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Abalone has a first name, it's nanocomposites

June 08, 2016

A nanocomposite is a composite in which one phase, or part, has a length scale of less than 100 nanometers, approximately 1/1,000th the width of a human hair.

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The shell of an abalone (above) is made up of microscopic calcium carbonate tiles, which function like
a naturally occurring nancomposite.

Nanocomposites are composites in which one phase has a length scale of less than 100 nanometers. Typical nanocomposites can be materials with a high porosity, colloids and gels, and copolymers but are generally a combination of a bulk material and nanoscale second phase. An example of a natural nanocomposite is the material that makes up abalone shells, which contain microscopic calcium carbonate tiles that stack like bricks. Protein fills the space between the layers of tiles and stretches to absorb the shock incurred when the shell is struck.

Because nanocomposites have such a high surface area to volume ratio for the reinforcing phase (which can be in the form of particles, fibers, or sheets), the material properties are much better than for conventional composites. A very small amount of reinforcement material can have a significant effect on the macroscale mechanical properties of the composite. The weight percentage of the reinforcing material is generally kept below 5% because of the low percolation threshold for fillers with a high surface area to volume ratio.

Ceramic-matrix Nanocomposites

In a ceramic-matrix nanocomposite, the bulk material is a ceramic, and generally the second component is a metal. The two components should be dispersed into each other finely enough that the desired nanoproperties can be achieved. When combining ceramics and metals, it is important to consider the phase diagram of the two components to ensure that no chemical reaction will occur, thereby reducing the desired enhanced properties. This can be achieved most easily by choosing a combination of metal and ceramic that are immiscible at the high temperatures required for ceramic processing. TiO2 and Cu are widely used for this case.

Metal-matrix Nanocomposites

Metal-matrix nanocomposites, or reinforced metal matrix composites, can be classified as either continuous or non-continuous reinforced materials. Carbon nanotube metal matrix composites (CNT-MMC) are a new material in this vein that uses the high electrical conductivity and tensile strength of carbon nanotubes in their composite design. In order to make CNT-MMC viable, synthesis techniques must be developed which are economically sound, produce a homogenous dispersion of the nanotubes in the matrix, and which produce a string adhesion between the matrix and nanotubes.

Polymer-matrix Nanocomposites

The simplest form of polymer-matrix nanocomposites, known as nanofilled polymer composites, involve adding nanoparticulates to a polymer matrix, enhancing the matrix’s performance using the properties of the nanofiller. This process often yields very high performance composites, especially when the filler is well dispersed in the matrix. When new physical properties and behaviors are created from the addition of nanoscale components, genuine nanocomposites, or hybrids, are formed. Some examples of new behaviors that may be created in hybrids are fire resistance or accelerated biodegradability.

Although nanocomposites do not differ much from conventional composites, depending on the matrix, nanocomposites must be prepared in different ways to better enhance the properties of the matrix. Mixing the reinforcing phase and bulk material on the nanoscale allows for much better property enhancement than conventional composites can achieve and will lead the way in new composite materials for construction, aerospace, and beyond.

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