Papers by Author: Hong Qiang Ru

Abstract: B₄C-SiC-Si ceramic composites were fabricated based on molten silicon infiltration method. The influence of preforms^' forming pressure on the microstructure and mechanical properties of B₄C-SiC-Si ceramic composites was studied by X-ray diffraction (XRD), scanning electron microscopy (SEM) and electron universal testing machines, etc. The results showed that the ceramic consists of B₄C, B₁₂(C,Si,B)₃, SiC and Si phases. The microstructure analysis showed that: the volume percent of free silicon decreased with the increase in forming pressures. The Vikers-hardness of B₄C-SiC-Si ceramic composites increased, while the bending strength and fracture toughness both increased initially and then decreased with the increase in forming pressures of which the optimal pressure is 200 MPa. The optimum bending strength, fracture toughness and Vikers-hardness of the obtained B₄C-SiC-Si ceramic composites are 319±13 MPa, 4.9±0.1 MPa·m^1/2 and 24±1 GPa, respectively. The volume density and open porosity of the obtained B₄C-SiC-Si ceramic composites are 2.58 g/cm³ and 0.19 %, respectively.

Abstract: TiB₂-SiC-Si composite was fabricated by reaction bonding. The influence of carbon content on the phase compositions, microstructure, density and mechanical properties was studied. The results showed that the composite consists of TiB₂, SiC and Si phases. The vol% of SiC increased with the increase of C contents, while that of TiB₂ and free silicon reduced respectively. The mechanical properties of TiB₂-SiC-Si composites are improved initially and then deteriorated with the increase in C contents of which the optimal amount is 8 %. The optimum open porosity, volume density, Vikers-hardness, flexural strength and fracture toughness of the obtained TiB₂-SiC-Si composite are 0.12 %, 3.73 g/cm³, 17 GPa, 290 MPa and 5.9 MPa·m^1/2, respectively.

Abstract: cBN/SiAlON composites were prepared by spark plasma sintering (SPS) method using Si₃N₄, AlN, Al₂O₃, cBN and Y₂O₃ powders as raw materials. The sintering process is at the temperature of 1500°C holding for 5 min. Effect of the Y₂O₃ content on phase composition, microstructure, bulk density, hardness and fracture toughness of the cBN/SiAlON composite was investigated. The experimental results showed that when the Y₂O₃ content was 0.2 wt. % the bulk density and fracture toughness of the composite had the maximum values of 3.0 g/cm³ and K_IC = 5.7 MPa∙m^1/2, respectively. The cBN/SiAlON composite with 0.8 wt. % Y₂O₃ addition got the maximum hardness of 16.4 GPa.

Abstract: Dense iron-containing hydroxyapatite (HA)/titanium composites were synthesized via pressureless sintering at a relatively low temperature using nanosized HA powders and Ti-Fe mixed powders. XRD analysis showed that desirable Ti phase still remained in the HA matrix. The addition of iron improved the densification by enhancing the sinterability of titanium, and reduced the decomposition rate of HA and the interaction between HA and titanium. The mechanical tests showed that both the flexural strength and fracture toughness of the composites were significantly improved. The Ti-Fe reinforcing particles exhibited plastic stretching and bridged an advancing crack, making a significant contribution to the improvement of mechanical properties of the composites.

Abstract: In the present work, using nanosized rare earth oxide CeO₂ as filler and acetonitrile as organic solvent, a novel solid-state composite polymer electrolyte (CPE) films (PEO)₁₀LiClO₄-x wt.%CeO₂ (x=0,2,6,9,12,15) was prepared by solution-casting technique. The effect of CeO₂ filler concentration on morphology and electrical characteristics of CPE films has been investigated and analyzed. The AC impedance measurements show that the ionic conductivity of CPE can be efficiently enhanced by adding appropriate CeO₂. The highest room temperature (25^OC) ionic conductivity of 1.71×10^-5S•cm^-1 is achieved with the CeO₂ content of 9 wt.%. With the CeO₂ content continues to increase, CPE ionic conductivity begin to decline. This is because appropriate CeO₂ can disorder the chain structure and effectively inhibit the crystallization of PEO, which expands the amorphous region required for the lithium-ion transport.

Abstract: Pure hydroxyapatite (HA) is brittle and it cannot be directly used for the load-bearing biomedical applications. Aim of this paper was to present a new iron-containing hydroxyapatite/titanium composites synthesized via pressureless sintering at a relatively low temperature of 1000°C using nano-sized HA powders and Ti-33%Fe mixed powders. The microstructure and composition of the new type composites were evaluated. The results showed that the uniformly distributed reinforcing particles had a unique and favorable core/shell microstructure after sintering that consisted of outer titanium and inner iron. The mechanism for the formation of the core/shell structure was discussed. The addition of iron reduced the decomposition rate of HA and the interaction between HA and titanium.

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.