Zeng Min Shen

Preparation of Carbon Nanotube Reinforced Epoxy Resin Coating and its Microwave Characteristics

The carbon nanotubes were prepared by catalytic decompose of benzene using floating transition method at 1100~1200°C. Benzene was used as carbon source and iron as catalyst with sulfur. The carbon nanotubes are straight with diameter 30~80nm, internal diameter 10~50nm and length 50~100μm. The carbon nanotubes and epoxy resin were sufficiently mixed. The mixture was smeared on to a pure aluminum plate layer by layer until the thickness of the composite layer reached 1.0 mm. The coating resin was cured by heating under infrared radiation. Complex permittivity, permeability and microwave reflectivity of carbon nanotubes reinforced epoxy resin coating had been investigated at the frequency ranges of 8.2~12.4GHz and 2~18GHz respectively. The real part (ε′) of complex permittivity of this coating ranges from 14.87 to 13.86, and the imaginary part (ε″), from 6.42 to 5.87, the loss tangent tgδε (ε″/ε′), from 0.42 to 0.45. The real part (μ′) of complex permeability of this coating ranges from 1.02 to 1.14, and the imaginary part (μ″), from 0.08 to 0.11, the loss tangent tgδμ (μ″/μ′), from 0.06 to 0.11. The maximum absorbing peak of the carbon nanotube reinforced epoxy resin coating is 22.89 dB at 11.40GHz. The band width (R<-10dB) of this coating with thickness of 1.0 mm is 3.0GHz, band width (R<-5dB) is 4.7GHz at the frequency range of 8~18GHz. This carbon nanotube reinforced epoxy resin coating would be a good candidate for microwave absorbing material.

Microstructure and Mechanical Property of Three-Dimensional Needled C/SiC Composites Prepared by Precursor Pyrolysis

Three-dimensional needled carbon/silicon carbide (C/SiC) composites with pyrolytic carbon interfacial layer were fabricated by precursor pyrolysis. The microstructure and mechanical property of the three-dimensional needled C/SiC composites were investigated. A thin pyrolysis carbon layer (0.2m) was firstly deposited on the surface of carbon fiber as the interfacial layer with C3H6 at 850 °C and 0.1 MPa by chemical vapor infiltration. Polycarbosilane and divinylbenzene were selected as a precursor to silicon carbide ceramics and a cross-linking reagent for PCS, respectively. The density of the composites was 1.94 g cm-3. The flexural strength of the three-dimensional needled C/SiC composites was 135 MPa. The three-dimensional needled C/SiC composites with pyrolytic carbon interfacial layer exhibit good mechanical properties and a typical failure behavior involving fibers pull-out and brittle fracture of sub-bundle.

Microstructure and Mechanical Property of Carbon Nanotube and Continuous Carbon Fiber Reinforced Epoxy Resin Matrix Composites

The carbon nanotubes (CNTs) were prepared by catalytic decompose of benzene using floating transition method at 1100-1200°C. Benzene was used as carbon source and ferrocene as catalyst with thiophene. The carbon nanotubes are straight with diameter 20-50 nm, internal diameter 10-30 nm and length 50-1000 μm. The carbon nanotube and continuous carbon fiber (T300) reinforced unidirectional epoxy resin matrix composites was fabricated. The volune fraction of continuous carbon fiber (first filler) in the composites without second filler (carbon nanotube) was 60%. The mechanical properties of the composites were investigated under bending, shear, and impact loading. The flexural strength and modulus of the composites increased firstly and then decreased with the increasing of carbon nanotube contents in epoxy resin matrix. The flexural strength of the composites reached the maximum value of 1780 MPa when the weight percent of carbon nanotube in epoxy resin matrix was 3%.

Preparation and Microwave Absorbing Properties of Cu-Doped Ni-Zn Spinel Ferrites

Ni-Zn spinel ferrite and Cu-doped spinel ferrite were prepared by a conventional ceramic processing method. Microwave absorption, complex permittivity and permeability of the (Ni0.5Zn0.5)Fe2O4 and (Ni0.4Cu0.2Zn0.4)Fe2O4 spinel ferrites within the frequency range of 0.5-18 GHz were investigated. The reflection loss calculation results show that the Ni-Zn spinel ferrite and Cu-doped Ni-Zn spinel ferrite are good electromagnetic wave absorbers in the microwave range. The single layer (Ni0.4Cu0.2Zn0.4)Fe2O4 spinel ferrite absorber with a thickness of 9.2 mm achieved a reflection loss below -10 dB (90% absorption) at 0.5-2.3 GHz, and the minimum value is -35.63 dB at 1.1 GHz. When the first layer and second layer are (Ni0.5Zn0.5)Fe2O4 and (Ni0.4Cu0.2Zn0.4)Fe2O4 spinel ferrites respectively, the laminated absorbers with double spinel ferrite layers with a thickness of 3 mm achieved a reflection loss below -10 dB at 9.9-12.3 GHz, and the minimum value is -35.3 dB at 11.7 GHz.

Preparation and Microwave Absorbing Property of Microwave Absorbers with FSS Embedded in Multilayer Composites

In this paper, we present the experimental results of microwave absorbing materials with a frequency-selective surface (FSS) embedded in the multilayer structural composites. Microwave absorbing materials with the FSS pattern embedded in multilayer structural epoxy resin matrix composites were fabricated. The effects of the FSS on multilayer structural composites for microwave absorbing material design have been investigated. Comparisons were made with the microwave absorptions of the multilayer composites with FSSs of different positions in composites. The microwave absorption properties of the multiplayer composites samples with FSSs are higher than those of the samples without FSSs. The experiment results show that the incorporation of a FSS can effectively change the reflection property of the composite.

Carbon Fiber Paper Modified with Carbon Nanotube for Proton Exchange Membrane Fuel Cell

Carbon fiber paper was modified by adding carbon nanotubes to make it reach the demand of gas diffusion layer (GDL) by the process of impregnation with phenolic resin solution dispersed with carbon nanotubes, molding, and carbonization. The properties of modified carbon fiber paper, thickness, density, porosity, gas permeability, specific resistance and tensile strength, were characterized. The results indicate that surface treatment is helpful to disperse carbon nanotubes in phenolic resin. Phenolic resin is used to bond the carbon fibers, and carbon nanotube could reduce the specific resistance of the carbon fiber paper. When carbon nanotube content is 5 %, modified carbon fiber paper is prepared with thickness of 0.30 mm, density of 0.43 g/cm3, porosity of 77 %, gas permeability of 2400 mL•mm/(cm2•h•mmAq), specific resistance of 0.020 Ω•cm and tensile strength of 15 MPa, which basically qualifies for the application requirement.

Synthesis and Luminescent Properties of Mn2+-Doped Zinc Silicate Phosphors by Sol-Gel Method

Abstract. Green light emitting Mn2+-doped Zn2SiO4 (Zn2SiO4:Mn2+) phosphor nano-particles were synthesized by sol-gel method combined with a furnace firing from the sol-gel solution made with ZnO, MnCO3 and tetraethoxysilan. The influences of annealing temperatures on the microstructures and photoluminescent properties of the Zn2SiO4:Mn2+ phosphors were investigated. The structural details of the phosphors were examined through XRD and SEM. The photoluminescent properties of the Zn2SiO4:Mn2+ phosphors were characterized by excitation and emission spectra. The results indicate that the XRD patterns of the Zn2SiO4:Mn2+ phosphors exhibit a willemite structure (-Zn2SiO4). Green photoluminescence whose emission peak is located at 525 nm were observed from the synthesized phosphor particles under UV excitation. The photoluminescent mechanisms of the Zn2SiO4:Mn2+ phosphors were discussed.

Effect of Carbon Fiber Felt Pretreatment on Properties of Carbon Fiber Paper

Gas diffusion layer is a very important component in fuel cell, and carbon fiber paper is widely used as substrate of gas diffusion layer. This paper has developed one way to produce carbon fiber paper from carbon fiber felt with or without pretreatment. The properties and microstructure of carbon fiber paper were also stdied. The results show that the pretreatment of carbon fiber felt is helpful to prepare carbon fiber paper with good properties. The content of carbon derived from resin during pretreatment has effects on density, thickness, porosity, gas permeability, porosity and tensile streagth of carbon fiber paper. Carbon fiber paper made from carbon fiber felt with pretreatment has better interface adhension than that of carbon fiber paper made from carbon fiber felt without pretreatment. Carbon fiber paper was produced with thickness of 0.28mm, density of 0.43g/cm3, porosity of 77%, gas permeability of 2500 mL•mm/(cm2•hr•mmAq), specific resistance of 0.017Ω•cm and tensile strength of 18MPa, which is a promising materials for fuel cell electrode.

Processing and Characterization of Nano Silicon Carbide Ceramics via Precursor Pyrolysis

Nano silicon carbide ceramics were prepared via precursor pyrolysis. Polycarbosilane (PCS) and divinylbenzene (DVB) were selected as a precursor to silicon carbide ceramics and a cross-linking reagent for PCS, respectively. The cross-linking properties and pyrolysis of PCS and DVB were investigated by changing the mass ratios of PCS/DVB. The mass ratio of PCS/DVB has a great effect on silicon carbide ceramic yield. The cured PCS/DVB with a mass ratio of 1:0.5 has the highest SiC ceramic yield (63.1%) at the temperature up to 1500 °C and its pyrolyzates consiste of nano silicon carbide with a diameter of 10-40 nm. The microstructures of the nano silicon carbide ceramics were characterized by SEM and XRD. The pyrolysis behavior of the cured PCS/DVB was characterized by thermogravimetry in nitrogen atmosphere.

Electrical Resistance Response of Carbon Nanotube / PMMA / PVAc Composite Sensors to Organic Vapours at Low Vapour Concentrations

Thin films of poly(methyl methacrylate) (PMMA)，poly(vinyl acetate) (PVAc) and carbon nanotube composites were produced by different coating methods. The best way to produce the carbon nanotube / PMMA / PVAc composite film with conductive network is dispersing carbon nanotubes in PMMA and PVAc by ultrasonic and by solution casting. Electrical resistance responses of carbon nanotube / PMMA / PVAc composite sensors against various organic vapors at low concentrations are investigated. The experimental results indicate that the composites have high selectivity to various organic vapors at the same concentration. In addition, the electric resistance response of the composites against organic vapors takes place in step with their vapor adsorption procedure. Compatible blends of poly(methyl methacrylate) and poly(vinyl acetate) would be a good candidate to produce a series of electrically conducting carbon nanotubes composite film whose resistance is sensitive to the nature and concentration of an analyte in the vapor phase. The results indicate that the carbon nanotube / PMMA / PAVc composite film can be used as a novel organic vapor sensor to detect, quantify and discriminate various organic vapors.