Nano Materials methods and preparation of nanomaterials

Nanomaterials are materials with at least one dimension of 1–100 nanometers. Nanomaterials can have different physical and chemical properties than their bulk-form counterparts.
They can have different optical, magnetic, and other properties.
Nanomaterials can have a high surface area to volume ratio

1. Methods o f Preparation of Nanomaterials By Dr.M.Reka devi Assistant Professor of Physics V.V.Vanniaperumal College For Women Virudhunagar Nano Physics

2. Nano materials are substances that are have been reduced in size to the range from 1 nm to ~ 100 nm. Crystalline nature Examples : Oxides, metals and ceramics Oxides are chemical compounds with one or more oxygen atoms combined with another element A ceramic is a material that is neither metallic nor organic . It may be crystalline, glassy or both crystalline and glassy.

3. Carbon black is a nano material that is used for car tyres. It provides black colour . Nanomaterials represent the increasing surface area. Substances with high surface area have enhanced chemical , mechanical, optical and magnetic properties. Materials made from metal and oxides of silicon and germanium exhibit superplastic behaviour because the individual nano sized particles can expand relative to each other.

4. To retain the desired properties of the nanomaterial a stabiliser must be used to prevent further reaction. This enables them to wear resistant ,erosion resistant and corrosion resistant. These are used for protection mechanism.

5. Plasma Arcing : It is an ionized gas A plasma is achieved by providing a potential difference across the two electrodes so that gas gives its electrons and thus ionizes. Heat is used for ionizing the materials. This method is used for forming carbon nanotubes. It consists of two electrodes An arc passes from one electrode to the other. The first electrode (anode) vaporizes as electrons are taken from it by the potential difference . Carbon electrodes are used for making carbon nano tubes atomic carbon cations are produced. ( A carbocation is an ion with a positively-charged carbon atom.) These positively charged ions pass to the other electrode pick up electrons and are deposited to form nano tubes.

6. Electrodes can be made of conducting and non conducting materials. During heating the non conducting material is vaporized and ionized so that it also becomes part of the plasma arc and is transported and deposited on the cathode . Plasma arcing can be used to make deposits on surfaces In this process the nano material can be deposit in the surface is little Nanomaterial can be deposited in one dimension each particle must be nanosized and independent It is interacting by hydrogen bonding or vander waals forces

7. Plasma arcing is flame ionization If a material is sprayed in to a flame ions are produced and these can also be collected and deposited in nano crystalline formation. This system can achieve high in terms of film flatness and particle fineness , which is impossible with other systems.

8. Chemical vapour deposition This method depositing nano particle material from the gas phase. Material is heated to form a gas and then allowed to deposit as a solid on a surface . It may be direct deposition or deposition by chemical reaction. This process is used to form nano powders of oxides and carbides of metals. Microwaves tuned to metal excitation frequencies are used to melt and vaporize the reactants to produce a plasma at temperatures up to 1500 °C. (It uses a continuous microwave source to create and help to maintain a highly reactive plasma made up of the reacting chemicals and necessary catalysts .)

9. After cooling to 700°C or another appropriate temperature these particles are filtered from the exhaust gas flow at high temperature. Depending on the material slow introduction of a stabiliser helps reduce their reactivity by forming a thin protective coating. An object to be coated is allowed to stand in the presence of the chemical vapour . The first layer of molecules or atoms deposited may or may not react with the surface( acting template on which material can grow). Formed structure grow vertically This is done by electron lithography and etching Electron Lithography process uses a focused beam of electrons to form patterns by material modification . Etching- Etching is traditionally the process of using strong acid or mordant to cut into the unprotected parts of a metal surface Dip pen nano lithography It can be used to write on the surface

10. high rates of physical mixing with uniform temperature ; (ii) high turnover frequency (iii) high heat transfer coefficients and high mass-transfer rates.

11. Ball milling Ball milling is a grinding method that grinds nanotubes into extremely fine powders. During the ball milling process, the collision between the tiny rigid balls in a concealed container will generate localized high pressure. Usually, ceramic, flint pebbles and stainless steel are used. The ball milling method consists of balls and a mill chamber and over all a ball mill contains a stainless steel container and many small iron, hardened steel, silicon carbide, or tungsten carbide balls are made to rotate inside a mill (drum).

12. The powder of a material is taken inside the steel container. This powder will be made in to nanomaterials using the ball milling technique. A magnet is placed outside the container to provide the pulling force to the material and this magnetic force increases the milling energy when milling container or chamber rotates the metal balls.

13. The rotation directions of the bowl and turn disc are opposite, the centrifugal forces are alternately synchronized. Thus friction resulted from the hardened milling balls and the powder mixture being ground alternately rolling on the inner wall of the bowl and striking the opposite wall. This process of ball milling is done approximately 100 to 150 hrs to get uniform fine powder. Advantages: Nano powders of 2 to 20 nm in size can be produced. The size of nano powder also depends upon the speed of the rotation of the balls. It is an inexpensive and easy process. This method produces crystal defects.

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