Composites

Incorporation of carbon nanotubes or graphene into some form of matrix, and preparation of composite material is the simplest way of transferring their unique properties from nanoscale to the world of macroscopic structures. In our group we work with polymer, ceramic and metal matrices.

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Polymer matrix composites - Composites for high wear resistance performance.

Polymer composite materials have many advantages such as low weight, corrosion resistance, high fatigue strength and faster assembly etc, however they are soft and easily damaged by erosion which may lead to expensive equipment failure. For example, in a 12 month period to 2003 the US army sustained helicopter rotor blade renewal cost amounted to $189M on just three aircraft types, due to sand erosion. Another example of the poor erosion resistance of polymer composites is the far higher levels of surface damage sustained by fibre-reinforced plastic (FRP) compared to alloy metal based composites. In the past, efforts have been made to obtain good erosion resistance for polymers but progress has been limited

It has been recognised that the high strength-to-weight performance of polymer composites is key to enhancing product performance in both aerospace and wind turbine industries as well as in road and rail vehicles along with other advanced applications. Therefore the use of erosion-resistant fibre reinforced composites would be a highly attractive proposition to these areas of industry, to extend equipment life thereby saving cost. Traditional fibres such as carbon and glass contribute little to strengthening the erosive wear resistance in polymer composites and may even have a detrimental effect on this property.  Polymer composites have not as yet reached the same levels of performance as steel, nickel alloys or metal composites in terms of their erosive wear resistance. We have explored the use of CNTs for polymer matrix reinforcement and demonstrated significant gains in erosive wear resistance comparable to carbon steel in terms of weight loss. We have also shown that the altering of CNT structures (i.e. alignment morphologies) may change the erosive wear behaviour. Future research in this area will focus on an in-depth understanding of erosion mechanisms in relation to CNT composites and their correlation with CNT structures. In particular we are exploring the use of ceramic materials to make ceramic-CNT hybrid structures, however, the method of assembling/bonding ceramic nanoparticles, CNTs and polymers will be one of the key challenges.

Our polymer composite research focuses not only on the improvement of wear resistance, but also on exploring multi-functional properties of composite structures containing carbon nanomaterials. This research has had significant impact in the academic community and is of strong national importance for UK where the aerospace industry is the third largest in the world and currently worth £22 billion. This industry steadily increases the use advanced carbon-fibre polymer composites to decrease aeroplane weight and reduce CO2 emissions. In special configurations CNT composites can be ten times stronger than steel, but with only one-fifth the weight, thus making such composites even more attractive than carbon fibre composites for use in aeroplanes and satellites as well as cars, trains or even body armour. Therefore, we plan to continue the research in this area as we expect that the development of new CNT-polymer composites can make significant improvements in many areas of engineering.


Carbon nanotube reinforced polymer matrix composite

Polymer matrix composites - Composites for radiation protection.

Unwanted radiation is a problem in nuclear power facilities, nuclear medicine, radioisotope projects, particle accelerator work and a number of other settings. It is vital that both people and structural materials are protected from exposure to its potentially harmful and damaging effects. There are various types of radiation shielding materials and protective clothing available on the market with lead having been used in the production of protective clothing for a number of years.  However lead is not without its drawbacks: it is toxic, environmentally unfriendly, costly to dispose of and heavy. These issues have stimulated the attempts to develop a lead-free radiation protection material for use in protective clothing for example by incorporating less toxic metal powders into polymer layers.

 


Different types of composite explored in our group for shielding application.

We are currently exploring a new lead-free composite material based on carbon nanotubes and metals in an epoxy matrix for use as shielding against radiation.  This material will be lightweight, non-toxic, inexpensive to dispose of and environmentally friendly whilst providing equivalent or better protection than traditional lead based materials. This composite could be used in high temperature radiation environments where both the properties of shielding and high thermal conductivity are required. Furthermore, the material can be coated, painted, easily shaped, used as filler in the wall of the radiation treatment facilities, as a protective coating on electronic devices and as a protective shield tailored to the individual anatomies of patients undergoing radiological procedures.  

 

Metal matrix composites.
The unique properties of graphitic materials, including low density, high decomposition temperature, excellent thermal conductivity, resistivity to corrosion and erosion as well as great mechanical performance in wide range of temperatures might render them unrivalled candidates for the applications in many areas of industry. However, the difficulty of joining of these structures together or to other materials such as metals has always been one of the major constraints limiting the application of classic carbon materials and nowadays becomes an obstacle for the potential use of nanostructured carbon materials. Properties of metal matrix composites reinforced with carbon nanotubes depend on several factors including thermal and chemical stability of carbon material in metal matrix, thermodynamic aspects of carbide formation and finally wetting of carbon material by liquid metal.

Carbon nanotubes reinforced metal matrix composite

Wetting of nanostructural carbon materials by liquid metals plays a key role in the production of metal matrix composites reinforced with carbon nanotubes (MM-CNT). Wettability, described by the wetting angle between solid and liquid phase, depends on several factors including characteristic surface energies of interacting phases and also parameters of the process such as temperature, pressure and gaseous atmosphere. High temperature required by processes such as casting, preform infiltration, thermal spraying and welding (arc, plasma and laser melting) may be responsible for the formation of crystallographic defects or even total decomposition of nanotubes due to their uncontrolled reaction with the molten metal. Understanding the interaction between carbon nanotubes and the molten metals is a key factor which will enable full exploitation of their potential. Our research focuses on thermal stability of carbon nanotubes in molten metals, the design of metal alloys that wet the carbon nanotubes and development of new procedures for formation of metal-matrix composites.


Silver-CNT composite made by metal infiltration of CNT arrays: a) as made composite, b) bottom view of composite and “razor blade-test” of infiltration thickness