Papers

06/2014
Replacing copper wires with carbon nanotube wires in electrical transformersAdvanced Functional Materials 24, 619 (2014)
L. Kurzepa, A. Lekawa-Raus, J. Patmore, K. Koziol

Carbon nanotubes with their unique physical properties have the potential to outperform conventionally used electrical wiring metals. Any improvement in this area of technology would be of great importance to industry, the economy and the environment as the global need for electrical energy and its efficient transfer and conversion rapidly increases. Carbon nanotube fibers, which are assemblies made purely of carbon nanotubes, can uniquely be used in macroscopic electrical applications including electrical wires and devices where the operation is enabled by these conductors. This paper presents details of the working prototype of an electrical machine - a transformer, where conventional copper wires have been replaced with conducting wires made purely of carbon nanotube fibers. 

doi: 10.1002/adfm.201302497
06/2014
Microwave conductivity of sorted CNT assembliesScientific Reports 4, 3762 (2014)
J.S. Bulmer, J. Martens, L. Kurzepa, T. Gizewski, M. Egilmez, M.G. Blamire, N. Yahya, K.K. Koziol

Recent progress with tailored growth and post-process sorting enables carbon nanotube (CNT) assemblies with predominantly metallic or semi-conducting concentrations. Cryogenic and microwave measurements performed here show transport dimensionality and overall order increasing with increasing metallic concentration, even in atmospheric doping conditions. By 120 GHz, the conductivity of predominantly semi-conducting assemblies grew to 400% its DC value at an increasing growth rate, while other concentrations a growth rate that tapered off. A generalized Drude model fits to the different frequency dependent behaviors and yields useful quality control parameters such as plasma frequency, mean free path, and degree of localization. As one of the first demonstrations of waveguides fabricated from this material, sorted CNTs from both as-made and post-process sources were inserted into sections of practical micro-strip. With both sources, sorted CNT micro-strip increasingly outperformed the unsorted with increasing frequency-- illustrating that sorted CNT assemblies will be important for high frequency applications.

doi: 10.1038/srep03762
06/2014
A facile water-assisted route for synthesis of tungsten dioxide (WO2) nanopowdersPowder Technology 256, 1 (2014)
S. Coskun, K.K. Koziol

The possibility of reducing the size of bulk materials, particularly making nanoparticles with controlled size, structure and shape offers massive benefits for various applications. In this respect, we report a novel water-assisted method to produce clusters of WO2 nanopowders with very high conversion yields of 90%. The proposed process is simplistic in its nature and carried out at room temperature. Nanopowders were obtained as a result of the hydrolysis of the tungsten precursor (WCl6) in the presence of NaBH4. Particle sizes of the as-synthesised partially crystallized nanopowders show a uniform distribution around 35 nm. Fully crystallized nanopowders without any morphological alteration were successfully produced already after annealing at 500 °C for 2 h. The nanopowders were examined using electron microscopy, XRD and DSC.

doi: 10.1016/j.powtec.2014.01.093
06/2014
Effect of fibre spinning conditions on the electrical properties of cellulose and carbon nanotube composite fibres spun using ionic liquid as a benign solventeXPRESS Polymer Letters 8, 154 (2014)
C. Zhu, J. Chen, K. K. Koziol, J. W. Gilman, P. C. Trulove, S. S. Rahatekar

The aim of this study was to develop electrically conductive fibres from cellulose. To achieve this, the effect of fibre extrusion speed and fibre winding speed on the degree of alignment of multiwall carbon nanotubes (MWNTs), as well as the resulting electrical properties of the cellulose/MWNTs composite fibres were systematically studied. 1-Ethyl-3- Methylimidazolium Acetate (EMIMAc) was used as an environmentally benign solvent for dissolution of cellulose as well as for dispersion of MWNTs in the solution dope. To achieve good dispersion of MWNTs in the cellulose solution dope, MWNTs were non-covalently functionalized using carboxymethyl cellulose (CMC). This significantly improved the dis- persion of MWNTs in the solution dope. The degree of alignment of MWNTs after both fibre extrusion and winding, was studied using scanning electron microscopy (SEM) and wide angle X-ray diffraction (WAXD). The degree of alignment of MWNTs was correlated with the electrical properties. A significant decrease in electrical conductivity accompanied the increase in degree of alignment of MWNTs when fibres were spun with higher extrusion speed. The decrease was also measured when fibres were spun with higher winding speed using a constant extrusion speed. However, the decrease in conductivity due to winding was low relative to fibres spun at highest extrusion speed.

doi: 10.3144/expresspolymlett.2014.19
06/2014
A review of production methods of carbon nanotube and graphene thin films for electrothermal applicationsNanoscale 6, 3037 (2014)
D. Janas, K.K. Koziol

Electrothermal materials transform electric energy into heat due to the Joule effect. To date, resistive wires made of heavy metal alloys have primarily been used as heat source in many appliances surrounding us. Recent discoveries in the field of carbon nanostructures revealed that they can offer a spectrum of advantages over the traditional materials. We review the production methods of thin films composed of carbon nanotubes or graphene and depict how they can be used as conductive coatings for electrothermal applications. We screen all reports from the field up to now and highlight the features of designed nanoheaters. A particular focus is placed on the analysis of general findings how to tune their electrothermal properties, why carbon nanostructures devices operate the way they do and in what aspects they are superior to the currently available materials on the market.

doi: 10.1039/C3NR05636H
06/2014
Swift modification of resistively heated carbon nanotube films by the action of hydrogen peroxideMaterials Letters 119, 114 (2014)
D. Janas, A.P. Herman, S. Boncel, K.K. Koziol

We have developed a benign technique of modification of electrical and structural properties of horizontally aligned carbon nanotube (CNT) films. The as-made CNT films were immersed in 30% wt. aqueous solution of hydrogen peroxide whilst current was passed through the nanotube bundles to bring the temperature of CNTs up to 200°C. Depending on the employed conditions, we either successfully removed extraneous material contaminating CNT films and decreased its resistance by 40% or initiated introduction of functional groups. The whole process lasted only 1 minute and was more straightforward, less expensive and more ecologically friendly than the current post-processing technologies. We imagine that such a method of tweaking up electrical and/or structural properties could be successfully employed to a range of nanomaterials with a particular focus on carbon C-sp2 nanostructures.

doi: 10.1016/j.matlet.2014.01.001
06/2014
Shear-induced crystallisation of molten isotactic polypropylene within the intertube channels of aligned multi-wall carbon nanotube arrays towards structurally controlled compositesMaterials Letters 116, 53 (2014)
S. Boncel, J. Gorka, M.S.P. Shaffer, K.K.K. Koziol

A melt processing route was successfully applied in the manufacturing of aligned multi-wall carbon nanotube/isotactic polypropylene (MWCNT-iPP) composites. As high as 25 wt% content of the catalytic Chemical Vapour Deposition (c-CVD) derived nanotube filler could be introduced into the iPP matrix. The composite was characterised by a practically retained nanotube alignment as well as an enhanced crystallisation of iPP. Analysis of the phase iPP composition in the composite using XRD and DSC revealed a dominating α-phase with polymer molecules uniaxially oriented in the same direction as the nanotube alignment. Furthermore, kinetic in situ Synchrotron XRD studies verified that the enhanced crystallisation was induced mainly by shear stress occurring in the initial stage of infiltration MWCNT arrays by flowing molten polymer and, to a lesser extent, by the template-based growth of iPP crystallites.

doi: 10.1016/j.matlet.2013.10.084
06/2014
Improved performance of ultra-fast carbon nanotube film heatersJournal of Automation and Control Engineering 2, 150 (2014)
D. Janas, K.K.K. Koziol

With current level of development, mankind is about to face many energy-related problems unless we find ways for more efficient power generation and transmission. In this paper, we depicted the operation of high-performance carbon nanotube film heaters, which show a clear advantage over traditionally employed materials. The material was synthesized by a facile one-step method and used as resistive heating element. The results have shown very effective conversion of electric power into heat. To improve the homogeneity of the heaters electrical resistance, we explored a selection of volatile solvents. Such a pretreatment step prior to heaters use caused densification of the material and favorable changes to the electrothermal behavior.

doi: 10.12720/joace.2.2.154-159