Carbon nanotube metal matrix composites
Encyclopedia
Carbon nanotube metal matrix composites (CNT-MMC) are an emerging class of new materials that are being developed to take advantage of the high tensile strength and electrical conductivity of carbon nanotube
Carbon nanotube
Carbon nanotubes are allotropes of carbon with a cylindrical nanostructure. Nanotubes have been constructed with length-to-diameter ratio of up to 132,000,000:1, significantly larger than for any other material...

 materials. Critical to the realization of CNT-MMC possessing optimal properties in these areas are the development of synthetic techniques that are (a) economically producible, (b) provide for a homogeneous dispersion of nanotubes in the metallic matrix, and (c) lead to strong interfacial adhesion between the metallic matrix and the carbon nanotubes. Since the development of CNT-MMC is still in the research phase, the current focus is primarily on improving these latter two areas.

Carbon nanotubes reinforced metal matrix composites production methods

According to the new production systems, Carbon nanotubes reinforced metal matrix composites (CNT-MMC) may produce several different methods. These production methods are:
Powder metallurgy
Powder metallurgy
Powder metallurgy is the process of blending fine powdered materials, pressing them into a desired shape , and then heating the compressed material in a controlled atmosphere to bond the material . The powder metallurgy process generally consists of four basic steps: powder manufacture, powder...

 Route Technics
  1. Conventional Sintering
  2. Hot Pressing
  3. Spark Plasma Sintering
  4. Deformation Processing


Electrochemical Routes(for non-structural applications)
  1. Electro-deposition
  2. Electroless Deposition


Thermal spraying
Thermal spraying
Thermal spraying techniques are coating processes in which melted materials are sprayed onto a surface. The "feedstock" is heated by electrical or chemical means ....

  1. Plasma Spraying
  2. HVOF Spraying
  3. Cold Kinetic Spraying


Melt Processing
  1. Casting
  2. Melt Infiltration


Novel Techniques
  1. Molecular Level Mixing
  2. Sputtering
    Sputtering
    Sputtering is a process whereby atoms are ejected from a solid target material due to bombardment of the target by energetic particles. It is commonly used for thin-film deposition, etching and analytical techniques .-Physics of sputtering:...

  3. Sandwich Processing
  4. Torsion/Friction Processing
  5. CVD and PVD (Physical vapor deposition
    Physical vapor deposition
    Physical vapor deposition is a variety of vacuum deposition and is a general term used to describe any of a variety of methods to deposit thin films by the condensation of a vaporized form of the desired film material onto various workpiece surfaces...

    )
  6. Nanoscale Dispersion
  7. Pulsed laser deposition
    Pulsed laser deposition
    Pulsed laser deposition is a thin film deposition technique where a high power pulsed laser beam is focused inside a vacuum chamber to strike a target of the material that is to be deposited...



Indigenous techniques
  1. Such as molecular level mixing (in which CNTs are dispersed into a metal-salt bath, forming a metal-CNT precursor).

Powder metallurgy technics
Sintering is one of the oldest method in production technics and used to produce density-controlled materials and components from metal or ceramic powders by applying thermal energy.
Synthesis and sintering of nanocrystalline ceramic powders have attracted much attention due to
their promising properties. The high active surface area of nanopowders results in lowering sintering temperature relative to coarser powders. Although low temperature sintering suppresses the grain
growth, high density of interfaces and grain boundaries in nanocrystalline powders leads to accelerated grain growth during sintering.

  1. Conventional Sintering
    Sintering
    Sintering is a method used to create objects from powders. It is based on atomic diffusion. Diffusion occurs in any material above absolute zero, but it occurs much faster at higher temperatures. In most sintering processes, the powdered material is held in a mold and then heated to a temperature...

     is the simplest method for producing CNT metal matrix composite compacts.The CNTs and metal powders are mixed by a process of mechanical alloying/blending and then are compressed to form a greencompact, which is then sintered to get the final product. Metallic compacts are subject to oxidation as compared to ceramics and hence the sintering has to be done in an inert atmosphere or under vacuum.
  2. Microwave sintering is one of them and fundamentally different from conventional sintering.In microwave sintering process,the material is heated internally and volumetrically unlike in a conventional process where heat originates from an external heating source.Sintering cycle time for microwave sintering is much shorter as compared with the conventional sintering cycle.
  3. Spark plasma sintering
    Spark plasma sintering
    Spark plasma sintering , also known as field assisted sintering technique or pulsed electric current sintering , is a sintering technique....

    is a quiete new technique which takes only a few minutes to complete a sintering process compared to conventional sintering which may take hours or even days for the same.High sintering rate is possible in SPS since high heating rates can be easily attained due to internal heating of the sample as oppsed to external heating seen in case of conventional sintering.For conventional sintering usually a green compact needs to be prepared externally using a suitable die and hdraulic machine for applying the neccesary pressure.In SPS the powder is directly fed into the graphite dies and the die is enclosed with suitable punches.All types of materials, even those dificult to densify can be easily sintered in SPS.Due to advantage of high heating rate and less holding time, SPS can restrict the unwanted sintering reactions in highly reactive systems as opposed to conventional sintering and hence formation of undesirable product phaeses can be avoided.

Mechanical Properties

Carbon nanotubes are the strongest and stiffest materials yet discovered in terms of tensile strength
Tensile strength
Ultimate tensile strength , often shortened to tensile strength or ultimate strength, is the maximum stress that a material can withstand while being stretched or pulled before necking, which is when the specimen's cross-section starts to significantly contract...

 and elastic modulus
Elastic modulus
An elastic modulus, or modulus of elasticity, is the mathematical description of an object or substance's tendency to be deformed elastically when a force is applied to it...

 respectively. This strength results from the covalent sp2 bonds formed between the individual carbon atoms.Multi-walled carbon nanotube was tested to have a tensile strength of 63 gigapascals
Pascal (unit)
The pascal is the SI derived unit of pressure, internal pressure, stress, Young's modulus and tensile strength, named after the French mathematician, physicist, inventor, writer, and philosopher Blaise Pascal. It is a measure of force per unit area, defined as one newton per square metre...

 (GPa). .Further studies, conducted in 2008, revealed that individual CNT shells have strengths of up to ~100 GPa, which is in good agreement with quantum/atomistic models. Since carbon nanotubes have a low density for a solid of 1.3 to 1.4 g/cm3, its specific strength
Specific strength
The specific strength is a material's strength divided by its density. It is also known as the strength-to-weight ratio or strength/weight ratio. In fiber or textile applications, tenacity is the usual measure of specific strength...

 of up to 48,000 kN·m·kg−1 is the best of known materials, compared to high-carbon steel's 154 kN·m·kg−1.
CNTs are not nearly as strong under compression. Because of their hollow structure and high aspect ratio, they tend to undergo buckling
Buckling
In science, buckling is a mathematical instability, leading to a failure mode.Theoretically, buckling is caused by a bifurcation in the solution to the equations of static equilibrium...

 when placed under compressive, torsional, or bending stress.
Comparison of mechanical properties
Material Young's modulus
Young's modulus
Young's modulus is a measure of the stiffness of an elastic material and is a quantity used to characterize materials. It is defined as the ratio of the uniaxial stress over the uniaxial strain in the range of stress in which Hooke's Law holds. In solid mechanics, the slope of the stress-strain...

 (TPa)
Tensile strength
Tensile strength
Ultimate tensile strength , often shortened to tensile strength or ultimate strength, is the maximum stress that a material can withstand while being stretched or pulled before necking, which is when the specimen's cross-section starts to significantly contract...

 (GPa)
Elongation at break (%)
SWNTE ~1 (from 1 to 5) 13–53 16
Armchair SWNTT 0.94 126.2 23.1
Zigzag SWNTT 0.94 94.5 15.6–17.5
Chiral SWNT 0.92
MWNTE 0.2–0.8–0.95 11–63–150
Stainless steel
Stainless steel
In metallurgy, stainless steel, also known as inox steel or inox from French "inoxydable", is defined as a steel alloy with a minimum of 10.5 or 11% chromium content by mass....

E
0.186–0.214 0.38–1.55 15–50
Kevlar
Kevlar
Kevlar is the registered trademark for a para-aramid synthetic fiber, related to other aramids such as Nomex and Technora. Developed at DuPont in 1965, this high strength material was first commercially used in the early 1970s as a replacement for steel in racing tires...

–29&149E
0.06–0.18 3.6–3.8 ~2


EExperimental observation; TTheoretical prediction

Potential applications

Nanonetwork

Nanonetworks are expected to expand the capabilities of single nanomachines both in terms of complexity and range of operation by allowing them to coordinate, share and fuse information. CNT metal matrix composites enable new applications of nanotechnology in the military technology and industrial and consumer goods applications.

Nanorobotics
Nanorobotics
Nanorobotics is the emerging technology field of creating machines or robots whose components are at or close to the scale of a nanometer . More specifically, nanorobotics refers to the nanotechnology engineering discipline of designing and building nanorobots, with devices ranging in size from...

Nanomachines are largely in the research-and-development phase, but some primitive molecular machine
Molecular machine
A molecular machine, or nanomachine, is any discrete number of molecular components that produce quasi-mechanical movements in response to specific stimuli . The expression is often more generally applied to molecules that simply mimic functions that occur at the macroscopic level...

s have been tested. An example is a sensor having a switch approximately 1.5 nanometers across, capable of counting specific molecules in a chemical sample. The first useful applications of nanomachines might be in medical technology, which could be used to identify and destroy cancer cells. Another potential application is the detection of toxic chemicals, and the measurement of their concentrations, in the environment.In addition CNT-MM composite will be the main material for the military robots, especially to strentgh the robot soldier's armours.

Future Soldier
Future Soldier
Future Soldier is the overall name given to a multi-nation military project by the United States and its allies launched in the late 1990s. A Future Soldier is also a Soldier who has enlisted in the United States Military, but is delayed in shipping...

Today's militaries often use high-quality helmets made of ballistic materials such as Kevlar
Kevlar
Kevlar is the registered trademark for a para-aramid synthetic fiber, related to other aramids such as Nomex and Technora. Developed at DuPont in 1965, this high strength material was first commercially used in the early 1970s as a replacement for steel in racing tires...

 and Aramid
Aramid
Aramid fibers are a class of heat-resistant and strong synthetic fibers. They are used in aerospace and military applications, for ballistic rated body armor fabric and ballistic composites, in bicycle tires, and as an asbestos substitute. The name is a portmanteau of "aromatic polyamide"...

, which offer improved protection. Some helmets also have good non-ballistic protective qualities, though many do not. Non-ballistic injuries may be caused by many things, such as concussive shock wave
Shock wave
A shock wave is a type of propagating disturbance. Like an ordinary wave, it carries energy and can propagate through a medium or in some cases in the absence of a material medium, through a field such as the electromagnetic field...

s from explosion
Explosion
An explosion is a rapid increase in volume and release of energy in an extreme manner, usually with the generation of high temperatures and the release of gases. An explosion creates a shock wave. If the shock wave is a supersonic detonation, then the source of the blast is called a "high explosive"...

s, physical attacks, motor vehicle accidents, or falls..Another application for the future soldier is powered exoskeleton system. Powered exoskeleton
Exoskeleton
An exoskeleton is the external skeleton that supports and protects an animal's body, in contrast to the internal skeleton of, for example, a human. In popular usage, some of the larger kinds of exoskeletons are known as "shells". Examples of exoskeleton animals include insects such as grasshoppers...

, also known as powered armor, or exoframe, is a powered mobile machine consisting primarily of an exoskeleton-like framework worn by a person and a power supply that supplies at least part of the activation-energy for limb movement.Powered exoskeletons are designed to assist and protect the soldiers and officers.Currently MIT is working on combat jackets that use CNT fibers to stop bullets and to monitor the condition of the wearer.

Advanced Modular Armor Protection
Advanced Modular Armor Protection
Advanced Modular Armor Protection is modular composite armour concept, developed by the German company IBD Deisenroth Engineering. According to IBD AMAP is a 4th generation composite armour, making use of nano-ceramics and modern steel alloy technologies.AMAP is the successor of MEXAS.Some modules...

Advanced Modular Armor Protection (AMAP) is modular composite armour
Composite armour
Composite armour is a type of vehicle armour consisting of layers of different material such as metals, plastics, ceramics or air. Most composite armour are lighter than their all-metal equivalent, but instead occupy a larger volume for the same resistance to penetration...

 concept, developed by the German company IBD Deisenroth Engineering. According to IBD AMAP is a 4th generation composite armour, making use of nano-ceramics and modern steel alloy technologies.
AMAP is making use of new advanced steel alloys, Aluminium-Titanium alloys, nanometric steels, ceramics and nano-ceramics. The new high-hardened steel needs 30% less thickness to offer the same protection level as ARMOX500Z High Hard Armour steel.
While Titanium
Titanium
Titanium is a chemical element with the symbol Ti and atomic number 22. It has a low density and is a strong, lustrous, corrosion-resistant transition metal with a silver color....

 requires only 58% as much weight as rolled homogeneous armour
Rolled homogeneous armour
Rolled homogeneous armour is a type of steel which is used to armour vehicles.-Composition:Armoured steel must be hard yet impervious to shock in order to resist high velocity metal projectiles. Steel with these characteristics is produced by processing cast steel billets of appropriate size and...

 (RHA) for reaching the same level of protection, Mat 7720 new, a newly developed Aluminium-Titanium alloy, needs only 38% of the weight. That means that this alloy is more than twice as protective as RHA of the same weight.

AMAP is also making use of new nano-ceramics, which are harder and lighter than current ceramics, while having multi-hit capability. Normal ceramic tiles and a liner backing have a mass-efficiency (EM) value of 3 compared to normal steel armour, while it fulfills STANAG 4569
STANAG 4569
NATO AEP-55 STANAG 4569 is a NATO Standardization Agreement covering the standards for the "Protection Levels for Occupants of Logistic and Light Armored Vehicles".The standard covers strikes from Kinetic Energy, artillery, and IED blasts....

. The new nano-crystalline ceramic materials should increase the hardness compared to current ceramics by 70% and the weight reduction is 30%, therefore the EM value is larger than 4. Furthermore the higher fracture toughness increases the general multi-hit capability. Some AMAP-modules might consist of this new ceramic
Ceramic
A ceramic is an inorganic, nonmetallic solid prepared by the action of heat and subsequent cooling. Ceramic materials may have a crystalline or partly crystalline structure, or may be amorphous...

 tiles glued on a backing liner and overlaid by a cover, a concept which is also used by MEXAS
MEXAS
The Modular Expandable Armor System is a ceramic composite armour developed by the German company IBD Deisenroth Engineering. MEXAS was introduced in 1994 and has been applied on over 20,000 combat vehicles worldwide...

. Lightweight SLAT armour is also part of the AMAP family.

Nano Armour

The TK-X (MBT-X) project, the new Type 10
Type 10
The is an advanced Japanese main battle tank.-Overview:The TK-X project aims to produce the new Type 10 main battle tank, to replace or complement the existing Type 74 and Type 90 main battle tanks that are currently in service with the Japan Ground Self Defense Force. Development began in the...

 main battle tank design use composition of modular components of nano-crystal steel (nor Triple Hardness Steel), Modular ceramic composite armor, partly reinforced MMC and Light weight upper armor.

Space Elevator
Space elevator
A space elevator, also known as a geostationary orbital tether or a beanstalk, is a proposed non-rocket spacelaunch structure...

Space elevator is a proposed non-rocket spacelaunch structure (a structure designed to transport material from a celestial body's surface into space).The required strength of the cable will vary along its length, since at various points it has to carry the weight of the cable below, or provide a centripetal force to retain the cable and counterweight above. While some variants of the space elevator concept are technologically feasible, current technology is not capable of manufacturing tether materials that are sufficiently strong and light
Specific strength
The specific strength is a material's strength divided by its density. It is also known as the strength-to-weight ratio or strength/weight ratio. In fiber or textile applications, tenacity is the usual measure of specific strength...

 to build an Earth-based space elevator of the geostationary orbital tether type. Recent concepts for a space elevator are notable for their plans to use carbon nanotube
Carbon nanotube
Carbon nanotubes are allotropes of carbon with a cylindrical nanostructure. Nanotubes have been constructed with length-to-diameter ratio of up to 132,000,000:1, significantly larger than for any other material...

 or boron nitride nanotube based materials as the tensile element in the tether design, since the measured strength of carbon nanotubes appears great enough to make this possible.

Materiomics
Materiomics
Materiomics is defined as the study of the material properties of natural and synthetic materials by examining fundamental links between processes, structures and properties at multiple scales, from nano to macro, by using systematic experimental, theoretical or computational methods.The term has...

Materiomics is defined as the study of the material properties of natural and synthetic materials by examining fundamental links between processes, structures and properties at multiple scales, from nano to macro, by using systematic experimental, theoretical or computational methods and refers to the study of the processes, structures and properties of materials from a fundamental, systematic perspective by incorporating all relevant scales, from nano to macro, in the synthesis and function of materials and structures. The integrated view of these interactions at all scales is referred to as a material's materiome.

Materiomics includes the study of a broad range of materials, which includes metals, ceramics and polymers as well as biological materials and tissues and their interaction with synthetic materials. Materiomics finds applications in elucidating the biological role of materials in biology, for instance in the progression and diagnosis or the treatment of diseases. Others have proposed to apply materiomics concepts to help identify new material platforms for tissue engineering applications, for instance for the de novo development of biomaterials. Materiomics might also hold promises for nanoscience and nanotechnology, where the understanding of material concepts at multiple scales could enable the bottom-up development of new structures and materials or devices, including biomimetic and bioinspired structures.

Nanotough
Nanotough
Nanotough is a European framework project that focuses on developing tough plastic materials using nanotechnology. A total of 11 partners from Germany, France, Italy, Spain, Romania and Denmark are participating in the project...

Nanotough is to obtain a deeper understanding of the interfacial structure of nanocomposites within a polyolefin
Polyolefin
A polyolefin is a polymer produced from a simple olefin as a monomer. For example, polyethylene is the polyolefin produced by polymerizing the olefin ethylene. An equivalent term is polyalkene; this is a more modern term, although polyolefin is still used in the petrochemical industry...

 matrix and thus use nanoparticles like nanoclay to turn upside down the construction of a number of well-known products, where today metals or plastics are used in for example cars or aircrafts. The project will enable realization of the great performance potential of these materials through development of novel multiphase and hybrid nanocomposites. Nanotough project aims to improve the stiffness of polyolefin nanocomposites while not only maintaining but also improving the toughness of the matrix considerably. The technical objective is to optimize and, through novel interface design
Interface design
Interface design deals with the process of developing a method for two modules in a system to connect and communicate. These modules can apply to hardware, software or the interface between a user and a machine...

, to develop new cost effective hybrid (nanofiller-fibre) nanocomposites as an alternative to heavily filled polymers and expensive engineering polymers and fulfill industry requirements for high performance materials in high tech applications.
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