Production
of
nanomaterials
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.
 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 recondensed 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