Coatings Technology Handbook Episode 2 Part 1 potx

35

-6

Coatings Technology Handbook, Third Edition

Coatings used for high-temperature applications require high thermal stability. Refractory compounds
having low vapor pressure and high decomposition temperature are generally suitable in these cases,
depending on service environment. Other properties, such as abrasion resistance, oxidation resistance,
thermal shock resistance, and compatible thermal expansion characteristics, are also important. Thus,
typical coatings used in these applications include certain refractory metals, Al

2

O

3

, B

4

C, SiC, Si

3

N

4

, SiO

2

,
and ZrO

2

, and refractory metal silicides. Composite coatings such as Al

2

O

3



+

ZrO

2

and Al

2

O

3



+

Y

2

O

3

have also been studied. Most of these coatings can be deposited by CVD. Typical applications for these
coatings include rocket nozzles, reentry cones, ceramic heat exchanger components, afterburner parts in
rocket engines, and gas turbine and automotive engine components. Another well-known example of a
protective refractory coating is the SiC-coated hardware used in the microelectronics field for manufac-

FIGURE 35.4

Photography showing a 17–4 PH stainless steel compressor blade coated with a tungsten carbide
coating in a MTCVD process. The blade is first coated with an interlayer of nickel by electrolytic or electroless plating
techniques to protect it from the corrosive action of hydrofluoric acid gas generated during the deposition reaction.

FIGURE 35.5

Photography showing cemented tungsten carbide cutting tool inserts coated with TiC and TiN coating

in a conventional CVD process. These coatings impart improved wear resistance to the carbide tools, allowing them
to run at higher speeds and chip loads in the machining of various materials.

DK4036_book.fm Page 6 Monday, April 25, 2005 12:18 PM
© 2006 by Taylor & Francis Group, LLC
turing coated silicon wafers. Figure 35.8 shows typical examples of graphite susceptor components coated
with SiC. An iridium-coated rhenium thrust chamber for spacecraft was shown in Figure 35.2.

Chemical Vapor Deposition

35

-7

FIGURE 35.6

Steady state erosive wear rate of ultrafine-grained CVD tungsten–carbon (CM 500L) and SiC (CM
4000) coatings and other hardfacing materials, coatings, and ceramics. The eroding medium is 200-micron SiC
particles impinging at a velocity of 30 ms

–1

at room temperature. [Data from Hickey et al.,

Thin Solid Films,

vol. 118,
p. 321 (1984). Reprinted with permission from Elsevier Sequoia, S.A., Switzerland.]
0
0.1

0.2
0.3
0.4
30°90° 30°90° 30°90° 30°90° 30°90° 30°90°30°90° 90° 90° 90°
0.011
0.011
0.047
0.053
0.0114
0.0322
0.038
0.068
0.092
0.246
0.071
0.201
0.053
0.059
0.098
0.381
0.203
Steady State Erosion Rate (cm
3
/g) × 10
−4
San Fernando Labs
CM500L, CNTD Tungsten Carbide
Heat Treated 1 hr., 600°C
Union Carbide
LW-15 Tungsten Carbide

San Fernando Labs
CM4000 CNTD Silicon Carbide
Kennametal
K701 Silicon Carbide
Norton NC-203
Hot Pressed Silicon Carbide
Norton NC-132
Hot Pressed Silicon Nitride
Braze Coat
Flame Spray
Plasmaspray
1020 Steel
1403
VHN
1400
VHN
3266
VHN
439
VHN
542
VHN
150
VHN
1090
VHN
2747
VHN
1791
VHN

525
VHN
AMS 4777
87% Ni 7% Cr 4% Si 3% Fe 3% B
An
g
le of Im
p
in
g
ement

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© 2006 by Taylor & Francis Group, LLC

Chemical Vapor Deposition

35

-9

In recent years, advances in the technology of carbon–carbon composites have led to the fabrication
of components out of these materials, which are then coated by CVD or the new technology of chemical
vapor infiltration (CVI) with various refractory compound coatings, most notably SiC. Other ceramic
fiber composites based on alumina and silica have also been coated in a similar manner for high
temperature service. Figure 35.9 illustrates one of the techniques used for coating of porous fiber preforms
by CVI.
The more exotic CVD techniques that were mentioned earlier, such as PACVD and LCVD, have found
tions is the deposition of diamond films by PACVD. The diamond films have unique properties and
application potential ranging from wear-resistant coatings for cutting tools to coatings for laser mirrors,

of a diamond film deposited on silicon, with the characteristic Raman peak at 1332 cm

–1

, Coatings
deposited by the LCVD technique find applications in laser photolithography, repair of VLSIC masks,
laser metallization, and laser evaporation deposition.

35.4 Summary

The chief characteristics of CVD may be summarized as follows:
1. The solid is deposited by means of a vapor phase chemical reaction between precursor compounds
in gaseous form at moderate to high temperatures.
2. The process can be carried out at atmospheric pressure as well as at low pressures.
3. Use of plasma and laser activation allows significant energization of chemical reactions, permitting
deposition at very low temperatures.
4. Chemical composition of the coating can be varied to obtain graded deposits or mixtures of
coatings.

FIGURE 35.9

Schematic diagram showing a technique of chemical vapor infiltration of porous fiber preforms, in
which a coating of a protective material such as SiC is deposited. In this method, a thermal gradient across the
preform allows diffusion of the reactive gas mixture progressively from the hot surface to the cold surface, uniformly
coating the preform. [Data from Stinton et al.,

Ceramic Bulletin

, vol. 65, p. 347 (1986). Reprinted with permission
from The American Ceramic Society.]

Hot Zone
1200°C
Exhaust Gas
Heating
Element
Retaining
Ring
Water-Cooled
Holder
Coating
Gas
Cold Surface
Fibrous
Preform
Infiltrated
Composite
Hot Surface

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© 2006 by Taylor & Francis Group, LLC
important applications for the deposition of new types of coatings. One of the most interesting applica-
fiber-optics, dielectric films, and heat sinks in microelectronic circuits. Figure 35.10 shows an example
Chemical Vapor Deposition 35-11
Holzl, R. A., “Chemical vapor deposition techniques,” Techniques of Materials Preparation and Handling
— Part 3 (Techniques of Metals Research Series, vol. 2). R. F. Bunshah, Ed. New York: Interscience
Publishers, 1968, p. 1377.
Pierson, H. O. (Ed.), Chemically Vapor Deposited Coatings. Columbus, OH: American Ceramic Society,
1980.
Powell, C. F., J. H. Oxley, and J. M. Blocher, Jr. (Eds.), Vapor Deposition. New York: John Wiley & Sons,
1966.

Ye e , K. K., International Metals Reviews, Review No. 226 (1978).
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© 2006 by Taylor & Francis Group, LLC

36

-1

36

Solvent Vapor

Emission Control

36.1 Regulatory Background

36-

1
36.2 Alternative Control Processes for Volatile
Organic Compounds

36-

2

36.3 Vapor Oxidation

36-

3
36.4 Solvent Recovery

36-

5

For business operations that include the wet coating of a surface, followed by drying, the amount of
volatile organic compound (VOC) released to the atmosphere is important. Increased awareness of
ambient air quality, and various regulations affecting solvent vapor emissions do not change the need to
make a business economically profitable.

36.1 Regulatory Background

For a perspective on the VOC regulations, the government now monitors ambient air quality to measure
several contaminants: particulates (dust), sulfur dioxide (SO

2

), ozone, and others. The amount of ozone
is associated with “smog” and volatile organics in the air; it is most noticeable on hot summer days and
in metropolitan areas. Industrial coating operations are important point sources that may emit tons of
VOC. Automotive traffic and refueling release much more VOC, but the thousands of smaller sources
are not as easy to control.
The federal Clean Air Act of 1961 promulgated an important set of regulations that establish limits
and also require the states to act to meet ambient air quality standards. State regulations may be more
stringent than federal regulations, but not less. Also, local regulations, such as county, municipal, or
regional authority, may be more stringent. In some areas, the state or local authorities are judged by
some to be too lenient toward emissions and by others to be antibusiness in enforcement of regulations.
In many areas, the industrial emissions have been reasonably well controlled, but the ambient ozone

standard of 0.12 ppm ozone has not been attained. (This is unrelated to the “ozone depletion” problem
at high altitudes.)
The federal government now discriminates between “attainment areas” and “nonattainment areas.”
Regulations also discriminate between New Sources and Existing Sources. New source performance
standards may be based on a cost–benefit analysis, but in some nonattainment areas, a more stringent
LAER (lowest achievable emission rate) may be required, to be negotiated on a case-by-case basis. Existing
sources and some new sources may be subject to RACT (reasonable available control technology).

Richard Rathmell

Consultant, Londonderry, NH

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© 2006 by Taylor & Francis Group, LLC
Safety • Operating Costs
Carbon Adsorption • Direct Vapor Condensation

36

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Coatings Technology Handbook, Third Edition

However, if the vapor concentration is maintained close to 40% LEL or above, the solvent vapor can
supply substantially all the energy required. At lower concentrations, it becomes increasingly necessary
to supply auxiliary fuel or to provide more air–air heat transfer to preheat the vapor laden air.
For example, one cubic foot of toluene vapor diluted with more or less air in the exhaust flow to be
incinerated will be as shown in Table 36.1.
From Table 36.1, it can be appreciated that a reduction in airflow (for a given flow of solvent vapor)
will proportionately reduce the size of the vapor incinerator, but the size of heat exchanger or the amount

of added fuel required is affected to a much greater degree.
It is theoretically possible to provide enough heat exchanger capacity to obviate the need for additional
fuel for normal operation. In practice, an auxiliary fuel burner is needed for start-up, and it must be
kept ignited and ready to heat the air when the vapor concentration decreases.
Heat exchangers for vapor thermal oxidizers usually are the shell-and-tube type, using stainless steel
tubes, or ceramic beds. Some metal plate–plate exchangers also are used, but in every case, it is important
to prevent leakage or short-circuiting of vapor-laden air to the exhaust gases, or bypassing the combustion
zone. Such leakage or bypassing can generate objectionable odors from partially oxidized organics.
The ceramic bed heat exchangers operate by periodically reversing the flow direction through at least
two or more beds, which are alternately heated and cooled. Outgoing hot combustion gases flow through
a bed until the ceramic pieces reach a set temperature, then the flow is reversed and vapor-laden gases
are heated so they flow through the hot bed into the combustion zone. There is no problem if the vapor-
laden gases ignite in the bed prior to the combustion space, but before flows are switched back, it is
desirable to first purge vapor-laden gases from the cooking bed into the combustion zone. Nonoxidized
vapors should not be pushed out with exhaust flow. With relatively large beds, it is practical (but not
inexpensive) to provide the high heat transfer area needed to accommodate relatively dilute vapor flows.
The bed size required can be minimized by a high frequency of flow switching; the airtight dampers
may be switched every few minutes. The ceramic pieces must be selected to tolerate frequent temperature
changes and to accommodate the thermal expansion–contraction cycle that occurs. If dust is released
by thermal movements or abrasion, it may prevent direct usage of the residual hot gases in the dryers
and ovens.
Metal surface heat exchangers, with hot combustion gases in one side and the cooler vapor-laden gases
on the other side, operate continuously, without flow reversal or switching dampers. Thermal expan-
sion–contraction can be a problem, leading to torn welds or fractures and to leakage of the higher pressure
vapor-laden air into the lower pressure oxidized discharge flow. Such leakage can generate objectionable
odors by the scorching of the vapors.

TA BLE 36.1

Operating Variables

a

for Thermal and Catalytic Incinerators

Va riable

Type of Incinerator
Thermal Catalytic

LEL in exhaust, % 40 25 10 10 5
Vo lume of exhaust, ft

3

/min 208 333 833 833 1667
Assumed exhaust temperature 200 200 200 100 100
Assumed combustion temperature 1400 1400 1400 900 900
Te mperature rise required 1200 1200 1200 800 800
Te mperature rise resulting from vapor oxidation 1160 725 290 290 145
Te mperature rise required from preheater or auxiliary fuel 40 745 910 510 655
Requirement from preheater or other fuel, Btu

×

10

3

/h 9 170 820 460 1180

Available temperature differential across heat exchanger
(with no other fuel used)
1160 725 290 290 145
Ratio of heat exchanger area

b

required (to avoid auxiliary
fuel consumption)
1126.75 35

a

All temperatures in degrees Fahrenheit.

b

Assuming equal coefficient;

A



=



Q

/

∆

T

, where

A



=

the heat transfer area,

Q



=

heat flow, and

∆

T



=

temperature differential.

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© 2006 by Taylor & Francis Group, LLC

36

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Coatings Technology Handbook, Third Edition

The sources of inert (low oxygen) gas required include the flue gas of a gas-fired steam boiler and
purchased liquid nitrogen or carbon dioxide. Where flue gases are used, the gas burner must be of the
type that can maintain a low ratio of excess air to fuel for various fuel firing rates. A compressor and
pressurized storage tank can provide the ready reservoir for last start-up and fail-safe shutdowns, or a
tank of liquid nitrogen with vaporization facilities can be used.
In some important respects, the operation of an inerted airtight dryer is inherently safer than a
conventional air-swept dryer. In an air-swept dryer there is a transition zone between a flammable wet
interface and a nonflammable exhaust, and there is the potential for a temporary excess solvent loading
into the dryer to produce a large volume of combustible mixture. In an inerted dryer, there is no
flammable interface, and any temporary excess solvent loading will not make a combustible mixture.
When the coating process and wet web is stopped for any reason, there is no tendency for outside air to
exchange with the atmosphere contained in the dryer, except as air may be drawn in to replace the volume
of vapor condensed, or to make up for gas volume contraction as the contained gas cools down. In the
Wolverine systems, the normal operating vapor concentration in the dryer is designed to prevent the
condensation due to vapor volume of any unsafe air inhalation into the dryer. Normally, the vapor
condenser temperature is selected to draw the vapor concentration below the organic LEL level when
the coating process is stopped. This then provides a double safety factor with both a safe O

2

LEL level
and a safe organic-in-air LEL level.
When a dryer is shut down overnight or for a weekend, it is not necessary or desirable to purge the
contained atmosphere to the outside atmosphere.

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© 2006 by Taylor & Francis Group, LLC

37

-1

37

Surface Treatment

of Plastics

37.1 Introduction

37-

1
37.2 Functions of Surface Preparation

37-

1

37.3 Factors Impacting Preparation Intensity

37-

2

37.4 Surface Preparation Techniques

37-

3

37.5 Evaluation of Surface Preparation

37-

6
Bibliography

37-

7

37.1 Introduction

No single step in the coating process has more impact on film adhesion than surface preparation. Film
adhesion to a plastic is primarily a surface phenomenon and requires intimate contact between the
substrate surface and the coating. However, intimate contact of that plastic surface is not possible without
appropriate conditioning and cleansing.

Plastic surfaces present a number of unique problems for the coater. Many plastics, such as polyethylene
or the fluorinated polymers, have a low surface energy. Low surface energy often means that few materials
will readily adhere to the surface. Plastic materials often are blends of one or more polymer types or have
various quantities of inorganic fillers added to achieve specific properties. The coefficient of thermal
expansion is usually quite high for plastic compounds, but it can vary widely depending on polymer
blend, filler content, and filler type. Finally, the flexibility of plastic materials puts more stress on the
coating, and significant problems can develop if film adhesion is low due to poor surface preparation.

37.2 Functions of Surface Preparation

Treatment of the plastic surface performs a great many functions depending on the individual polymer
type involved.

William F. Harrington, Jr.

Uniroyal Adhesives and Sealants
Company, Inc.

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© 2006 by Taylor & Francis Group, LLC
Removal of Contamination • Control of Surface Roughness •
Solvent Cleaning • Detergent Cleaning • Mechanical
Matching of Surface to Adhesive • Providing a Boundary Layer •
Treatment • Chemical Treatment • Other Treatments
Control of Oxide Formation • Control of Absorbed Water
Type of Plastic • Surface Contamination • Initial and Ultimate
Strength Requirements • Service Environment • Time •
Component Size • Cost 2

Surface Treatment of Plastics

37

-5

Virtually all chemical etch procedures require water rinsing (once or twice), and an elevated temper-
ature drying is recommended. With active ingredient treatments, it is imperative that solution strength
be monitored and renewed at appropriate intervals.

37.4.4.1 Sulfuric Acid–Dichromate Etch

By far the most commonly recommended chemical treatment for plastic parts, the sulfuric acid–dichro-
mate etch is used on acrylonitrile–butadieme–styrene (ABS), acetal, melamine or urea, polyolefins,
polyphenylene oxide, polystyrene, polysulfone, and styrene–acrylonitrile (SAN). For each plastic, a dif-
ferent ingredient ratio and immersion temperature and time may be recommended.
The following list is offered as a guide to a possible range of parameters:
While the ranges are extremely wide, experimental trials coupled with test results will allow the user
to identify the most appropriate values for a given plastic.

37.4.4.2 Sodium Etch

For truly difficult surfaces to coat, such as the various fluoroplastics and some thermoplastic polyesters,
highly reactive materials must be used. Metallic sodium (2 to 4 parts) is dispersed in a mixture of
naphthalene (10 to 12 parts) and tetrahydrofuran (85 to 87 parts).
Immersion time is approximately 15 min at ambient temperatures, followed by thorough rinsing with
solvent (ketone) before water rinsing.

37.4.4.3 Sodium Hydroxide

A mixture of 20 parts by weight of sodium hydroxide and 80 parts of water is an effective treatment of

thermoplastic polyesters, polyamide, and polysulfone. Heating the solution to 175 to 200

°

F and immers-
ing for 2 to 10 min is appropriate.

37.4.4.4 Satinizing

Satinizing is a process developed by DuPont for their homopolymer grade of acetal (U.S. Patent
3,235,426). Parts are dipped in a heated solution of dioxane, paratoluene sulfonic acid, perchloroethylene,
and a thickening agent. After the dip cycle, parts are heat treated, rinsed, and dried according to a
prescribed procedure.

37.4.4.5 Phenol

Nylon is often etched with an 80% solution of phenol in water. Generally, the treatment is conducted at
room temperature by brushing onto the surface and drying for about 20 min at approximately 150

°

F.

37.4.4.6 Sodium Hypochlorite

A number of plastics, particularly the thermoplastic types and the newer thermoplastic rubbers, can be
chlorinated on the surface by applying a solution of the following ingredients (parts by weight):
Water: 95 to 97
Sodium hypochlorite, 15%: 2 to 3
Concentrated hydrochloric acid: 1 to 2

Parts can be immersed for 5 to 10 min at room temperature, or the solution can be brushed onto the
surface for the same period.

Ingredient Parts by Weight Range

Potassium or sodium dichromate 5 0.5–10.0
Concentrated sulfuric acid 85 65.0–96.5
Water10 0–27.5
Time 10 sec to 90 min
Te m p e r ature Room temperature to 160

°

F

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38

-1

38

Flame Surface

Treatment

38.1 Introduction

38-

1
38.2 Surface Treatment

38-

1
38.3 Burners

38-

2

Atmospheric Burners • Power Burners

38.4 Film Treatment

38-

4

38.1 Introduction

The need for surface treatment was recognized shortly after the development of polyolefin materials,
resulting in the evolution of various treatment methods. W. H. Kreidl pioneered the process of using an
oxidizing flame on polyolefins to produce a surface receptive to printing and coating. At the same time,
Kreidl’s assistant, Kritchever, was developing the concept of using an electrical corona to produce the
same result. The two men went their separate ways, and both methods have been widely used for the
past 30 years for various surface treating applications.

38.2 Surface Treatment

The exact mechanism of surface treatment is still unknown. In spite of repeated efforts, using sophisticated
instrumentation and complex laboratory methods, we still do not have an accurate understanding of the
process. Fortunately, we do not need this information to use the process.
Solid surfaces have a surface energy specific for various materials. For a liquid drop to spread on a
given surface, the liquid surface tension must be lower than the critical surface tension of the solid. Metal
and glass exhibit a high surface energy, whereas plastics have a low surface energy. Pretreatment increases
the surface energy and therefore its wettability. It may also eliminate a weak boundary layer, thus
improving adhesion.
In flame treating, the high temperature of the combustion gases causes oxygen molecules to become
disassociated, forming free, highly chemically active oxygen atoms. In addition, because of the energy in
the high temperature combustion process, oxygen atoms may also lose electrons to become positively
charged oxygen ions. Such an electrically neutral gas made of equal amounts of positively and negatively
charged particles is known as a plasma. Plasma may be hot or cold.
In flame treating, these high speed, energetic, very reactive oxygen ions or free oxygen atoms bombard
the plastic surface and react with the molecules. This process oxidizes the surface and requires an oxidizing
flame, which is a flame with an excess of oxygen.
In corona treating, high voltage fields cause the oxygen molecules to break into free atoms, which can
react with the plastic. Those that do not react with the surface recombine into molecules of normal

H. Thomas Lindland

Flynn Burner Corporation

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Flame Surface Treatment

38

-3

natural gas, but only 480

°

C to ignite propane. The cool metal surrounding a port will quench the flame,
provided there is sufficient mass to absorb the heat. This explains the need for a certain port depth.
The key in resolving these problems is to lower the velocity of a portion of the air–gas mixture or to
limit the capacity of the burners. Gun-type nozzles were developed, as illustrated in Figure 38.3. A portion
of the air–gas mixture is diverted into the small protected area (1). The velocity of this portion of the
mixture is reduced until the piloting will provide continuous ignition to the main air–gas stream emitting
from the large center port (2).
This allows the rate of mixture velocity out of the nozzle to be increased, increasing the heat output.
This feature, known as flame retention, is inherent in all power burners. Unlike atmospheric burners,
power burners utilize a power source of combustion air.
The flame retention feature was introduced to lien burners, such as drilled pipe burners. A single row
of ports was drilled down the center and, following the pattern of the flame retention nozzle, rows of
small holes were drilled on each side. Deflectors or ignition rails were placed over the two rows of piloting
widely used in the industry today.
casting and the ribbon stack inserted. The velocity of a portion of the air–gas mixture was reduced,
establishing piloting along each side of the rows of main ports, which were produced by the ribbon

FIGURE 38.2

Pipe burner with drilled holes.

FIGURE 38.3

Gun-type nozzles.
Piloting Ports
Main Port
Air-gas
Mixture

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© 2006 by Taylor & Francis Group, LLC
holes (Figure 38.4). Figure 38.5 illustrates a cross section of a typical drilled port line burner that is
Ribbon burners (Figure 38.6) were developed by Harold Flynn. A suitable slot was milled out on a

38

-6

Coatings Technology Handbook, Third Edition

but not the web surface. To treat the substrate with direct flame, sufficient thermal energy had to be
developed to penetrate this layer. Furthermore, the exit velocity of the burner flame had to be adjusted
to varying web speeds.
The principle of a burner design to meet these requirements is shown in Figure 38.8. The ribbon
channels of piloting or ignition flames firing at reduced exit velocities provide a constant supply of
ignition to the center ribbon channel, enabling it to fire at exit velocities far in excess of the normal speed
of flame propagation, greatly increasing the energy output of the burner.
lower energy output requirement. The water cooling is built into the face. The side bars assure a smooth
flame, which is required for the posttreatment process. The capacity, flame velocity, and flame retention
capability are all related to the ribbon configuration. By varying the number of ports and the width of
the ribbon stack, it is possible to produce a customized flame pattern for each application.

FIGURE 38.8

Type 3800 water-cooled smooth flame burner.
4 1/2"
“A”
“B”
3 1/4"
4 5/8"
4 1/2"
3 7/8"
5 15/16"
3 5/8"
2 5/16"
1 11/16"
11/16"
1/16" Gasket
1/16"
Gasket
1"
1"
1/2"
1/2"
Flame Space
O.A. Length
Removeable Water Cooling Assembly
(both sides)
1/8" N.P.T. Water Connections
2 1/2" N.P.T.
Each End

Ignition
Electrode
Flame Rod
End View
Flynn
Smooth Flame
Three Slot
Burner
Assemblies
Series WC–3800
Water Cooled
Water Cooled
Three Slot
Flynn Smooth Flame
Ribbon Burner
Use with all Gases
Natural
• Manufactured • Mixed
Propane
• Butane
Catalog No. “A” Flame Space “B” O.A. Length BTU/Hr Shipping Weight
WC–3800–60 59 3/4" 62 7/8" 900,000 132 lbs
155 lbs
176 lbs
203 lbs
105 lbs
1,080,000
1,200,000
1,260,000
720,000

74 7/8"
83 3/8"
87 1/2"
50 3/4"
71 3/4"
80 1/4"
84 3/8"
47 5/8"
WC–3801–72
WC–3802–80
WC–3803–84
WC–3804–48
Patented under the following:
United States Pat. No.
3,047,056
3,053,316
2,647,569
665,440
662,919
503,393
Canadian Pat. No. 932,688
934,339
Canadian Pat. No.
Other Foreign Patents

DK4036_book.fm Page 6 Monday, April 25, 2005 12:18 PM
© 2006 by Taylor & Francis Group, LLC
Figure 38.9 shows a burner designed for film posttreatment application. It has a single slot due to the

39

-1

39

Plasma Surface

Treatment

39.1 Introduction

39-

1
39.2 Types of Plasma

39-

1
39.3 A Typical Plasma Process Cycle

39-

2
39.4 Plasma Chemistry

39-

2
39.5 Surface Treatment Approaches

39-

3
39.6 Plasma Activation of Plastics

39-

4
39.7 Adhesion

39-

5
39.8 Summary

39-

6
References

39-

6

39.1 Introduction

Gas plasmas make up 99% of our universe, existing mainly as stars. Although rare on earth, natural
characterizes them by particle density and temperature.
Plasmas can be produced and controlled by ionizing a gas with an electromagnetic field of sufficient

power. One useful form of gas plasma is made by introducing gas into a reaction chamber, maintaining
pressure between 0.1 and 10 torr, and then applying radio frequency (rf) energy. Once ionized, excited
gas species react with surface of materials placed in the glow discharge.
The physical and chemical properties of plasmas depend on many variables; chemistry, flow rate,
distribution, temperature, and pressure of the gases. Additionally, rf excitation frequency, power level,
reactor geometry, and electrode design are equally important. Dissociated gas molecules quickly recom-
bine to their natural state when the plasma’s power source is shut off.

39.2 Types of Plasma

Plasmas occur over a wide range of temperatures and pressures, however, all plasmas have approximately
equal concentrations of positive and negative charge carriers, so that their net space charge approaches zero.
In general, all plasmas fall into one of three classifications. Elements of high-pressure plasmas, also
called

hot plasmas,

are in thermal equilibrium (often at energies >10,000

°

C). Examples

1

illustrated in
Ta ble 39.1 include stellar interiors and thermonuclear plasmas.

Mixed plasmas

have high temperature
electrons in mid-temperature gas (~100 to 1000

°

C) and are formed at atmospheric pressures. Arc welders
and corona surface treatment systems use mixed plasmas.

Cold plasmas,

the focus of this chapter, are not
in thermal equilibrium. While the bulk gas is at room temperature, the temperature (kinetic energy) of
the free electrons in the ionized gas can be 10 to 100 times higher (as hot as 10,000

°

C),

2

thus producting
an unusual, and extremely chemically reactive environment at ambient temperatures.

Stephen L. Kaplan

Plasma Science, Inc.

Peter W. Rose

Plasma Science, Inc.

DK4036_book.fm Page 1 Monday, April 25, 2005 12:18 PM
© 2006 by Taylor & Francis Group, LLC
plasmas include lightning, the aurora borealis, and St. Elmo’s fire. Table 39.1 lists certain plasmas and