Plasma Device And Technology
CONTENTS
• Introduction(plasma)
• Properties
• Current Applications
• Future Applications
• Advantages and Disadvantages
• Conclusions
• References
INTRODUCTION TO PLASMA
Plasma is a state of matter similar to gas in which a certain portion of the
particles are ionized. The basic premise is that heating a gas dissociates its
molecular bonds, rendering it into its constituent atoms. Further heating leads
to ionization (a loss of electrons), turning it into a plasma: containing charged
particles, positive ions and negative electrons.
Plasma is a special state of matter in which existing at the same time positive
ions, negative ions, electrons... and the total positive charge is equal to
negative charge.
it had been first developed by M. Faraday in 1880s and plasma concept was
first proposed by I. Langmuir in 1928. Today, plasma is in some consumer
product as neon light, plasma TV and so on.
PLASMA - FOURTH STATE OF MATTER
PLASMA CATEGORIES
According to the temperature of plasma:
Cold Plasma
Low Temperature Plasma
Plasma Hot Plasma
High Temperature Plasma
Confinement Nuclear Fusion, Te=Ti, Ti=108~109K
PLASMA PROPERTIES
• Plasma Density
• Temperatures
• Debye length
• Plasma frequency
PLASMA DENSITY
• For plasma to exist, ionization is necessary. The term "plasma density" by itself
usually refers to the "electron density", that is, the number of free electrons per unit
volume.
• The degree of ionization of a plasma is the proportion of atoms which have lost
electrons, and is controlled mostly by the temperature.
• The degree of ionization a is defined as a = ni/(ni + na) where ni is the number
density of ions and na is the number density of neutral atoms.
TEMPERATURES
• Because of the large difference in mass, the electrons come to thermodynamic
equilibrium amongst themselves much faster than they come into equilibrium
with the ions or neutral atoms. For this reason the "ion temperature" may be very
different from (usually lower than) the "electron temperature". This is especially
common in weakly ionized plasmas, where the ions are often near the ambient
temperature.
• Temperature controls the degree of plasma ionization. A plasma is sometimes
referred to as being "hot" if it is nearly fully ionized, or "cold" if only a small
fraction (for example 1%) of the gas molecules are ionized. Even in a "cold"
plasma the electron temperature is still typically several thousand degrees Celsius.
DEBYE SCREENING
The Debye length is the distance over which significant charge separation can
occur. A Debye sphere is a volume whose radius is the Debye length, in which
there is a sphere of influence, and outside of which charges are screened.
The Debye length ZD defined by:
PLASMA FREQUENCY
Plasma Frequency are rapid oscillations of the electron density in conducting media
such as plasmas. The oscillations can be described as an instability in the dielectric
function of a free electron gas. The frequency only depends weakly on the
wavelength.
the electron plasma frequency the ion plasma frequency
the plasma frequency:
APPLICATIONS OF PLASMA TECHNOLOGY
• Plasma Arc Welding
• Plasma Cutting
• Plasma Spraying
• Plasma Medicine
• Food processing (nonthermal plasma, aka "cold plasma")
• Plasma arc waste disposal (convert waste into reusable material with
plasma).
PLASMA WELDING
• Plasma beam is used for fusion welding process. Plasma arc welding is a gas
shielding process.
• Done with or without filler wire addition.
• Coalescence of metals is achieved through heat transferred by arc created
between tungsten electrode and the workpiece.
• The arc is compressed in a copper alloy nozzle opening to form a highly
paralleled arc column.
• variable polarity plasma arc is used.
• electrode is +ve for short time(ms) and –ve for long time(ms)
during former there will be cleaning action which removes the oxides
from work piece as heavy ions strike the work piece and during the
later there will be penetration.
Advantages:
• Automation is possible.
• Low currents are used.
• Minimum human exposure is involved.
• Ozone emission low.
Disadvantages:
• Complicated torch design.
• High maintenance cost.
• Protection from electric shocks is required
• Electromagnetic waves hazards.
Uses:
In welding titanium and its alloys. Corrosion resistance will not be affected, hence
used In welding stainless steel alloys.
PLASMA CUTTING
It is an erosion process. It utilizes a constricted arc in the form of a high velocity
jet of ionized gas to melt the material.
An inert gas is focused under pressure through a small opening in front of the
cutting torch connected to the DC power supply.
In the torch a portion of inert gas is ionized by the electric discharge from the
power source. The arc is created between a negative tungsten electrode in the
torch through which the gas flows to the work piece.
Plasma arcs are extremely hot and are in the range of 15,000 degrees Celsius.
Hand-held torches can usually cut up to 2 inch (48 mm) thick steel plate, and
stronger computer-controlled torches can pierce and cut steel up to 12 inches (300
mm) thick.
Plasma Cutting
Advantages:
• Very high quality cuts are obtained.
• High speed cuttings can be done.
• Automation is possible.
• Process is applicable to all metal and alloys.
Disadvantages:
• Hazardous fumes and gases, high level of noise.
• Proper clothing, helmets etc. is very much essential.
PLASMA SPRAYING
• Molten metallic or non metallic material is sprayed on to a prepared substrate to
form a coating.
• The sprayed material is in the powder form. It is incited by a stream of ionized gas
on to the substrate. The particles striking the surface gets flattened to form thin
platelets.
• The substrate surface which can be kept below 473K eliminating metallurgical
changes in base material.
• The temperature is as high as 1100C. The powder size is 10-44 microns for free flow.
Spherical powders are best.
• Powders of Al, Ni, Cr, WC-CO are used in this technique.
• Thickness of coating is 0.0025 - 0.075mm. The hardness of coating is 150 – 350
VHN.
• This technique is used in shafts, liners, pistons, valves, cast metal rams.
Plasma Spraying
Advantages:
• Oxidation of powder is minimal.
• Highly dense coating are produced.
• Mechanical and metallurgical properties are superior due to high temperature and
high velocity as well.
• Decomposition of powder is minimized.
Disadvantages:
• Very high temperatures are required.
• Process is noisy.
• Radiation hazards and toxic fumes, high volume of waste products.
FUTURE APPLICATIONS
• Thermonuclear fusion, Magneto hydro dynamic generator and plasma rocket
engines are some of the futuristic applications of plasma.
• In thermo nuclear fusion high temperature of several million degrees is
required.
• In MHD, efficiency is more for convention of thermal energy to electrical
energy, but temperatures slightly low compared to nuclear fusion process.
• In plasma engines the weight of the fuel required is reduced due to very
high velocity. This enhances the maneuverability of spaceship in mid air as
weight of fuel to be carried is less.
ADVANTAGES AND DISADVANTAGES
Advantages:
• Plasma technology provides another means of producing and transferring heat to
waste materials. Unlike combustion, no oxygen is required to produce the heat.
• The gas stream produced is much smaller than with combustion technology and,
therefore, can be easier and less expensive to manage.
• Plasma technology can be controlled to achieve higher temperatures in the melted
materials.
• Depending on the waste materials and supplemental feeds, metals and inorganics
may form separate layers, allowing the recovery of metals.
Disadvantages:
• The air management system will have to be designed to form a seal between the
inside and outside of the unit to prevent air emissions of gases leaving the plasma
unit as the plasma arc melts the waste materials.
• The graphite electrodes used to produce an arc and the lining of the treatment
vessel or chamber are degraded and/or consumed gradually during the waste
melting cycle.
• Maintenance to repair or replace unit components requires a well thought out plan
to protect workers, to avoid spreading contamination and to appropriately handle
materials removed from the unit.
CONCLUSIONS
• Plasma technology is widely used in metallurgy and materials processing
for welding, cutting, spraying, sintering, melting, surface treatment etc.
• It holds a great assurance for the future with plasma engines, electricity
production, nuclear reactors economically on a large scale.
• Modern day Plasma Technology has a very rich and multifaceted character
with not only a vast number of applications but also many fundamental
areas of research, and interesting linkages with several areas of physics,
chemistry and mathematics.
REFERENCES
• Sturrock, Peter A. (1994). Plasma Physics: An Introduction to the Theory of
Astrophysical, Geophysical & Laboratory Plasmas.. Cambridge University Press.
• Nicholson, Dwight R. (1983). Introduction to Plasma Theory.
• Hazeltine, R.D.; Waelbroeck, F.L. (2004). The Framework of Plasma Physics.
Westview Press.
• www.plasmas.org/basics.htm
• www.wikipedia.org/
THANK YOU
