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08 December 2009 NANO Magazine - Issue 6

Carbon Nanotubes

We explore the range of applications carbon nanotubes will offer

Image Credit: NANO Magazine.

Imagine a cable, almost 36 thousand kilometres long, extending from the surface of the earth and capable of transporting payloads and people into space. Carbon nanotubes, considered as the wonder material of the 21st century, are a potential candidate material in this revolutionary concept of the Space elevator. Kshitij Aditeya Singh explores the range of applications carbon nanotubes will offer and provides a perspective on the emerging nanomaterials marketplace.

The range of physical, chemical, optical, electronic, thermal and mechanical properties offered by carbon nanotubes has created an immense interest in this nanomaterial. Their use has been demonstrated in over 25 applications ranging from nano-scale electronics, biomedical, composites, structural, and storage, while many more are being researched.

Research groups and companies are actively working in applications of carbon nanotubes such as interconnects, probes in microscopes, reinforcements and polymer composites. Arrays of vertically aligned carbon nanotubes intercalated with silicon dioxide are being developed for interconnect applications. Such interconnects are ideal for use in Dynamic Random Access Memories and developing three dimensional architecture. Stanford University in collaboration with Toshiba Corporation have demonstrated a CMOS circuit with using carbon nanotube as interconnects. The processor ran at 1GHz speed is comparable with other CMOS chips. Tennis rackets were one of the first applications to have been reinforced with carbon nanotubes. The concept of CNT reinforcement has evolved since and, a group led by Professor Nikhil Koratkar have developed a method using carbon nanotubes for detecting and repairing cracks in nearly all types of polymers. Carbon nanotubes have also been demonstrated in light bullet proof vests and body armor of vehicles. Researchers at the University of Sydney are studying the impact of projectiles on carbon nanotubes for use as a shield and explosion proof blankets.

Among the applications of carbon nanotubes that use electronic and thermal conductivity are thin film transistors, flat panel displays and thermal management system. Thin film transistors made from networks of single walled carbon nanotubes at Hanyang University in Seoul have demonstrated the potential of thin film transparent electronics that can be used in e-paper, flat panel displays, opto-electronics and electronic windscreen. Nano Emissive Displays developed by Motorola as a 5 inch prototype have demonstrated the use of carbon nanotubes in display. This development is expected to change the design and fabrication of flat panel displays. Carbon nanotubes intercalated with copper create a composite material exhibiting good thermal properties that can be ideal for chip cooling. Researchers at Rensselaer Polytechnic Institute have demonstrated that carbon nanotubes can dissipate heat as effectively as copper, while being 10 times lighter and more flexible gives them added advantage.

Carbon nanotube applications in sensing applications such as biosensors, chemical and pressure sensors are being investigated. NASA has demonstrated Multi-walled Carbon Nano tube array electrode functionalised with DNA, act as an ultra sensitive sensor for detecting the hybridisation of target DNA’s. Surrey University has recently demonstrated chemical sensors while Rensselaer researchers have demonstrated that a small block of carbon nanotubes can be used as a highly effective pressure sensor.

Carbon nanotubes have the potential for use across biomedical, energy, industrial adhesives and textile sectors. One of the biomedical applications of nanotube is its use as a drug delivery vehicle. Researchers at the University of London are investigating the carbon nanotube penetration of cells membranes and their interaction with different cell types. Carbon nanotubes in energy applications have been demonstrated in fuel cells as backing material for the electrodes in the membrane electrode assembly and also for the storage of hydrogen. In solar cell applications, Georgia Tech Research Institute have used carbon nanotubes as supports for arrays of photovoltaic material and also serve to connect them to the silicon wafers. University of Akron has demonstrated an adhesive application with 200 times the gripping power of gecko’s foot. It is expected to be used as a dry adhesive in microelectronics, robotics, space and other fields. Carbon nanotubes just 10-50nm in size spun in a yarn have great potential for use within textiles. Such yarns are strong, durable, flexible and retain the electrical properties of the nanotubes.

Emerging application examples of the carbon nanotubes have been observed in vibration isolation applications and are being considered in the design of NASA morphing wing of gliders. The nanomatteress developed at the Nanyang Technological University, consists of a layer of diamond-like carbon over a layer of aligned carbon nanotubes. The composite material has excellent mechanical properties and can provide vibration isolation and wear resistance applications in harsh environments. Researchers at University of California have demonstrated a nanoscale radio where the main component of the circuit consists of a single carbon nanotube. This is expected to be used in mobile phones and environment sensors.

The carbon nanotubes market can be viewed as a market of the material and applications. The challenges of each application vary at each stage of the development cycle and technology adoption.

Carbon nanotubes have three main variations based on the diameter of the tubes – single walled, double walled and multi-walled carbon nanotubes. The production capacity of individual companies remains in hundreds of tonnes. For example Nanocyl has recently demonstrated a production capacity of 100 tonnes per annum. No accurate estimate of production capacity is available though it remains in few thousands of tonnes.

Poor definition of market segments and the subsequent positioning in the market has been one of the main blocks in realizing potential. An example of this is the nanocomposite market of carbon nanotubes. In relation to market understanding, acquisition of intellectual property has assumed a disproportionately more important role in positioning of products within the carbon nanotube market. In a recent paper by Raj Bawa, President of Bawa Biotechnology, significant patent thickets were reported for carbon nanotubes, mainly in the general category and electronics applications. Patent thickets and potential litigation remains a serious issue to be addressed if the markets are to realize their potential.

Pricing plays an important role in successful uptake of products in the market. The main factors affecting the pricing of carbon nanotube are type of tube, diameter, purity, functionality, and quantity. For example the price of a functionalized nanotube is more than 90%-purity nanotubes, which are in turn more expensive than 60%-purity tubes. Also, the smaller the diameter of tube, the higher the price. For instance an 8nm tube is more expensive than a 30nm diameter nanotube. There is also a decrease in the price of carbon nanotubes with increasing quantities. This change is noticeable for single-walled carbon nanotubes more than multi-walled carbon nanotubes. Sharp price decreases for nanotubes have been observed around 100 gram. Analysts in 2004 had predicted the cost for a kilogram of carbon nanotube to reach $ 284 in three years. The level of scale-up required for production units by 2007, to bring prices down has not been achieved. Therefore it is important that forecasting figures are assessed with cautious optimism.

One of the causes of uncertainty in the development of the market has been the toxicity of carbon nanotubes on health and the environment. The toxicity results available are not consistent and not conclusive as yet. Governmental organizations are keen to regulate the market in order to avoid a fiasco similar to that resulting from the use of asbestos in the 1980’s. The risk governance frameworks developed by organizations such as IRGC and first certification of risk management and monitoring such as CENARIOS® seek to address some of the issues raised by the uncertainties of carbon nanotubes. These will have a positive impact on the development of the carbon nanotube market. Among other factors that will assist the development of mass market of carbon nanotube is standardization and codes of conduct. Organisation in Europe such as ISO, BSI and CEN are developing carbon nanotube characterization related standards. ASTM in the United States, along with organizations in China, Korea and Russia are also active. Codes of conduct, such as those developed by European Commission for responsible conduct in research and Responsible NanoCode developed in UK, will have a positive bearing by defining boundaries of carbon nanotube companies and their behaviour in capital market.

Researchers are constantly coming out with new ideas and applications of carbon nanotubes are expected to grow over the next decade. The development and rate of maturity of these applications will be determined by a range of causal factors. However not all applications will make it to the market. It is none the less certain that the use of carbon nanotube as a material for multi-disciplinary engineering will continue to increase and may one day become a commodity material.

Source: NANO Magazine - Issue 6 /...

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