Papers by Author: Wen Jian Weng

Abstract: Srm-3Bi4TimO3m+3 (m =3, 4, 5, and 6) bulk ceramics were prepared by conventional solid-state reaction process. Their phase structures and morphologies were observed by XRD and SEM respectively. The dielectric properties and hysteresis loops of the ceramics were measured by impedance analyzer and hysteresis meter respectively. Results showed that the lattice parameters along the c axis are 32.79, 41.11, 48.83, and 58.17Ǻ for m=3, 4, 5, and 6 respectively. The microstructures of plate-like crystalline phases are shown in all the ceramics with different m. Curie temperature of Srm-3Bi4TimO3m+3 decreases from 668°C to 295°C with increasing m from 3 to 6. The remnant polarizations Pr are 32.46 and 19.44 μC/cm2 for odd m of 3 and 5, and 11.84 and 10.58 μC/cm2 for even m of 4 and 6 respectively.

Abstract: Lead zirconate titanate (PZT) ceramics are of great technological interest due to their excellent piezoelectric and ferroelectric properties. In the present work, a modified coprecipitation method for PZT phase preparation was proposed by combining the advantages of partial oxalate method and coprecipitation method. Firstly, the zirconium and titanium hydroxides were coprecipitated to form the precipitate of (Zr,Ti)O(OH)2. Then, the lead hydroxide was precipitated into a ammonia solution in which the precipitate of (Zr,Ti)O(OH)2 obtained above was well dispersed. The single perovskite PZT phase was directly synthesized without any intermediate phase appearing by calcinations the precursor at 500oC-800oC. The method proposed in the paper is an effective route for the synthesis of PZT powders.

Abstract: The effect of SrO/BaO ratio on the phase structure of the (1-x)BaO.xSrO.0.7TiO2.0.3Nb2O5 composite ceramics was investigated by XRD and SEM. The results showed that the SrO/BaO ratio increased in the perovskite phase and kept almost constant in the tungsten bronze phase as the content of SrO increased in the composite system. The constant SrO/BaO ratio in the tungsten bronze phase was about 0.667. The crystal lattices of the perovskite phase in the composite system were larger and smaller respectively than that in pure (1-x)BaO.xSrO.TiO2 system when SrO/BaO ratio were respectively <0.667 and >0.667. The crystal lattices of the perovskite phases in both systems showed the same crystal lattices when SrO/BaO = 0.667. Affected by the SrO/BaO ratio required in the tungsten bronze phase in composite system, the contents and average grain size of the perovskite phase decreased, while the content of tungsten bronze phase increased as the SrO/BaO ratio increased.

Abstract: Silver dispersed lead titanate films were prepared with different Pb/Ti ratio precursors. The influence of lead excess in precursor on the formation and dielectric properties of silver-dispersed lead titanate film was investigated. Firstly, Pb excess in precursor will eliminate the formation of pyrochlore PbTi3O7 and increase c/a ratio of perovskite PbTiO3. Secondly, excessive Pb will react with silver, and they can produce volatile product, which evaporate during heat treatment process. The volatility of the reaction product varies with the increase in lead excess. When lead excess is low (Pb/Ti=1.1), volatility of reaction product is high. At this time, only small amount of silver remain in the film. The remanent silver aggregate to form small silver particles. When lead excess is high (Pb/Ti=1.2 and Pb/Ti=1.3), volatility of reaction product gradually becomes poor. At this time, the content of remanent silver in the film increase with the increase in lead excess. Compared with the film prepared with low Pb/Ti ratio, the dispersive degree of silver in film prepared with high Pb/Ti ratio is higher. Due to the decrease of remanent silver content in the film, dielectric constant and dissipation factor both decrease when Pb/Ti initially increase from 1 to 1.1. And after that, dielectric constant and dissipation factor both increase with the addition of excessive Pb in precursor, due to the increase in the content and dispersion degree of silver, and increase in c/a ratio of PbTiO3 lattice with the addition of excess Pb. The film prepared with appropriate excessive lead (Pb/Ti=1.3) precursor expresses higher dielectric constant and lower dissipation factor than the film prepared with stoichiometric Pb/Ti ratio.

Abstract: BST/PLT composite thick films with various content of PbO-B2O3 glass additive from 5mol% to 25mol% were successfully prepared by screen-printing the paste onto alumina substrates. XRD, SEM and impedance meter were used to analyze the phase structures, morphologies and dielectric properties of the thick films. The results showed that the BST phase has no interaction with PbO-B2O3 glass in the composite thick films at 750 oC. Diffusion between PLT phase and PbO-B2O3 glass phase occurs and the c axis of PLT phase in thick films reduces slightly. The high infiltration between the glass phase and particles densify the composite thick films and the uniform microstructure can be obtained in the thick films with PbO-B2O3 glass additive content of 10mol%. Good temperature stability of dielectric properties is achieved with the 25mol% content of PbO-B2O3 glass additive and the variance of the relative dielectric constant in the temperature range between 0oC and 300oC is 15%.

Abstract: Nanocomposites consisting of biologically active ions, which can enhance cell viability and activate gene expression, are regarded as promising bone regenerative materials. We report a new method for the layer-by-layer (LbL) assembly of biologically active strontium ions in the core-shell Silica@OCP system for an efficient controlled-release. The strontium ions were assembled by using a pH-responsive electrostatic interaction to generate three-dimensional gradients within the silica nanospheres, and then a porous OCP (octacalcium phosphate) shells was coated on the microunits tailored by polyelectrolyte molecules. This core-shell-like microstructure can achieve the multicomponents administration and controlled release of essential trace silicon and zinc ions based on the barrier effect of OCP shell and pH-dependent manner, respectively.

Abstract: Bone-Like Microstructured β-TCP/Collagen Layer on Fluoridated Hydroxyapatite Coating, which could able to create a biodegradation layer with enhancing bone formation, was prepared in wet synthesis. The formation of the layer was characterized and discussed.

Abstract: It is known that the organic molecules can provide effective means to tailor the surface properties of the biodegradable ceramic. In this paper, a long-chain organic silane- Octadecyltrichlorosilane(OTS) was used as coupling agent and hydroxyapatite(HA) was the candidate ceramic. Samples were characterized by means of XPS technique. XPS results indicated that Si-O-P bond was formed on the HA surface after surface-modification, which means OTS was grafted onto the HA surface through covalent bond , XPS results also showed that by regulating the surface-modification process Si(Atomic percentage) content on HA surface could be changed from 0 to 2.88%.

Abstract: Two starting collagens, sponge and floc collagen, were used to prepare collagen/tricalcium phosphate (TCP) composites. The resulting composites were porous and had 200μm pore size. However, there was a difference in the microstructure of the pore walls for the composites derived from the two collagens, the pore walls in sponge collagen/TCP composite were still porous and had 200 nm micropores size, TCP particles were trapped in collagen matrices. While floc collagen/TCP composite had smooth and dense walls in which TCP particles were embedded. The difference could be attributed to the starting collagen with different status. Sponge collagen has a soft structure, which easily becomes disassembled fibrils during alkali treatment, the disassembled fibrils are integrated again to form a dense morphology for pore walls after freeze-drying. While floc collagen has already a low disassembly degree, the alkali treatment could not be able to separate the fibrils, this remains as micropores in pore walls after freeze-drying. Both porous composites are significant in bone tissue engineering or regeneration. MTT test results showed the two composites had good cytocompatibility, and sponge collagen/TCP composite was somewhat better than floc collagen/TCP composite, which could result from that micropores derived roughness in pore walls of sponge collagen/TCP composite is suitable for cell growth.

Abstract: Porous β-tricalcium phosphate (β-TCP)/ Poly L-lactic acid (PLLA) composites were prepared by thermally induced phase separation method. The results showed that the composite had an interconnected pore structure with ～200μm macropores. The inorganic particle content in the composites varied from 50% to 80% and these particles were homogeneously dispersed in PLLA matrix. The composites obtained in this study could act as a promising scaffold for bone tissue engineering because of the pore structure and the mechanical properties.