47 research outputs found
Graded SiC reinforced magnesium wires: towards high throughput composite alloy discovery
No full textHigh-throughput methods can accelerate the development of metal alloys and (nano)composites, both empirically and as input to computational methods. This study introduces a new route to fabricating composite wires with longitudinally varying composition using the byproduct of stationary-shoulder friction stir channelling (SS-FSC); this sample format is attractive for a variety of rapid read-out options in the future. The concept is illustrated by preparing Mg composite wires with a longitudinally graded concentration of SiC-particles. Spark plasma sintering (SPS) was used to encode a step-change in SiC concentration within a feedstock billet. Subsequent SS-FSC transformed this discrete compositional step into a continuous, graded extruded wire. Microstructural analysis revealed significant grain refinement from the SPS billet (44.3 ± 2.3 µm) to the SS-FSC wire (7.4 ± 0.5 µm), with even finer grains in SiC-loaded regions (5.1 ± 0.5 µm), attributed to particle-stimulated nucleation. Mechanical characterisation confirmed a hardness increase, from 65.8 ± 1.2 HV3 to 68.9 ± 2.7 HV3 (high SiC-content). This proof-of-concept study confirms the effectiveness of SS-FSC in producing high-quality wires with tailored microstructural and mechanical gradients. Additional compositions could be readily multiplexed in the original billet, providing a robust high-throughput technique for comprehensive structure–property investigations of advanced alloys and composites
From organometallic zinc and copper complexes to highly active colloidal catalysts for the conversion of CO2 to methanol
No full textA series of zinc oxide and copper(0) colloidal nanocatalysts, produced by a one-pot synthesis, are shown to catalyze the hydrogenation of carbon dioxide to methanol. The catalysts are produced by the reaction between diethyl zinc and bis(carboxylato/phosphinato)copper(II) precursors. The reaction leads to the formation of a precatalyst solution, characterized using various spectroscopic (NMR, UV–vis spectroscopy) and X-ray diffraction/absorption (powder XRD, EXAFS, XANES) techniques. The combined characterization methods indicate that the precatalyst solution contains copper(0) nanoparticles and a mixture of diethyl zinc and an ethyl zinc stearate cluster compound [Et4Zn5(stearate)6]. The catalysts are applied, at 523 K with a 50 bar total pressure of a 3:1 mixture of H2/CO2, in the solution phase, quasi-homogeneous, hydrogenation of carbon dioxide, and they show high activities (>55 mmol/gZnOCu/h of methanol). The postreaction catalyst solution is characterized using a range of spectroscopies, X-ray diffraction techniques, and transmission electron microscopy (TEM). These analyses show the formation of a mixture of zinc oxide nanoparticles, of size 2–7 nm and small copper nanoparticles. The catalyst composition can be easily adjusted, and the influence of the relative loadings of ZnO/Cu, the precursor complexes and the total catalyst concentration on the catalytic activity are all investigated. The optimum system, comprising a 55:45 loading of ZnO/Cu, shows equivalent activity to a commercial, activated methanol synthesis catalyst. These findings indicate that using diethyl zinc to reduce copper precursors in situ leads to catalysts with excellent activities for the production of methanol from carbon dioxid
Rapid quantitative mapping of multi-walled carbon nanotube concentration in nanocomposites
No full textInhomogeneous distributions of nanoparticles in polymer nanocomposites have a strong influence on final material properties. Quantitative methods to characterise particle dispersion are rarely applied but are critical for advancing understanding of material behaviour, developing accurate computer models, and optimizing processing. Two complementary quantitative methods were developed to map local concentration, based on Raman spectroscopy and simple optical absorbance, respectively. The approaches are demonstrated for a model multi-walled carbon nanotube (MWNT) epoxy nanocomposite, but should be widely applicable. Maps of absolute concentration can be produced with submicron resolution, allowing analysis of the uniformity of MWNT concentration distribution via the coefficient of variation. The two approaches correlate closely, providing validation of both methods. However, the optical absorbance approach is likely to be more practical, in most cases, as it uses a standard laboratory microscope to analyse large areas rapidly
“Binary salt” of hexane‐1,6‐diaminium adipate and “carbon nanotubate” as a synthetic precursor of carbon nanotube/Nylon‐6,6 hybrid materials
No full textThe Influence of Variability and Defects on the Structural Performance of Discontinuous Composites
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High-speed imaging of CNT deagglomeration in aqueous solution with surfactant
No full textThis study investigates the mesoscale deagglomeration mechanisms of multi-walled carbon nanotubes (MWCNTs) in aqueous solutions with and without added surfactant (Triton X-100), using high-speed imaging and numerical simulations. High-speed observations revealed that within the cavitation zone (CZ, defined as the region of high bubble intensity), the addition of surfactant had no obvious effects on deagglomeration behaviour, with most agglomerates remaining intact and only occasional fragmentation events observed. In contrast, in regions outside the CZ, surfactant addition significantly increased the number and stability of microbubble clusters, leading to more frequent interactions with MWCNT agglomerates. Numerical simulations performed under matched experimental conditions confirmed aspatial variation in bubble dynamics, with enhanced microbubble formation and persistence in surfactant-containing solutions, particularly at distances away from the sonotrode. These findings provide direct mechanistic evidence that surfactant not only stabilises dispersed CNTs but also facilitates microbubble-mediated deagglomeration outside the CZ. The results highlight the role of structured bubble activity in extending the effective dispersion region during ultrasonication, offering insight into the optimisation of CNT processing in surfactant-assisted systems
Mapping carbon nanotube orientation by fast fourier transform of scanning electron micrographs
No full textA 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
Evaluation of healable epoxy matrices as covalent adaptive networks in uniaxial compression
No full textVitrimers provide dynamic bonding that can allow a degree of self-healing capability in cross-linked resins. A commercial amine-cured epoxy resin, Prime 27 was observed to show a compressive yield stress, measured in compression, of 88 2 MPa and a compression modulus of 3.41 0.03 GPa. This base resin was modified by incorporating various proportions of two commercial vitrimers, either Thioplast EPS35 (an aliphatic epoxy-terminated polysulfide) or Vitrimax T130 (an imine-cured DGEBA epoxy resin). The addition of increasing amounts of Thioplast EPS35 into the resin led to a rapid drop in the glass transition temperature of the matrices and also a reduction in compressive performance. After an initial test in quasi-static, uniaxial compression, samples containing vitrimers were heated for 1h at 100°C and then subjected to a second compression test; all of the matrices loaded with Thioplast EPS35 were able to recover their full initial compression performance. Addition of increasing amounts of Vitrimax T130 to the same commercial epoxy resin did not cause any change in its glass transition temperature. However, after initial compression testing, followed by heating (1h at 100°C), only the formulation containing 40 wt% Vitrimax T130-loaded matrix regained its full initial compressive performance. Optimal results in terms of healing capability, measured as the recovery of the initial compression performance during a second identical test, following a heating step, were achieved by incorporating 10 wt% of EPS35 or 40 wt% Vitrimax T130, with little to no drop in glass transition temperature. For these selected formulations, the incorporation of 10% Thioplast EPS35 in Prime 27 gave a yield stress of 83 2 MPa and a compression modulus of 3.13 0.02 GPa, while the addition of 40% Vitrimax T130 gave a yield stress of 79 2 MPa and a compression modulus of 3.30 0.02 GPa
PROBING COMPRESSIVE BEHAVIOUR AND FAILURE IN SINGLE FIBRE CARBON FIBER COMPOSITES: IN-DEPTH ANALYSIS USING IN SITU LASER RAMAN SPECTROSCOPY
No full textCompressive failure of fibres in unidirectional composites is often characterised by microbuckling and the formation of kink bands. Developing insight into the behaviour of reinforcing fibre and the fibre-matrix interface before, during, and after failure is crucial for enhancing compressive performance. Direct mechanical testing of single fibres is limited due to scale considerations, necessitating alternative approaches, additionally, characterising interfacial behaviour in compressive loading lacks a direct quantitative method.In this study, Raman spectroscopy is utilised as a non-contact method for characterising micromechanical behaviour and interfacial responses during compressive loading. In situ laser Raman spectroscopy is employed to investigate compressive stress-strain behaviour of single fibres as well as generate spatially resolved stress maps of single carbon fibres under compression. Two experimental setups are discussed: a four-point bending setup for static Raman analysis and a uniaxial compression setup for stress map generation. High-resolution Raman stress maps, scanning electron microscopy, and confocal laser scanning microscopy are used to examine the evolution of failure of high modulus carbonfibres. This research contributes to a deeper understanding of compressive performance in carbon fibre composites, crucial for advancing their design and future application
