Qiangang Fu

Carbon Nanotube–Multilayered Graphene Edge Plane Core–Shell Hybrid Foams for Ultrahigh‐Performance Electromagnetic‐Interference Shielding

Materials with an ultralow density and ultrahigh electromagnetic-interference (EMI)-shielding performance are highly desirable in fields of aerospace, portable electronics, and so on. Theoretical work predicts that 3D carbon nanotube (CNT)/graphene hybrids are one of the most promising lightweight EMI shielding materials, owing to their unique nanostructures and extraordinary electronic properties. Herein, for the first time, a lightweight, flexible, and conductive CNT-multilayered graphene edge plane (MLGEP) core-shell hybrid foam is fabricated using chemical vapor deposition. MLGEPs are seamlessly grown on the CNTs, and the hybrid foam exhibits excellent EMI shielding effectiveness which exceeds 38.4 or 47.5 dB in X-band at 1.6 mm, while the density is merely 0.0058 or 0.0089 g cm-3 , respectively, which far surpasses the best values of reported carbon-based composite materials. The grafted MLGEPs on CNTs can obviously enhance the penetration losses of microwaves in foams, leading to a greatly improved EMI shielding performance. In addition, the CNT-MLGEP hybrids also exhibit a great potential as nano-reinforcements for fabricating high-strength polymer-based composites. The results provide an alternative approach to fully explore the potentials of CNT and graphene, for developing advanced multifunctional materials.

Silicide Coating Fabricated by HAPC/SAPS Combination to Protect Niobium Alloy from Oxidation

A combined silicide coating, including inner NbSi2 layer and outer MoSi2 layer, was fabricated through a two-step method. The NbSi2 was deposited on niobium alloy by halide activated pack cementation (HAPC) in the first step. Then, supersonic atmospheric plasma spray (SAPS) was applied to obtain the outer MoSi2 layer, forming a combined silicide coating. Results show that the combined coating possessed a compact structure. The phase constitution of the combined coating prepared by HAPC and SAPS was NbSi2 and MoSi2, respectively. The adhesion strength of the combined coating increased nearly two times than that for single sprayed coating, attributing to the rougher surface of the HAPC-bond layer whose roughness increased about three times than that of the grit-blast substrate. After exposure at 1200 °C in air, the mass increasing rate for single HAPC-silicide coating was 3.5 mg/cm(2) because of the pest oxidation of niobium alloy, whereas the combined coating displayed better oxidation resistance with a mass gain of only 1.2 mg/cm(2). Even more, the combined coating could significantly improve the antioxidation ability of niobium based alloy at 1500 °C. The good oxidation resistance of the combined silicide coating was attributed to the integrity of the combined coating and the continuous SiO2 protective scale provided by the oxidation of MoSi2.

A Cr–Al–Si oxidation resistant coating for carbon/carbon composites by slurry dipping

A Si-Al-Ir oxidation resistant coating was prepared for SiC coated carbon/carbon composites by slurry dipping. The phase composition, microstructure and oxidation resistance of the as-prepared Si-Al-Ir coating were studied by XRD (X-ray difiraction), SEM (scanning electron microscopy), and isothermal oxidation test at 1773 K in air, respectively. The surface of the as-prepared Si-Al-Ir coating was dense and the thickness was approximately 100 „m. Its anti-oxidation property was superior to that of the inner SiC coating. The weight loss of SiC/SiAl-Ir coated carbon/carbon composites was less than 5 wt. pct after oxidation at 1773 K in air for 79 h. The local oxidation defects in the coating may result in the failure of the SiC/Si-Al-Ir coating.

Fabrication and Tribological Properties of B2O3 as Friction Reducing Coatings for carbon-carbon Composites

B2O3 lubricating coatings for the SiC coated C/C composites were prepared by a slurry brushing method. The morphologies, components, and structure of the as-prepared coatings were characterized by SEM and XRD. The friction coefficient of the coatings was also tested. The lubricating mechanism of the coating is discussed. Results show that the friction coefficient of the coatings is 0.06-0.08, which is less than that of the carbon/carbon composites (0.15-0.18). The decrease of the friction coefficient of C/C composites after adding a SiC/B2O coating is attributed to the formation of a lubricious layer of boric acid from the boron oxide after exposure to the moisture in air.

Supersonic plasma sprayed MoSi2–ZrB2 antioxidation coating for SiC–C/C composites

A dense and crack free MoSi2–ZrB2 coating was prepared on the SiC coated carbon/carbon (C/C) composites using a supersonic plasma spraying technique. The coated composites were characterised using scanning electron microscopy and X-ray diffraction. The analysis shows that the as prepared MoSi2–ZrB2 coating, with a thickness of ∼100 μm, combines well with the inner SiC coating. After oxidation at 1200°C for 72 h in air, the mass loss of MoSi2–ZrB2/SiC coated C/C is only 4.24 wt-%, which is significantly lower than that of MoSi2/SiC coated C/C (11.35 wt-%). The excellent oxidation protective ability of the MoSi2–ZrB2 coating is mainly attributed to ZrSiO4 produced by dispersive ZrO2 particles and SiO2 in the coating at high temperature.

Density functional theory study on the interactions of l-cysteine with graphene: adsorption stability and magnetism

Understanding the interactions between graphene and biomolecules is of fundamental relevance to the area of nanobiotechnology. Herein, we take l-cysteine as the probe biomolecule and investigate its adsorption on pristine graphene and B-, N-, Al-, Ni-, Ga-, Pd-doped graphene using density functional theory calculations. Three kinds of upright adsorption configurations, via unprotonated functional groups (-SH, -NH2, -COOH), are considered. The calculations reveal pristine graphene physically adsorbs l-cysteine. N-doped graphene shows physisorption towards the S-end and N-end l-cysteine, and chemisorption towards the O-end radical. Strong chemisorption, with site-specific preference, occurs on Al-, Ni-, Ga- and Pd-doped graphene, accompanied by severe structural changes. Spin polarization with an unusual mirror symmetry on Ni- and Pd-doped graphene is induced by chemisorption of unprotonated l-cysteine, except for O-end adsorption on Pd-doped graphene. The magnetization arises mainly from spin polarization of the C 2pz orbital, with a minor magnetism located on Ni or Pd. The influence of van der Waals forces is also evaluated. A thorough analysis of the adsorption stability and magnetism of these systems would be beneficial to facilitate applications in graphene-based biosensing, biomolecule immobilization, magnetic bio-separation and other fields in bionanotechnology.

Microstructure and oxidation protective ability of MoSi2-SiC-Si coating toughened with SiC whiskers for carbon/carbon composites

Abstract To prevent carbon/carbon (C/C) composites from oxidation at high temperatures, a SiC whisker (SiCw) toughened MoSi2–SiC–Si coating was prepared on the C/C surface by a two step technique of slurry and pack cementation. Scanning electron microscopy (SEM) analysis shows that, with the content of SiCw increasing, the dimensions and frequency of cracks in the coating decrease obviously. At the same time, the thickness and compact degree of the coating reduce with the increase of the SiCw content. Oxidation tests show that, as the content of SiCw is 10 wt-%, the coating possesses a better anti-oxidation property, and the weight loss of the coated sample is only 0˙8% after oxidation at 1773 K for 200 h. The weight loss of the as-coated C/C composites is primarily due to the reaction of the C/C matrix and oxygen diffusing through the penetration cracks and holes in the coating.

Novel insights into L-cysteine adsorption on transition metal doped graphene: influences of the dopant and the vacancy

Exploring potential applications of transition metal (TM) doped graphene in biomolecular adsorption is of fundamental relevance to the area of nanobiotechnology. Herein, we investigated L-cysteine adsorption on first-row transition metal (Sc–Zn) doped single-vacancy and double-vacancy graphenes (MSVs and MDVs) using density functional theory calculations. Three types of upright adsorption configurations, via unprotonated S-end, O-end and N-end functional groups, were considered. All the MSVs chemically adsorb L-cysteine with no regular variation tendency. MDVs show decreasing chemisorption from V to Co, followed by emergence of physisorption from Ni to Zn. L-Cysteine adsorption on MDVs is weaker than that on MSVs, starting from Mn to Zn. Both the TM dopant and the vacancy type contribute to adsorption tendency. In addition, site-specific chemisorption is revealed. The magnetic behaviour of the adsystems is also interesting. In particular, FeSV, ZnSV and NiSV become magnetic after all three end-type adductions. L-Cysteine adsorption induced distribution of the increasing number of 3d electrons and TM–C interactions could account for the magnetism mechanism. Interesting magnetization patterns of MSVs and MDVs occur in most magnetic chemisorbed systems, exhibiting different mirror symmetries. This study could facilitate applications of TM doped graphenes in biosensing, biomolecule immobilization, magnetic bioseparation and other fields in bionanotechnology.

Mo–Si–B ALLOYS OXIDATION PROTECTIVE COATING FOR SiC-COATED CARBON/CARBON COMPOSITES

A novel Mo–Si–B double-layer coating was prepared for the carbon/carbon (C/C) composites by pack cementation in an argon atmosphere. The structures of the double-layer coatings were characterized by XRD and SEM. The as-received coating shows an excellent oxidation resistance at high and intermediate temperature. It could effectively protect C/C composites from oxidation for 30 h with a weight loss of 0.9% in air at 1873 K, and for 25 h with a weight loss of l.7% at 1173 K. The oxidation protective coating was principally due to producing eutectic glass film for decreasing oxygen diffusing through the penetrable cracks in the coating.

Influence of silicon content on microstructure and antioxidation property of SiC coating for carbon–carbon composites

Abstract A SiC coating for carbon–carbon composites was prepared by the pack cementation method in an argon atmosphere. The influence of the silicon content in the pack cementation powder on the microstructure and antioxidation property of SiC coatings were studied. As the silicon content’s <82·4 wt-%, the as obtained coating possesses a porous structure with β-SiC phase. While the silicon content is up to 85·7 wt-%, the as prepared coating is of a dense structure consisting of β-SiC, α-SiC and Si. The thickness of the coating increases with the increase in silicon content. Oxidation test shows that the antioxidation property of the coating improves greatly as the silicon content is >82·4 wt-%.