A nanocomposite is a multiphase solid material in which one of the phases has one, two or three dimensions of below 100 nm, or structures with nanoscale repeat distances between the different phases making up the material. This definition encompasses colloids, porous media, copolymers and gels; however, mostly it is the solid combination of a nano-dimensional phase and a bulk matrix with distinct properties because of differences in chemistry and structure.
The electrical, mechanical, thermal, electrochemical, optical and catalytic properties of the nanoparticle will significantly differ from the component materials.
Nanocomposites occur naturally in structures like bone and abalone shell. Nanoscale organo-clays have been utilized from the mid 1950s for the control of polymer solution flow or gel constitution for example as a thickening substance in cosmetics with homogenous preparations. Clay/polymer composites became very popular by the 1970s though the term nanocomposites was not coined yet.
The nanoscale phase in a nanocomposite material will typically have an exceptionally high surface to volume ratio and/or an exceptionally high aspect ratio. The reinforcing material can comprise sheets, particles or fibers. The interface area between the reinforcement phase and the matrix is an order of magnitude greater than traditional composite materials. Matrix material properties in the vicinity of the reinforcing phase are impacted significantly.
Addition of carbon nanotubes to a ceramic matrix can enhance the thermal and electrical conductivity. Other types of nanoparticulates may result in improved dielectric properties, optical properties, heat resistance or mechanical properties such as strength, stiffness and resistance to damage and wear.
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Carbon nanotubes can improve the electrical, thermal and mechanical properties of ceramic materials. Image Credits: Georgia Tech Research News
Types of Nanocomposites
Ceramic-Matrix Nanocomposites
In this composite group, a ceramic such as a chemical compound from a group of nitrides, oxides, silicides and borides occupy the major part of the volume. In most ceramic-matrix nanocomposites, a metal is the second component. In an ideal scenario, both the ceramic and the metallic components are dispersed evenly to elicit specific nanoscopic properties.
Metal-Matrix Nanocomposites
The other name for metal matrix nanocomposites is reinforced metal matrix composites. This composite type can be classified as non-continuous and continuous reinforced materials. Carbon nanotube metal matrix composites is an important nanocomposite that takes advantage of the high electrical conductivity and tensile strength of carbon nanotube materials. The new research areas on metal matrix nanocomposites are carbon nitride metal matrix composites and boron nitride reinforced metal matrix composites.
The energetic nanocomposite is another kind of nanocomposite normally as a a hybrid sol–gel with a silica base, which, that when combined with nanoscale aluminum powder and metal oxides forms superthermite materials.
Polymer Nanocomposite
The addition of nanoparticulates to a polymer matrix improves its performance by using the properties and nature of the nanoscale filler. When the nanoscale filler properties are better or different from the matrix reinforcement and when the filler is dispersed well, this strategy works perfectly.
The enhancement in mechanical properties may not be restricted to strength or stiffness. By adding nanofillers, time-dependent properties can be improved. On the other hand, the improved properties of high-performance nanocomposites is because of the high surface area of fillers and the high aspect ratio as nanoparticulates have increased surface area to volume ratios when there is a good dispersion.
Properties of Carbon Nanotube Ceramic Matrix Nanocomposites
Composites comprising nanocrystalline ceramic materials and carbon nanotube (CNT) fillers exhibit less brittleness compared to monolithic ceramic materials. For instance, a material having nanophase alumina particles as the matrix and dispersions of both single and double walled carbon nanotubes as fillers results in 25% increase in fracture resistance without compromising the ceramic matrix strength.
The features of this proof-of-concept material are applicable to a broad range of nanophase ceramic oxide materials. It is also possible to make the fillers from other nanoscale materials such as silicon nitride, boron nitride and silicon carbide. These materials have a higher hardness than graphite fiber-reinforced ceramic composites.
Applications of CNT Ceramic Matrix Nanocomposites
Applications of CNT ceramic matrix nanocomposites are:
- Load-bearing structural parts
- Wear or friction surfaces
- Medical devices and implants
- Automotive, aerospace, and power generation applications
- Tool and die materials
Recent Developments
New multifunctional materials are being developed as a result of the increasing availability of nanotubes and nanopowders, and their integration with novel processing techniques. Carbon nanotubes have become renowned for their electrical, mechanical and thermal properties, and commercial scale manufacturing of nanotubes has been rapidly improving.
In a recent study, alumina nanocomposites with CNTs were developed. CNTs are prone to agglomeration in ceramic matrices - however, dimethylformamide was found to successfully disperse the CNTs throughout the material, and the resulting materials had correspondingly better electrical and mechanical properties. Alumina-coated CNTs were found to be best suited for interfacial adhesion with the ceramic matrix.
Conclusion
Ceramic–CNT nanocomposites show great promise, especially for applications that require good thermal and electrical properties. Most of the research to date has served simply to better our understanding of the properties nanocomposites and how to make them. The commercial development of CNT-ceramic composites, as with many other nanomaterial-based technologies, will be tied to the price and availability of CNTs. Nanocomposites using other, more readily available materials, which are more easily adapted to current manufacturing methods, are already beginning to find commercial applications in high-stress scenarios.