Review of various conventional and noble techniques to convert Particles to Nano Scale (13-16)
There are various conventional and noble techniques by which we can produce nanoparticles.
There are two different type of approaches by which we can prepare nanoparticles (Top down method and Bottom up method) (Fig.4).
Following are some vastly used techniques to prepare nanoparticles.
- Mechanical grinding
- Wet Chemical Synthesis of Nanomaterials
- Gas Phase synthesis of nanomaterial
- Sputtered Plasma Processing
- Particle precipitation aided CVD
- Laser ablation
Fig. 4:Schematic diagram of various approaches for preapring nanoparticles
Mechanical attrition is a typical example of 'top down' method of synthesis of nanomaterials, where the material is prepared not by cluster assembly but by the structural decomposition of coarser-grained structures as the result of severe plastic deformation. This has become a huge popular method to make nanocrystalline materials because of its simplicity, the relatively inexpensive equipment needed, and the applicability to the synthesis of all classes of materials. The major advantage of mechanical grinding is the possibility for easily scaling up to large quantities of material for various applications.
In principle we can classify the wet chemical synthesis of nanomaterials into two broad groups:
1. The top down method: In this method single crystals are broken down in an aqueous solution for producing nanomaterials. For example, by using electrochemical etching technique porous nano silica can be prepared.
2. The bottom up method: The best example of this technique is sol-gel method and precipitation etc. The sol-gel process is designed to produce inorganic networks to form a colloidal suspension (sol) and then the sol is gelated to form a network in a continuous liquid phase (gel).
In recent years, the gas-phase synthesis technology is one of the best methodologies for creating nano scale drug particles because of its effective way to modulate process parameters in order to produce nanostructure with desired product size, shape and chemical composition. The synthesis route is based on the production of small clusters aggregating to form nanoparticles through condensation. Supersaturating vapor will initiate the condensation process and homogeneous nucleation is started in the gas phase to form nanoparticles. This can be accomplished both by physical and chemical methods.
In this method, the material which is to be converted to nanoparticles is sputtered using rare gases such as helium gases and the target compound are allowed to agglomerate to form nanomaterial. Both direct current and radio frequency sputtering wave has been utilized to synthesize nanoparticles. In addition, multi target sputtering has been explored to produce nano material based alloys and/or oxides, carbides, nitrides of materials etc. This method is particularly applicable for the formation of ultrapure and non-agglomerated nanoparticles of metal.
Particle-precipitation-aided chemical vapor deposition (PP-CVD) is a little bit modification of the traditional CVD process, where an aerosol of colloidal clusters of materials is used to prepare nanoparticles. The particles are formed in the gas phase and are deposited on a substrate. The driving force for particle deposition is called thermophoresis. In principle, the PP-CVD process is a very effective method for the synthesis of thin porous layers of ceramics. By using this modern technology CVD reaction conditions are so set that particles form by condensation in the gas phase and collect onto a substrate, which is kept under a different condition that allows heterogeneous nucleation. By this method both nanoparticles and particulate films can be prepared. An example of this method has been used to form nanomaterials SnO2, by a method called pyrosol deposition process, where clusters of tin hydroxide are transformed into small aerosol droplets, following which they are reacted onto a heated glass substrate.
Laser ablation has been extensively investigated for the synthesis of nano particulate films. In this technology a laser beam is impeded upon solid sample as the primary excitation source of ablation for generating nanoclusters. This method will not only produce the nanoparticles but also produce thick films. For this reason this method could be considered an efficient tool for the production of different kind of Nano composites including ceramic particles and carbon nanotubes.
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1.There are two different type of approaches by which we can prepare nanoparticles (Top down method and Bottom up method)
2.The most convenient technique used for synthesis of nanotechnology are Mechanical grinding, Wet Chemical Synthesis of Nanomaterials, Gas Phase synthesis of nanomaterial, Sputtered Plasma Processing, Particle precipitation aided CVD, Laser ablation etc.