Papers by Author: Jian Bao Li

Abstract: SiC/Al₂O₃ composite porous ceramics were prepared by an in situ reaction bonding technique and sintering in air with SiC and A1(OH)₃ as starting materials. The pores in the ceramics were formed by stacking particles of SiC and A1₂O₃. The surface of SiC was oxidized to SiO₂ at high temperature. With further increasing the temperature, SiO₂ reacted with A1₂O₃ to form mullite. The reaction bonding characteristics, phase composition, and mechanical strength as well as microstructure of porous SiC ceramics were investigated.

Abstract: Silicon carbide ceramic composite filter membrane materials were prepared by dry pressure molding and synchronous sintering process at sintering temperature of 1300oC for 3h. and research the influence of on the molding pressure structure of SiC filtration membrane,effect of particle size on porosity, average pore size and filter pressure drop of filtration membrane, SEM was performed to examine the morphology, The porosity ,average pore size and filter pressure drop of filtration membrane were tested by Archimedes method ,bubble point method and filter pressure drop instrument. It is demonstrated that while the molding pressure (F) varied from 1MPa to 10MPa, the filter membrane material achieved preferable morphology and best performance when F equals to 5MPa. Under this modeling pressure, while silicon carbide particle size increased from 1 to 23μm, the pore ratio decreased from 48.0% to 36.2% and the average pore size increased from 0.35μm to 9.4μm, while the air gas velocity changed from 0 to 0.112m/s, the filter pressure drop increased, when the velocity is stable, the filter pressure drop reduced as the silicon carbide particle size.

Abstract: Barium titanate (BaTiO3) ceramics with grain size varied from 1000 to 8 nm were prepared by two step sintering method (TSS) and spark plasma sintering (SPS), respectively. Mixture structures of BaTiO3 ceramics were proved by in-situ temperature high resolution x-ray diffraction. Multiple ferroelectric domains present in nano-crystalline BaTiO3 ceramics were observed by transmission electron microscope. The evolution of phase transitions supported the existence of intrinsic mechanism. Dielectric loss of fine grain size BaTiO3 was higher than coarse grain size during Curie phase transition due to diffuse phase transition and grain boundary effects.

Abstract: BaZr_0.25Ti_0.75O₃ (BZT) ceramics were prepared by conventional ceramic process at a relatively low sintering temperature and with an addition of Li₂O as the liquid-phase sintering aid. X-ray diffraction characterized results showed that the main crystal phase of the samples with 1.0wt% Li₂O additive sintered at 1050°C～1250°C for 4h presented perovskite structure. The dielectric properties of BZT ceramics have been investigated. The dielectric constant of 1.0wt% Li₂O doped BZT sintered at 1150°C decreased, and the dielectric loss increased by 0.0012 compared with that of the pure BZT sintered at 1450°C.

Abstract: MnO₂ nanostructure was synthesized via a redox reaction of potassium permanganate in hydrochloric acid solution below 100°C at open environment. The effects of pH value in solution and reaction temperature on the crystal structure and morphology of MnO₂ were investigated. It was revealed that layer folded δ-MnO₂ microspheres were obtained at low reaction temperature and low HCl concentration, whereas α-MnO₂ single-crystal nanorods were fabricated with increasing reaction temperature and HCl concentration. The possible formation mechanism of δ-MnO₂ microspheres and α-MnO₂ nanorods is suggested.

Abstract: Titania nanotube arrays were fabricated in deionize water and glycerol mixed electrolyte containing a certain amount of NH₄F. Three different polishing methods were used for pretreatment of Ti substrates: polished by hand with abrasive paper, by polishing machine, or by chemical polishing fluid (HF:HNO₃=1:4, in volumetric ratio). The morphology of three different samples were imaged by scanning electron microscopy, and their photoelectrical properties were studied as well. Experimental results showed that Titania nanotube arrays grown on the Ti substrate and polished by polishing fluid has highly-ordered and well-defined nanotube structure. The effects of anodization potential and duration on synthesis of highly-ordered TiO₂ nanotubes were also studied in this paper. Both the layer thickness and nanotube diameter linearly increase with the increasing potential. The layer thickness also increases with prolongation of anodization time. By optimizing the preparation conditions, we can successfully control the geometrical structure of TiO₂ nanotube arrays with diameters in the range between 50 and 200 nm and the layer thickness between 800 and 2000 nm.