The mechanical and electrical properties of direct-spun carbon nanotube mat-epoxy composites

Composites of direct-spun carbon nanotube (CNT) mats and epoxy are manufactured and tested in order to determine their mechanical and electrical properties. The mats are spun directly from a floating catalyst, chemical vapour deposition reactor. The volume fraction of epoxy is varied widely by suitable dilution of the epoxy resin with acetone. Subsequent evaporation of the acetone, followed by a cure cycle, leads to composites of varying volume fraction of CNT, epoxy and air. The modulus, strength, electrical conductivity and piezoresistivity of the composites are measured. The CNT mats and their composites exhibit an elastic-plastic stress-strain response under uniaxial tensile loading, and the degree of anisotropy is assessed by testing specimens in 0{\deg}, 45{\deg} and 90{\deg} directions with respect to the draw direction of mat manufacture. The electrical conductivity scales linearly with CNT volume fraction, irrespective of epoxy volume fraction. In contrast, the modulus and strength depend upon both CNT and epoxy volume fractions in a non-linear manner. The macroscopic moduli of the CNT mat-epoxy composites are far below the Voigt bound based on the modulus of CNT walls and epoxy. A micromechanical model is proposed to relate the macroscopic modulus and yield strength of a CNT mat-epoxy composite to the microstructure

Mapping the parameter space for direct-spun carbon nanotube aerogels

Industrial-scale use of carbon nanotube (CNT) materials and prototype development is limited by availability of economic, high throughput production methods. Recent investigations have demonstrated the feasibility of producing direct-spun macroscopic CNT materials via floating catalyst chemical vapour deposition. However, few quantitative results have been reported regarding process yield and correlations with product quality. Validation of results is therefore challenging as identification of the key fundamental process parameters is hindered. This first meta-analysis quantifies atomic input rates and correlates them with product outputs to map the current parameter space of 55 successful conditions leading to spinnable aerogels. All mapped processes fall within a bulk residence time of 5–240 s, operating temperature of 1100–1500°C and an atomic S:Fe of 0.1–10. Low (high) S/Fe ratios favour single (multi)-wall CNTs in the direct-spun product. A high atomic carbon dilution, only 3% of the input atoms being C, is a common feature across many systems. Furthermore, we connect the findings to known catalyst and product growth behaviour, as well as the thermodynamics of intermediates, to create an emerging picture of direct-spun CNT product formation. Elucidation of the most important factors influencing material synthesis, and the relationships between them, provides opportunities for gains in industrial-scale synthesi

The mechanical and electrical properties of direct-spun carbon nanotube mats

The mechanical and electrical properties of a direct-spun carbon nanotube mat are measured. The mat comprises an interlinked random network of nanotube bundles, with approximately 40 nanotubes in a bundle. A small degree of in-plane anisotropy is observed. The bundles occasionally branch, and the mesh topology resembles a 2D lattice of nodal connectivity slightly below 4. The macroscopic in-plane tensile response is elasto-plastic in nature, with significant orientation hardening. In-situ microscopy reveals that the nanotube bundles do not slide past each other at their junctions under macroscopic stain. A micromechanical model is developed to relate the macroscopic modulus and flow strength to the longitudinal shear response of the nanotube bundles. The mechanical and electrical properties of the mat are compared with those of other nanotube arrangements over a wide range of density

Catalyst‐mediated enhancement of carbon nanotube textiles by laser irradiation: Nanoparticle sweating and bundle alignment

The photonic post-processing of suspended carbon nanotube (CNT) ribbons made by floating catalyst chemical vapor deposition (FC-CVD) results in selective sorting of the carbon nanotubes present. Defective, thermally non-conductive or unconnected CNTs are burned away, in some cases leaving behind a highly crystalline (as indicated by the Raman G:D ratio), highly conductive network. However, the improvement in crystallinity does not always occur but is dependent on sample composition. Here, we report on fundamental features, which are observed for all samples. Pulse irradiation (not only by laser but also white light camera flashes, as well as thermal processes such as Joule heating) lead to (1) the sweating-out of catalyst nanoparticles resulting in molten catalyst beads of up to several hundreds of nanometres in diameter on the textile surface and (2) a significant improvement in CNT bundle alignment. The behavior of the catalyst beads is material dependent. Here, we show the underlying mechanisms of the photonic post-treatment by modelling the macro- and microstructural changes of the CNT network and show that it is mainly the amount of residual catalyst which determines how much energy these materials can withstand before their complete decomposition.</jats:p

On the Origin of S0 Galaxies

I will review the basic properties of S0 galaxies in the local Universe in relation to both elliptical and spiral galaxies, their neighbours on the Hubble sequence, and also in relation to dwarf spheroidal (dSph) galaxies. This will include colours, luminosities, spectral features, information about the age and metallicity composition of their stellar populations and globular clusters, about their ISM content, as well as kinematic signatures and their implications for central black hole masses and past interaction events, and the number ratios of S0s to other galaxy types in relation to environmental galaxy density. I will point out some caveats as to their morphological discrimination against other classes of galaxies, discuss the role of dust and the wavelength dependence of bulge/disk light ratios. These effects are of importance for investigations into the redshift evolution of S0 galaxies -- both as individual objects and as a population. The various formation and transformation scenarios for S0 and dSph galaxies will be presented and confronted with the available observations.Comment: Invited Review, 18 pages, ``BARS 2004'' Conference, South Africa, June 2004, eds.: K. C. Freeman, D. L. Block, I. Puerari, R. Groess, Kluwer, in pres

Spinning of carbon nanotube fibres using the floating catalyst high temperature route: Purity issues and the critical role of sulphur

The CVD process for the spinning of carbon nanotube (CNT) fibres combines the nucleation, growth and aggregation of CNTs in the form of an aerogel with fibre spinning into a single process step. The optimisation of the process requires agility in multi-dimensional parameter space, so one tends to find parameter 'islands' where spinning is possible, while exploration tends to follow 'routes' through this space. Here, we follow two such routes, one of which drastically improves fibre purity, the other changes the nature of the nanotubes comprising the fibres from multiwall to single wall. In the first case there is only a modest enhancement of the mechanical properties, but in the second a very considerable improvement is seen. In terms of the conditions required to make fibres comprising predominately single wall CNTs, the key factor appears to be the rigorous control of the sulphur addition, in trace quantities, coupled with the availability of carbon atoms at the earliest stage after injection, typically in the range 400-500 °C. A model is presented for the role of sulphur in floating catalysts CNT synthesis

Mapping the parameter space for direct-spun carbon nanotube aerogels

Industrial-scale use of carbon nanotube (CNT) materials and prototype development is limited by availability of economic, high throughput production methods. Recent investigations have demonstrated the feasibility of producing direct-spun macroscopic CNT materials via floating catalyst chemical vapour deposition. However, few quantitative results have been reported regarding process yield and correlations with product quality. Validation of results is therefore challenging as identification of the key fundamental process parameters is hindered. This first meta-analysis quantifies atomic input rates and correlates them with product outputs to map the current parameter space of 55 successful conditions leading to spinnable aerogels. All mapped processes fall within a bulk residence time of 5–240 s, operating temperature of 1100–1500°C and an atomic S:Fe of 0.1–10. Low (high) S/Fe ratios favour single (multi)-wall CNTs in the direct-spun product. A high atomic carbon dilution, only 3% of the input atoms being C, is a common feature across many systems. Furthermore, we connect the findings to known catalyst and product growth behaviour, as well as the thermodynamics of intermediates, to create an emerging picture of direct-spun CNT product formation. Elucidation of the most important factors influencing material synthesis, and the relationships between them, provides opportunities for gains in industrial-scale synthesi