In this lecture, we are going to learn about the Nanomaterials, synthesis of nanomaterials, their properties, and in the ned applications. So let’s start with the introduction of the nanomaterials.
Nanomaterials play a vital role in the recently developed science and technology.
Nanomaterials are materials containing nanocrystals, i.e., their grain size is in the 1 to 100 nm range. The nanomaterials may be metals, alloys, intermetallics, or ceramics.
Conventional materials have grain sizes ranging from a few microns to several millimeters and contain several billion atoms each. But nanomaterials contain only nine hundred atoms each. As the grain size decreases, there is a significant increase in the volume fraction at grain boundaries or interfaces.
In general, the nanomaterials exhibit greatly altered properties such as physical, chemical, and mechanical compared to their normal large-sized grain counterparts with the same chemical composition. Because of their unique microstructure, the nanomaterials are said to have high strength, hardness, formability, and toughness and are more brittle.
Synthesis of Nanomaterials
Using a variety of synthesis methods, it is possible to produce nanostructured materials in the form of thin film, coatings, powders, and bulk material.
The methods used for the synthesis of nanoparticles can be broadly classified into two types:
- Physical Methods
- Chemical Methods
The most commonly used techniques of nanomaterials preparation are explained in brief in this section. They are:
|Inert gas condensation
1. Mechanical Alloying
- It is a solid-state material processing technique in which the materials can be synthesized even at room temperature. This technique is also used to produce metastable structures. Ultrafine nanomaterial with high homogeneity is prepared by this technique. Since the starting material is powder, this technique is of low cost but of high efficiency.
2. Inert Gas Condensation
- In this technique, the base material is evaporated and the evaporated material is allowed to pass through a chamber filled with inert gases like argon or nitrogen. When the evaporated atoms come into contact with the inert gases, they get condensed into spherical particles. Process parameters can be used to control the size of particles.
3. Sol-Gel Technique
- In this technique, nitrates or carbonates are taken as precursors which are dissolved in deionized water. The solution is kept at a suitable temperature and some amount of gelling agents are added to it. Thus the viscosity, temperature, and pH of the solution are controlled in this technique. The nanomaterials in the form of thin film coatings are made by this technique.
- For thin film coating, substrates like copper, nickel, or glass are taken and dipped in the solution before gel formation. Finally, annealing has to be done to get the thin film.
From the above three techniques, the sol-gel synthesis technique is most widely used due to the following reasons:
- In the sol-gel technique, material, both ceramic and metals can be produced at ultra-low temperatures.
- Any type of material can be synthesized in large quantities at a low cost.
- Extremely homogenous alloys can composites can be produced.
- High purity in synthesized materials can be obtained.
- In this technique, the microstructure and physical, chemical, and mechanical properties of the final products can be controlled.
- Co-synthesis of two or more materials simultaneously is possible.
Also Read: Band Theory of Solids
Properties of Nanomaterials
There are several properties of nanomaterials:
- The nanomaterials have high strength, hardness, formability, and toughness.
- These materials are more brittle.
- These materials exhibit superplasticity. (i.e., undergoing large deformation without necking or fracture) even at lower temperatures.
- The magnetic moment of nanomaterials can be increased by decreasing the particle size.
- The optical density of these materials can be varied with the diameter.
- The size of the grains controls the mechanical, electrical optical chemical, semiconducting and magnetic properties.
- The melting point of nanomaterials gets reduced by reducing the grain size.
- The magnetization and coercivity are higher.
Applications of Nanomaterials
The applications of nanomaterials are:
- Nanomaterials are used for the fabrication of signal-processing elements such as filters, delay lines, switches, etc.
- Using these materials, soft and permanent magnets can be manufactured, which is said to have a wider application.
- Nanocrystalline materials like tungsten carbide, tantalum carbide, and titanium carbide are used in making cutting tools, These tools are much harder and last longer than their conventional counterparts.
- These materials are used to make semiconductor lasers, nano transistors, memory devices, such as recording heads and magnetic storage devices, etc.
- Hydrogen-based sensors made of nanomaterials are used in power generation.
- Nanomaterials are used for the manufacture of small-size, lightweight microstrip antennas. These miniaturized antennas are said to have large bandwidth, tunability, and mechanical flexibility.
- These materials are used in enzymes removal of CO2 from the air and waste management.
- Nanocrystalline ZnO thermistors are used in current-controlling devices.
- SiC nanocrystalline is used in making artificial heart valves due to its low weight, high strength, inertness, extreme hardness, and wear resistance.
- When nanocrystalline ceramics such as zirconia and alumina are used as liners in automobile engine cylinders, they help in retaining heat more efficiently and result in complete and efficient combustion of the fuel.