**2. Classification of nanocomposites**

### **2.1 Metal matrix nanocomposites (MMCs)**

Since the late nineteenth century, composite materials were widely applicable in many systems with greater efficacy [5]. MMCs are one of the largest groups of compounds that are often strengthened with clay. The combination of metals and ceramic structures offers a variety of applications. There have been different ways of making MMCs but, powdered metallurgy is considered a unique process. Indeed, powdered metallurgy (PM) has been considered an effective method that has transformed the material industry by allowing them to build complex structural elements that control the precise strength, flexibility of composite design, and produce highly soluble materials with desirable compositions [6]. It seems that there are two main factors that determine the mechanisms of action in MMCs, that is the desired features of a material and technical constraints. If manufacturing a special type of alloy, for example, it is imperative of establishing a hot phase that allows a phase transformation into a metallic wire form; however, the scientific possibility still exists to design it from a large billet but, technological hurdles would have not allowed it to do so. We would otherwise need to apply high strain and thermal modulus, which can eventually damage the required structure. Therefore, multistep processing channels are used to improve features and overcome technical barriers that are the backbone of the process. To elaborate further, two-step sintering (TSS) and multistep isothermal forging (MIF), and isothermal rolling (IR) as a good plastic deformation (SPD) process have been used.

The sorting of building materials to meet the desired mechanical requirements followed by fine grain sizes and high density is a challenge for MMCs, as it requires very high temperature and often requires to be aligned with mechanical stress in a standard environment, that is very costly for samples having large sizes. The process offered a constricted geometry of the sample matrix [7]. Such a challenge can be remedied by using pressure-less two-step sintering (TSS) where the exfoliated sintering has resulted in fine heat resistance-granular material that is highly pure and more stable. TSS is a robust

and productive method for obtaining a good microstructure with theoretical density. The mechanism includes heating of the composite until it reaches a high temperature and gains 70–90% of theoretical density then returns to a lower temperature to obtain higher density with controlled grain growth. As the grain boundary responsible for grain growth, it has a higher enthalpy compared to the grain boundary distribution at a certain temperature, the latter accomplishes during the second-step sintering in mild thermal conditions, suppresses grain growth, and cause pores annihilation and full densification. In addition, the TSS can overcome the problems associated with performing cold compression/filtration and/or compaction of the water phase leading to the metal agglomeration, respectively. Many other studies have shown that MMCs obtained through different processes provide a higher initial temperature for many clay materials, such as zinc oxide, magnesium-niobium-doped yttrium oxide, barium titinate, and silicon carbide, as well as other compounds. Ceramic matrix materials include compounds that are titanium boride 40% by weight, titanium nitride, and aluminum oxide 10% by volume.

#### **2.2 Ceramic matrix nanocomposites (CMNCs)**

Ceramic matrix nanocomposites (CMNCs) are added with solitary or multiple layers of ceramics to strengthen the crack resistance, heat absorption, and chemical resistance. Whereas, the main flaws of ceramics are their stiffness and less durability that keep them away from being used for industrial references. The limitation has been overcome by the production of ceramic-matrix (CMNCs) nanocomposites. The CMNC model incorporates a matrix in which energy dispelling components (fiber, platelets, or particulates) are added to CMNCs to reduce stiffness and increase crack resistance [2]. Raw materials for CMNC matrixes include alumina, SiC, SiN, etc. Generally, all reinforcements of the nanocomposites are of nanometric sizes. Iron and other metal powders: TiO2, silica, clay are used for amorphous reinforcements. The most common reinforcements are clays and silicates, due to their low particle sizes and well-studied chemical interactions. The addition of clays and silica layers even in small amounts modify matrix structures. Many different approaches are designed for CMNCs integrations. Recently modified techniques are single source-precursor technology that is based on melt spinning of mixed raw materials followed by pyrolysis of the nanofibers. Some established mechanisms are PM; polymeric monomer method, spray-pyrolysis, and vapor methodologies (CVD and PVD) [8]. Chemical methods are the sol-gel process, colloidal method, and rain synthesis [9].

Mixtures of metal amalgamation and mechanical milling are widely used to process a promising program but these methods require an accurate measurement of powdered concentrations to produce a system in a metastable state and then there are a few steps that make strong semifinal products. Various combinations of metallic reactants are another method of directly producing the metallic bulk, for example, the Mg system is a hybrid matrix that includes fusion welding and composite casting requiring metal in the form of a liquid or roll cladding/bonding of solid-state welding. In all of these ways, metals present a diffusion-bound under relatively moderate pressure at a higher temperature for a long time; so, it is not possible to produce a good microstructures. In the process, the metal disk is pressed in high pressure environment with simultaneous torsion straining and processing, which is usually carried out at room temperature (RT), the process is equally effective even on hard as well as on amorphous substances, such as Mg alloys. Also, processed metals usually show improvements in physical and mechanical properties through the use of critical grain refinement and deep introduction of point and line disorders (see **Tables 1**–**3**).

*Recent Progress and Overview of Nanocomposites DOI: http://dx.doi.org/10.5772/intechopen.102469*


#### **Table 1.**

*Examples of ceramic-based nanocomposites.*


#### **Table 2.**

*Examples of metal-based nanocomposites.*

When fine-grained ceramic or other solid particles are embedded in a "soft" metal matrix to form metal matrix compounds (MMCs), the elements of the matrix materials can be greatly improved and strengthened. The strengthening of the mechanism for MMCs has been tested by many researchers. It has been thought that desired characteristics of composite metal structures with nano-sized ceramic particles (1.0–100 nm), called MMNCs, can be greatly improved even in these lowest volume conditions. Currently, mechanical mixing (e.g., high-power ball milling) for metal

#### *Nanocomposite Materials for Biomedical and Energy Storage Applications*


*PANI = polyanialine, PPY = polypyrrole, PVA = Polyvinyl Alcohol, PEO = Poly(ethylene oxide), PVDF = Polyvinylidene fluoride.*

#### **Table 3.**

*Examples of polymer-based nanocomposites.*

#### *Recent Progress and Overview of Nanocomposites DOI: http://dx.doi.org/10.5772/intechopen.102469*

and ceramic powders is generally used to study the characteristics of MMNCs. Mixing ceramic particles with nanosize is energy as well as a time-consuming and costly procedure. Exfoliation, like the liquid-phase process, is best known for its ability to produce products with complex shapes. It will be desirable to synthesize MMNCs parts that are not as heavy as cast with the distribution of good reinforcement and integrity of the structure. However, there are ceramic particles with nanosize that put forth several problems that is very difficult to disperse the same is true for liquid metals because of their unwetting nature, the metal matrix having large surface to volume ratios, which facilitates agglomeration and cluster formation. Powerful ultrasonic waves have been proven very helpful in the context that they produce important indirect effects of liquids, namely transient cavitation as well as acoustic radiation. Acoustic cavitation covers the formation, growth, folding, and collapse of small object bubbles, which produce momentary (in microseconds) small "hot spots" that can attain temperatures (5000°C), pressures (1000 atm), and temperature rise and drops of 1010 K/s. The combination of impact with higher temperatures can also create improvements in the wetting between liquids and particles, thus facilitating the preparation of diffused compounds with effective microparticles.

It is thought that strong cavitation of the microscale transient, as well as macroscopic dispersion, may effectively disperse nanoparticles into soluble alloys and improve their wetting, thus making them more productive in performance as highly castable, light-weighted MMNCs.

Most CMNCs have low fracture resistance and are brittle. In addition to the discovery of ceramic coated CMNCs and silicon carbide (SiC), the modern focus is on the construction of ceramic-based nanocomposites with improved properties. Carbon nanotubes agglomeration increases the material's toughness by energy quenching through elastic modulus in the deformation stage. However, the design complexities have put a limit on the syntheses of these nanomaterials. The main drawback has been the nonuniformity of carbon nanotubes (CNTs) in the matrix suspension. The deformation of CMNCs has often been associated with high thermal and reactive environments that occur during the production of CMNCs. Nevertheless, there is sizeable progress in the field of nanocomposites but still, these are just preliminary steps to develop nanocomposites, a significant amount of exploration and effort is further required to ultrafine these manufacturing techniques. For example, a team from the University of California, Davis, has developed alumina ceramic by combining a single wall of carbon nanotubes (SWCNTs) with Al2O3 nanopowders using PM method. The resulting nanocomposite had advanced thermal, electronic, and mechanical characteristics. The highly potent anisotropic nanocomposite has a thermal ratio of 3:1 in an aligned plane. Electrical conductivity was far better than pure alumina matrix. Most importantly, the fracture strength was thrice higher than alumina with the crack resistance, heat absorption, and shock resistance capacity. Recently, at Tohoku University, a research group has synthesized a sophisticated CMNC on alumina ceramic through multi-walled carbon nanotubes. This process has reduced the phase separation that has resulted in a nanocompound with more uniformity in its structural phase. The addition of 0.9% acid-contained MWCNTs produced a component with a crack capacity of 5.90–0.27 MPa m1/2, greater than pure alumina NC (3–5 MPa m1/2) and a stronger bending capacity of 27%. A Chinese group of Qingdao University of Science and Technology has reported the MWCNT/ zircona CMNCs produced by spark-sintering process had 18% higher fracture strength as compared to pure zircona. Another study by US Nano Labs has prepared

a high-density boron carbide (B4C) containing CMNCs. This composite was produced by the hot pressure-sintering process. However, none of these techniques have produced significant fracture toughness and heat dispelling properties, such as those in SiC-fiber-reinforced composite.

### **2.3 Polymer nanocomposites (PMNCs)**

While nanotechnology still presents a picture of the future, nanocomposites set an example for realistic and rapidly booming applications. For instance, Geoff Ogilvy won the 2006 US Open golf tournament by using a nanomaterial-reinforced polymerbased club. Nanocomposites include materials that is CNTs, mineral materials, metals, and other fillers that can greatly improve composite structures. They attract a lot of awareness and some have been commercially available, having abilities to offer all kinds of uniqueness. Polymer-based products are the best-selling categories of NCs and covered global revenue of approximately, 223 million US dollars, in the year 2009. The nanomaterial's inclusions to the polymeric materials can enhance polymer characteristics that is robustness and strength, Young's modulus, impact endurance and scratch proofing, heat absorption, chemical defiance with electrical insulation and thermal adherence, stability toward the thermal shocks. Currently, minerals compounds and CNTs-based materials are more widely used than NPs. One of the premier commercial systems for PMNCs was used by Toyota, which has used nanoclay with nylon-6 PMNC [56] in their engine component showed an excellent result. In the late 1980s, Toyota Central Research Labs partnered with Ube Industries, a Japanese supplier of fossils, to cement a new 6-nylon composite coated with layers of montmorillonite (naturally occurring silicate clay). The component of this clay has enhanced Toyota's new model's performance which subsequently found its uses in a time belt cover, benefiting from improved temperature adherence and size stability. Since then, few car manufacturers have used nanocomposites of clay material in auto parts, such as rocker box coverings, body panels; the latter is 60% lighter and is more fracture-proof than regular automotive parts. The cargo bed for the 2005 GM model Hummer used approximately 3-kilogram of molded parts of nanoclay/polypropylene nanocomposite in its trim, mid-bridge, canvas panel, and box protectors. Polymer barrier technology was also benefited from these material NCs. Nylon/nanoclay composite is also applied for beverage bottles and in the food packaging industries. The addition of clay can significantly reduce gas/vapor infiltration, as clay platelets and thus prevent mobility, leading to significant improvements in shelf life. CNTbased nanocomposites are gaining increased industrial use from sports and leisure to technology, automotive, and defense motives. CNTs are attractive because of their excellent physical properties that often surpass many highly advanced materials and are now embedded in many polymeric NCs. Many automotive systems are sprayed with electrostatic paints. Plastic body panels need to be carefully processed for the paint to work properly. CNT is being applied as an alternative to carbon black, an expensive primer. The extra edge is being low CNT loading is needed to acquire the required conduction for the polymer to retain half of its actual length than 3–4% length saved when using carbon black. Importantly it is ensured that a panel must maintain its strength at a critical decrease of temperatures and never breaks. In addition, CNTs are so minute and used for such a low load that the higher end of class "A" is available in obtained NCs. The high-power output of CNT-nanocomposites is also utilized in the electronic industry, mainly to reduce the chances of damage caused by electrostatic accumulation or emissions. The PMNCs have found their applications in

#### *Recent Progress and Overview of Nanocomposites DOI: http://dx.doi.org/10.5772/intechopen.102469*

integrated circuits (IC). Joint Electronic Engineering Council trays wafer carriers and IC test that burn sockets because of high potential differences, combined with these materials having superior thermophysical properties to avoid the disaster. An example of a substance used in the industry is the Plasticyl range of CNTs/thermoplastic and nanocomposites, produced by the Nanocyl component as a precursor. Other benefits of PMNCs are seawater-cooled intercoolers on large diesel engines and in the power stations, where PMNCs will offer a robust substitution to copper-containing alloy, thermal rescue systems from fire hydrants and flue gases, working under 3008 celsius, whereas commercially used MMNCs systems lose their robustness in the chemical management as well as in processing industries where fissile environments prevail [56]. Demonstrating their strength and toughness, these materials have found applications from being used in baseball bats, bicycle frames, and power boats to military boats and aircraft. The leading company in nanocomposite technology is Applied Nanotech Holdings.

However, adding PMNCs, especially CNTs, in a resin or other matrices is not an easy task. Problems, such as segmentation, merging, poor disintegration, and poor adherence to host, should be overcome during integration. Some companies have developed methods that are specific for certain NP. For example, Zyvex uses new technologies based on solid composite polymers, in which large interactions within the polymer core and the nanotube surface occur with noncovalent ("aromatic") interactions. Although these interactions are much weaker with fragile bonds than covalent interactions, their total impact strengthens the composite leading to stable systems. Similarly, dispersing nanoparticles of clay onto polymers requires special techniques, most commonly involving solution, *in situ* polymerization, and intercalation using clay with appropriate treatment. Some manufacturers now produce CNTs based on chemical incorporation on compounds while others offer PMNCs masterbatches, which usually contain 10–20% polymer composite by weight. A variety of polymers, including acrylonitrile, poly styrene, butadiene, polybutylene, polycarbonate, polystyrene, terephthalate, and polyamide. Similarly, masterbatches containing scattered nanoclays are available commercially. As CNTs have excellent properties overall that often they overshadow many highly advanced material compounds. Therefore, the chain resources are easily existing now to produce composite materials having more adapted and refined characteristics.
