1. Atmospheric Plasma Spray
Hossein Movla1,*
with significant contributions from
Jafar Fathi2, Sirous Khorram3, Mohammad Ali Mohammadi2,4,
Arash Nikniazi1, Foozieh Sohrabi2
And With Special Thanks to
Mohammad Soltanpour
1 Department of Solid State Physics, Faculty of Physics, The University of Tabriz, Tabriz
2 Department of Atomic and Molecular Physics, Faculty of Physics, The University of Tabriz, Tabriz
3 Plasma lab, Research Institute for Applied Physics and Astronomy (RIAPA), The University of Tabriz
4 Sahand Plasma Focus Lab, Research Institute for Applied Physics and Astronomy (RIAPA), The University of Tabriz, Tabriz
Atmospheric Plasma Spray

2. What is Plasma? Fourth state of matter Gas-like
Consists of neutral atoms/molecules, ions, and electrons
High energy, highly reactive substance
Electrons have 10,000 K worth of energy
Activates surfaces
What is Plasma?

3. Gas discharge plasma Electric field causes acceleration of electrons
electron-impact ionization
current to flow through gas

4. Electrical properties of plasma
Negative and positive charges balance each other
Plasma is electrically neutral. Property known as quasi-neutrality
Plasma is electrically conductive
Electrical conductivity comparable to that of metals at room temperature
Electrical properties of plasma

5. Thermal and nonthermal plasma
Thermal and nonthermal plasmas
If Te ≈ Tion then we have a thermal plasma
If Te » Tion then plasma is nonthermal or nonequilibrium or cold plasma
In a thermal plasma, there is Local Thermodynamic Equilibrium (LTE)
LTE requires…
Te ≈ Tion
Excitation equilibrium
Chemical equilibrium
Thermal and nonthermal plasma

6. Natural and man-made plasma
Natural plasma
Lightning strikes, high pressure, high luminosity
Aurora borealis, low pressure, low luminosity
Man-made plasma
Flames, low ionisation level
Glow discharge, low pressure
1 eV = 7740 K
Natural and man-made plasma
Source: Boulos et al. “Thermal Plasmas Fundamentals and Applications V. 1, 1994, Vol. 1”

8. Atmospheric Plasma Non-equilibrium plasma
Electrons at 10-20,000 ºC
Ions, molecules at ºC
Relatively uniform energy distribution
Does not require special vacuum chambers like low pressure plasma
Atmospheric Plasma

9. Physics of the Vacuum Arc – The Arc Discharge
D.C. Discharges
Corona
High V, Low I
At sharp point
Glow Discharge
V ~ 100’s V, I ~mA’s
Cathode fall V, depends on gas and cathode material
Arc
10’s of volts, A-kA
Cathode spots
Physics of the Vacuum Arc – The Arc Discharge

10. Gas discharge plasma At atmospheric pressure:
Breakdown voltage is very high
Breakdown mechanism is often streamer breakdown (spatially nonuniform)
breakdown voltage
Paschen curves
Breakdown voltage increases with the product of gas pressure & electrode separation
Gas discharge plasma
Schütze et al. 1998

11. Composition of a plasma gas Gas mixtures - Air
Dissociation
N2 ↔ N + N
O2 ↔ O + O
Recombination
N + O ↔ NO
N + O2 ↔ N2
Ionization
NO ↔ NO+ + e-
N2 ↔ N2+ + e-
N ↔ N+ + e-
N+ ↔ N++ + e-
O2 ↔ O2+ + e-
O ↔ O+ + e-
O+ ↔ O++ + e-
Ar ↔ Ar+ + e-
Ar+ ↔ Ar++ + e-
Composition of a plasma gas Gas mixtures - Air

12. Difference between Glow and Arc – cathode electron emission process
‘individual’ secondary emission of electrons by:
Ions (depends on ionization energy, not kinetic energy)
Excited Atoms
Photons
Not enough!
Multiplication in avalanche near cathode
Need high cathode drop (100’s of V’s)
Used in sputtering to accelerate bombarding ions into ‘target’ cathode
Arc
Collective electron emission
Current at cathode concentrated into cathode spots
Combination of thermionic and field emission of electrons
Can get sufficient electron current
Low cathode voltage drop (10’s of V’s)
High temp. in cathode spot gives high local evaporation rate – used in vacuum arc deposition
Difference between Glow and Arc – cathode electron emission process

13. Generating a thermal plasma
High intensity arcs
Free burning arcs, e.g. steel furnaces
Wall stabilized arcs, e.g. arc lamp (lab studies)
Convection-stabilized arcs, e.g. hot button plasma torches
Magnetically stabilized arcs, e.g. plasma torches with magnetic field
Thermal RF discharge
Capacitive coupling: HF electrical field
Inductive coupling: Time-varying magnetic field
Microwave discharge
The discharge is part of the MW circuit. Impacts plasma configuration and volume
Low pressure operation results in deviation from equilibrium
More recently, stable higher pressure plasma possible
Generating a thermal plasma

14. Commercial Plasma Applications
Lighting
Steel Melting Furnaces
Cutting and Welding
Thermal spray
Atmospheric plasma spray (APS)
Vacuum plasma spray (VPS)
Chemical Vapour deposition (CVD)
Physical Vapour deposition (PVD)
Waste Recycling
Commercial Plasma Applications

15. Why Coating? high temperature resistance, high corrosion resistance,
chemical inertness,
high hardness,
high wear, abrasion and erosion resistance,
creep resistance,
good adhesion,
high fracture toughness,
good thermal conductivity,
thermal shock resistance,
smooth surface/low porosity, and
thermal fatigue cracking resistance.
Why Coating?

16. Wear and Corrosion-resistant Coatings
Pure Carbides (TiC, ZrC, HfC, NbC, TaC, WC)
Cemented Carbides, and
Tungsten Carbide/Cobalt Coatings (WC/Co)
Titanium Carbide-based Coatings (TiC-TaC-NbC, TizAlC)
Chromium Carbide-based Coatings (CrZrAlC)
Boride-based Coatings (CrB2, BN)
Oxide Coatings
Alumina-based Coatings (A12O3/TiO2, A12O3/ZrO2)
Chromia-based Coatings (Cr2O3)
Metallic Coatings
Refractory Metal Coatings (Mo, Ti and W)
Superalloy Coatings (NiCoCrAlY)
Diamond Coatings
Wear and Corrosion-resistant Coatings

17. Coating Methods Chemical coatings Sol-gel coatings
Chemical Vapor deposition (CVD)
Physical Vapor deposition (PVD)
Vacuum Evaporation technique
Sputtering methods
Laser ablation
Thermal Spraying
Coating Methods

18. Ceramic Coatings in the Industrial Environment
39% were produced by physical vapor deposition techniques (PVD)
26% by chemical vapor deposition (CVD)
23% by thermal spraying
12% by wet processing including sol-gel technique
Ceramic Coatings in the Industrial Environment
annual average growth rate of 12%
US $3 billion by the year 2000
US $6.5 billion by the year 2009
individual annual growth rates are:
engines (28%),
marine equipment (18%),
chemical processing (15%),
military (11%)',
and construction (11%).

19. Total projected sales = $4.1 billion (1995)
80% Coating
Total projected sales = $4.1 billion (1995)
7.8 % Carbides
5.2% Nitrides
4.2% Oxides
2.8% Other

20. three basic methods Flame spraying Arc spraying and Plasma spraying.
There are three basic methods of creating and delivering the necessary molten metal, spray, and these are ：
Flame spraying
Arc spraying and
Plasma spraying.
three basic methods

21. flame spraying Arc spraying
Temperature limited by internal heat of gasses
Oxyacetylene torch ( T = 2700 ºC)
Detonation gun (D-gun) ( T = 3200 ºC)
Jet Kote system ( T = 3000 ºC)
Hypervelocity oxyfuel gun ( T = 3000 ºC)
Arc spraying
Temperature unlimited, controlled by energy input
Electric arc wire-spraying
Air plasma spraying (APS) ( T = ºC)
Inductive plasma (IPS) ( T > ºC)
Reduced pressure ('vacuum') plasma ( T > ºC)
RF-Plasma spraying ( T > ºC)
Low pressure laser spraying ( LPLS ) ( T = ºC)

22. Advantages of Plasma Systems
Plasma acts as a resistive heating element that cannot melt and fail
Torch operates with most gases – not a combustion process
Temperature unlimited (T > ºC)
High temperatures, presence of ions, free electrons and UV allow for highly efficient coating
The high intensity plasma heat allows for designing compact systems
Vacuum not applied
No by-products (reduced by-products)
High efficient and Cost-effective
Advantages of Plasma Systems

23. Types of plasma torches
Source: Camacho, S.L., “Industrial-worthy plasma torches: state of the art”, Pure and Appl. Chem, Vol 60, No. 5, pp , 1988

24. Plasma Spray Gun

25. The objective of the our work are:
Choosing the best type of Plasma Spray
Solving the technological problems of Plasma spray production
Producing protective coatings using the method of gas-dynamic spraying,
improving technological effectiveness of spraying
Reducing the cost of materials for spraying
Manufatoring a lab-scale plasma spray
The objective of the our work are:

30. Plasma Disadvantages/Challenges
New technology perception
Control of NOx emissions from air torch
Developing markets for slag
Scale-up risks
Limitation of size of commercially available torches
Markets’ risks
Plasma Disadvantages/Challenges

31. Future Work Using a high-power rectifier (36 KW)
Coating of multiple materials by changing the deposition parameters
Processing of oxygen sensitive materials due to processing in controlled atmosphere.
Robotic control
Use of reactive gases such as hydrogen to reduce impurities such as carbon and oxygen.
Techniques to enable the VPS of the ultra-fine powders are currently being evaluated.
Modeling the processes in this system
Manufacturing an industrial-scale of plasma spray
Future Work

32. Thanks for your attention