Imperial College London


Faculty of EngineeringDepartment of Aeronautics

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Publication Type

14 results found

Nasiri S, Greff C, Wang K, Yang M, Li Q, Moretti P, Zaiser Met al., 2020, Multilayer structures of graphene and Pt nanoparticles: a multiscale computational study, Advanced Engineering Materials, Vol: 22, Pages: 1-11, ISSN: 1438-1656

Multiscale simulation study results of multilayer structures consisting of graphene sheets with embedded Pt nanoparticles is reported. Density functional theory is used to understand the energetics of Pt–graphene interfaces and provide reference data for the parameterization of a Pt–graphene interaction potential. Molecular dynamics simulations then provide the conformation and energetics of graphene sheets with embedded Pt nanoparticles of varying density, form, and size. These results are interpreted using a continuum mechanical model of sheet deformation, and serve to parameterize a meso‐scale Monte Carlo model to investigate the question under which conditions the free volume around the Pt nanoparticles forms a percolating cluster, such that the structures can be used in catalytic applications. This article is concluded with a discussion of potential applications of such multilayer structures.

Journal article

Nasiri S, Wang K, Yang M, Li Q, Zaiser Met al., 2019, Nickel coated carbon nanotubes in aluminum matrix composites: a multiscale simulation study, European Physical Journal B: Condensed Matter and Complex Systems, Vol: 92, Pages: 1-9, ISSN: 1434-6028

In this work we use density functional theory (DFT) calculations to benchmark empirical potentials for the interaction between nickel and sp2 bonded carbon nanoparticles. These potentials are then used in order to investigate how Ni decorated or coated carbon nanotubes (CNT) affect the mechanical properties of Al/CNT composites. In particular we look at the pull-out behaviour of pristine as well as Ni-decorated and Ni-coated CNT from an Al matrix. Our result shows that Ni coating may produce an extended interface (“interphase”) where a significant amount of energy is dissipated during CNT pull-out, leading to a high pull-out force. We also demonstrate that surface decorated CNT may act as efficient nano-crystallization agents and thus provide a novel strengthening mechanism not previously discussed in the literature. We discuss our results in view of promising approaches for engineering CNT-metal interfaces such as to achieve high strength metal-CNT composites.

Journal article

Fomenko LS, Lubenets S, Natsik VD, Prokhvatilov A, Galtsov NN, Li QQ, Koutsos Vet al., 2019, Investigation of the low-temperature mechanical behavior of elastomers and their carbon nanotube composites using microindentation, LOW TEMPERATURE PHYSICS, Vol: 45, Pages: 568-576, ISSN: 1063-777X

The micromechanical properties of epoxy resin elastomers and their carbon nanotube composites were studied using a microhardness tester equipped with low-temperature chamber. X-ray diffraction analysis indicated that all specimens were free of any crystalline components and were amorphous with only short-range order domains. The Vickers microhardness of all samples has been estimated in the temperature range 230–300 K. The measurements demonstrated that at room temperature these materials are elastomers (notably, they are in high-elastic state) and on cooling in the range of 250–270 K the glass transition takes place. Analysis of the temperature dependence of microhardness suggested that the thermomechanical and relaxation properties of the materials studied are consistent with a rheological model of a standard linear solid where the relaxation time (or viscosity) depends exponentially on the temperature in accordance with the Arrhenius equation for the rate of thermally activated process. Empirical estimates for the nonrelaxed and relaxed Young’s moduli and also for the activation energy (U = 0.75 eV) and the period of attempts (τ0 = 10–12 s) of the molecular process which determines the relaxation properties and the glasstransition of the materials have been obtained. The addition of carbon nanotubes into elastomeric epoxy resin had no effect on its micromechanical characteristics as measured by the microhardness tester. It is shown that the conventional microindentation method is an efficient tool of investigating the thermomechanical properties of elastomers nearby and below the glass transition temperature.

Journal article

Brandley E, Greenhalgh E, Shaffer M, Li Qet al., 2018, Mapping carbon nanotube orientation by fast fourier transform of scanning electron micrographs, Carbon, Vol: 137, Pages: 78-87, ISSN: 0008-6223

A novel method of applying a two-dimensional Fourier transform (2D-FFT) to SEM was developed to map the CNT orientation in pre-formed arrays. Local 2D-FFTs were integrated azimuthally to determine an orientation distribution function and the associated Herman parameter. This approach provides data rapidly and over a wide range of lengthscales.Although likely to be applicable to a wide range of anisotropic nanoscale structures, the method was specifically developed to study CNT veils, a system in which orientation critically controls mechanical properties. Using this system as a model, key parameters for the 2D-FFT analysis were optimised, including magnification and domain size; a model set of CNT veils were pre-strained to 5%, 10% and 15%, to vary the alignment degree. The algorithm confirmed a narrower orientation distribution function and increasing Herman parameter, with increasing pre-strain.To validate the algorithm, the local orientation was compared to that derived from a common polarised Raman spectroscopy. Orientation maps of the Herman parameter, derived by both methods, showed good agreement. Quantitatively, the mean Herman parameter calculated using the polarised Raman spectroscopy was 0.42 ± 0.004 compared to 0.32 ± 0.002 for the 2D-FFT method, with a correlation coefficient of 0.73. Possible reasons for the modest and systematic discrepancy were discussed.

Journal article

Brandley E, Li Q, Greenhalgh E, Shafferr MSPet al., 2017, Full paper – Alignment study of CNT veils and the influence on their composites, 21 st International Conference on Composite Materials

© 2017 International Committee on Composite Materials. All rights reserved. A methodology was developed to measure the alignment of carbon nanotubes in pre-strained samples of carbon nanotube veils via image processing techniques. The methodology was used on samples of as-received and pre-strained carbon nanotube veils and calculated an increased Herman parameter for the pre-strained sample relative to the as-received. A number of image processing techniques, specifically high and low pass filters, were tested in order to increase the signal of the carbon nanotubes in the scanning electron micrographs, however it was found filtering the micrograph prior did not enhance nanotube signal and did not improve the calculated orientation distribution function.

Conference paper

Li Q, Nasiri S, Zaiser M, 2017, Full paper – Magnesium composites reinforced by metal coated carbon nanotubes, 21st International Conference on Composite Materials

© 2017 International Committee on Composite Materials. All rights reserved. The interest to use carbon nanotubes (CNTs) to reinforce light metals has increased in recent years due to their potential application as lightweight high performance materials. One challenge in producing CNT composites is to achieve a homogenous dispersion of CNTs in the metal matrix. In order to effectively disperse CNTs in the Mg melt, we for the first time introduced the idea of using metal coated CNTs to promote the integration into Mg matrix. In this paper, Pt was selected to coat the CNT surface. TEM and EDX confirm that atomic Pt has been successfully deposited onto CNTs. The dispersion and stability of metal coated CNTs in solution have been investigated and compared to CNTs without metal coating. The Pt coated CNT reinforced Mg composites were also produced via a melt stirring process. The mechanical properties of such composites also showed a clear upward tendency, which we attribute to the Pt coating to help the dispersion of CNTs.

Conference paper

Li Q, Zaiser M, Blackford JR, Jeffree C, He Y, Koutsos Vet al., 2014, Mechanical properties and microstructure of single-wall carbon nanotube/elastomeric epoxy composites with block copolymers, Materials Letters, Vol: 125, Pages: 116-119, ISSN: 0167-577X

Single-wall carbon-nanotube (SWNT) reinforced elastomeric epoxy composites were fabricated by adding 0.03 wt% SWNTs and using 0.3 wt% block copolymer to obtain a good dispersion of carbon nanotubes in the epoxy matrix. Young׳s modulus, fracture stress and strain of the SWNT/epoxy composites with block copolymer were increased by 141%, 127% and 43%, respectively, compared to the pure epoxy resin. Scanning electron microscopy observation revealed that using the block copolymer as a dispersing agent significantly improved both SWNT dispersion in the epoxy matrix and interfacial bonding/load transfer.

Journal article

Hippmann S, Li Q, Addinal R, Volk Wet al., 2013, Carbon nanotubes–reinforced copper matrix composites produced by melt stirring, Proceedings of the Institution of Mechanical Engineers, Part N: Journal of Nanoengineering and Nanosystems, Vol: 227, Pages: 63-66, ISSN: 1740-3499

<jats:p> Due to their geometry and extraordinary mechanical properties, carbon nanotubes have been envisioned as promising enhancements for metal matrix composites. In this article, we report on our melt stirring approach for incorporation of carbon nanotubes into a copper alloy matrix and on the experimental results obtained by assessing the material properties. The existence of carbon nanotubes in the copper matrix after processing was proven by Raman analysis. We found that the small amounts of carbon nanotubes (0.1 wt%) in the composites influenced mechanical and abrasive wear properties. </jats:p>

Journal article

Li Q, Turhan MC, Rottmair CA, Singer RF, Virtanen Set al., 2012, Influence of MWCNT dispersion on corrosion behaviour of their Mg composites, MATERIALS AND CORROSION-WERKSTOFFE UND KORROSION, Vol: 63, Pages: 384-387, ISSN: 0947-5117

Journal article

Turhan MC, Li Q, Jha H, Singer RF, Virtanen Set al., 2011, Corrosion behaviour of multiwall carbon nanotube/magnesium composites in 3.5% NaCl, ELECTROCHIMICA ACTA, Vol: 56, Pages: 7141-7148, ISSN: 0013-4686

Journal article

Li Q, Rottmair CA, Singer RF, 2010, CNT reinforced light metal composites produced by melt stirring and by high pressure die casting, Composites Science and Technology, Vol: 70, Pages: 2242-2247, ISSN: 0266-3538

Light metal matrix composites are of great interest due to their potential for reducing CO2 emission through lightweight design e.g. in the automotive sector. Carbon nanotubes can be considered as ideal reinforcements, due to their high strength, high aspect ratio and thermo-mechanic properties. In this research, CNT reinforced light metal composites were produced by melt stirring and by high pressure die casting, which can be both easily scaled up. The light metal composites showed significantly improved mechanical properties already at small CNT contents. The influence of CNT concentration on the composites was also studied. © Elsevier Ltd.

Journal article

Li Q, Viereckl A, Rottmair CA, Singer RFet al., 2009, Improved processing of carbon nanotube/magnesium alloy composites, Composites Science and Technology, Vol: 69, Pages: 1193-1199, ISSN: 0266-3538

Carbon nanotubes (CNTs) are promising reinforcements for light weight and high strength composites due to their exceptional properties. However, until now, the main obstacle is to obtain a homogenous dispersion of the CNTs in the desired material matrix. Quite a few methods have been studied to help improving the dispersion of CNTs in a polymer matrix. But not much research has been conducted on how to disperse CNTs in metal matrices. In this study, a two-step process was applied. In the first stage, a block copolymer was used as a dispersion agent to pre-disperse multiwall carbon nanotubes (MWNTs) on Mg alloy chips. Then the chips with the well dispersed MWNTs on their surface were melted and at the same time vigorously stirred. The molten MWNT Mg alloy composites were poured into a cylindrical mould to solidify quickly. For the pre-dispersion step, the microstructures of the Mg alloy chips were studied under SEM. MWNTs were quite successfully dispersed on the surfaces of the Mg alloy chips. The mechanical properties of the MWNT/Mg composites were measured by compression testing. The compression at failure, the compressive yield strength and ultimate compressive strength have all been improved significantly up to 36% by only adding 0.1 wt% MWNTs to the Mg alloy. In order to predict the potential yield strengths of the MWNT reinforced Mg alloy composites, the contributions by load transfer, Orowan strengthening and thermal mismatch were added up. © 2009 Elsevier Ltd. All rights reserved.

Journal article

Bright I, Koutsos V, Li Q, Cheung Ret al., 2006, Carbon nanotubes for integration into nanocomposite materials, Microelectronic Engineering, Vol: 83, Pages: 1542-1546, ISSN: 0167-9317

Journal article

Li Q, Zaiser M, Koutsos V, 2004, Carbon nanotube/epoxy resin composites using a block copolymer as a dispersing agent, physica status solidi (a), Vol: 201, Pages: R89-R91, ISSN: 0031-8965

Journal article

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