Papers by Author: Liang Yu

Abstract: In this study, nano-hydroxyapatite (HA) powders were synthesized via a simple sol-gel method using Ca(NO3)2•4H2O and P2O5 as starting materials. Two different precursors, with and without citric acid (CA), were prepared. The transformation process of HA from precursors, purity and particle size of the obtained HA powders were evaluated. HA derived from the precursor with CA showed a different transformation process from that without CA. It was observed that the content of CaO as an unavoidable major impurity was reduced due to the addition of CA. In the calcined powders from the CA-free precursor, X-ray diffraction (XRD) patterns revealed an intense CaO peak. For the calcined powders from the CA-addition precursor, XRD analysis showed a very weak CaO peak. It was also found that the synthesized HA powders from precursor with CA were finer than those without CA. The mechanism of the influence of CA on the formation, purity and particle size distribution of HA powders was discussed.

Abstract: Gp/SiC composite was prepared with electrode graphite particle and SiC powders as the raw materials, using coating process and hot-pressing sintering technology. The microstructure and phase constitution was measured by X-ray diffraction (XRD), scanning electron microscopy (SEM) and electron energy spectrum (EDS). It was found that the graphite cores are embedded in the SiC matrix as the islands. The apparent porosity increased, density decreased, with graphite particle content increasing, the bending strength decreased, however, fracture toughness increased with the graphite particle content increasing. Increasing hot-pressing sintering temperature imparted Gp/SiC composite characteristic behaviors of better mechanical strength. The apparent porosity, bulk density, bending strength, fracture toughness were 4.0%, 2.58 g•cm-3, 50 MPa, 6.3 MPa•m1/2, respectively, with the size 200 μm graphite core at 2050 °C, while the volume rate of SiC and graphite was 6:4.

Abstract: B4C-TiB2 composite was prepared using hot pressure sintering. The microstructures and mechanical properties of the B4C-TiB2 composite were investigated. The B4C-TiB2 composite with 43 mass % TiB2 showed the optimized properties. The relative density, hardness, flexural strength and fracture toughness of that were 98.2 %, 25.9 GPa, 458 MPa and 8.7 MPa•m1/2, respectively. A number of toughening mechanisms, including fine grain, crack deflection and grain pull-out, were observed during microstructural analysis of the composite. The fracture mode of the B4C-TiB2 composite was greatly affected by the existence of the second phase of TiB2.