ARYA COLLEGE OF ENGINEERING AND I.T.

Department of Computer Science & Information Technology

Seminar On

Plasma Device And Technology

By:

Atul Mittal

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

Low Temperature Plasma

Plasma Hot Plasma

Cold Plasma

High Temperature Plasma

Confinement Nuclear Fusion, Te=Ti, Ti≈108 ～ 109K

Te=Ti, Ti≈2000 ～ 20000K

Te＞＞ Ti, Ti near to home temperature

PLASMA CATEGORIES

According to the temperature of plasma:

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 α is defined as α = 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 λD 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 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.

PLASMA WELDING

http://www.substech.com/dokuwiki/lib/exe/detail.php?id=plasma_arc_welding_paw&cache=cache&media=plasma_arc_welding.png&DokuWiki=711e5d021d2cdc5d8a60a04c18331a36

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