ISO 540:2025
(Main)Hard coal — Determination of ash fusibility
Hard coal — Determination of ash fusibility
This document specifies a method of determining the characteristic fusion temperatures of ash from hard coal. NOTE Descriptors: fossil fuels, ash, ashes, tests, high temperature tests, determination, and fusibility.
Houille — Détermination de la fusibilité des cendres
General Information
Relations
Buy Standard
Standards Content (Sample)
International
Standard
ISO 540
Fifth edition
Hard coal — Determination of ash
2025-08
fusibility
Houille — Détermination de la fusibilité des cendres
Reference number
© ISO 2025
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
Email: copyright@iso.org
Website: www.iso.org
Published in Switzerland
ii
Contents Page
Foreword .iv
Introduction .v
1 Scope . 1
2 Normative references . 1
3 Terms and definitions . 1
4 Principle . 2
5 Reagents . 2
6 Apparatus . 2
7 Test conditions . 4
7.1 Test atmosphere .4
7.2 Shape of test piece .4
8 Calibration check . 6
9 Preparation of the test piece . 6
10 Procedure . 7
11 Precision of the method . 7
11.1 Repeatability limit .7
11.2 Reproducibility limit .8
12 Test report . 8
13 Precision statement . 8
Bibliography . 9
iii
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 document 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).
ISO draws attention to the possibility that the implementation of this document may involve the use of (a)
patent(s). ISO takes no position concerning the evidence, validity or applicability of any claimed patent
rights in respect thereof. As of the date of publication of this document, ISO had not received notice of (a)
patent(s) which may be required to implement this document. However, implementers are cautioned that
this may not represent the latest information, which may be obtained from the patent database available at
www.iso.org/patents. ISO shall not be held responsible for identifying any or all such patent rights.
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 27, Coal and coke, Subcommittee SC 5, Methods
of analysis.
This fifth edition cancels and replaces the fourth edition (ISO 540:2008), which has been technically revised.
The main changes are as follows:
— change of the document title;
— removal of coke from scope;
— increase of the allowance of the pyramid to between 12 mm and 19 mm.
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.
iv
Introduction
The method for determination of the fusibility temperatures of coal ash described in this document provides
information about the fusion and melting behaviour of the composite inorganic constituents of the ash at
high temperatures. The standard method is based on the “Seger Cone” method, which is well known in the
ceramic industry, the use of which predates the year 1900. The conditions of the test, as well as basic studies
on the influence of ash chemistry and of gas composition on ash fusibility temperatures (which have led to
[1]
the standardization of the method), arose from the pioneering work of Fieldner, Hall and Field .
In the laboratory, the ash used for the test is a homogeneous mixture prepared from a representative sample
of the coal, and the determination is performed at a controlled rate of heating in either a reducing or an
oxidizing atmosphere. In contrast, under industrial conditions, the complex processes of combustion and
fusion involve heterogeneous mixtures of particles, heating rates (that can be several orders of magnitude
greater than those used in the standard test) and variable gas composition.
During the first quarter of the 20th century, laboratory, pilot-scale and field studies were undertaken to
establish that the ash fusibility test can provide a reasonable indication of the propensity of ash to form
[2]
fused deposits (referred to as “clinker”) in stoker and other fuel-bed type furnaces. Subsequently, the test
has been used as a general indicator of the tendency for ash to fuse on heating and of ash slagging propensity
in pulverized coal-fired furnaces.
v
International Standard ISO 540:2025(en)
Hard coal — Determination of ash fusibility
1 Scope
This document specifies a method of determining the characteristic fusion temperatures of ash from hard coal.
NOTE Descriptors: fossil fuels, ash, ashes, tests, high temperature tests, determination, and fusibility.
2 Normative references
The following documents are referred to in the text in such a way that some or all of their content constitutes
requirements of this document. For dated references, only the edition cited applies. For undated references,
the latest edition of the referenced document (including any amendments) applies.
ISO 1171, Coal and coke — Determination of ash
3 Terms and definitions
For the purposes of this document, the following terms and definitions apply.
ISO and IEC maintain terminology databases for use in standardization at the following addresses:
— ISO Online browsing platform: available at https:// www .iso .org/ obp
— IEC Electropedia: available at https:// www .electropedia .org/
3.1
deformation temperature
DT
temperature at which the first signs of rounding, due to melting, of the tip or edges of the test piece occur
Note 1 to entry: Shrinkage or distortion of the test piece, or rounding of cracks and fins, are not criteria for deformation
temperature and should be ignored if the tip and edges remain sharp. However, for some hard coals, the temperature
at which the test piece shrinkage begins can be of interest and should be reported as a feature noted during the
determination.
3.2
sphere temperature
ST
temperature, in the case of pyramidal and truncated-cone test pieces, at which the height is equal to the
width of the base, and temperature, in the case of cubical or cylindrical test pieces, at which the edges of the
test pieces become completely round with the height remaining unchanged
3.3
hemisphere temperature
HT
temperature at which the test piece forms approximately a hemisphere, i.e. when the height becomes equal
to half the base diameter
3.4
flow temperature
FT
temperature at which the ash melt is spread out over the supporting tile in a layer, the height of which is
one-third of the height of the test piece at the hemisphere temperature
4 Principle
A test piece made from the ash is heated under standard conditions and continually observed at intervals
of temperature change. The temperatures at which characteristic changes of shape occur are recorded. The
characteristic temperatures are defined in Clause 3 (See also Figures 2, 3 and 4).
Although the determination is usually performed in a reducing atmosphere, additional information can
sometimes be obtained by performing a further determination in an oxidizing atmosphere. In general, the
reducing atmosphere in 7.1 gives the lowest characteristic temperatures.
5 Reagents
5.1 Dextrin, 100 g/l solution.
Dissolve 10 g of dextrin in 100 ml of water.
5.2 Petroleum jelly.
5.3 Gold wire, of diameter 0,5 mm or larger, or gold plate, of thickness 0,5 mm to 1,0 mm, with a purity of
99,99 % and a melting point of 1 064 °C.
5.4 Nickel wire, of diameter 0,5 mm or larger, or nickel plate, of thickness 0,5 mm to 1,0 mm, with a
purity of 99,9 % and a melting point of 1 455 °C.
5.5 Palladium wire, of diameter 0,5 mm or larger, or palladium plate, of thickness 0,5 mm to 1,0 mm
with a purity of 99,9 % and a melting point of 1 554 °C.
5.6 Carbon dioxide.
5.7 Hydrogen or carbon monoxide.
6 Apparatus
6.1 Furnace, electrically heated, which satisfies the following conditions.
a) It shall be capable of reaching the maximum temperature at which the properties of the ash are
determined (a temperature of 1 500 °C or more can be required).
NOTE Some furnaces can have a practical upper operating temperature, e.g. 1 480 °C or 1 540 °C, due to the
type of heating elements used in their manufacture.
b) It shall provide an adequate zone of uniform temperature in which to heat the test piece(s).
c) It shall provide means of heating the test piece(s) at a uniform rate from 815 °C upwards.
d) It shall be capable of maintaining the required test atmosphere (see 7.1) around the test piece(s).
e) It shall provide a means of observing the change of shape of the test piece(s) during heating.
It is recommended to provide a facility for inserting, between the end window of the furnace and the optical
viewing instrument, a piece of cobalt-blue or similar glass to protect the retina of the operator from radiation
emitted at elevated temperatures.
6.2 Pyrometer, comprised of a platinum/platinum-rhodium thermocouple.
The thermocou
...
FINAL DRAFT
International
Standard
ISO/FDIS 540
ISO/TC 27/SC 5
Hard coal — Determination of ash
Secretariat: SA
fusibility
Voting begins on:
2025-05-13
Voting terminates on:
2025-07-08
RECIPIENTS OF THIS DRAFT ARE INVITED TO SUBMIT,
WITH THEIR COMMENTS, NOTIFICATION OF ANY
RELEVANT PATENT RIGHTS OF WHICH THEY ARE AWARE
AND TO PROVIDE SUPPOR TING DOCUMENTATION.
IN ADDITION TO THEIR EVALUATION AS
BEING ACCEPTABLE FOR INDUSTRIAL, TECHNO
LOGICAL, COMMERCIAL AND USER PURPOSES, DRAFT
INTERNATIONAL STANDARDS MAY ON OCCASION HAVE
TO BE CONSIDERED IN THE LIGHT OF THEIR POTENTIAL
TO BECOME STAN DARDS TO WHICH REFERENCE MAY BE
MADE IN NATIONAL REGULATIONS.
Reference number
ISO/FDIS 540:2025(en) © ISO 2025
FINAL DRAFT
ISO/FDIS 540:2025(en)
International
Standard
ISO/FDIS 540
ISO/TC 27/SC 5
Hard coal — Determination of ash
Secretariat: SA
fusibility
Voting begins on:
Voting terminates on:
RECIPIENTS OF THIS DRAFT ARE INVITED TO SUBMIT,
WITH THEIR COMMENTS, NOTIFICATION OF ANY
RELEVANT PATENT RIGHTS OF WHICH THEY ARE AWARE
AND TO PROVIDE SUPPOR TING DOCUMENTATION.
© ISO 2025
IN ADDITION TO THEIR EVALUATION AS
All rights reserved. Unless otherwise specified, or required in the context of its implementation, no part of this publication may
BEING ACCEPTABLE FOR INDUSTRIAL, TECHNO
LOGICAL, COMMERCIAL AND USER PURPOSES, DRAFT
be reproduced or utilized otherwise in any form or by any means, electronic or mechanical, including photocopying, or posting on
INTERNATIONAL STANDARDS MAY ON OCCASION HAVE
the internet or an intranet, without prior written permission. Permission can be requested from either ISO at the address below
TO BE CONSIDERED IN THE LIGHT OF THEIR POTENTIAL
or ISO’s member body in the country of the requester.
TO BECOME STAN DARDS TO WHICH REFERENCE MAY BE
MADE IN NATIONAL REGULATIONS.
ISO copyright office
CP 401 • Ch. de Blandonnet 8
CH-1214 Vernier, Geneva
Phone: +41 22 749 01 11
Email: copyright@iso.org
Website: www.iso.org
Published in Switzerland Reference number
ISO/FDIS 540:2025(en) © ISO 2025
ii
ISO/FDIS 540:2025(en)
Contents Page
Foreword .iv
Introduction .v
1 Scope . 1
2 Normative references . 1
3 Terms and definitions . 1
4 Principle . 2
5 Reagents . 2
6 Apparatus . 2
7 Test conditions . 4
7.1 Test atmosphere .4
7.2 Shape of test piece .4
8 Calibration check . 7
9 Preparation of the test piece . 7
10 Procedure . 7
11 Precision of the method . 8
11.1 Repeatability limit .8
11.2 Reproducibility limit .8
12 Test report . 8
13 Precision statement . 9
Bibliography .10
iii
ISO/FDIS 540:2025(en)
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 document 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).
ISO draws attention to the possibility that the implementation of this document may involve the use of (a)
patent(s). ISO takes no position concerning the evidence, validity or applicability of any claimed patent
rights in respect thereof. As of the date of publication of this document, ISO had not received notice of (a)
patent(s) which may be required to implement this document. However, implementers are cautioned that
this may not represent the latest information, which may be obtained from the patent database available at
www.iso.org/patents. ISO shall not be held responsible for identifying any or all such patent rights.
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 27, Coal and coke, Subcommittee SC 5, Methods
of analysis.
This fifth edition cancels and replaces the fourth edition (ISO 540:2008), which has been technically revised.
The main changes are as follows:
— change of the document title;
— removal of coke from scope;
— increase of the allowance of the pyramid to between 12 mm and 19 mm.
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.
iv
ISO/FDIS 540:2025(en)
Introduction
The method for determination of the fusibility temperatures of coal ash described in this document provides
information about the fusion and melting behaviour of the composite inorganic constituents of the ash at
high temperatures. The standard method is based on the “Seger Cone” method, which is well known in the
ceramic industry, the use of which predates the year 1900. The conditions of the test, as well as basic studies
on the influence of ash chemistry and of gas composition on ash fusibility temperatures (which have led to
[1]
the standardization of the method), arose from the pioneering work of Fieldner, Hall and Field .
In the laboratory, the ash used for the test is a homogeneous mixture prepared from a representative sample
of the coal, and the determination is performed at a controlled rate of heating in either a reducing or an
oxidizing atmosphere. In contrast, under industrial conditions, the complex processes of combustion and
fusion involve heterogeneous mixtures of particles, heating rates (that can be several orders of magnitude
greater than those used in the standard test) and variable gas composition.
During the first quarter of the 20th century, laboratory, pilot-scale and field studies were undertaken to
establish that the ash fusibility test can provide a reasonable indication of the propensity of ash to form
[2]
fused deposits (referred to as “clinker”) in stoker and other fuel-bed type furnaces. Subsequently, the test
has been used as a general indicator of the tendency for ash to fuse on heating and of ash slagging propensity
in pulverized coal-fired furnaces.
v
FINAL DRAFT International Standard ISO/FDIS 540:2025(en)
Hard coal — Determination of ash fusibility
1 Scope
This document specifies a method of determining the characteristic fusion temperatures of ash from hard coal.
NOTE Descriptors: fossil fuels, ash, ashes, tests, high temperature tests, determination, and fusibility.
2 Normative references
The following documents are referred to in the text in such a way that some or all of their content constitutes
requirements of this document. For dated references, only the edition cited applies. For undated references,
the latest edition of the referenced document (including any amendments) applies.
ISO 1171, Coal and coke — Determination of ash
3 Terms and definitions
For the purposes of this document, the following terms and definitions apply.
ISO and IEC maintain terminology databases for use in standardization at the following addresses:
— ISO Online browsing platform: available at https:// www .iso .org/ obp
— IEC Electropedia: available at https:// www .electropedia .org/
3.1
deformation temperature
DT
temperature at which the first signs of rounding, due to melting, of the tip or edges of the test piece occur
Note 1 to entry: Shrinkage or distortion of the test piece, or rounding of cracks and fins, are not criteria for deformation
temperature and should be ignored if the tip and edges remain sharp. However, for some hard coals, the temperature
at which the test piece shrinkage begins can be of interest and should be reported as a feature noted during the
determination.
3.2
sphere temperature
ST
temperature, in the case of pyramidal and truncated-cone test pieces, at which the height is equal to the
width of the base, and temperature, in the case of cubical or cylindrical test pieces, at which the edges of the
test pieces become completely round with the height remaining unchanged
3.3
hemisphere temperature
HT
temperature at which the test piece forms approximately a hemisphere, i.e. when the height becomes equal
to half the base diameter
3.4
flow temperature
FT
temperature at which the ash melt is spread out over the supporting tile in a layer, the height of which is
one-third of the height of the test piece at the hemisphere temperature
ISO/FDIS 540:2025(en)
4 Principle
A test piece made from the ash is heated under standard conditions and continually observed at intervals
of temperature change. The temperatures at which characteristic changes of shape occur are recorded. The
characteristic temperatures are defined in Clause 3. (See also Figures 2, 3 and 4.)
Although the determination is usually performed in a reducing atmosphere, additional information can
sometimes be obtained by performing a further determination in an oxidizing atmosphere. In general, the
reducing atmosphere in 7.1 gives the lowest characteristic temperatures.
5 Reagents
5.1 Dextrin, 100 g/l solution.
Dissolve 10 g of dextrin in 100 ml of water.
5.2 Petroleum jelly.
5.3 Gold wire, of diameter 0,5 mm or larger, or gold plate, of thickness 0,5 mm to 1,0 mm, with a purity of
99,99 % and a melting point of 1 064 °C.
5.4 Nickel wire, of diameter 0,5 mm or larger, or nickel plate, of thickness 0,5 mm to 1,0 mm, with a
purity of 99,9 % and a melting point of 1 455 °C.
5.5 Palladium wire, of diameter 0,5 mm or larger, or palladium plate, of thickness 0,5 mm to
...
ISO/FDIS 540:2025(en)
ISO/TC 27/SC 5
Secretariat: SA
Fifth edition
Date: 2025-17-0204-29
Hard coal — Determination of ash fusibility
Houille et coke — Détermination de la fusibilité des cendres
FDIS stage
ISO/FDIS 540:2025(en)
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'sISO’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
Email:
E-mail: copyright@iso.org
Website: www.iso.org
Published in Switzerland.
ii
ISO/FDIS 540:2025(en)
Contents Page
Foreword . iv
Introduction . v
1 Scope . 1
2 Normative references . 1
3 Terms and definitions . 1
4 Principle . 2
5 Reagents . 2
6 Apparatus . 2
7 Test conditions . 6
8 Calibration check . 9
9 Preparation of the test piece. 10
10 Procedure . 10
11 Precision of the method . 11
12 Test report . 11
13 Precision statement . 12
Bibliography . 13
iii
ISO/FDIS 540:2025(en)
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 document 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).
ISO draws attention to the possibility that the implementation of this document may involve the use of (a)
patent(s). ISO takes no position concerning the evidence, validity or applicability of any claimed patent rights
in respect thereof. As of the date of publication of this document, ISO had not received notice of (a) patent(s)
which may be required to implement this document. However, implementers are cautioned that this may not
represent the latest information, which may be obtained from the patent database available at
www.iso.org/patents. ISO shall not be held responsible for identifying any or all such patent rights.
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 27, Coal and coke, Subcommittee SC 5, Methods
of analysis.
This fifth edition cancels and replaces the fourth edition (ISO 540:2008), which has been technically revised.
The main changes are as follows:
— — change of the document title;
— — removal of coke from scope;
— editorial revisions throughout document;
— — increase of the allowance of the pyramid to between 12 mm and 19 mm.
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.
iv
ISO/FDIS 540:2025(en)
Introduction
The method for determination of the fusibility temperatures of coal ash described in this document provides
information about the fusion and melting behaviour of the composite inorganic constituents of the ash at high
temperatures. The standard method is based on the “Seger Cone” method, which is well known in the ceramic
industry, the use of which predates the year 1900. The conditions of the test, as well as basic studies on the
influence of ash chemistry and of gas composition on ash fusibility temperatures (which have led to the
[1[1] ]
standardization of the method), arose from the pioneering work of Fieldner, Hall and Field . .
In the laboratory, the ash used for the test is a homogeneous mixture prepared from a representative sample
of the coal, and the determination is performed at a controlled rate of heating in either a reducing or an
oxidizing atmosphere. In contrast, under industrial conditions, the complex processes of combustion and
fusion involve heterogeneous mixtures of particles, heating rates (that can be several orders of magnitude
greater than those used in the standard test) and variable gas composition.
During the first quarter of the 20th century, laboratory, pilot-scale and field studies were undertaken to
establish that the ash fusibility test can provide a reasonable indication of the propensity of ash to form fused
[2 [2]]
deposits (referred to as “clinker”) in stoker and other fuel-bed type furnaces. Subsequently, the test has
been used as a general indicator of the tendency for ash to fuse on heating and of ash slagging propensity in
pulverized coal-fired furnaces.
v
ISO/FDIS 540:2025(en)
Hard coal — Determination of ash fusibility
1 Scope
This document specifies a method of determining the characteristic fusion temperatures of ash from hard coal.
NOTE Descriptors: fossil fuels, ash, ashes, tests, high temperature tests, determination, and fusibility.
2 Normative references
The following documents are referred to in the text in such a way that some or all of their content constitutes
requirements of this document. For dated references, only the edition cited applies. For undated references,
the latest edition of the referenced document (including any amendments) applies.
ISO 1171, Coal and coke — Determination of ash
3 Terms and definitions
For the purposes of this document, the following terms and definitions apply.
ISO and IEC maintain terminology databases for use in standardization at the following addresses:
— — ISO Online browsing platform: available at https://www.iso.org/obp
— — IEC Electropedia: available at https://www.electropedia.org/
3.1 3.1
deformation temperature
DT
temperature at which the first signs of rounding, due to melting, of the tip or edges of the test piece occur
Note 1 to entry: Shrinkage or distortion of the test piece, or rounding of cracks and fins, are not criteria for
deformation temperature and should be ignored if the tip and edges remain sharp. However, for some hard coals, the
temperature at which the test piece shrinkage begins can be of interest and should be reported as a feature noted during
the determination.
3.2 3.2
sphere temperature
ST
temperature, in the case of pyramidal and truncated-cone test pieces, at which the height is equal to the width
of the base, and temperature, in the case of cubical or cylindrical test pieces, at which the edges of the test
pieces become completely round with the height remaining unchanged
3.3 3.3
hemisphere temperature
HT
temperature at which the test piece forms approximately a hemisphere, i.e. when the height becomes equal to
half the base diameter
3.4 3.4
flow temperature
FT
temperature at which the ash melt is spread out over the supporting tile in a layer, the height of which is
one--third of the height of the test piece at the hemisphere temperature
ISO/FDIS 540:2025(en)
4 Principle
A test piece made from the ash is heated under standard conditions and continually observed at intervals of
temperature change. The temperatures at which characteristic changes of shape occur are recorded. The
characteristic temperatures are defined in Clause 3Clause 3. (See also Figures 2Figures 2, 3, 3 and 44.).)
Although the determination is usually performed in a reducing atmosphere, additional information can
sometimes be obtained by performing a further determination in an oxidizing atmosphere. In general, the
reducing atmosphere in 7.17.1 gives the lowest characteristic temperatures.
5 Reagents
5.1 5.1 Dextrin, 100 g/l solution.
Dissolve 10 g of dextrin in 100 ml of water.
5.2 5.2 Petroleum jelly.
5.3 5.3 Gold wire, of diameter 0,5 mm or larger, or gold plate, of thickness 0,5 mm to 1,0 mm, with
a purity of 99,99 % and a melting point of 1 064 °C.
5.4 5.4 Nickel wire, of diameter 0,5 mm or larger, or nickel plate, of thickness 0,5 mm to 1,0 mm,
with a purity of 99,9 % and a melting point of 1 455 °C.
5.5 5.5 Palladium wire, of diameter 0,5 mm or larger, or palladium plate, of thickness 0,5 mm to
1,0 mm with a purity of 99,9 % and a melting point of 1 554 °C.
5.6 5.6 Carbon dioxide.
5.7 5.7 Hydrogen or carbon monoxide.
6 Apparatus
6.1 6.1 Furnace, electrically heated, which satisfies the following conditions.
a) a) It shall be capable of reaching the maximum temperature at which the properties of the ash are
determined (a temperature of 1 500 °C or more can be required).
NOTE Some furnaces can have a practical upper operating temperature, e.g. 1 480 °C or 1 540 °C, due to the
type of heating elements used in their manufacture.
b) b) It shall provide an adequate zone of uniform temperature in which to heat the test piece(s).
c) c) It shall provide means of heating the test piece(s) at a uniform rate from 815 °C upwards.
d) d) It shall be capable of maintaining the required test atmosphere (see 7.17.1)) around the test piece(s).
e) e) It shall provide a means of observing the change of shape of the test piece(s) during heating.
It is recommended to provide a facility for inserting, between the end window of the furnace and the optical
viewing instrument, a piece of cobalt-blue or similar glass to protect the retina of the operator from radiation
emitted at elevated temperatures.
6.2 6.2 Pyrometer, comprised of a platinum/platinum-rhodium thermocouple.
ISO/FDIS 540:2025(en)
The thermocouple is positioned so that the thermo-junction is on the longitudinal axis in the centre of the zone
of uniform temperature.
6.3 6.3 Mould, of brass, stainless steel, or other suitable material, for preparing the test piece. (See
example in Figure 1Figure 1.).)
ISO/FDIS 540:2025(en)
Dimensions in millimetres
ISO/FDIS 540:2025(en)
Key
1 base plate
2 mould(s)
Figure 1 — Example of a mould suitable for making a pyramidal specimen
6.4 6.4 Support for the test piece, of such a material that the support does not either become
distorted or react with or absorb the ash during the determination. Supports of sintered alumina or fine-
textured mullite are generally satisfactory, but difficulties can arise with individual ashes, in which case a non-
absorbent interface such as platinum foil can be used between the original support and the test piece.
6.5 6.5 Flowmeters, two, for measuring the components of the reducing gases (see 7.17.1);); it is
not necessary to measure the flow rate when using an oxidizing gas.
If the flowmeter contains a liquid, this liquid shall be a non-volatile oil.
6.6 6.6 Agate mortar and pestle.
ISO/FDIS 540:2025(en)
6.7 6.7 Test sieve, of aperture 0,075 mm (or less) and diameter of approximately either 100 mm or
...
Questions, Comments and Discussion
Ask us and Technical Secretary will try to provide an answer. You can facilitate discussion about the standard in here.