He Jun Li

The Effect of SiC Coating on the Joint of C/C and LAS

The SiC coating on C/C composites was prepared by CVD and pack-cementation method in this paper, then SiC coated C/C composites was jointed with LAS glass ceramic at 1423K for 30min and the pressure of 15 MPa. The structure and morphology of the SiC coating and as-received joints were analyzed by SEM and XRD; shear strength of joint was examined through the Instron universal testing tensile machine. The results show that the thickness of SiC coating prepared by CVD is about 30μm, while the thickness of SiC layer by pack-cementation is nearly 100μm, and the layer is easier to connect with LAS glass ceramic owing to the rough surface and wedge-shaped structure on the SiC coating; the shear strength of joint between SiC coating coated C/C and LAS by pack-cementation is greater than the joint of C/C- LAS with SiC coating prepared by CVD.

Catalytic Activity of Tetranitro-Copper Phthalocyanine Supported on Carbon Nanotubes towards Oxygen Reduction Reaction

Acid-functionalized multiwalled carbon nanotube (AF-MWCNT)-supported tetranitro-copper phthalocyanine (TNCuPc) assemblies were prepared by solid phase synthesis method. The products were characterized by infrared spectroscopy, scanning electron microscopy and XRD. The electrocatalytic activity of the obtained AF-MWCNT-supported TNCuPc assemblies was measured by cyclic voltammetry (CV) and rotating disk electrode (RDE) techniques in an oxygen-saturated 0.1 M KOH. The results showed that the catalytic activity of TNCuPc/AF-MWCNTs towards oxygen reduction was a two-step, two-electron process for oxygen reduction.

Effects of Bending Cyclic Load on Mechanical Properties of 2D Carbon Cloth Laminated C/C Composites

Bending cyclic fatigue tests of 2D laminated C/C composites were conducted under load control at a sinusoidal frequency of 10 Hz. And three-point bending tests of fatigued specimens with various cycles were conducted at room temperature to evaluate the effects of cyclic load on mechanical properties. 2D C/C specimens were prepared by an isothermal chemical vapor deposition (CVD) process. The mechanical properties of composites were improved after cyclic loading at most the flexural strength by about 46% and the modulus 38%. The results show that the flexural properties of C/C composites were enhanced with the increase in fatigue cycles. It is suggested that the weakened interface between matrix and fibers by cyclic load play important roles in enhancing the property of C/C composites.

Mechanical Properties of Csf/AZ91D Composites Fabricated by Extrusion Forming Process Directly Following the Vacuum Infiltration

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.

Finite Element Simulation of Effects of Process Parameters on Deposition Rate of SiC by Chemical Vapor Deposition

A two-dimensional mathematical model for deposition behavior of SiC coating on C/C composites in a hot-wall CVD reactor was developed. Deposition rate of SiC was calculated by finite element method and optimized by using an orthogonal L9(3)4 test. The single and coupling effects of process parameters on deposition rate of SiC, including deposition temperature, the flux of mixed gases, the volume ratio of H2 and Ar, and that of MTS and mixed gases, were calculated and discussed. The optimal deposition rate of SiC was obtained.

Evolution of Porous Structure and Fatigue Behavior of C/C Composites

Porous structure is an important component in C/C composites, which directly affects the fatigue behavior of materials. Therefore, it is necessary to discuss the evolution of porous structure in C/C composites under the fatigue loading. In present work, the character of porous structure in original C/C composites was summarized and the evolution of porous structure after fatigue loading was analyzed. The positive effect of the porous structure evolution after fatigue loading on the reinforcing behavior of fatigue was proposed as well, which could provide a basis for further studies on the fatigue mechanisms of C/C composites.

Microstructures and Electrocatalytic Properties of Nitrogen Doped Graphene Synthesized by Pyrolysis of Metal Tetrapyrazinoporphyrazine

Nitrogen doped graphene (NG) was synthesized by chemical vapor deposition at 950 °C, using metal tetrapyrazinoporphyrazine (MPTpz, M= Fe, Co, the mass ratio of FePTPz/ CoPTpz is 1: 1) as a precursor. IR testing of FePTpz indicates the existence of C−N and C=N, which was prepared through microwave method. The NG shows a uniformly distributed and cotton-like structure. TEM images suggests that the single and multilayer NG coexists in the products and it is of a graphite-like structure. Electrocatalytic activity of the NG towards oxygen reduction reaction (ORR) was investigated by the cyclic voltammetry at different scan rates from 20 mV·s-1 to 100 mV·s-1 in an acidic solution. Peak currents and background currents of the NG rose as the scan rate increasing. The maximum peak current is 290.24 mA·cm−2, exhibiting well electrocatalytic activity of the NG toward ORR.

Response of MG63 Osteoblast-Like Cells on Pyrolytic Carbon Coated Carbon/Carbon Composites

In order to improve the biocompatibility of carbon/carbon(C/C) composites used for hip prosthesis, pyrolytic carbon coating was prepared on their surface by chemical vapor deposition. The microstructures of the samples were analyzed by scanning electron microscopy (SEM) and the biomedical response was assessed by the morphology and proliferation of MG63 osteoblast-like cells. The results show that the texture on the surface of C/C composites changes from chaotic structure to uniform state after the pyrolytic carbon coating is prepared. Osteoblasts cultured on pyrolytic carbon coating present flat shape with thin thickness, and display better proliferation in comparison with those on the uncoated C/C composites surface.

Microstructure of Pyrolytic Carbon Matrix in Carbon/Carbon Composites after Graphitization

The morphologies and textures of the pyrolytic carbon matrix in 2D-C/C composites after graphitization were investigated by means of polarized light microscope (PLM) and high resolution transmission electron microscope (HRTEM). The microstructure parameters of the pyrolytic carbon matrix before and after graphitization were characterized with X-ray diffraction (XRD) technology. It was found that the interplanar distance of (002) planes (d002) of pyrolytic carbon matrix decreases, and the microcrystalline stack height (LC) increases after graphitization. Graphitization treatment resulted in a coarsening of the surface texture and in the formation of circumferential cracks within the matrix. The lattice fringes of the pyrolytic carbon matrix are continuous and longer in each domain and the (002) peak spot is smaller and more intense after graphitization.

Influence of Pulse Frequency on the Structure and Oxidation Resistance of AlPO4 Ceramics Coating and its Deposition Dynamics

A facile pulse arc discharge deposition method was developed to prepare AlPO4 oxidation resistant outer coating on SiC pre-coated carbon/carbon composites (SiC-C/C). The deposition dynamics and the influence of pulse frequency on composition, microstructure and oxidation resistance of the as-prepared coating were investigated. Results show that pulse arc discharge deposition is an effective route to achieve dense and crack-free AlPO4 coatings. The deposition activation energy of the AlPO4 coating is calculated to be 3.07 kJ·mol-1. The AlPO4 coating prepared at a pulse frequency of 2000 Hz exhibits good oxidation resistance, which can effectively protect C/C composites from oxidation in air at 1773 K for 262 h with a weight loss of 1.58%.