Can Sun

SiC–MoSi2/ZrO2–MoSi2 coating to protect C/C composites against oxidation

Abstract To improve the oxidation resistance of carbon/carbon (C/C) composites in air at high temperatures, a SiC–MoSi 2 /ZrO 2 –MoSi 2 coating was prepared on the surface of C/C composites by pack cementation and slurry method. The microstructures and phase compositions of the coated C/C composites were analyzed by scanning electron microscopy and X-ray diffraction, respectively. The result shows that the SiC–MoSi 2 /ZrO 2 –MoSi 2 coating is dense and crack-free with a thickness of 250–300 μm. The preparation and the high temperature oxidation property of the coated composites were investigated. The as-received coating has excellent oxidation protection ability and can protect C/C composites from oxidation for 260 h at 1773 K in air. The excellent anti-oxidation performance of the coating is considered to come from the formation of ZrSiO 4 , which improves the stability of the coating at high temperatures.

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 thermal conductivity of carbon/carbon composites containing zirconium carbide

Carbon/carbon (C/C) composites containing zirconium carbide (ZrC) were prepared by a novel method. Carbon fiber felt with addition of zirconia was prepared by a microwave-hydrothermal reaction, followed by densification and graphitization. The crystalline structure of the pyrolytic carbon and morphology of the composites were investigated by X-ray diffraction, Raman spectrascope, polarized light microscope, and scanning electron microscopy. Results show that the ZrC grains with sub-micron size present a homogeneous distribution in carbon matrix. The degree of order of the pyrolytic carbon matrix is decreased due to adding ZrC into the C/C composites. Graphitization degree of the C/C composites is decreased by the addition of ZrC. ZrC grains uniformly embedded in the pyrolytic carbon matrix act as pinning particles blocking the conversion of disordered to ordered structure during graphitization. Thermal conductivity is higher in the C/C composites containing ZrC, which is attributed to the increased phonon-defect interaction produced by the thermal motion of the CO in the micropores and gaps of the composites.