Preparation of Fibrous, Porous Hydroxyapatite Ceramics from Hydroxyapatite Whiskers

Hydroxyapatite (HAp) whiskers have been used to prepare fibrous, porous HAp ceramics. The fibrous microstructure was retained in all cases after hot-pressing the HAp whiskers at 800-900°C (1 h, 30 MPa). The fracture path in the fibrous, porous HAp ceramics was partially intergranular, indicating the occurrence of crack deflection, bridging, and pull-out effects. When the whiskers were hot-pressed at 1000-1100°C (1 h, 30 MPa), only large equiaxed grains were present in the HAp ceramics; thus no toughening occurred. When nonstoichiometric HAp whiskers were used to fabricate a porous body, β-TCP precipitated on the whisker surface without destroying the fibrous microstructure. Sintering the HAp whiskers is thus an easy way for in situ fabrication of HAp/β-TCP fibrous, porous materials with a controlled biodegradation rate.     

多孔羟基磷灰石材料的研究及制备

本文综述了羟基磷灰石陶瓷的合成方法、成形工艺及各种性能。     

多孔羟基磷灰石的制备及其性能研究

以多孔支架材料的设计出发,采用化学共沉淀法制备了纳米羟基磷灰石粉末,并通过添加造孔剂工艺,于800℃烧结处理4 h后经过水洗处理除去造孔剂,再于1 250℃高温处理3 h,得到不同含量比的多孔羟基磷灰石生物陶瓷。通过一系列性能表征包括孔洞结构、物相组成、力学性能以及孔隙率测试等,研究多孔羟基磷灰石陶瓷性能。     

Barium Titanate Ceramics with High Piezoelectricity Fabricated from Fibrous Particles

Barium titanate ceramics with high degrees of c-axis orientation were fabricated from fibrous particles. The maximum piezoelectric constant, d₃₃, obtained was ≅270 pC/N, which is much higher than values reported previously.     

羟基磷灰石多孔陶瓷的制备和性能

本工作采用造孔剂（ＰＦＡ）干压工艺制备羟基磷灰石多孔陶瓷。通过两种造孔剂制得的多孔羟基磷灰石陶瓷性能的对比,发现两种造孔剂可制得多孔羟基磷灰石陶瓷。并借助ＳＥＭ、压汞仪等仪器和设备,对多孔体的性能进行了测试,讨论了造孔剂粒径、添加量及形状对多孔体性能的影响,结果表明：采用碳粉作造孔剂制得的多孔体具有较高的强度,而采用聚甲基丙烯酸甲酯（ＰＭＭＡ）作造孔剂制得的多孔体孔径的可控性高。     

Transparent Hydroxyapatite Ceramics through Gelcasting and Low-Temperature Sintering

Transparent hydroxyapatite (HAP) was prepared by sintering gel-cast powder compacts at 1000°C for 2 h; the resultant HAP material was studied using X-ray diffractometry, transmission electron microscopy, scanning electron microscopy, and microhardness measurement. Nanoscale HAP crystallites were prepared using a precipitation method that involved calcium nitrate and ammonium dihydrogen orthophosphate solutions; the preparation was conducted at a temperature of 0°C. The precipitate was gel-cast and sintered at 1000°C in the form of a transparent ceramic that had a uniform grain size of 250 μm. The maximum Vickers microhardness obtained for a sample sintered at 1000°C was 6.57 GPa. The sintering behavior of gel-cast samples prepared from high-temperature-precipitated HAP was compared with that of material prepared at 0°C.     

Carbon Dioxide Sensor Mechanism of Porous Hydroxyapatite Ceramics

Hydroxyapatite and Cl⁻ -containing hydroxyapatite powders are prepared and characterized. Reversible substitution of CO^2-₃ for OH⁻ at the surface is presumed to be responsible for the sensor function. The role of Cl⁻, which is necessary to realize the sensor function and is incorporated during soaking treatment, is considered as follows. It may reduce the strain caused by the incorporation of CO^2-₃ (which is larger than OH⁻), and, hence, promote the reversible substitution reaction. This behavior is presumed because Cl⁻ -containing hydroxyapatite samples exhibit sensor characteristics typical of CO₂ without any treatment.     

Effect of Sodium Phosphate on Sintering of Hydroxyapatite Ceramics

The effect of Na₃PO₄ additive introduced into hydroxyapatite ceramics in amounts of 1 and 2% on their sintering shrinkage, formation of microstructure, phase composition, and mechanical properties is considered. The conditions for maximum mechanical properties of densely sintered ceramics are determined.     

New Processing Technique for Hydroxyapatite Ceramics by the Hydrothermal Hot-Pressing Method

A new processing technique for preparing hyroxyapatite (HAp) ceramics has been developed using the hydrothermal hot-pressing (HHP) method. Powder mixed dibasic calcium phosphate dihydrate and calcium hydroxide mixed with a Ca/P ratio of 1.67 was treated at 150°C and 40 MPa. The HHP method with the selection of the powder enabled the HAp to be solidified at the low temperature. The resulting HAp ceramics had a tensile strength of approximately 10 MPa. Furthermore, the HAp ceramics possessed a lamellar microstructure and high porosity.     

Effects of an Electric Field on the Fracture Toughness of Poled Lead Zirconate Titanate Ceramics

Compact tension tests and indentation-fracture tests have been conducted to study the effects of an applied electric field on the fracture toughness ( K _{I C} ) of poled commercial lead zirconate titanate (PZT) ceramics. The experimental results show that an applied electric field, either parallel or antiparallel to the poling direction, considerably reduces the K _{I C} value of the PZT ceramics. The reduction in K _{I C} for a negative field is larger than that for a positive field of the same strength. The failure mode in the PZT ceramics is basically transgranular, insensitive to the applied electric field.     

Enhanced Ferroelectric Phase Stability and High Temperature Piezoelectricity in PN Ceramics via Multisite Co‐Doping

The tungsten bronze‐type lead metaniobate (PbNb₂O₆, PN) is a promising material for high‐temperature piezoelectric devices, while its application is limited by the difficulty in fabrication. In this study, the microstructure and electrical properties of Ca‐doped PN and Ca, Mn‐co‐doped PN ceramics sintered at different temperatures were investigated. Doping promoted the formation of the originally metastable ferroelectric orthorhombic phase. This might be partly attributed to the increased lattice distortion of the orthorhombic phase in the doped samples compared to that reported for pure PN. However, in single A‐site Ca‐doped PN the ferroelectric orthorhombic structure showed a low stability and started to transform to paraelectric phase far below 300°C, resulting in unstable high temperature piezoelectric properties. Interestingly, such a phase transition was completely depressed by A‐site Ca and multisite Mn‐co‐doping, which also improved the piezoelectric performance (d₃₃ = 71 pC/N) and thermal stability in both structure and piezoelectricity. The better stability and performance of the co‐doped samples were explained by the improved sintering behavior and poling efficiency as well as its ability to occupy different sites in the TTB lattice.     

Porous Hydroxyapatite Scaffolds Coated With Bioactive Apatite–Wollastonite Glass–Ceramics

The objective of this study was to fabricate porous hydroxyapatite (HA) scaffolds coated with bioactive A/W glass–ceramics and to examine their mechanical and biological properties. Firstly, the HA scaffolds were prepared by the polymeric sponge replication method, and then A/W glasses were coated on the surface of the struts. All of the scaffolds had a highly porous structure with well-interconnected pores. It was observed that the bioactive glass coating markedly increased the strength of the HA scaffolds. This enhancement was attributed to the formation of a dense and strong coating layer on the weak HA struts. The in vitro bioactivities of the scaffolds were markedly improved by the coatings. When the coated scaffolds were soaked in a simulated body fluid (SBF), the bone-like apatite crystals were well mineralized on their surfaces. Osteoblast-like cells (MC3T3) adhered, spread, and grew well on the porous scaffolds. The cells placed on the glass-coated HA scaffold showed a higher proliferation rate and alkaline phosphatase (ALP) activity than those on the pure HA scaffold. These results demonstrate that the bioactive glass coating is effective in improving the strength and bioactivity of the porous HA scaffolds.     

(1-x)NBT-xBaTiO3系陶瓷材料制备过程中极化条件的研究

选取部分样品，采用不同的极化电压、极化温度和保温时间，测试其压电性能，确定最佳的极化工艺制度。     

Effects of an Applied Electric Field on the Modulus of Rupture of Poled Lead Zirconate Titanate Ceramics

The effects of applied dc electric fields of ±10 kV/cm on the modulus of rupture of poled PZT-841 ceramics were studied using three-point bending tests. At each level of the applied electric field, 54 or 55 samples were tested and the data were statistically analyzed. The results showed that the measured moduli of rupture followed a Weibull distribution with a Weibull modulus of 10.6 when no electric field was applied. When the applied electric field was either parallel or antiparallel to the poling direction, the distribution of the modulus of rupture revealed two peaks and was fitted by a two-peak Weibull distribution. One peak occurred at about 95 MPa, approximately the same as that without the presence of the applied electric field, while the other peak occurred around 50 MPa under either a positive or a negative electric field. Obviously, either a positive or a negative electric field assisted the applied mechanical loading to fracture the samples.     

(1-x)NBT-xBaTiO3系陶瓷材料制备过程中极化条件的研究

选取部分样品，采用不同的极化电压、极化温度和保温时间，测试其压电性能，确定最佳的极化工艺制度。     

Controlled Crystallization of Calcite Under Surface Electric Field Due to Polarized Hydroxyapatite Ceramics

We examined effects of surface electric fields for the crystallization of calcite on polarized hydroxyapatite ceramics with and without polyacrylic acid (PAA) as soluble additive. Both on negatively and positively charged surfaces without PAA, the only precipitates were rhombohedra calcite crystals with the face of the {10.4} plane favorably oriented parallel to the surfaces. This oriented growth was explained by the nucleation theory in the presence of an external electric field. However, the addition of PAA drastically changed the situation of the calcite crystals, i.e., the crystallites were the hemispheric aggregates of calcite needles with a facetted rhombohedral {10.4} end face and flat island-shaped aggregates of ones with a rough (00.1) end face having a triangular shape. The calcite needles grew along the crystallographic [00.1] axis. This oriented growth was explained by epitaxy on the PAA–Ca²⁺ complexes adsorbing on the surfaces. The morphology of the PAA–Ca²⁺ complex assemblies adsorbing on the surfaces before the calcite nucleation was an important factor to control the structure of calcite aggregates formed following. This morphology was controlled by properties of the surface electric field and the spatial distribution of the negatively and positively charged sites in the PAA–Ca²⁺ complexes.     

Piezoelectricity in acrylonitrile/methylacrylate copolymer

Summary The piezoelectric strain coefficient d₁₃ of stretched and unstretched acrylonitrile/methylacrylate copolymer films has been investigated as a function of poling conditions. The maximtun d₃₁ values obtained for stretched and unstretched films were around 3 and 0.85 pC/N, respectively. The time stability of piezoelectricity is relatively low.     

(1-x)NBT-xBaTiO3系陶瓷材料制备过程中极化条件的研究

选取部分样品,采用不同的极化电压、极化温度和保温时间,测试其压电性能,确定最佳的极化工艺制度。     

Domain Structure of Poled (K0.50Na0.50)1−xLixNbO3 Ceramics with Different Stabilities

Domain structure of several poled (K_0.50Na_0.50)_1?xLi_xNbO₃ ceramics (with chemical compositions of x = 0.03, 0.065, and 0.08, respectively) was investigated by means of observing the domain patterns with an acid‐etching technique. Among the three ceramics, the one with x = 0.03 is of orthorhombic phase and the other two are of tetragonal phase at room temperature. It was found that these ceramics possess distinctly different features of domain patterns and show a large difference in the time‐aging stability of piezoelectric properties. For the ceramic with x = 0.03, domain patterns consist of simply one single set or a few sets of parallel stripes inside the polycrystalline grains. In contrast, for those with x = 0.065 or 0.08, herringbone‐type patterns and a large number of watermarks are additionally observed. Furthermore, the ceramic with x = 0.03 was confirmed to have a much better time‐aging stability of piezoelectric properties than the other two. The results indicate that domain structure is more stable in orthorhombic phase than in tetragonal phase.