Hoffman D.M., Singh B., Thomas J.H. (Eds). Handbook of Vacuum Science and Technology

482 Chapter 4.6: Demountable Seals for Flanges

and

Valves

flange puq)oses for diameters up to 12 inches. For larger sizes and noncircular

shapes, Helicoflex® seals are about the only choice. However, they are expensive,

may have long delivery times if made to order, and should be evaluated by use to

gain experience before making a final decision to use them in a large project.

It is probable that development of metal seals will continue, driven by the trend

to ever lower pressures for semiconductor device fabrication, and by the con-

struction of large storage ring accelerators where both extremely low pressures

and high reliability are important.

REFERENCES

1.

Viton® is a registered trademark of DuPont Co., Wilmington, DE 19898.

2.

Flourel® is a registered trademark of 3M Co., St. Paul, MN 55144.

3.

VITON

Fluid Resistance Guide

VT-500.1

(R2) 191281E (DuPont, Wilmington, DE, December

1994).

4.

The

General

Chemical Resistance

of

Various

Elastomers (Los Angeles Rubber Group, Inc., Los

Angeles, 1970).

5. Standard Test Methods for Rubber Property ^Compression Set, ASTM D395-89 (American

Society for Testing and Materials, Philadelphia 1989).

6. CHEMRAZ DATA SHEET HC 789 (Greene, Tweed & Co., Inc., Kulpsville, PA 1989).

7. M. H. Van de Voorde and C. Restat, Selection Guide to Organic Materials for Nuclear Engi-

neering, CERN Report 72-7 (CERN, Geneva 17 May 1972).

8. B. B. Dayton, in 1959 Sixth

Nat.

Symp.

Vac.

Technol. Trans. (Pergamon Press, New York, 1960),

pp.

101-119.

9. R W. Hait, Vacuum, 17 (1967) 547.

10.

G. Thieme, Vacuum, 13 (1963) 137.

11.

L. de Csernatony, Vacuum, 16 (1966) 129.

12.

B. B. Dayton, J.

Vac.

Sci. Technol, A13 (1995) 451.

13.

J. R. Young, J.

Vac.

Sci. Technol., 6 (1969) 398.

14.

E. DeLaurentis, S. Wu, J. Salfelder, and Y. Uritsky, Microcontamination, 3 (1994) 45.

15.

A. W. Chesterton Co., Stoneham, MA 02180.

16.

T J. Edwards, J. R. Budge, and W. Hauptli, J.

Vac.

Sci. Technol., 14 (1977) 740.

17.

B. W. L. M. Sessink and N. F. Verster, Vacuum, 23 (1973) 319.

18.

Parker

O-Ring

Handbook (Parker Seal Group, Lexington, KY, 1992), Sec. A2, p. 15.

19.

Parker

O-Ring

Handbook (Parker Seal Group, Lexington, KY, 1992), Sec. A4, pp. 8-9.

20.

O-Ring

Handbook (Precision Rubber Products Corp., Lebanon, TN, January 1984), Sec. 2, p. 6.

21.

L. Laurenson, Vacuum 27 (1976) 431.

22.

Fomblin is a registered trademark of Montedison USA, New York.

23.

L. de Csernatony, Vacuum, 16 (1966) 13.

24.

D. Alpert, Rev. Sci. Instru., 22 (1951) 536.

25.

D. G. Bills and F G. Allen, Rev. Sci. Instru., 26 (1955) 654.

26.

Granville-Phillips Co., Boulder, CO

80301.

27.

F O. Rathbun, Jr., ed., Sealing Action at the Seal Interface, NASA Report N63-18.159 (1963).

28.

L. G. Gitzendanner and F. O. Rathbun, Jr., Design Criteria for Zero Leakage

Connectors

for

Launch Vehicles, NASA Report N65-30841 (1965).

References 483

29.

J. A. Bain and J. P. Laniewski, Zero Leakage Design for Ducts and

Tube

Connections for Deep

Space Travel, NASA Report 68-20974 (1967).

30.

D. J. Grove, 1958 Fifth

Nat.

Symp.

Vac.

Technol Trans. (Pergamon Press, New York, 1959), p. 9.

31.

R. Souchet, Le Vide, No. 123 (1966) 235.

32.

W. J. Lange and D. Alpert, Rev. Sci. Instru., 28 (1957) 726.

33.

W. R. Wheeler and M. Carlson, 1961 Trans. Eighth Nat. Vac. Symp. (Pergamon Press, New

York, 1962), p. 1309.

34.

W. R. Wheeler, 1963 Trans. Tenth Nat.

Vac.

Symp. (Macmillan, New York, 1963), p. 159.

35.

Conflat® is a registered trademark of Varian Vacuum Products, Lexington, MA 02173.

36.

M. A. Carlson and W R. Wheeler, U.S. Patent 3,208,758 issued September 28, 1965.

37.

T. Wikberg and E. Dodelin,

Vacuum,

41 (1990) 2082.

38.

K. Kitamura, K. Itoh, T. Uchida, M. Kondoh, K.Obara, K. Nakamura, and Y. Murakami, J. Vac.

Sci. Technol., A12 (1994) 3217.

39.

Helicoflex® is a registered trademark of CEFILAC S.A., St. Etienne, France.

40.

C. Abbes, S. Bianchi, R. Chevallereau, M. Moreau, J. Rogement, R. Roques, C. Rouaud, and

H. Royer, U.S. patent 3,820,799, issued June 28, 1974.

41.

R. de Villepoix, J. Pages, R. Forges, C. Abbes, and C. Rouaud, U.S. Patent 4,561,662, issued

31 Dec. 1985.

42.

R. B. Fleming, R. W Brocker, D. H. Mullaney, and C. A. Knapp, J.

Vac.

Sci. Technol., 17 (1980)

337.

43.

K. M. Welch, G. T. Mclntyre, J. E. Tuozzolo, R. Skelton, D. J. Pate, and S. M. Gill, Vacuum, 41

(1990)1924.

44.

W Unterlerchner,

Vacuum,

41 (1990) 1920.

45.

H. Fend,

Vacuum,

47 (1996) 527.

46.

VAT VAKUUMVENTILE AG, Haag/SG, Switzerland.

47.

A. Roth, J.

Vac.

Sci. Technol., 9 (1972) 14.

48.

A. Roth, J.

Vac.

Sci. Technol., Al (1983) 211.

49.

G. Armand, J. Lapujoulade, and J. Paigne, Vacuum, 14 (1964) 53.

50.

P J. van Heerden, Rev. Sci. Instru., 26 (1955) 1130.

51.

A. Inbar,

Vacuum,

22 (1972) 187.

52.

L. Verheyden and K. Klein, Vacuum, 21 (1971) 401.

53.

T. Wikberg, J.

Vac.

Sci. Technol., 5 (1968) 205.

CHAPTER

4.7

Outgassing of Materials

Benjamin B. Dayton

Consultant

4.7.1

RELATIONSHIPS AMONG SYSTEM PRESSURE,

PUMPING

SPEED,

AND OUTGASSING

4.7.1.1 System Parameters That Must Be Known or Measured

NET PUMPING SPEED IN VACUUM CHAMBER

A typical vacuum plant or system consists of a main vacuum chamber, of known

volume V and exposed wall area A of known material and surface condition, in

which a process is to be carried out at a measured low pressure/? maintained by a

vacuum pump of rated speed 5p. If the pump is ah oil diffusion pump, it may be

provided with a suitable baffle or cold trap of known conductance, C^, between

pump and chamber to prevent vapor diffusing back into the chamber from the

pump which also usually has internal means of reducing backmigration of oil va-

por. If the pump is a turbomolecular pump or cryopump, no trap is necessary, but

the turbo pump may have a protective screen at the inlet. A high-vacuum valve of

known conductance, C^, may be included to isolate the pump from the chamber

during venting to atmosphere. In addition, it is sometimes necessary to take into

consideration the added impedance, 1/Cp, to gas flow caused by short lengths of

pipe between the chamber and the valve housing, particularly when this pipe con-

nection includes a right-angle bend. The net pumping speed 5n available at the

connection to the chamber is then given by

l/5n = 1/Cb + 1/Cv + 1/Cp + l/5p (1)

$25.00 All rights of reproduction in any form reserved.

484

4.7.1 Relationships Among Pressure,

Speed,

and Outgassing Rate

485

where the conductances Q, Cv, and Cp are assumed to have been measured or

calculated without entrance or exit corrections, because the diameter of the pipe

connections and the valve and baffle housings is usually about the same as the di-

ameter of the intake opening to the pump. If the pump speed, 5p, has been mea-

sured with a test dome according to AVS (American Vacuum Society) or ISO

(International Standards Organization) standard recommended practice, it will in-

clude the only entrance correction that need be made, because the location of the

vacuum gauge is chosen so that the measured speed simulates that for gas flowing

from a large entrance chamber across the pump inlet [1]. Of

course,

if no baffle or

valve is used, the corresponding impedance terms are omitted from Equation (1).

Pump speeds are usually expressed in liters per second and conductances in torr-

liters per second per torr pressure drop.

4.7.1.2 Intrinsic or Free Outgassing Rate

The intrinsic or "free outgassing rate" (outgassing rate at pressures so low that

readsorption is negligible), ATfh, of the chamber walls and other surfaces exposed

inside the chamber at room temperature can be estimated from [2,3,4]

/^fh = ^n/^h" (2)

where r^ is the pumping time in hours up to a limiting time, t^^, (usually several

hours) at which this simple equation cannot be used, a is usually constant and

about equal to 1 for metal surfaces up to a time fhm» which depends on the thick-

ness of the oxide layer on the metal and about equal to 0.5 for elastomers and

plastics up to a time

rhm»

which depends on the thickness of the material, and

K^i

is the free outgassing rate (in torr • liter

s~^cm~^)

after one hour of pumping,

which is independent of the ratio of net pumping speed, S^, to exposed outgassing

area, A,„.

To convert outgassing rate in torr • liter

s~^cm"^

to Pa m s~^ multiply by

1333.22. To convert from torr • liter

s~^cm~^

at 25°C to molecules

s~^cm~'^,

multiply by 3.24 X 10^^.

PROPERTIES OF THE MATERIALS EXPOSED TO THE VACUUM

The material of the chamber wall is usually stainless steel or aluminum, but may

be mild steel or copper, and for these metals the value of ^f] depends primarily on

the thickness and condition of the thin oxide film that always exists on the surface

and on the partial pressure,

P^,

of water vapor in the air to which the surface was

exposed for a given time t^ prior to pump down. Values of Kfi as calculated from

measurements of the outgassing rate of stainless steel and aluminum for various

exposures to water vapor are given in Table 1.

4«6 Chapter 4.7: Outgassing of Materials

Table

1

Measured Outgassing Rate Constants for Stainless Steel and for Aluminum Alloy,

and Calculated Free Outgassing Rate

Material and Surface Treatment

A, Stainless steel

1.305 baked 24hl50°C

2.

304 baked 48h 150°C

a. Electropolished

b.

Electropolished +He glow

discharge

c. Vacuum remelt/detergent

d. Mill finish/detergent

3.

304

first

pumpdown

a. Belt-polished

b.

Buff-polished

4.

304 baked 24h 150°C, immersed

in water

5.SSKhl8N9T

b.

Cord-brushed

c. Ultrasonic

d. Mechanical polished

e. Chemical polished

6. 304 highly polished, pumped to

8X 10-'0torrl2''C

a. First exposure 12°C

b.

Second exposure 12°C

c. Third exposure 12°C

d. Fourth exposure 12°C

7. 304 No heat treatment, pumped to

<10"'^torr

a. First exposure

b.

Second exposure

c. Third exposure

d. Fourth exposure

e. Fifth exposure

f. Sixth exposure

8. 304 baked at 180°C, pumped to

ultimate pressure

a. First exposure

b.

Second exposure

B.

Aluminum alloy

1.

A6063-EX bak. 24h 150°C

2.

6061 baked 48hl50°C

a. Inert extrude (EX)TIG

b.

Mirror finish

c. Mill fin./detergent

AJS,,.

2410

717

in

111

790

1198

134

14

2.36

19

2410

717

Pe

18

15

10?

23

10?

10

1

0.1

0.01

18

4X 10-5

18

15

U

0.33

1.0

>24

24

>24

0.5

0.25

1/60

1/12

1/2

3

19

48

0.5

0.17

0.33

1.0

10'K„„

0.7

8.3

4.1

4.6

4.9

1.6

1.0

0.8

28

7.0

3.1

2.1

1.8

8.0

4.3

1.9

0.8

40

80

160

400

600

0.80

0.34

10

7.5

6.4

7.8

«i

1.3

1.11

0.92

1.17

1.14

0.9

1.0

1.2

1.4

1.2

1.1

1.0

l.O

1.1

1.2

1.3

1.35

1.33

1.2

1.1

1.0

0.8

1.1

1.12

1.19

lO^/^f,

623

1410

694

779

830

153

96

88

486

372

165

117

96

103

119

114

103

873

783

655

761

805

799

558

399

8890

1270

1080

1320

R

N

[

[:

['

[:

b

['

b

I

[:

(continue

4.7.1 Relationships Among Pressure, Speed, and Outgassing Rate 487

Material and Surface Treatment

3.

A6063-EX immersed H2O

4.

A6063-EX argon glow discharge.

chemical etch

a. First exposure

b.

Second exposure

Table

I-

/i,„/0\v

2256

2X 10^

2X 10-*

-Continued

P^

23

9

0.01

^e

24

0.25

io^/^„„

13

0.47

0.08

«!

1.2

1.1

1.2

10^/^f,

2670

4980

8180

Ref.

No.

[4]

[9]

Note:

A,n

- exposed geometric area of outgassing material (cm-)

5vv = pumping speed for water vapor at 25°C (L/s)

K,n\

= measured outgassing rate at

1

h (torr L/s~'cm~^)

«] = absolute value of slope of log-log graph of measured outgassing rate vs. time after

1

h of pumping

Pe = partial pressure (in torr) of water vapor during exposure of preconditioned vacuum system for time

fc (in h) before pumpdown at room temperature

A^fi = calculated free outgassing rate at

1

h (torr L/s"' cm ~^)

References

1.

J. Chen et al., 7.

Vac.

Sci. Technoi, A5 (1987) 3422.

2.

H. F. Dylla, D. M. Manos, and

P.

H. LaMarche, J.

Vac.

Sci. Technoi., All (1993)

2623.

3.

N. Yoshimura and H. Hirano, J.

Vac.

Sci. Technoi, A7 (1987) 3351.

4.

J. Chen and Y. Liu, J.

Vac.

Sci. Technoi, A5 (1987) 262.

5.

V. Zhilnin, L. Zhilnina, and A. Kuzmin, Proc. 4th Internat. Vac. Congress, Manchester 1968, Pt. 2 (Inst.

Physics and Physical Soc, London, 1968), pp. 801-808.

6. H. J. Schuetze and K. E. Hennings —See B. Dayton, J.

Vac.

Sci Technoi, A13 (1995) 451.

7.

H. Galron, Vacuum, 23 (1973) 177.

8. R. Strehlow and D. Richardson, Proc. 4th Internat.

Vac.

Congress, 1968, Pt. I (Inst. Physics and Physical

Soc,

London, 1968) pp. 175-178.

9. J. Chen et al., J.

Vac.

Sci Technoi, A12 (1994) 1750.

If the chamber wall is baked at temperatures of 150 to 200°C for a sufficient

time during the pumpdown, most water adsorbed in the oxide layer can be re-

moved, and the outgassing rate of the chamber wall then depends on the content

of hydrogen, oxygen, and other gases that are dissolved in the underlying metal

and that diffuse to the exposed surface, as well as on the desorption of residual

water molecules chemisorbed in the oxide layer. Under these conditions, the ex-

ponent a is usually somewhat less than 1. To obtain ultra-high-vacuum pressures,

it is necessary to clean the surface thoroughly and to remove most of the dis-

solved hydrogen by baking under vacuum at 300 to 500°C for several hours

[5,6].

In addition to outgassing from the walls of the chamber, baffle housing, and

vacuum valve, there will be outgassing from any elastomer gaskets used to seal

the flange connections and the valve plate. The elastomer material must be known

and the total exposed area estimated. For elastomers and plastics, the exponent a

is usually about 0.5 except for silicone elastomer, for which a is about 1. Values

of Kfi for elastomers and plastics are given by

K„^i

in Table 2.

4«8

Chapter 4.7: Outgassing of Materials

Table 2

Outgassing Rate Constants for Elastomers and Plastics Calculated from Experimental Data

Material

Araldite B

Araldite D

Araldite F

Convaseal

Epicote

Eppon, Shell Oil Co.

Epoxy Resin (CIBA)

Hypalon

Kel-F

Methylmethacrylate

Natural rubber

Neoprene

Nylon

Perbunan

Pcrtinax

Permafil (G.E)

Plexiglass M222 (Rohm and Haas)

Plexiglass (Alsthom)

Plexiglass

Polyacrylate

Polyamid (Bayer)

Polyethylene (BASF)

Polyethylene (Dynamit-AG)

Polystyrol (Dynamit-AG)

Polystyrol (BASF)

Polystyrol

Polyurethane (Bayer)

Polyvinylcarbazol (BASF)

PTFE

Silastic

Silicone (74)

Silicone (54)

Silicone (R 60, 1.7 mm thick)

Silicone (R 30, 1.4 mm thick)

Silicone (R 30, 4 mm thick)

Teflon, Dupont

Teflon

Ultramid (BASF)

Viton

Viton A

^,n

30

65

82

41

39

25

65

174

25

65

25

—

65

25

22.7

57

12

30

8

25

12

110

12

—

25

14

12

65

32

25

12

25

10-^

^'a

0.7

3.7

0.7

0.4

1

(0.1)

1.5

0.7

(O.l)

3.7

(0.1)

1

I

3.7

(0.1)

0.6

0.4

0.10

0.7

0.6

(0.1)

0.12

0.10

0.23

0.14

0.6

0.85

0.23

1

I

(0.1)

0.18

0.23

1.5

0.6

(0.1)

0.1

(O.l)

300

10^/^.,,

18

19

15

14

25

40

27

18

0.4

42

63

330

31

70

120

35

28

60

400

19

31

7

132

46

2.4

2.6

15

6

5

16

3

30

66

83

20

40

80

4

5

0.7

3.3

17

0.13

0.19

«i

0.4

0.3

0.5

1.2

0.4

0.5

0.57

0.9

0.5

0.3

0.5

0.31

1.8

0.43

0.4

0.43

0.5

0.59

0.5

0.45

1.3

1.00

0.63

0.75

1.0

0.7

0.68

0.48

0.68

0.5

0.51

0.5

Ref.

No.

[1]

[7]

[2]

[5]

[14]

[8]

[5]

[2]

[8]

[7]

[8]

[3]

[7]

L8]

[6]

[5]

[3]

[1]

[6]

[8]

[4]

14]

[4]

[6]

[4]

[3]

[8]

[10]

[4]

[5]

[6]

[8]

[4]

[8]

[9]

{continues)

4.7.1 Relationships Among Pressure,

Speed,

and Outgassing Rate 489

Table 2—Continued

Note:

A,n

= exposed geometric area of outgassing material (cm^)

5a = pumping speed for air at 25"C (L/s)

A',,,] = measured outgassing rate after

1

h of pumping (torr L/s~' cm~-)

«! = absolute value of slope of log-log graph of measured outgassing rate vs. time

after I h of pumping

References

1.

R. Geller, Le Vide, 13 (74) (1958) 71.

2.

J. C. Boulassier, Le Vide, 14 (80) (1959) 39.

3.

B. D. Power and D. J. Crawley, Traus. 1st Intenwt.

Vac.

Congress, Nanutr, Vol.

1

(Pergamon

Press,

New York, 1960), pp.

206-211.

4.

R. Jaeckel and F. J. Schittko,

Forschungsberichte

des

Wirtschafts-

iind

Verkehrsministeriwn

Nordrliein-Westfalen Nr. 369, Westdeutscher Verlag, Cologne, 1957.

5.

B. B. Dayton, Trans. 6th Nat. Vac. Symp. (Pergamon Press, New York, 1960), pp. 101-119.

6. G. Thieme, Vacuum, 13 (1963) 137.

7.

J. Blears, E. Greer, and J. Nightingale, Trans.

1st

Internat. Vac. Congr, Namur, Vol. 2 (Perga-

mon Press, New York, 1960), pp. 473-479.

8. W. Beckmann, Vacuum, 13 (1963) 349.

9. B. B. Dayton, J.

Vac.

Sci. TechnoL, A13 (1995) 451.

10.

H. von Munchausen and F. Schittko, Vacuum, 13 (1963) 549.

11.

A. Schram, Le Vide, 18 (103), (1963) p. 55.

12.

F J. Schittko, Vacuum, 13 (1963) 525.

13.

R. Jaeckel,

Trans.

8th Nat.

Vac.

Symp. and 2nd

Internat.

Vac. Congress, Vol. 1 (Pergamon

Press,

New York, 1962), pp. 17-26.

14.

B. H. Colwell,

Vacuum,

20 (1970) 481.

There may also be some permeation of gases in the atmosphere through elas-

tomer seals between flanges as well as permeation of hydrogen through some

metals due to reaction of the outer surface with water, particularly for metals

(such as iron) that do not form a protective coating [7].

The rate of permeation in torr

•

liters per s per cm^ of exposed wall or gasket

area of gas at the partial pressure P^ and absolute temperature T outside the en-

closure through an elastomer gasket or through a glass or metal wall of thickness

w,„ (in mm) into a vacuum is given by

K, = (760/273) X 10--^

T{U,JwJP„'^

(3)

where

U,„„

is the permeability coefficient, which varies with the absolute temper-

ature r,„ of the mih material according to

U,uu

=

^n,n

exp(-10-^ E„JjRTJ (4)

where the preexponential factor,

a,„,^,

is nearly constant over a wide temperature

range and has the permeability units of cm^(STP)/cm^ per torr pressure differ-

490 Chapter 4.7: Outgassing of Materials

ential per mm thickness of a sheet of the material, £„„, is the activation energy

for permeation in kcal/mol, j is the dissociation number (; = 1 for most gases

through plastics and elastomers and j = 2 for diatomic molecules permeating

metal),

and R is the gas constant in calories per degree K per mole {R =

1.987).

(STP is the standard temperature of 273 K and pressure of 760 torr.)

In the absence of leaks in the welds and residual pump fluid vapor in the sys-

tem, the ultimate pressure is determined by permeation through gaskets and walls

according to

/7,

= K^A,/S (5)

where A^ is the effective area through which permeation occurs and S is the net

pumping speed for the permeating gases.

Table 3 lists the constants for permeation and diffusion of some gases through

nonmetallic materials. Table 4 lists values of the permeability coefficient,

U,„„,

for gases through nonmetallic materials at room temperatures. Additional infor-

mation can be found in the references cited.

Table 3

Constants for Permeation and Diffusion of Gases Through Nonmetallic Materials

Material

Rubber (natural)

Neoprene G

Perbunan

Pyrex

Gas

H2

O2

N2

He

H2

O2

N2

He

6.9

6.6

9.3

6.5

8.1

9.9

10.6

11.0

7.0

6.2

^lun

6.0

X

10-4

1.1 X 10-3

6.2 X 10-3

1.8 X lO-'*

1.2 X 10-3

7.1 X 10-3

7.4

X

10-3

1.4

X

10-2

1.6 X 10"*

2.6 X 10-«

H„,n

5.9

7.5

8.7

—

6.6

9.4

10.3

10.2

—

6.5

d,n„

0.23

0.57

2.9

—

0.28

3.1

9.3

7.2

—

4.8 X lO-'*

Ref.

No.

[1]

[I]

[1]

[I]

[2]

Note:

E„,„

= activation energy for permeation in kcal/mol

H,f,„

—

activation energy for diffusion in kcal/mol

<3„„,

= permeation preexponential factor in cm3(STP)/cm2 per torr pressure differential per mm of

material thickness

<i,„„ = diffusion preexponential factor in cm^/s

Temperature range: 10-100°C

References

1.

G. J. van Amerongen, 7. Appl

PJiys.,

17 (1946) 972.

2.

W. A. Rogers, R. S. Buritz and D. Alpert,

J.

Appl Phys., 25 (1954) 868.

4.7.1 Relationships Among

Pressure,

Speed,

and

Outgassing Rate

491

Table

4

Permeability Coefficient,

f/,„„,

for

Gases Through Nonmetallic Materials

in

cm^(STP)s~' cm"^

for

a

Pressure Gradient

of

1 torr/mm

Ref.

Material

Gas

Temp.

°C U„„, No.

Buna-S

Butyl rubber

Hycar

Kel-F

Mylar

Neoprene

Pyrex

Rubber

Teflon

FEP

Teflon

FEP

Teflon

FEP

Viton-A

N2

O2

H2O

N2

O2

H2O

N2

O2

H2O

N2

O2

H2O

N2

O2

H9O

H2

He

air

H2O

N2

O2

H2O

N2

O2

H2O

20-30

20-39

20-30

27.1

20-30

18.2

20

25

20-30

6.35 X lO-'o [1]

1.72X10-9

[1]

2.4 X 10"^ [1]

3.2 X 10"" [1]

1.3X10-'°

[1]

4X10-9-2X10-8

[1]

2.4 X

10-"-2.5

X 10-10 fij

9.6 X

10-"-8.2x

10"'° [1]

1 X 10-"^ [1]

9X

10-'3-l.3

X 10-'' [1]

2.5 X

10-'2-5.4X

10-'' [1]

3 X

10-"-3.6X

10-9 pj

1.3

X

10-8-2.3

X

10-8

[1]

1.18X10-'°

[1]

1.27X10-'°

[2]

4.0X10-'°

[1]

1.8X10-^

[1]

9.0X10-'°

[2]

5.6XlO-'3

[2]

4.2

X

10-'°

[2]

2.5

X

10-^

[2]

2.2X10"'°

[1]

5.9X10-'°

[1]

5.0X10-9

[1]

4.4

X

10-"

[1]

1.5

X

10"'°

[1]

5.2

X

10-9

[1]

References

1.

A.

Lebovits, Modem Plastics,

43

(March 1966)

139.

2.

R. M.

Barrer, Diffusion

in and

Through Solids (Cambridge University Press, London, 1941).

47.L2 Relationships Among System Pressure, Pumping Speed,

Outgassing

Rates,

and Chamber Dimensions

GENERAL EQUATION FOR THE PRESSURE IN THE CHAMBER

Assuming that there are n different volatile constituents that can outgas from the

m different materials exposed

in

the vacuum chamber, the principle

of

material

Hoffman D.M., Singh B., Thomas J.H. (Eds). Handbook of Vacuum Science and Technology

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