Papers by Author: Hai Bo Ouyang

Abstract: Zinc borate (4ZnO·B₂O₃·H₂O) crystallites at diverse pH values were prepared by a hydrothermal method. The phase composition, morphologies and photocatalytic properties of the samples were characterized by XRD, SEM, UV–vis spectro-scopy and UV–vis diffuse reflectance spectro-scopy. Results show that the 4ZnO·B₂O₃·H₂O microcrystalline obtained at pH=9 shows a new clintheriforms morphologies assembled by nanowiskers. Superior UV-light photocatalytic activity of the samples for MB, RhB and MO is observed especially higher than that of P25 for MB. These samples exhibit morphology-related ultraviolet absorbing ability with different optical band gaps from 4.01 eV to 4.22 eV. Band gaps are responsible for the highly UV-light photocatalytic activity.

Abstract: A B₂O₃-modified ZrSiO₄ outer coating was prepared by Pulsed arc Discharge Deposition on the surface of SiC bonding layer coated carbon fiber reinforced carbon (C/C) composites. The phase compositions of the prepared coatings were analyzed by X-ray diffraction (XRD), the morphologies of the multi-layer coatings were observed by scanning electron microscopy (SEM). The influence of pulsed arc discharge deposition electric voltage and time on the phase composition, microstructure of the mixed coatings was particularly investigated. And the invalidation behavior of the as-prepared coating coated samples at 1273K was analyzed. XRD results show that the outer layer of the coating was mainly composed of B₂O₃ and ZrSiO₄ phase. When the deposition electric voltage was 400V, single deposition time was 8 min, total time was 32min, the structure and thickness of the outer layer was compact and uniform. The coating prepared at optimal technological conditions could effectively protect C/C composites from oxidation at 1273K in air for 600min with a weight loss of 4.063%. The failure of the coating at intermediate temperature is due to the generation of some cross-cracks in the coating and sectional volatilization of B₂O₃.

Abstract: Magnesium matrix composites are attractive for weight critical application, such as automotive and aerospace components, because of its high specific strength and stiffness. Extrusion process directly following vacuum infiltration (EVI) can eliminate the porosity and obtain the well-aligned and uniform fiber distribution during the fabrication of Csf/AZ91D composite. This process combines the advantages of gas pressure infiltration, squeeze casting, and semi-solid extrusion. The mechanical properties of the magnesium are improved greatly by introducing the carbon fibers into the magnesium matrix through the EVI process. In the present study, the carbon short fiber reinforced magnesium matrix composites Csf/AZ91D were fabricated by EVI process. The microstructure and tensile property of Csf/AZ91D composites were investigated. The results showed that the microstructure of the composite presented a uniform distribution of carbon short fibers in the matrix and good interfacial integrity. The yield strength and stiffness of the composites increased with increasing carbon short fiber content, but at the cost of ductility. Nonetheless, Csf/AZ91D can keep relatively high ductility during the improvement of strength compared with reported composites in the literatures. Increasing carbon fiber content in the composite was not always beneficial to the ultimate tensile strength at the same magnitude. When the fiber content exceeds 10%, the matrix was not strengthened as greatly as under 10% fiber content. The yield strength improvement was attributed to (i) load-bearing effects due to the presence of carbon short fiber reinforcements; (ii) grain size refinement due to the large extrusion deformation; (iii) generation of dislocations to accommodate CTE mismatch between the matrix and the particles.

Abstract: Extrusion directly following vacuum infiltration is a special forming technique that combines the advantages of liquid metal infiltration and semisolid extrusion. The major advantages of this process are elimination of porosity and shrinkage, good surface finish, good dimensional accuracy, high strength to weight ratio and near net shaping. Magnesium matrix composites are fabricated usually through stirring casting, powder forming, injecting deposition, liquid metal infiltration or die casting at present time. However few investigations on magnesium matrix composite are conducted for the specific characteristics of magnesium alloy, such as high chemical activity and easy oxidation. The present paper is focused on Csf/Mg composites obtained via infiltration of porous short carbon fiber preform by liquid Magnesium. The complete experiment setup is designed and fabricated by ourselves, which include the forming molds, the unit for melting the magnesium, the unit for vacuuming and the monitoring and collecting system of forming process parameters. In this method the whole experiment setup is vacuumed firstly. Then the pressurized nitrogen is used to infiltrate the magnesium melt through a porous preform of short carbon fibers. After the infiltration completed, the punch of the press extrude the magnesium-infiltrated preform out of the forming die to form the tubes or bars. X-ray diffraction (XRD), optical and SEM microscopes were used to characterize the infiltration and the microstructure of fabricated composites. The compression test was used to characterize the mechanical properties of fabricated composites. The results show that the preform was infiltrated thoroughly by melt magnesium and the fabricated Csf/Mg composites have excellent mechanical properties compared with the magnesium alloys. Csf/Mg composites should be very promising candidates for automobile parts and portable electronic appliance parts in the future.