Chunxiang Lu

Thermally reduced graphene oxide films as flexible lateral heat spreaders

A thermally reduced graphene oxide film (r-GOF), with tailorable micro-structures and macro-properties, is fabricated by annealing a filtrated graphene oxide film (GOF) in a confined space. The structural evolution of the film at different annealing temperatures is systematically investigated, and further correlated to the thermal conductivity and mechanical performances. With the increase of temperature, more oxygen-containing functional groups are removed from the film by a simultaneous conversion from sp3 to sp2 carbon in the graphitic lattice. As the temperature reached 1200 °C, the r-GOF achieves an ultrahigh thermal conductivity of ca. 1043.5 W m−1 K−1, while 1000 °C is a critical temperature in enhancing the thermal conductivity. Moreover, G1200 exhibits excellent mechanical stiffness and flexibility with a high tensile strength (13.62 MPa) and Youngs modulus (2.31 GPa). The combined conductivity and mechanical performances render the r-GOFs promising materials as flexible lateral heat spreaders for electronics.

Catalytic removal of SO2 over ammonia-activated carbon fibers

Abstract Nitrogen-containing functional groups were introduced onto the surface of activated carbon fibers (ACF) by activating an ethylene tar pitch-based carbon fiber with ammonia water. The activity of the ACF for the conversion of SO2 to aq. H2SO4 in the presence of H2O and O2 is significantly higher than that of other commercial ACF studied before. Both the SO2 adsorption capacity and oxidation activity of ACF are enhanced very much by the nitrogen-containing functional groups.

Preparation of PVDF/graphene ferroelectric composite films by in situ reduction with hydrobromic acids and their properties

A new two-step process was developed to prepare PVDF/reduced graphene oxide (PVDF/rGO) composite films: the synthesis of PVDF/GO composite films and immersion of such films in hydrobromic acids for reduction. This method avoided the agglomeration of rGO during reduction in PVDF/GO solutions and efficiently improved the dispersion effect of rGO in the PVDF matrix. Meanwhile, it simplified the preparation process due to no modification of GO being required, and opened a feasible way to scale up the production of PVDF/rGO composites. Experiments showed that PVDF with nearly all β phase was obtained when the content of rGO was 0.1 wt% (PrGO-0.1), and the dielectric constant increased from 10 for the neat PVDF to 41 for PrGO-0.1 at 1 kHz. The ferroelectric, piezoelectric, and dynamic mechanical properties of the PVDF/rGO composites were also comprehensively studied. As the content of the β phase was nearly 100%, the piezoelectric constant and remnant polarization of the PrGO-0.1 film increased by 78.6% and 69.3%, respectively, compared with those of the neat PVDF, and therefore became the highest among all composite films. The rGO also, to a great extent, helped to enhance the mechanical properties of the PVDF composites. As a result, the improved piezoelectric and ferroelectric properties made the PVDF/rGO composite films with 0.1 wt% rGO content much better piezoelectric energy transfer and ferroelectric storage materials than the neat PVDF.

Resistivity of carbon fibers/ABS resin composites

Abstract The resistivity of carbon fiber/acrylonitrile–butadiene–styrene (ABS) resin composites was investigated. Short carbon fibers (unoxidized and oxidized) were blended with ABS resin using chloroform as solvent and samples were made by hot pressing method. The composites display good conductivity when fiber volume content is larger than 2%, then the resistivity of composites gradually decreases with increasing filler fraction and the experimental data is in good agreement with the percolation theory. Raising carbon fiber lengths reduces the resistivity of composites. The oxidation of carbon fibers greatly increases the resistivity of composites.

Influence of graphene oxide additions on the microstructure and mechanical strength of cement

Abstract The effect of adding graphene oxide (GO) to cement on its microstructure and mechanical strength was investigated. A paste of cement (16.5 wt% of water?and GO (0.05 wt%) was prepared together with an identical mixture to which sand (3x the weight of the cement) had been added to form a mortar. The fluidity, viscosity and setting time of the mortar and the morphology, pore structure and compressive and flexural strengths of both the hardened cement paste and mortar, were investigated using SEM, nitrogen adsorption, and fluidity, viscosity, mechanical and hydration tests. The influence of the GO addition on the hydration heat of the cement was also tested. Results show that the addition of GO increases the viscosity, decreases the fluidity and shortens the setting time of the mortar. It also reduces the heat of hydration of the cement. The compressive and flexural strengths of the hardened cement paste at different times are increased by the addition of GO. The flexural strength was greater by 86.1, 68.5 and 90.5% after 3, 7 and 28 days, respectively, and the corresponding compressive strength increases were 52.4, 46.5 and 40.4%. For the hardened mortar, the corresponding increases are 69.4, 106.4 and 70.5% for flexural strength and 43.2, 33 and 24.4% for compressive strength. The addition of GO promotes hydration, decreases pore volume, accelerates crystallite formation and causes the crystallites to align, which increases the tightness of both the hardened cement paste and mortar.

Effect of electrophoretically deposited carbon nanotubes on the interface of carbon fiber reinforced epoxy composite

The interface between reinforcing fiber and matrix is a crucial element in composite performance. Homogeneous and interconnected carbon nanotubes (CNTs) were deposited onto the surface of carbon fibers to produce multiscale reinforcement by electrophoretic deposition (EPD). Single fiber tensile tests showed that the tensile strength and Weibull modulus of the resulting multiscale materials were increased by 16 and 41%, respectively. Compared with as-received carbon fibers, CNTs-deposited carbon fibers provided the decreased surface energy by 20% and the increased adhesion work by 22% using modified Wilhelmy method. Results from single fiber pull-out testing showed that a significant improvement (up to 68.8%) of interfacial shear strength was obtained for the composites containing by CNTs/Carbon fiber multiscale reinforcement. All results strongly suggest that EPD process can provide a feasible platform for improving interface properties of advanced composites.

Polyacrylonitrile/lignin sulfonate blend fiber for low-cost carbon fiber

Polyacrylonitrile/lignin sulfonate (PAN/LS) blend fibers were spun via a wet spinning process. The fiber structure, mechanical properties and thermal stability of the precursor fibers were studied by FT-IR, SEM, tensile tester, and TG-DSC. Results indicated that there was no chemical crosslinking between PAN and LS during the process of wet spinning. PAN and LS had good compatibility in the blend fibers. LS could weaken the skin of the blend fibers and reduce the fiber structure defects. The increase of dope concentration could improve the fiber structure and mechanical properties. LS blending with PAN could reduce fiber weight loss in the thermal stabilization process, and most importantly the precursor fibers could be stabilized rapidly without fiber fusion. Through polymer blending and wet spinning, this study provided a promising way to prepare a precursor fiber for carbon fiber.

Influence of CO-evolving groups on the activity of activated carbon fiber for SO2 removal

An investigation was made into the influence of CO-evolving and CO2-evolving groups on the activities of activated carbon fibers (ACFs) for the oxidative conversion of SO2 into aq. H2SO4 in the presence of O2 and H2O. The results indicated that the amount of evolved CO determined the SO2 removal activity of ACFs, whereas, the amount of evolved CO2 did not correlate with the ACFs activity for SO2 removal. A direct proportionality between the amount of evolved CO and the enhanced activity of SO2 removal was confirmed by using different oxidizing agents for changing the types and amount of oxygen functional groups in ACFs.

Nitrogen- and oxygen-enriched 3D hierarchical porous carbon fibers: synthesis and superior supercapacity

A nitrogen- and oxygen-enriched hierarchical porous carbon fiber was fabricated by phase-separable wet-spinning and the subsequent chemical activation of polyacrylonitrile (PAN) precursors. The wet-spinning could readily offer an interpenetrating 3D meso-/macro-porous network owing to the phase-separation of PAN in the coagulation bath (DMSO/H2O), caused by the different solubility of PAN in DMSO and H2O, and the different content of PAN in the fiber and the coagulation bath. The latter chemical activation introduced abundant small-sized nanopores within the meso-/macro-porous network skeleton. The obtained hierarchical porous carbon fiber exhibited a high specific surface area of 2176.6 m2 g−1 and a large pore volume of 1.272 cm3 g−1, and was highly doped with heteroatoms of nitrogen and oxygen. When it was used as a supercapacitor electrode, high performance of reversible specific capacitances of 329 F g−1 at 0.1 A g−1 and 223 F g−1 at 20 A g−1 as well as the capacitance retention of 97.6% after 2000 cycles were achieved in a two-electrode cell.

Improving the corrosion resistance of Mg–4.0Zn–0.2Ca alloy by micro-arc oxidation

In this paper, corrosion resistance of the Mg-4.0Zn-0.2Ca alloy was modified by micro-arc oxidation (MAO) process. The microstructure and phase constituents of MAO layer were characterized by SEM, XRD and X-ray photoelectron spectroscopy (XPS). The corrosion resistance of MAO treated Mg-4.0Zn-0.2Ca alloy in the simulated body fluid were characterized by potentiodynamic polarization and electrochemical impedance spectroscopy (EIS) techniques. The microstructure results indicated that a kind of ceramic film was composed by MgO and MgF2 was formed on the surface of Mg-4.0Zn-0.2Ca alloy after MAO treatment. The electrochemical test reveals that the corrosion resistance of MAO treated samples increase 1 order of magnitude. The mechanical intensity test showed that the MAO treated samples has suitable mechanical properties.