Hongjie Fang

Microstructures and properties of Al-50%SiC composites for electronic packaging applications

Abstract Al–50%SiC (volume fraction) composites containing different sizes of SiC particles (average sizes of 23, 38 and 75 μm) were prepared by powder metallurgy. The influences of SiC particle sizes and annealing on the properties of the composites were investigated. The results show that SiC particles are distributed uniformly in the Al matrix. The coarse SiC particles result in higher coefficient of thermal expansion (CTE) and higher thermal conductivity (TC), while fine SiC particles decrease CTE and improve flexural strength of the composites. The morphology and size of SiC particles in the composite are not influenced by the annealing treatment at 400 °C for 6 h. However, the CTE and the flexural strength of annealed composites are decreased slightly, and the TC is improved. The TC, CTE and flexural strength of the Al/SiC composite with average SiC particle size of 75 μm are 156 W/(m·K), 11.6×10 −6 K −1 and 229 MPa, respectively.

Improvement of the mechanical properties and corrosion resistance of biodegradable β-Ca3(PO4)2/Mg-Zn composites prepared by powder metallurgy: the adding β-Ca3(PO4)2, hot extrusion and aging treatment

In this study, 10%β-Ca3(PO4)2/Mg-6%Zn (wt.%) composites with Mg-6%Zn alloy as control were prepared by powder metallurgy. After hot extrusion, the as-extruded composites were aged for 72h at 150°C. The effects of the adding β-Ca3(PO4)2, hot extrusion and aging treatment on their microstructure, mechanical properties and corrosion resistance were investigated. The XRD results identified α-Mg, MgZn phase and β-Ca3(PO4)2 phase in these composites. After hot extrusion, grains were significantly refined, and the larger-sized β-Ca3(PO4)2 particles and coarse MgZn phases were broken into linear-distributed β-Ca3(PO4)2 and MgZn phases along the extrusion direction. After aging treatment, the elements of Zn, Ca, P and O presented a more homogeneous distribution. The compressive strengths of the β-Ca3(PO4)2/Mg-Zn composites were approximately double those of natural bone, and their densities and elastic moduli matched those of natural bone. The immersion tests and electrochemical tests revealed that the adding β-Ca3(PO4)2, hot extrusion and aging treatment could promote the formation of protective corrosion product layer on the sample surface in Ringers solution, which improved corrosion resistance of the β-Ca3(PO4)2/Mg-Zn composites. The XRD results indicated that the corrosion product layer contained Mg(OH)2, β-Ca3(PO4)2 and hydroxyapatite (HA). The cytotoxicity assessments showed the as-extruded β-Ca3(PO4)2/Mg-Zn composite aged for 72h was harmless to L-929 cells. These results suggested that the β-Ca3(PO4)2/Mg-Zn composites prepared by powder metallurgy were promising to be used for bone tissue engineering.

Synthesis and characterization of porous cobalt oxide/copper oxide nanoplate as novel electrode material for supercapacitors

Abstract A promising Co 3 O 4 /CuO composite electrode material was successfully synthesized through a facile hydrothermal and calcination process. Effects of the surfactants hexadecyltrimethyl ammonium bromide (CTAB) and polyvinylpyrrolidone (PVP) on the morphology and electrochemical performance of the composite were investigated. Powder X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM) and nitrogen adsorption-desorption experiment were employed to characterize the microstructures and morphologies of the composite. Meanwhile, the electrochemical performances of the samples were studied using cyclic voltammetry (CV), galvanostatic charge-discharge test and electrochemical impedance spectroscopy (EIS). The results show that the porous Co 3 O 4 /CuO-CTAB nanoplates own the best performance and exhibits a high specific capacitance of 398 F/g at 1 A/g with almost 100% capacitance retention over 2000 cycles, and it retains 90% of capacitance at 10 A/g.

Compressive properties and energy absorption characteristics of open-cell nickel foams

Abstract Open-cell nickel foams with different relative densities and pre-stretching degrees were subjected to room temperature quasi-static compressive tests to explore their compressive properties. The compressive properties of the nickel foams including yield strength, elastic modulus, energy absorption density and energy absorption efficiency were calculated accurately. The results show that the compressive properties of yield strength, elastic modulus and energy absorption density increase with the increase of relative density of nickel foams. The compressive properties are sensitive to the pre-stretching degree, and the values of yield strength, elastic modulus and energy absorption density decrease with the increase of pre-stretching degree. However, the energy absorption efficiency at the densification strain state exhibits the independence of relative density and pre-stretching degree. The value of energy absorption efficiency reaches its peak when the strain is at the end of the collapse plateau region.

Layer roughness reduction and light harvest from Ag nanowires on a silicon surface through wet etching embedding

Wet etching as a clean method for embedding Ag nanowires into a silicon substrate has been employed to reduce the Ag nanowires layer roughness. Close attachment of the etching holes with Ag nanowires with various diameters was obtained using a simple etching process. Finite-Difference Time-Domain (FDTD) results show that the significant enhancement in light intensity and an increase in light path are caused by the embedding of Ag nanowires into the silicon substrate. These results show that embedding of Ag nanowires into a semiconductor material by etching can simultaneously lead to significant roughness reduction, light scattering enhancement, and charge collection capacity. It is expected that the embedding process will greatly improve the transparency and conductivity of semiconductor materials and has great potential for application in light emitting diodes (LEDs) or solar cells.

Fabrication of cobalt aluminum-layered double hydroxide nanosheets/carbon spheres composite as novel electrode material for supercapacitors

Abstract A new design route was presented to fabricate cobalt aluminum-layered double hydroxide(CoAl-LDH) thin layers which grow on carbon spheres(CSs) through a growth method. The CoAl-LDH thin layers consist of nanoflakes with a thickness of 20 nm. The galvanostatic charge–discharge test of the CoAl-LDH/CSs composite shows a great specific capacitance of 1198 F/g at 1 A/g (based on the mass of the CoAl-LDH/CSs composite) in 6 mol/L KOH solution, and the composite displays an impressive specific capacitance of 920 F/g even at a high current density of 10 A/g. Moreover, the composite remains a specific capacitance of 928 F/g after 1000 cycles at 2 A/g, and the specific capacitance retention is 84%, indicating that the composite has high specific capacitance, excellent rate capability and good cycling stability in comparison to pristine CoAl-LDH.