Bangalore Plasmatek can, at present, deposit following coatings
on cutting tools and other components.
Aluminium, Titanium, Nickel, Copper, Stainless steel, Gold,
Silver, Special alloys, Titanium Nitride (TiN), Titanium
Carbide, Titanium Carbonitride (TiCN), Multilayer coatings,
RESEARCH & DEVELOPMENT
The coating system at Bangalore Plasmatek, which includes vacuum
arc and magnetron sources, was developed indigenously. The
processes for various coatings are also developed in house.
Bangalore Plasmatek enjoys taking up challenging research and
Plasma is like any other gas like
oxygen, nitrogen etc. in many respects. However a plasma has
many more interesting and complex properties. In an ordinary gas
the molecules or the atoms are electrically neutral i.e. they
carry no net electric charge either positive (+) or negative
(-). A neutral atom has equal number of negatively charged
electrons and positively charged protons. Electrons are very
light and they move around the centre of the atom in different
orbits some what similar to the planets in our solar system.
Protons are about 2000 times heavier than electrons and they are
concentrated at the centre of the nucleus. In a plasma there are
always some atoms where one of the electrons is removed. Such
atoms thus carry one electron less and hence have one net
positive charge. These atoms are said to be ionized. If such
ions and electrons are present in a gas in substantial numbers
the gas is said to be ionised and is called a plasma. It is
believed that more than 90% of the universe is in plasma state.
The sun, stars, inter stellar space are all made up of plasma.
Only cold places like the earth and other planets are not in
plasma state. On earth one can find plasma in the ionosphere a
region beyond the earth's atmosphere. Many of the modern gadgets
like the fluorescent lamps ( tube lights), sodium lamps, mercury
vapour lamps, electric arcs used for welding and cutting metals,
plasma displays etc all have plasmas in them.
Some plasma properties:
A plasma has many interesting and useful properties. These arise
due to the presence of ions, electrons, neutral atoms in higher
energy states as well as neutral atoms in the ground state which
form a majority in most of the man made plasma. Plasmas can be
manipulated by electric and magnetic fields. As in a gas, the
particles in a plasma are always colliding with each other. In
the process electrons and ions may recombine to form a neutral
atom in an excited state or a ground state, a neutral atom may
get ionised. Excited atoms loose energy and go to ground state
by emitting light. This is how light is generated in fluorescent
lamps ( tube lights ), neon tubes, sodium lamps, mercury vapour
lamps, CFL's, electric arcs etc. This property makes plasma
attractive to look at with various colours. Sun and stars also
generate light by the same process.
+ - + - + -
- + - + - + - +
+ - + - + - + - + Plasma
- + - + - + -
+ - + - + -
Like an ordinary gas, plasma would also have some temperature.
But in a plasma there can be more than one temperature! For
example the electrons generally have an higher temperature than
the ions. The ions themselves could be at a higher temperature
than the neutral atoms. In other words, each species i.e.
electrons, ions and neutral behave like three different gases
with different temperatures. Colliding plasma particles may
exchange energy. The energy lost by one would be gained by the
other. Such collisions help in equalising the temperatures of
the different species. This happens when plasma densities are
very high and collisions are quite frequent as in the sun or in
welding and cutting electric arcs. Such plasmas are said to be
in thermal equilibrium. The plasma in tube lights, CFL's, sodium
lamps, mercury vapour lamps etc are all non equilibrium plasmas.
Some times even a given species, say electrons, may not have a
well defined unique temperature. Some times they are
characterised by two temperatures. These properties play an
important role in some plasma applications.
Shielding and quasi neutrality:
An important property of a plasma is the so called quasi
neutrality. In any small region (or volume ) of a plasma there
are equal number of positive and negative electric charges.
n = ne = ni
Here n is the plasma density, ne is electron density and ni is
ion density. The densities are expressed in number of particle
per unit volume.
This ensures that there can be no appreciable electric field in
a plasma. The quasi neutrality comes about because a positive
ion surrounds itself with a number of negatively charged
electrons so that the effective charge in a sphere of radius
ld, called the Debye (shielding) length, is zero. Beyond this
Debye sphere of radius
ld the electric field is zero. This is
seen in following sketch.
Electric field due to a free charge q is E = q / r2
Electric field due to a shielded charge q in a plasma is
E = (q / r2 ) E-r /
What happens when we immerse two electrodes in a plasma and
apply a voltage? When this is done in air or vacuum a uniform
electric field is established between the two electrodes. This
is given by
E = V/d where d is the distance between the electrodes and V is
the applied potential.
But in a plasma most of the potential falls very close to the
cathode within a few Debye lengths and the bulk plasma would not
have any electric field. This region where the potential falls
is called the plasma sheath. Close to a cathode the sheath would
have excess positive charge. Quasi neutrality condition does not
hold good in this region.
In fact, some kind of sheath develops around any solid object
placed in a plasma. Sheaths play an important role in all
laboratory and industrial plasmas. Positive ions from the plasma
moving towards the cathode are accelerated by large negative
potential and bombard the cathode with large energy. This would
lead to many consequences as we would see later.
The Debye length depends on plasma parameters like plasma
density and temperature. It is given by
ld = (kT/4pne2)1/2½
where k is the Boltzmann constant, T is electron temperature of
the plasma, n is the plasma density and e is the unit electric
As mentioned earlier, plasma particles would be moving randomly
in all directions. In the process they collide with each other.
During such collisions several things can happen. Some of them
The kinetic energy colliding particles
can alter during such collisions. This can lead to sharing and equalisation of energy ( temperature) of different species in
the plasma. This is also called thermalisation. However, interna
energy or the internal structure of the colliding partners does
Inelastic collisions: Here the internal energy and structure
of the colliding partners may be altered. Some such processes
Excitation: e + A ® A* ® A + radiation
Ionisation: e + A ® A+ + 2e
Dissociation: e + B2 ® B + B + e
Recombination: e + A+ ® A + radiation
The rate at which a particular reaction occurs depends on the
type of reaction, the energy of the colliding partners, and the
frequency of collisions. While the energy depends on plasma
temperature, collision frequency depends on temperature as well
Such processes play crucial roles in all plasmas.
Collision frequency tell us how many times a particular type of
collision ( elastic, ionization etc) takes place per second in
given plasma. This, of course, depends on plasma density,
temperature and the type of collision.
Mean free path:
This is the average distance a particle travels
in the plasma between to successive collisions.
(to be continued)