Papers by Author: Ai Ying Wu

Abstract: A successful electrophoretic deposition (EPD) markedly depends on the stability of the suspension. In this study the role of Triethanolamine (TEA) as a stabilizer in EPD of thick films of TiTe₃O₈ is presented. TiTe₃O₈ powders were synthesized via a conventional solid-state-reaction method and dispersed in acetone with and without TEA. The stability of the suspensions was addressed by zeta-potential, UV light and FTIR measurements. The specific adsorption of TEA to TiTe₃O₈ particles results in a high zeta potential and improved stability of the suspensions, allowing the preparation of high quality TiTe₃O₈ thick films on Pt coated Si substrates. TiTe₃O₈ films sintered at 700 °C are dense and homogeneous.

Abstract: The main purpose of the present work is the sol-gel synthesis, structure and application of hybrid inorganic–organic hybrids based on different silica precursors and addition of the organic compound sepharose (SP). The structural evolution of the hybrid materials containing different amounts of SP is examined. Formation of silica nanocomposites by self-assembling processes was studied by AFM and roughness analysis. The average size of nanoparticles on the sample surface is about 7 to 14 nm and the formation of their self-organized structures is observed. The hybrids are used for immobilization of bacterial cells, producers of thermostable nitrilase. The biocatalysts show good operational stability for a long period-18 days, as well as high thermostability. The degradation capability is greater for the encapsulated cells in the hybrid matrix with 5% SP.

Abstract: Chain reorientation may be induced in polyvinylidene fluoride (PVDF) in its β-phase by applying a deformation perpendicular to the pre-oriented polymeric chains. This reorientation begins right after the yielding point and seems to be completed when the stress-strain curve stabilizes. As the deformation process plays an important role in the processing and optimisation properties of the material for practical applications, different deformation stress was applied to the PVDF lamellas and their topographic change and piezoelectric response were studied by means of scanning force microscopy in a piezo-response mode. The experimental results confirm the previously observed chain reorientation that occurs right after the yielding point and that is completed when the yielding region is passed. This reorientation is accompanied by a stretching of the granular structures observed in the topographical images and variations in the domain response. The observed results help to explain the variations in the macroscopic response of the material.

Abstract: Crystalline (Sr1-1.5xBix)TiO3 (SBiT) thin films (0.002 ≤ x ≤ 0.5) were prepared by sol-gel on Pt/TiO2/SiO2/Si substrates. Cubic monophasic SBiT films were obtained for samples with x ≤ 0.167. For films with x ≥ 0.267 a second phase identified as Bi4Ti3O12 was observed. The lattice parameter of SBiT films increases with increasing Bi content, similar to the variation observed in SBiT ceramics. No obviously variation of the grain size with the Bi content was observed. The dielectric constant ε´ at room temperature increases with increasing of Bi concentrations up to x ≤ 0.1. The loss tangent of Bi doped SrTiO3 films is approximately 0.05 and lower than undoped ST films at 10kHz. The higher values of ε´ of Bi doped ST films with x=0.1 and x=0.167 in comparison with undoped films may suppose the appearance of a dielectric anomaly at low temperatures, which will be dependent on the Bi content.

Abstract: In the current work two different routes, an alkoxide based sol-gel and an aqueous solution-gel route, were used to synthesize PZT (30/70) powders. The phase purity, morphology and particle size of both were studied by XRD, TEM and particle size analysis. The dispersion behavior of the powders in water was investigated by means of light scattering particle size analyzer and zeta potential measurements. The extent to which powder morphology, synthesis route and particle charge state relate to the resulting dispersion behaviour was established. Alkoxide sol-gel derived powders are better dispersed in aqueous media than aqueous solution-gel derived powders.