Papers by Author: Xiu Feng Wang

Abstract: Metastable crystal Bi₂SiO₅ has significant properties including dielectric, thermoelectricity and nonlinear optical properties. Metastable crystal Bi₂SiO₅ has been successfully prepared by melt cooling method in this study. Surface tension of high-temperature melt Bi₂SiO₅ was measured by Suspension method; metastable crystal Bi₂SiO₅ construction was assigned by IR(Infrared Radiation). The experimental result showed that Bi₂SiO₅ flux density decreased with the increasing temperature in 830-1095°C range; surface tension changed quadratic with the decreasing temperature. The [SiO₄]^4- anions of Bi₂SiO₅ originated from the isolated [SiO₄] tetrahedron in the glass to a chain connected structure.

Abstract: α-Al₂O₃ platelets were prepared in the interface of Na₂O-CaO-SiO₂ glass induced by Al. The morphology of the platelets was observed by Environmental Scanning Electron Microscopy (ESEM). The platelets are irregularly shaped at 720°C for 30mins and share mean thickness of 200nm. EDS shows that the platelets are rich in Si, reasonably due to the formation of Al-Si eutectic. At 1200°C, the prepared platelets have mean diameters between 400nm and 1000nm, most of which are aggregated and part through intergrowth. The crystals develop from the glass and can form good moistening with the glass matrix.

Abstract: α-Al₂O₃ platelets were prepared in the interface of Na₂O-CaO-SiO₂ glass induced by Al. Phase identification was accomplished by X-ray diffraction analysis. The morphology of the platelets was observed using an Environmental Scanning Electron Microscopy (ESEM). The changes for the mixtures of the Al powders and the glass powders that occurred during heating were characterized by a combination of differential scanning calorimetry (DSC) and thermalgravimety(TG) on a multi-functional instrument. Confirmed by XRD and ESEM, at 1200°C, the prepared platelets have mean diameters between 400nm and 1000nm. Most of them are aggregated and part of them through intergrowth. The crystals develop from the interface between glass and Al, and can form good moistening with the glass matrix. DSC/TG shows that γ-Al₂O₃ formed by oxidation of Al, transforms into α-Al₂O₃ and grow into the platelet α-Al₂O₃ crystals owing to the molten Al and the molten glass. On the other hand, part of the molten Al erodes into the glass and makes the deviation of the Na₂O-CaO-SiO₂ ternary system into Na₂O-Al₂O₃-SiO₂ ternary system, resulting in the formation of NaAlSiO₄.

Abstract: Pure Bi₁₂SiO₂₀ powder was successfully prepared by a molten salt method using Bi₂O₃ and SiO₂ as raw materials and using KCl-K₂CO₃ as flux at 635°C with the heating rate of 5°Cmin^-1. The phase composition and microstructure of these products were analyzed by X-ray diffraction and scanning electron microscopy, and the effects of the processing parameters, such as the ratio of Bi₂O₃/SiO₂, calciniation temperature, isothermal time and relative amount of salt, on the composition and particle size were investigated. The results indicated that regardless of changing the ratio of Bi₂O₃/SiO₂, calciniation temperature, isothermal time or relative amount of salt the reaction only yielded Bi₁₂SiO₂₀ without Bi₂SiO₅ and Bi₄Si₃O₁₂. Henceforth, KCl-K₂CO₃ molten salts may be considered as an ideal reaction medium to synthesize pure phase of Bi₁₂SiO₂₀. The particle size of Bi₁₂SiO₂₀ phase can be determined by changing the temperature, isothermal time and relative amount of salt.

Abstract: JPEG2000 algorithm has been developed based on the DWT techniques, which have shown how the results achieved in different areas in information technology can be applied to enhance the performance. Lossy image compression algorithms sacrifice perfect image reconstruction in favor of decreased storage requirements. Wavelets have become a popular technology for information redistribution for high-performance image compression algorithms. Lossy compression algorithms sacrifice perfect image reconstruction in favor of improved compression rates while minimizing image quality lossy.

Abstract: GA approach suitable for solving object Recognition problem is described and evaluated using a series of simple model problems. Usually GA calculation produces enormous amount of data that contains rich information, of which only a tiny section is commonly utilized runs through the design optimization. An application of Genetic Algorithm optimization with Noise characteristics would give many insights into how to allocate various image reconstruction options in different echelons, GA employing a global search might identify a better solution in an different area of the search space.

Abstract: A novel rapid prototyping technology for glass-alumina functionally gradient materials (G-A FGMs) based on the quick solidification of wax was proposed. The feature of the technology came from its layer-by-layer fabrication of the wax-glass/alumina composite layer. With the help of orthogonal experiment method, the influence of different parameters (sintering temperature, component ratio (the glass and the alumina), and number of layers) on the flexural strength of FGMs was discussed. Optimum conditions obtained from the above experiments were applied to prepare the G-A FGM with three layers. The G-A FGM was analyzed in detail, by observing it under an environmental scanning electron microscope (ESEM) coupled with an X-ray energy dispersive spectrometer (X-EDS). The results of orthogonal experiment show that number of layers is the principal parameter to the flexural strength of FGMs, component ratio is the secondary factor, and sintering temperature may be not an important factor. The special microstructure appears in the cross section of the G-A FGM, observed by ESEM. It is from the X-EDS graph concluded that alumina and glass probably react to form the special microstructure with part removal of wax.

Abstract: Hydroxyapatite (HA) doped with 3%yttria-stabilized 20wt% zirconia (ZrO2) ceramic were developed in order to produce a porous composite biomaterial by integrating the gel-casting technique with polymer sponge method with improved mechanical strength and controllable porous structure. The pore morphology, size, and distribution of the scaffolds were characterized using an electron microscope. The scaffolds prepared have an open, uniform and interconnected porous structure with a pore size of 300~500m. The porosity of the open pores in the scaffold can be controlled by changing HA-ZrO2 composite concentration and it is between 87%~35%. A compressive strength of 12MPa for HA-ZrO2 porous scaffolds with HA-ZrO2 concentration of 55wt% was achieved, which is comparable to that of cortical bone.

Abstract: A novel rapid prototyping manufacturing technology for glass-alumina functionally gradient materials (G-A FGMs) based on the quick solidification of wax was proposed. The feature of the technology came from its layer-by-layer fabrication of the wax-glass/alumina composite layer carved in accordance with the shape of each layer of the computer designed model and in situ casting of wax into the carved area. Removal of the wax in the G-A FGMs green body was investigated based on differential scanning calorimetry (DSC) analysis. Sintering properties of the G-A FGMs were discussed. Bending strength of the G-A FGMs was measured by a three-point flexural test. Microstructures of the prepared G-A FGMs were observed using environmental scanning electron microscope (ESEM) and the compositional distribution was determined according to energy dispersive spectrum (EDS). Samples were preliminarily and respectively held at 200°C and 300°C for a long time based on the DSC analysis. The range of the optimal sintering temperature is determined to be from 710°C to 720°C and the holding time is 30min. With the increasing alumina content, the bending strength increases and the maximum bending strength is 67.5MPa. There is no delamination of the G-A FGMs via ESEM. Homogeneous distribution of the ingredient materials is confirmed through EDS.

Abstract: Numerical modeling on falling of sodiumtetraborate aqueous solution drops as the initiator before the gelation of PVA-TiO2 suspensions was conducted. Effect of time and elevation angle of the PVA-TiO2 suspensions on the falling velocity of the sodiumtetraborate aqueous solution drops was analyzed. An ordinary differential equation was given. Integration of the ordinary differential equation was fulfilled using the fourth-order Runge-Kutta method in Matlab 6.5. From the model, a two-order nonlinear effect of time on the velocity of the drops during falling is determined and the quadratic term -3.408t2 serves as the time dependent air resistance. The component of the falling velocity along the suspensions increases with the increasing of the elevation angle. However, for the component vertical to the suspensions, with elevation angle increasing, it decreases.