Photonic crystals
4.15 STRUCTURAL APPLICATIONS
The increased rate of forming or the lower temperature related to the superplastic deformation of nanocrystalline materials would make superplasticity more industrially accessible, extending its possible limits of use. With nanocrystalline metals, superplastic deformation can extend rapid and large-scale forming processes. It is speculated that nanocrystalline superplasticity will have an advantage over traditional superplastic materials when materials chemistry may not be changed because of the nature of the application (for example, in electronics applications), or high strength is demanded after forming. Another area is that of diffusion bonding. It has been shown that the use of a superplastic intermediate layer in
diffusion bonding of non-superplastic stainless steel dramatically improves the properties of the joint, especially if the mating surfaces are rough. Superplasticity may also be utilised in the processing of nanocrystalline ceramics themselves. Nanocrystalline ceramics are difficult to produce by the pressureless sintering routes typically used for conventional ceramics, but they may be produced by sinter forging which uses the superplasticity of the materials itself by closing pores with the aid of plastic flow.
The higher strength of nanocrystalline materials may be utilised in several potential applications, when processing of the materials is adequately developed. The development of nanocrystalline M50 steel as the main shaft bearing material has improved the performance of engines in gas turbine industries. Development of WC–Co nanocomposites has been driven by the expectation of obtaining cutting tools and hard metal coatings with superior properties compared to their traditional counterparts. These materials are already starting to have commercial impact and are used in the manufacture of machine tools, drill bits and wear parts. Tools made of cemented carbide nanocomposites have enhanced hardness, fracture toughness and wear resistance compared to their conventional counterparts.
Currently, nanocrystalline titanium is considered to be a potential material for medical implants. In order to obtain adequate strength, titanium alloys (mainly Ti–6Al–4V) are used, for example, for hip prostheses. Development of nanocrystalline pure titanium for such an application would allow the alloying content to be decreased for increased biocompatibility. Both the static and the fatigue strength of commercially pure titanium fasteners and threaded articles could be substantially increased by ECA processing, producing a nanocrystalline grain structure. Nanocrystalline ceramics have also been considered for orthopedic and dental implants of the future. Nanomaterials with improved mechanical properties could then replace some of the conventional biomaterials and could be tailored to meet clinical requirements associated with anatomical differences or patient age.
Incorporation of nanotubes instead of carbon fibres as reinforcing elements into plastic, ceramic and metallic matrixes can potentially provide structural materials with dramatically improved modulus and strength. Many improvements have taken place in the use of
nanoparticles as filler materials in polymers. These include fillers in dental polymers to improve their performance, for example, wear resistance or stiffness as in polymer-layered silicate nanocomposites.
Applications of nanocrystalline metallic materials have been limited because of low ductility in tension. However, cold rolling of nanocrystalline copper has opened up interesting vistas for developing novel processing of some metallic materials utilizing the nanocrystalline structure. The traditional deformation–annealing technique routinely used may be much simplified by using nanocrystalline metals as starting materials. With proper post–heat treatments, microstructure may be easily controlled so that the desired properties in the final product can be achieved.
SUMMARY
Nanomaterials and technology are making their impact in almost all areas of life.
• Development of novel devices based on nano-opto-electronic materials, molecular devices and quantum structures are creating new directions for miniaturization with increased efficiency of nano-electronic systems.
• MEMS and NEMS find extensive use both as sensors and actuators in a wide spectrum of engineering application.
• An entire gamut of nanosensors for biomonitoring, health parameter surveillance, safety logics, environmental control, process control, etc., have been developed. • In the field of medicine, nanotechnology finds application for both diagnostic tools as
well as for advanced therapy.
• Development of smart textiles with in-built sensors and functional nanoparticles are set to be introduced on a wide scale both for defense as well as for domestic use. • Nanomaterials have a promising future in enhancing efficiencies of green energy
technologies, like solar cells, hydrogen cells, etc.
EXERCISE
1. Define: (a) Moore’s law, (b) Spintronics and (c) Quantum effect devices.
2. Write a note on the application of nanotechnology for energy production, storage and enhancing energy efficiency of buildings/appliances.
3. What are molecular devices? What are their advantages over conventional microelectronic devices?
4. Explain the possible applications of CNTs for pressure and gas sensor applications, with mechanisms of their working.
5. Discuss the role of NEMS technology in advanced engineering applications. 6. Write a note on the use of nanometallic particles as catalysts.
7. Discuss the role of nanotechnology in water treatment and environment control. 8. Explain the mechanisms and fabrication of at least three different biological sensors.
Gordon Earle Moore is the co-founder of Intel Corporation, USA. Born in 1929 at San Francisco, California, he obtained his doctoral degree in Physics and Chemistry from CalTech in 1954. Intel Corporation was co-founded by Moore in 1968, where he served as Executive Vice President until 1975, after which he became President and Chief Executive Officer. Dr Moore became Chairman of the Board and Chief Executive Officer in 1979. He became Chairman Emeritus of Intel Corporation in 1997.
9. Discuss the various possible applications of nanostructured silver, titanium oxide and zinc oxide.