Carbon Nanotubes (CNT) in Ceramic Matrix Composites

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Researchers have been perfecting techniques for making organic polymer and carbon nanotube (CNT) composites for years, but less has been done in creating ceramic or glass matrix composites.  Ceramic Matrix Composites (CMC) have been developed as an alternative to monolithic ceramics.  CMCs are less brittle and have more predictable failure characteristics than monolithic ceramics and glass while still maintaining their intrinsic strength and stiffness.  

Recent research has shown CNTs to be the best performing additive to ceramic and glass matrices.  CNTs have stiffness equivalent to the best carbon fibers while their strength is an order of magnitude higher.  These added benefits can be used to make crack and shatter resistant glass and ceramic products.  Additionally, the conductive properties of CNTs can enhance the metallic or optoelectric conductivity of the CMCs depending on the lenght and specific characteristics of the CNTs used in the matrix.  CNTs also have axial thermal conductivity greater than that of diamonds, greatly improvig the thermal conductivity of CMC applications.

One of the main challenges is properly dispersing the CNTs in the ceramic matrix.  Even dispersion of CNTs is critical since agglomeration act as a defect, creating a weak point in the ceramic or glass matrix.  In the manufacture of CMCs, CNTs are embedded in the cramic or glass matrix through a number of methods.  Chemical Vapor Deposition (CVD) techniques allow for the in-situ growth of CNTs in the ceramic matrix.  Powder processing is also a popular method for making CMCs where the CNTs are mixed with ceramic particles through various methods and formed into finished CMCs by hot pressing.  Material scientists are reseaching other methods embedding the CNTs and adhering CNTs to the surface of the CMCs as well.  Colloidal, Sol-Gel and Electrophoretic Deposition processing are techniques that are piquing interest as methods to directionally emplace the CNTs while reducing the energy demands for the manufacture of the final product.

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Ceramic composites are stronger (less brittle), improve insulation value and demonstrate improved electrical conductivity over monolithic ceramic and amorphous glass.

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Embedding CNTs in CMCs would enhance the structural stability of the ceramic composite, creating greater opportunites for ceramics in construction, defense and energy. CMCs with functionalized CNTs could find uses in advanced photonics, thin film applications, energy storage and generation devices and for use as reinforced building materials.

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Carbon Nanotubes can enter deep into the lungs, enter the blood stream, and pierce cell walls, making them toxic to living organisms. They pose little risk to the consumer since the CNTs are suspended in the ceramic composite, but 350 to 500 tons of CNTs are produced every year, creating health risks during the manufacturing stage. These risks are not completely understood, and there are a number of different methods of manufacturing the CNTs in this application.

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