plasma arcing

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PLASMA ARCING
 Production 
 of 
 nanomaterials
1
1
Nano material or nano particles are used in a broad spectrum 
 of applications.
Specific synthesis process are employed to produce the
 various nano particles
Defined production and reaction condition are crucial in 
 obtaning such size dependent paricle.
Particle size, chemical compositoin, crystallinity and shape
 can be controlled by temperature ,ph-value, concentration, 
 chemical composition, surface modification and 
 process control.
2
 Two basic strategies are used to produce nano particles…
 Top-down and 
 Bottom-up.
 Top-down:
Producing very small structures from larger pieces of material.
One way of acheving this is mechanical crushing of solid into 
 fine nano powder (ball milling)
Bottom-up:
The atoms or molecules array themselves into a structure due
 to their natural properties 
e.g: crystal grown
 (or)
In bottom-up stratergy, structures are built up by chemical process.
The selection of the respective process depends on the chemical 
 composition and the desired features specified for the
 nano particles
Method of preparation:
 Plasma arcing.
Physical vapour deposition(PVD).
Chemical vapour deposition(CVD).
Sol-gels.
Electro deposition.
Ball milling.
Plasma arcing method:
Plasma is an ionized gas.
A plasma is achieved by making a gas conduct electricity by
 providing a potential difference across two electrodes.
Electrodes are made of conducting material.
Electrodes can be made of mixture of conducting and 
 non-conducting materials.
A contracted plasma arc is generated by a plasma torch using 
 an inert gas which is used as heat source.
Plasma torch
In arc discharge method, two high purity graphite electrodes as anode and cathode are held at a distance under helium atmosphere.
Under these conditions, some of the carbon evaporated from the anode re-condensed as hard cylindrical deposit on the cathode rod.
An arc passes from one electrode to the other.
The electrons are emitted from the first electrode (anode) due
 to potential difference.
Positively charged ions pass to the other electrode(cathode) 
and gets deposited to form nano particle.
The depth of deposited surface must by only few layers 
Each particle must be nanosized and independent.
Conditions:
Average mass temperature of arc is higher than 104K , 
while its power density transferred onto the electrode
(anode) is approximately 2KW/mm2.
Using this method individaul carbon nanotubes could be achieved in general several hundred microns long.
Thus plasma arcing method is bottom-up method.
Plasma arc lamp
Plasma arc