ISO 3529-1:2019
(Main)Vacuum technology — Vocabulary — Part 1: General terms
Vacuum technology — Vocabulary — Part 1: General terms
This document defines general terms used in vacuum technology. It gives theoretical definitions as precise as possible, bearing in mind the need for use of the concept in practice.
Technique du vide — Vocabulaire — Partie 1: Termes généraux
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INTERNATIONAL ISO
STANDARD 3529-1
Second edition
2019-07
Vacuum technology — Vocabulary —
Part 1:
General terms
Technique du vide — Vocabulaire —
Partie 1: Termes généraux
Reference number
©
ISO 2019
© ISO 2019
All rights reserved. Unless otherwise specified, or required in the context of its implementation, no part of this publication may
be reproduced or utilized otherwise in any form or by any means, electronic or mechanical, including photocopying, or posting
on the internet or an intranet, without prior written permission. Permission can be requested from either ISO at the address
below or ISO’s member body in the country of the requester.
ISO copyright office
CP 401 • Ch. de Blandonnet 8
CH-1214 Vernier, Geneva
Phone: +41 22 749 01 11
Fax: +41 22 749 09 47
Email: copyright@iso.org
Website: www.iso.org
Published in Switzerland
ii © ISO 2019 – All rights reserved
Contents Page
Introduction .iv
Foreword .v
1 Scope . 1
2 Normative references . 1
3 Terms and definitions . 1
3.1 General terms . 1
3.2 Terms to define gases and vapours and their parameters . 3
3.3 Terms needed to characterize the movement of gas molecules and the flow of gases . 4
3.4 Terms to define surface und bulk effects in vacuum technology . 7
4 Symbols and abbreviated terms .10
Introduction
If difficulties arise in the use of the definitions in connection with measurement of some quantities, it
is recommended that reference be made to the International Standards related to the measurement of
those quantities for the practical interpretation of the terms.
iv © ISO 2019 – All rights reserved
Foreword
ISO (the International Organization for Standardization) is a worldwide federation of national standards
bodies (ISO member bodies). The work of preparing International Standards is normally carried out
through ISO technical committees. Each member body interested in a subject for which a technical
committee has been established has the right to be represented on that committee. International
organizations, governmental and non-governmental, in liaison with ISO, also take part in the work.
ISO collaborates closely with the International Electrotechnical Commission (IEC) on all matters of
electrotechnical standardization.
The procedures used to develop this document and those intended for its further maintenance are
described in the ISO/IEC Directives, Part 1. In particular, the different approval criteria needed for the
different types of ISO documents should be noted. This document was drafted in accordance with the
editorial rules of the ISO/IEC Directives, Part 2 (see www .iso .org/directives).
Attention is drawn to the possibility that some of the elements of this document may be the subject of
patent rights. ISO shall not be held responsible for identifying any or all such patent rights. Details of
any patent rights identified during the development of the document will be in the Introduction and/or
on the ISO list of patent declarations received (see www .iso .org/patents).
Any trade name used in this document is information given for the convenience of users and does not
constitute an endorsement.
For an explanation of the voluntary nature of standards, the meaning of ISO specific terms and
expressions related to conformity assessment, as well as information about ISO's adherence to the
World Trade Organization (WTO) principles in the Technical Barriers to Trade (TBT) see www .iso
.org/iso/foreword .html.
This document was prepared by Technical Committee ISO/TC 112, Vacuum technology.
This second edition cancels and replaces the first edition (ISO 3529-1:1981), which has been technically
revised. The main changes compared to the previous edition are as follows:
— standard conditions which are defined elsewhere were removed;
— ranges of vacuum were newly defined and reasons given;
— new term ultra clean vacuum was defined;
— knudsen number and rarefaction parameter were included;
— slip flow was defined;
— specific desorption, outgassing, and evaporation rate were newly defined;
— accommodation factor distinguished in energy and momentum accommodation factor.
Any feedback or questions on this document should be directed to the user’s national standards body. A
complete listing of these bodies can be found at www .iso .org/members .html.
INTERNATIONAL STANDARD ISO 3529-1:2019(E)
Vacuum technology — Vocabulary —
Part 1:
General terms
1 Scope
This document defines general terms used in vacuum technology. It gives theoretical definitions as
precise as possible, bearing in mind the need for use of the concept in practice.
2 Normative references
There are no normative references in this document.
3 Terms and definitions
For the purposes of this document, the following terms and definitions apply.
ISO and IEC maintain terminological databases for use in standardization at the following addresses:
— ISO Online browsing platform: available at https: //www .iso .org/obp
— IEC Electropedia: available at http: //www .electropedia .org/
3.1 General terms
3.1.1
vacuum
commonly used term to describe the state of a rarefied gas or the environment corresponding to such a
state, associated with a pressure or a molecular density below the prevailing atmospheric level
3.1.2
ranges of vacuum
various ranges of vacuum according to certain pressure intervals
Note 1 to entry: While there has been some variation in the selection of the limits of these intervals, the following
list gives typical ranges for which the limits are to be considered as approximations.
Note 2 to entry: The prevailing atmospheric pressure on ground depends on weather conditions and altitude and
ranges from 31 kPa (altitude of the Mount Everest, weather condition "low") up to 110 kPa (altitude Dead Sea,
weather condition "high").
Pressure range Definition The reasoning for the definition of the
ranges is as follows (typical circum-
stances):
Prevailing atmospheric pressure low (rough) vacuum Pressure can be achieved by simple materials
(31 kPa to 110 kPa) to 100 Pa (e.g. regular steel) and positive displacement
vacuum pumps; viscous flow regime for gases
<100 Pa to 0,1 Pa medium (fine) vacuum Pressure can be achieved by elaborate
materials (e.g. stainless steel) and positive
displacement vacuum pumps; transitional
flow regime for gases
Pressure range Definition The reasoning for the definition of the
ranges is as follows (typical circum-
stances):
-6
<0,1 Pa to 1 × 10 Pa high vacuum (HV) Pressure can be achieved by elaborate mate-
rials (e.g. stainless steel), elastomer sealings
and high vacuum pumps; molecular flow
regime for gases
-6 -9
<1x10 Pa to 1 × 10 Pa ultra-high vacuum (UHV) Pressure can be achieved by elaborate mate-
rials (e.g. low-carbon stainless steel), metal
sealings, special surface preparations and
cleaning, bake-out and high vacuum pumps;
molecular flow regime for gases
-9
below 1 × 10 Pa extreme-high vacuum (XHV) Pressure can be achieved by sophisticated
materials (e.g. vacuum fired low-carbon
stainless steel, aluminium, copper-beryllium,
titanium), metal sealings, special surface
preparations and cleaning, bake-out and ad-
ditional getter pumps; molecular flow regime
for gases
3.1.3
ultra clean vacuum
medium or high vacuum that requires special conditions for some gas species equivalent to UHV
conditions
Note 1 to entry: The requirements for the particular gas species (impurity) depend on the application.
Note 2 to entry: Hydrocarbons, CO, CO and H O are typical impurity gases.
2 2
Note 3 to entry: The particular requirements may also include specifications for low particle density.
3.1.4.1
pressure of a vacuum
p
normal component of the force exerted by a gas on an area of a real surface
divided by that area
Note 1 to entry: The orientation of the surface relative to the mass flow vector being specified if there is a net
mass flow of gas);
3.1.4.2
pressure of a vacuum
p
state of a gas according to the ideal gas law with corrections for
real gases if necessary
Note 1 to entry: When the ideal gas law is applied, the pressure p in a small infinitesimal volume is given by the
product of number density n of gas molecules in this volume, Boltzmann constant k and temperature T.
Note 2 to entry: For most practical applications in vacuum, the ideal gas law without corrections for real gases
(volume and interaction of gas molecules) is sufficient.
3.1.5
partial pressure
pressure due to a specified component of a gaseous mixture
3.1.6
total pressure
term used to denote the sum of all the partial pressures of the constituents of a gas mixture in contexts
where the shorter term "pressure" might not clearly distinguish between the individual partial
pressure and their sum
2 © ISO 2019 – All rights reserved
3.2 Terms to define gases and vapours and their parameters
3.2.1
gas
matter in a state such that the molecules are virtually unrestricted by intermolecular forces so that the
matter is free to occupy any available space
Note 1 to entry: In vacuum technology the word "gas" has been loosely applied to both the non-condensable gas
and the vapour.
3.2.2
non-condensable gas
gas whose temperature is above the critical temperature of the substance considered, i.e. one which
cannot be changed into the condensed phase by increase of pressure alone
3.2.3
vapour
gas whose temperature is below the critical temperature of the substance considered, i.e. one which
can be changed into the condensed phase by increase of pressure alone
3.2.4
saturation vapour pressure
p
L
pressure exerted by a vapour which is in thermodynamic equilibrium with one of its condensed phases
at the prevailing temperature
3.2.5
degree of saturation
ratio of the pressure exerted by a vapour to its saturation vapour pressure
3.2.6
saturated vapour
vapour which exerts a pressure equal to the saturation vapour pressure at a given temperature
Note 1 to entry: The vapour is always saturated when it is in thermodynamic equilibrium with one of the
condensed phases of the substance considered.
3.2.7
unsaturated vapour
vapour which exerts a pressure less than the saturation vapour pressure of the substance considered
for a given temperature
3.2.8
number density of molecules
n
number of molecules contained at time t in an
adequately chosen volume surrounding that point, divided by that volume
Note 1 to entry: The word "time" is used for brevity. More exactly, an average is to be taken over a short time
interval, centred about the time, of sufficient duration so that an adequate statistical average may be obtained.
3.2.9
unitary mass density
ρ
u
mass density of a gas divided by its pressure
3.2.10
bulk velocity
v
average velocity of molecules contained at time t in an adequately chosen volume surrounding that point
Note 1 to entry: The volume has to be chosen large enough that it contains a sufficient number of molecules so
that a robust statistical result can be obtained and small enough that the obtained value does not significantly
change in this volume.
3.2.11
temperature
T
quantity proportional to the average kinetic energy of molecules contained at time t in a small volume
calculated in the reference frame related to the bulk velocity in the same volume
Note 1 to entry: See note to entry in 3.2.10
3.2.12
quantity of gas in pressure-volume units
pV
perfect gas statistically at rest, the product of the volume occupied, and its pressure
Note 1 to entry: One shall specify the temperature of the gas.
Note 2 to entry: This quantity so defined is equal to the quotient of the mass of the gas by its unitary mass density.
Note 3 to entry: It is two-thirds of the intrinsic (or potential) energy of the gas contained in the occupied volume.
3.3 Terms needed to characterize the movement of gas molecules and the flow of gases
3.3.1
mean free path of molecules
l, λ
average distance which a molecule travels between two successive collisions with other molecules
of the gas
Note 1 to entry: The average should be taken over a sufficiently large number of molecules and over a sufficiently
long time interval to provide a statistically significant value.
Note 2 to entry: In this concept of mean free path, it is assumed that the interaction of molecules cuts off at
a certain distance of the molecules (hard sphere model or cut-off potentials). The mean free path can also be
defined for other types of interaction (e.g. Lennard_Jones potential). In this case, the quantity is equal to the
mean free path of a gas modelled by hard spheres having the same viscosity, te
...
INTERNATIONAL ISO
STANDARD 3529-1
Second edition
2019-07
Vacuum technology — Vocabulary —
Part 1:
General terms
Technique du vide — Vocabulaire —
Partie 1: Termes généraux
Reference number
©
ISO 2019
© ISO 2019
All rights reserved. Unless otherwise specified, or required in the context of its implementation, no part of this publication may
be reproduced or utilized otherwise in any form or by any means, electronic or mechanical, including photocopying, or posting
on the internet or an intranet, without prior written permission. Permission can be requested from either ISO at the address
below or ISO’s member body in the country of the requester.
ISO copyright office
CP 401 • Ch. de Blandonnet 8
CH-1214 Vernier, Geneva
Phone: +41 22 749 01 11
Fax: +41 22 749 09 47
Email: copyright@iso.org
Website: www.iso.org
Published in Switzerland
ii © ISO 2019 – All rights reserved
Contents Page
Introduction .iv
Foreword .v
1 Scope . 1
2 Normative references . 1
3 Terms and definitions . 1
3.1 General terms . 1
3.2 Terms to define gases and vapours and their parameters . 3
3.3 Terms needed to characterize the movement of gas molecules and the flow of gases . 4
3.4 Terms to define surface und bulk effects in vacuum technology . 7
4 Symbols and abbreviated terms .10
Introduction
If difficulties arise in the use of the definitions in connection with measurement of some quantities, it
is recommended that reference be made to the International Standards related to the measurement of
those quantities for the practical interpretation of the terms.
iv © ISO 2019 – All rights reserved
Foreword
ISO (the International Organization for Standardization) is a worldwide federation of national standards
bodies (ISO member bodies). The work of preparing International Standards is normally carried out
through ISO technical committees. Each member body interested in a subject for which a technical
committee has been established has the right to be represented on that committee. International
organizations, governmental and non-governmental, in liaison with ISO, also take part in the work.
ISO collaborates closely with the International Electrotechnical Commission (IEC) on all matters of
electrotechnical standardization.
The procedures used to develop this document and those intended for its further maintenance are
described in the ISO/IEC Directives, Part 1. In particular, the different approval criteria needed for the
different types of ISO documents should be noted. This document was drafted in accordance with the
editorial rules of the ISO/IEC Directives, Part 2 (see www .iso .org/directives).
Attention is drawn to the possibility that some of the elements of this document may be the subject of
patent rights. ISO shall not be held responsible for identifying any or all such patent rights. Details of
any patent rights identified during the development of the document will be in the Introduction and/or
on the ISO list of patent declarations received (see www .iso .org/patents).
Any trade name used in this document is information given for the convenience of users and does not
constitute an endorsement.
For an explanation of the voluntary nature of standards, the meaning of ISO specific terms and
expressions related to conformity assessment, as well as information about ISO's adherence to the
World Trade Organization (WTO) principles in the Technical Barriers to Trade (TBT) see www .iso
.org/iso/foreword .html.
This document was prepared by Technical Committee ISO/TC 112, Vacuum technology.
This second edition cancels and replaces the first edition (ISO 3529-1:1981), which has been technically
revised. The main changes compared to the previous edition are as follows:
— standard conditions which are defined elsewhere were removed;
— ranges of vacuum were newly defined and reasons given;
— new term ultra clean vacuum was defined;
— knudsen number and rarefaction parameter were included;
— slip flow was defined;
— specific desorption, outgassing, and evaporation rate were newly defined;
— accommodation factor distinguished in energy and momentum accommodation factor.
Any feedback or questions on this document should be directed to the user’s national standards body. A
complete listing of these bodies can be found at www .iso .org/members .html.
INTERNATIONAL STANDARD ISO 3529-1:2019(E)
Vacuum technology — Vocabulary —
Part 1:
General terms
1 Scope
This document defines general terms used in vacuum technology. It gives theoretical definitions as
precise as possible, bearing in mind the need for use of the concept in practice.
2 Normative references
There are no normative references in this document.
3 Terms and definitions
For the purposes of this document, the following terms and definitions apply.
ISO and IEC maintain terminological databases for use in standardization at the following addresses:
— ISO Online browsing platform: available at https: //www .iso .org/obp
— IEC Electropedia: available at http: //www .electropedia .org/
3.1 General terms
3.1.1
vacuum
commonly used term to describe the state of a rarefied gas or the environment corresponding to such a
state, associated with a pressure or a molecular density below the prevailing atmospheric level
3.1.2
ranges of vacuum
various ranges of vacuum according to certain pressure intervals
Note 1 to entry: While there has been some variation in the selection of the limits of these intervals, the following
list gives typical ranges for which the limits are to be considered as approximations.
Note 2 to entry: The prevailing atmospheric pressure on ground depends on weather conditions and altitude and
ranges from 31 kPa (altitude of the Mount Everest, weather condition "low") up to 110 kPa (altitude Dead Sea,
weather condition "high").
Pressure range Definition The reasoning for the definition of the
ranges is as follows (typical circum-
stances):
Prevailing atmospheric pressure low (rough) vacuum Pressure can be achieved by simple materials
(31 kPa to 110 kPa) to 100 Pa (e.g. regular steel) and positive displacement
vacuum pumps; viscous flow regime for gases
<100 Pa to 0,1 Pa medium (fine) vacuum Pressure can be achieved by elaborate
materials (e.g. stainless steel) and positive
displacement vacuum pumps; transitional
flow regime for gases
Pressure range Definition The reasoning for the definition of the
ranges is as follows (typical circum-
stances):
-6
<0,1 Pa to 1 × 10 Pa high vacuum (HV) Pressure can be achieved by elaborate mate-
rials (e.g. stainless steel), elastomer sealings
and high vacuum pumps; molecular flow
regime for gases
-6 -9
<1x10 Pa to 1 × 10 Pa ultra-high vacuum (UHV) Pressure can be achieved by elaborate mate-
rials (e.g. low-carbon stainless steel), metal
sealings, special surface preparations and
cleaning, bake-out and high vacuum pumps;
molecular flow regime for gases
-9
below 1 × 10 Pa extreme-high vacuum (XHV) Pressure can be achieved by sophisticated
materials (e.g. vacuum fired low-carbon
stainless steel, aluminium, copper-beryllium,
titanium), metal sealings, special surface
preparations and cleaning, bake-out and ad-
ditional getter pumps; molecular flow regime
for gases
3.1.3
ultra clean vacuum
medium or high vacuum that requires special conditions for some gas species equivalent to UHV
conditions
Note 1 to entry: The requirements for the particular gas species (impurity) depend on the application.
Note 2 to entry: Hydrocarbons, CO, CO and H O are typical impurity gases.
2 2
Note 3 to entry: The particular requirements may also include specifications for low particle density.
3.1.4.1
pressure of a vacuum
p
normal component of the force exerted by a gas on an area of a real surface
divided by that area
Note 1 to entry: The orientation of the surface relative to the mass flow vector being specified if there is a net
mass flow of gas);
3.1.4.2
pressure of a vacuum
p
state of a gas according to the ideal gas law with corrections for
real gases if necessary
Note 1 to entry: When the ideal gas law is applied, the pressure p in a small infinitesimal volume is given by the
product of number density n of gas molecules in this volume, Boltzmann constant k and temperature T.
Note 2 to entry: For most practical applications in vacuum, the ideal gas law without corrections for real gases
(volume and interaction of gas molecules) is sufficient.
3.1.5
partial pressure
pressure due to a specified component of a gaseous mixture
3.1.6
total pressure
term used to denote the sum of all the partial pressures of the constituents of a gas mixture in contexts
where the shorter term "pressure" might not clearly distinguish between the individual partial
pressure and their sum
2 © ISO 2019 – All rights reserved
3.2 Terms to define gases and vapours and their parameters
3.2.1
gas
matter in a state such that the molecules are virtually unrestricted by intermolecular forces so that the
matter is free to occupy any available space
Note 1 to entry: In vacuum technology the word "gas" has been loosely applied to both the non-condensable gas
and the vapour.
3.2.2
non-condensable gas
gas whose temperature is above the critical temperature of the substance considered, i.e. one which
cannot be changed into the condensed phase by increase of pressure alone
3.2.3
vapour
gas whose temperature is below the critical temperature of the substance considered, i.e. one which
can be changed into the condensed phase by increase of pressure alone
3.2.4
saturation vapour pressure
p
L
pressure exerted by a vapour which is in thermodynamic equilibrium with one of its condensed phases
at the prevailing temperature
3.2.5
degree of saturation
ratio of the pressure exerted by a vapour to its saturation vapour pressure
3.2.6
saturated vapour
vapour which exerts a pressure equal to the saturation vapour pressure at a given temperature
Note 1 to entry: The vapour is always saturated when it is in thermodynamic equilibrium with one of the
condensed phases of the substance considered.
3.2.7
unsaturated vapour
vapour which exerts a pressure less than the saturation vapour pressure of the substance considered
for a given temperature
3.2.8
number density of molecules
n
number of molecules contained at time t in an
adequately chosen volume surrounding that point, divided by that volume
Note 1 to entry: The word "time" is used for brevity. More exactly, an average is to be taken over a short time
interval, centred about the time, of sufficient duration so that an adequate statistical average may be obtained.
3.2.9
unitary mass density
ρ
u
mass density of a gas divided by its pressure
3.2.10
bulk velocity
v
average velocity of molecules contained at time t in an adequately chosen volume surrounding that point
Note 1 to entry: The volume has to be chosen large enough that it contains a sufficient number of molecules so
that a robust statistical result can be obtained and small enough that the obtained value does not significantly
change in this volume.
3.2.11
temperature
T
quantity proportional to the average kinetic energy of molecules contained at time t in a small volume
calculated in the reference frame related to the bulk velocity in the same volume
Note 1 to entry: See note to entry in 3.2.10
3.2.12
quantity of gas in pressure-volume units
pV
perfect gas statistically at rest, the product of the volume occupied, and its pressure
Note 1 to entry: One shall specify the temperature of the gas.
Note 2 to entry: This quantity so defined is equal to the quotient of the mass of the gas by its unitary mass density.
Note 3 to entry: It is two-thirds of the intrinsic (or potential) energy of the gas contained in the occupied volume.
3.3 Terms needed to characterize the movement of gas molecules and the flow of gases
3.3.1
mean free path of molecules
l, λ
average distance which a molecule travels between two successive collisions with other molecules
of the gas
Note 1 to entry: The average should be taken over a sufficiently large number of molecules and over a sufficiently
long time interval to provide a statistically significant value.
Note 2 to entry: In this concept of mean free path, it is assumed that the interaction of molecules cuts off at
a certain distance of the molecules (hard sphere model or cut-off potentials). The mean free path can also be
defined for other types of interaction (e.g. Lennard_Jones potential). In this case, the quantity is equal to the
mean free path of a gas modelled by hard spheres having the same viscosity, te
...
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