µm as a result of being spun four times. The crystallographic orientation of the films was controlled by adjusting the pyrolysis temperature; a (100) orientation was obtained by pyrolyzing at 300 °C and a (111) orientation by pyrolyzing at 350 °C. The electrical properties of the films were strongly dependent on the crystallographic orientation and PMN content. With increasing PMN content, the dielectric constant of all of the films increased. On the other hand, the remnant polarization of the (111)-oriented films decreased steadily with increasing PMN content, while that of the (100)-oriented films remained unchanged up to a PMN content of 20%. The piezoelectric coefficients of the (100)-oriented film were consistently higher than those of the (111)-oriented film with the same composition. The highest piezoelectric coefficient was observed for the (100)-oriented film with a composition of 0.2PMN-0.8PZT, indicating the morphotropic phase boundary between the rhombohedral PZT phase and the pseudocubic PMN phase is in the vicinity of this composition. [ABSTRACT FROM AUTHOR]

Objective: Biodegradable poly-L-lactic acid (PLLA) with a highly biocompatible surface via tantalum (Ta) ion implantation can be an innovative solution for the problems associated with current biodegradable stents. The purpose of this study is to develop a Taimplanted PLLA stent for clinical use and to investigate its biological performance capabilities. Methods: A series of in vitro and in vivo tests were used to assess the biological performance of bare and Ta-implanted PLLA stents. The re-endothelialization ability and thrombogenicity were examined through in vitro endothelial cell and platelet adhesion tests. An in vivo swine model was used to evaluate the effects of Ta ion implantation on subacute restenosis and thrombosis. Angiographic and histologic evaluations were conducted at one, two and three months post-treatment. Results: The Ta-implanted PLLA stent was successfully fabricated, exhibiting a smooth surface morphology and modified layer integration. After Ta ion implantation, the surface properties were more favorable for rapid endothelialization and for less platelet attachment compared to the bare PLLA stent. In an in vivo animal test, follow-up angiography showed no evidence of in-stent stenosis in either group. In a microscopic histologic examination, luminal thrombus formation was significantly suppressed in the Ta-implanted PLLA stent group according to the 2-month follow-up assessment (21.2% vs. 63.9%, p=0.005). Cells positive for CD 68, a marker for the monocyte lineage, were less frequently identified around the Ta-implanted PLLA stent in the 1-month follow-up assessments. Conclusion: The use of a Ta-implanted PLLA stent appears to promote re-endothelialization and anti-thrombogenicity. [ABSTRACT FROM AUTHOR]