Vitreous and porcelain enamels -- Determination of resistance to chemical corrosion

ISO 28706-2:2017 specifies a test method for the determination of the resistance of flat surfaces of vitreous and porcelain enamels to boiling acids, boiling neutral liquids, alkaline liquids and/or their vapours.
This method allows the determination of the resistance of vitreous and porcelain enamels to the liquid and vapour phases of the corrosive medium simultaneously.

Émaux vitrifiés -- Détermination de la résistance à la corrosion chimique

ISO 28706-2:2017 spécifie une méthode d'essai permettant de déterminer la résistance de surfaces planes en émail vitrifié ŕ des acides bouillants, des liquides neutres bouillants, des liquides alcalins et/ou leurs vapeurs.
La présente méthode permet de déterminer simultanément la résistance des émaux vitrifiés aux phases liquide et vapeur du milieu corrosif.

Steklasti in porcelanski emajli - Ugotavljanje odpornosti proti kemični koroziji

General Information

Status
Published
Publication Date
08-Jun-2021
Current Stage
6060 - National Implementation/Publication (Adopted Project)
Start Date
02-Jun-2021
Due Date
07-Aug-2021
Completion Date
09-Jun-2021

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SLOVENSKI STANDARD
SIST ISO 28706-2:2021
01-julij-2021
Nadomešča:
SIST ISO 28706-2:2009
Steklasti in porcelanski emajli - Ugotavljanje odpornosti proti kemični koroziji

Vitreous and porcelain enamels -- Determination of resistance to chemical corrosion

Émaux vitrifiés -- Détermination de la résistance à la corrosion chimique
Ta slovenski standard je istoveten z: ISO 28706-2:2017
ICS:
25.220.50 Emajlne prevleke Enamels
SIST ISO 28706-2:2021 en,fr,de

2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.

---------------------- Page: 1 ----------------------
SIST ISO 28706-2:2021
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SIST ISO 28706-2:2021
INTERNATIONAL ISO
STANDARD 28706-2
Second edition
2017-02
Vitreous and porcelain enamels —
Determination of resistance to
chemical corrosion —
Part 2:
Determination of resistance to
chemical corrosion by boiling acids,
boiling neutral liquids, alkaline
liquids and/or their vapours
Émaux vitrifiés — Détermination de la résistance à la corrosion
chimique —
Partie 2: Détermination de la résistance à la corrosion chimique par
des acides bouillants, des liquides neutres bouillants, ou des liquides
alcalins et/ou leurs vapeurs
Reference number
ISO 28706-2:2017(E)
ISO 2017
---------------------- Page: 3 ----------------------
SIST ISO 28706-2:2021
ISO 28706-2:2017(E)
COPYRIGHT PROTECTED DOCUMENT
© ISO 2017, Published in Switzerland

All rights reserved. Unless otherwise specified, 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
Ch. de Blandonnet 8 • CP 401
CH-1214 Vernier, Geneva, Switzerland
Tel. +41 22 749 01 11
Fax +41 22 749 09 47
copyright@iso.org
www.iso.org
ii © ISO 2017 – All rights reserved
---------------------- Page: 4 ----------------------
SIST ISO 28706-2:2021
ISO 28706-2:2017(E)
Contents Page

Foreword ..........................................................................................................................................................................................................................................v

Introduction ................................................................................................................................................................................................................................vi

1 Scope ................................................................................................................................................................................................................................. 1

2 Normative references ...................................................................................................................................................................................... 1

3 Terms and definitions ..................................................................................................................................................................................... 1

4 Principle ........................................................................................................................................................................................................................ 2

5 Reagents ........................................................................................................................................................................................................................ 2

6 Apparatus and materials.............................................................................................................................................................................. 3

6.1 Test apparatus ......................................................................................................................................................................................... 3

6.2 Test materials ........................................................................................................................................................................................... 8

7 Packing rings ............................................................................................................................................................................................................ 8

7.1 General ........................................................................................................................................................................................................... 8

7.2 Packing A ...................................................................................................................................................................................................... 8

7.3 Packing B ...................................................................................................................................................................................................... 9

8 Test specimens........................................................................................................................................................................................................ 9

9 Procedure..................................................................................................................................................................................................................... 9

10 Expression of results .....................................................................................................................................................................................10

10.1 Total loss in mass per unit area .............................................................................................................................................10

10.2 Corrosion rate .......................................................................................................................................................................................10

11 Boiling citric acid ..............................................................................................................................................................................................11

11.1 General ........................................................................................................................................................................................................11

11.2 Test solution ...........................................................................................................................................................................................11

11.3 Duration of the test ..........................................................................................................................................................................11

11.4 Test report ................................................................................................................................................................................................11

12 Boiling sulfuric acid .......................................................................................................................................................................................11

12.1 General ........................................................................................................................................................................................................11

12.2 Test solution ...........................................................................................................................................................................................11

12.3 Duration of the test ..........................................................................................................................................................................12

12.4 Test report ................................................................................................................................................................................................12

13 Boiling hydrochloric acid ..........................................................................................................................................................................12

13.1 General ........................................................................................................................................................................................................12

13.2 Test solution ...........................................................................................................................................................................................12

13.3 Duration of the test ..........................................................................................................................................................................12

13.4 Test report ................................................................................................................................................................................................13

14 Boiling distilled or demineralized water .................................................................................................................................13

14.1 General ........................................................................................................................................................................................................13

14.2 Test solution ...........................................................................................................................................................................................13

14.3 Duration of the test ..........................................................................................................................................................................13

14.4 Test report ................................................................................................................................................................................................14

15 Standard detergent solution .................................................................................................................................................................14

15.1 General ........................................................................................................................................................................................................14

15.2 Test solution ...........................................................................................................................................................................................14

15.3 Test temperature ................................................................................................................................................................................15

15.4 Duration of the test ..........................................................................................................................................................................15

15.5 Test report ................................................................................................................................................................................................15

16 Other test solutions and/or conditions .....................................................................................................................................15

16.1 General ........................................................................................................................................................................................................15

© ISO 2017 – All rights reserved iii
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ISO 28706-2:2017(E)

16.2 Test solution ...........................................................................................................................................................................................15

16.3 Duration of the test ..........................................................................................................................................................................15

16.4 Test report ................................................................................................................................................................................................16

Bibliography .............................................................................................................................................................................................................................17

iv © ISO 2017 – All rights reserved
---------------------- Page: 6 ----------------------
SIST ISO 28706-2:2021
ISO 28706-2:2017(E)
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 on 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 the following

URL: w w w . i s o .org/ iso/ foreword .html.

This document was prepared by Technical Committee ISO/TC 107, Metallic and other inorganic coatings.

This second edition cancels and replaces the first edition (ISO 28706-2:2008), which has been

technically revised with changes as follows.

— This document can also be used to determine resistance to chemical corrosion using alkaline

liquids. The title of this document has therefore been amended and a section on standard detergent

solutions has been included.

— Additional reagents can be used for testing purposes and these have been included.

A list of all parts in the ISO 28706 series can be found on the ISO website.
© ISO 2017 – All rights reserved v
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SIST ISO 28706-2:2021
ISO 28706-2:2017(E)
Introduction

Corrosion of vitreous and porcelain enamels by aqueous solutions is a dissolution process. The

main component of the enamel, SiO2, forms a three-dimensional silica network. After hydrolysis, it

decomposes and forms silicic acid or silicates. These are released into the attacking medium. Other

components, mainly metal oxides, are hydrolysed as well and form the corresponding hydrated metal

ions or hydroxides. All corrosion products are more or less soluble in the attacking medium. The whole

process results in a loss in mass per unit area.

For some aqueous solutions, the attack on the enamel proceeds linearly during the corrosion time;

for other aqueous solutions, the attack on the enamel proceeds in a logarithmic manner during the

corrosion time. Only for the first series of solutions can a scientifically exact rate of loss in mass per unit

area (g/m2·h) be calculated as well as a corrosion rate (millimetres per year).

The most important parameters influencing aqueous corrosion of the enamel are the enamel quality,

the temperature and the pH value. Inhibition effects resulting from the limited solubility of silica can

also contribute. The following list describes different types of enamel attack for different corrosion

conditions.

a) In aqueous alkali solutions such as 0,1 mol/l NaOH (see ISO 28706-4:2016, Clause 9), the silica

network of the enamel is considerably attacked at 80 °C. Silicates and most of the other hydrolysed

components are soluble in the alkali. Attack proceeds linearly during regular test times. Therefore,

test results are expressed in terms of a rate of loss in mass per unit area (mass loss per unit area

and time) and a corrosion rate (millimetres per year).

b) At room temperature, in weak aqueous acids such as citric acid (see ISO 28706-1:2008, Clause 9) or

also in stronger acids such as sulfuric acid (see ISO 28706-1:2008, Clause 10), there is only minor

attack on the silica network of the enamel. Other constituents are leached to some extent from

the surface. Highly resistant enamels will show no visual change after exposure. On less resistant

enamels, some staining or surface roughening will occur.

c) In boiling aqueous acids (as described in this document), the silica network of the enamel is being

attacked, and silica as well as the other enamel components are released into solution. However,

the solubility of silica in acids is low. Soon, the attacking solutions will become saturated with

dissolved silica and will then only leach the surface. The acid attack is inhibited and the rate of

corrosion drops markedly.

NOTE The glass test equipment also releases silica by acid attack and contributes to the inhibition of

the corrosion.

Inhibition is effectively prevented in vapour phase tests. The condensate formed on the test

specimen is free of any dissolved enamel constituents.

Examples of enamel corrosion proceeding in a logarithmic manner [see 1)] and linearly [see 2)] are

as follows:

1) Boiling citric acid (see Clause 11) and boiling 30 % sulfuric acid (see Clause 12).

Since only minute amounts of these acids are found in their vapours, the test is restricted to

the liquid phase. The attack is influenced by inhibition effects and corrosion depends on the

time of exposure. Therefore, test results are expressed in terms of loss in mass per unit area;

no rate of loss in mass per unit area is calculated.
2) Boiling 20 % hydrochloric acid (see Clause 13).

Since this is an azeotropic boiling acid, its concentration in the liquid and the vapour phase

are identical, and liquid phase testing need not be performed. Vigorous boiling supplies an

uninhibited condensate, and the attack proceeds linearly with time of exposure. Therefore,

vi © ISO 2017 – All rights reserved
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SIST ISO 28706-2:2021
ISO 28706-2:2017(E)

test results are only expressed in terms of rate of loss in mass per unit area (mass loss per unit

area and time) and the corrosion rate (millimetres per year).

d) At high temperatures, with tests in the liquid phase under autoclave conditions (see ISO 28706-5),

aqueous acid attack is severe. To avoid inhibition, the test time is restricted to 24 h and the ratio of

attacking acid to attacked enamel surface is chosen so that it is comparatively high (similar to that

in a chemical reaction vessel). In addition, only low-silica water is used for the preparation of test

solutions. Under these conditions, attack will proceed linearly with time of exposure. Therefore,

test results with 20 % hydrochloric acid (see ISO 28706-5:2010, Clause 8), artificial test solutions

(see ISO 28706-5:2010, Clause 10) or process fluids (see ISO 28706-5:2010, Clause 11) are also

expressed in terms of a rate of loss in mass per unit area (loss in mass per unit area and time).

e) In boiling water (see Clause 14), the silica network is fairly stable. The enamel surface is leached

and silica is dissolved only to a small extent. This type of attack is clearly represented by the vapour

phase attack. In the liquid phase, some inhibition can be observed with highly resistant enamels.

However, if the enamel being tested is weak, leached alkali from the enamel can raise pH values to

alkaline levels, thus increasing the attack by the liquid phase. Both liquid and vapour phase testing

can give valuable information.

f) Since the attack may or may not be linear, the results are expressed only in terms of loss in mass

per unit area and the test time should be indicated.

g) For standard detergent solution (see ISO 28706-3:2008, Clause 9), it will not be certain whether the

linear part of the corrosion curve will be reached during testing for 24 h or 168 h. Calculation of the

corrosion rate is therefore not included in the test report.

h) For other acids (see Clause 15) and other alkaline solutions (see ISO 28706-3:2008, Clause 10 and

ISO 28706-4:2016, Clause 10), it will also not be known if a linear corrosion rate will be reached

during the test period. Calculation of the corrosion rate is therefore not included in the test reports

of those parts of this document.

For vitreous enamels fired at temperatures below 700 °C, the test parameters (media, temperatures and

times) of this document are not appropriate. For such enamels, for example aluminium enamels, other

media, temperatures and/or times should be used. This can be done following the procedures described

in the clauses for “Other test solutions” in ISO 28706-1, ISO 28706-2, ISO 28706-3 and ISO 28706-4.

© ISO 2017 – All rights reserved vii
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SIST ISO 28706-2:2021
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SIST ISO 28706-2:2021
INTERNATIONAL STANDARD ISO 28706-2:2017(E)
Vitreous and porcelain enamels — Determination of
resistance to chemical corrosion —
Part 2:
Determination of resistance to chemical corrosion by
boiling acids, boiling neutral liquids, alkaline liquids and/
or their vapours

WARNING — This document calls for the use of substances and/or procedures that may be

injurious to health if adequate safety measures are not taken. This document does not address any

health hazards, safety or environmental matters associated with its use. Is it the responsibility

of the user of this document to establish appropriate health, safety and environmentally

acceptable practices and take suitable actions for any national and international regulations.

1 Scope

This document specifies a test method for the determination of the resistance of flat surfaces of vitreous

and porcelain enamels to boiling acids, boiling neutral liquids, alkaline liquids and/or their vapours.

This method allows the determination of the resistance of vitreous and porcelain enamels to the liquid

and vapour phases of the corrosive medium simultaneously.
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 48, Rubber, vulcanized or thermoplastic — Determination of hardness (hardness between 10 IRHD and

100 IRHD)

ISO 649-1, Laboratory glassware — Density hydrometers for general purposes — Part 1: Specification

ISO 718, Laboratory glassware — Thermal shock and thermal shock endurance — Test methods

ISO 3585, Borosilicate glass 3.3 — Properties
ISO 3696, Water for analytical laboratory use — Specification and test methods
ISO 4788, Laboratory glassware — Graduated measuring cylinders
ISO 4799, Laboratory glassware — Condensers

ISO 28764, Vitreous and porcelain enamels — Production of specimens for testing enamels on sheet steel,

sheet aluminium and cast iron
3 Terms and definitions
No terms and definitions are defined in this document.

ISO and IEC maintain terminological databases for use in standardization at the following addresses:

— IEC Electropedia: available at http:// www .electropedia .org/
© ISO 2017 – All rights reserved 1
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SIST ISO 28706-2:2021
ISO 28706-2:2017(E)
— ISO Online browsing platform: available at http:// www .iso .org/ obp
4 Principle

A set of similarly enamelled test specimens is placed in the liquid zone and/or in the vapour zone of

the test apparatus, as required, and exposed to attack by a boiling acid or boiling neutral liquid, or its

vapour, under specified conditions.

The same design of test apparatus and the same test principle is employed for the different liquids.

The loss in mass is determined and used to calculate the rate of loss in mass per unit area and, if

necessary, the corrosion rate.
5 Reagents

During the determination, use only reagents of recognized analytical grade, unless otherwise specified.

5.1 Water, conforming to the requirements of grade 3 of ISO 3696, i.e. distilled water or water of

equivalent purity.

5.2 Acetic acid solution, volume concentration 50 ml/l, for cleaning the test apparatus and test

specimens.

5.3 Degreasing solvent, such as ethanol, or water containing a few drops of liquid detergent, suitable

for cleaning the test apparatus and test specimens.
5.4 Citric acid monohydrate, (C H O ·H 0), crystalline.
6 8 7 2

5.5 Sulfuric acid, analytical grade, 30 % (by mass) solution, density range 1,217 g/ml to 1,220 g/ml

(measured with a hydrometer; see 6.2.7).

5.6 Hydrochloric acid, analytical grade, 20 % (by mass) solution, density range 1,097 g/ml to

1,099 g/ml (measured with a hydrometer; see 6.2.7).
5.7 Sodium tripolyphosphate (Na P O ).
5 3 10
5.8 Sodium carbonate (Na CO ), anhydrous.
2 3
5.9 Sodium perborate, hydrated (NaBO ·H O ·3H O).
2 2 2 2
5.10 Sodium silicate, containing about 81 % (by mass) of Na SiO .
2 3
5.11 Alkylsulfonate [CH (CH ) – C(SO Na)H – (CH ) – CH ].
3 2 x 2 2 3 3
2 © ISO 2017 – All rights reserved
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SIST ISO 28706-2:2021
ISO 28706-2:2017(E)
6 Apparatus and materials
6.1 Test apparatus

6.1.1 The test apparatus (see Figures 1 and 2) consists of a cylinder (6.1.2; see Figure 3), with an

adjacent support, having a standard socket for holding a reflux condenser (6.1.3) with a graduated

collector (6.1.4) on one side.

Two test specimens shall form the top and bottom of the cylinder. One of them may be replaced by

a glass plate (6.1.14) if required. The cylinder with the specimens shall be supported between two

plates (see Figure 2) locked at the corners by threaded bolts (6.1.8), wing nuts (6.1.7) and hexagonal

nuts (6.1.6). A synthetic-fibre washer (6.1.9) is fixed between the plates (6.1.5) and each specimen. The

specimens are sealed against the ends of the cylinder with packing rings (6.1.10), the material of which

is dependent on the type of test solution. Any uncoated area of the test specimen shall be protected

from exposure to the attacking medium.

When testing specimens cut from an enamelled article, the packing rings (6.1.10) are replaced by

protective envelopes (see Figure 5) in which the specimens are placed.
© ISO 2017 – All rights reserved 3
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SIST ISO 28706-2:2021
ISO 28706-2:2017(E)
Figure 1 — View of assembled test equipment
4 © ISO 2017 – All rights reserved
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SIST ISO 28706-2:2021
ISO 28706-2:2017(E)
Dimensions in millimetres
Key
1 socket for reflux condenser 7 packing ring
2 synthetic-fibre washer 8 heater
3 wing nut 9 electric socket
4 specimen 10 triangular plate
5 socket for thermometer 11 hexagonal nut
6 cylinder
Figure 2 — Test apparatus

The apparatus is heated externally by a heater (6.1.11) placed round the lower half of the cylinder

(6.1.2) such that the lower edge is, at the most, 3 mm above the lower packing ring. The test apparatus is

composed of the parts described in 6.1.2 to 6.1.15.

6.1.2 Cylinder (see Figure 3), made of borosilicate glass 3.3 conforming to the requirements of

ISO 3585, with ground ends. When tested in accordance with ISO 718, the cylinder shall pass the test

without breaking at a difference in temperature of at least 120 °C.

NOTE Cylinders having two sockets can also be used if the smaller socket is closed by a stopper which is

resistant to the boiling solution.
© ISO 2017 – All rights reserved 5
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SIST ISO 28706-2:2021
ISO 28706-2:2017(E)
Dimensions in millimetres
Key
1 ground-glass socket for condenser
2 ground-glass socket for thermometer
3 connecting piece
4 connecting piece
Figure 3 — Cylinder

6.1.3 Liebig-West reflux condenser, or equivalent reflux condenser conforming to ISO 4799, in which

there is no volume change during the test, with a nominal jacket length of 400 mm and standard ground

joint of borosilicate glass 3.3 conforming to the requirements of ISO 3585.
6.1.4 Graduated collector (see Figure 4), wi
...

INTERNATIONAL ISO
STANDARD 28706-2
Second edition
2017-02
Vitreous and porcelain enamels —
Determination of resistance to
chemical corrosion —
Part 2:
Determination of resistance to
chemical corrosion by boiling acids,
boiling neutral liquids, alkaline
liquids and/or their vapours
Émaux vitrifiés — Détermination de la résistance à la corrosion
chimique —
Partie 2: Détermination de la résistance à la corrosion chimique par
des acides bouillants, des liquides neutres bouillants, ou des liquides
alcalins et/ou leurs vapeurs
Reference number
ISO 28706-2:2017(E)
ISO 2017
---------------------- Page: 1 ----------------------
ISO 28706-2:2017(E)
COPYRIGHT PROTECTED DOCUMENT
© ISO 2017, Published in Switzerland

All rights reserved. Unless otherwise specified, 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
Ch. de Blandonnet 8 • CP 401
CH-1214 Vernier, Geneva, Switzerland
Tel. +41 22 749 01 11
Fax +41 22 749 09 47
copyright@iso.org
www.iso.org
ii © ISO 2017 – All rights reserved
---------------------- Page: 2 ----------------------
ISO 28706-2:2017(E)
Contents Page

Foreword ..........................................................................................................................................................................................................................................v

Introduction ................................................................................................................................................................................................................................vi

1 Scope ................................................................................................................................................................................................................................. 1

2 Normative references ...................................................................................................................................................................................... 1

3 Terms and definitions ..................................................................................................................................................................................... 1

4 Principle ........................................................................................................................................................................................................................ 2

5 Reagents ........................................................................................................................................................................................................................ 2

6 Apparatus and materials.............................................................................................................................................................................. 3

6.1 Test apparatus ......................................................................................................................................................................................... 3

6.2 Test materials ........................................................................................................................................................................................... 8

7 Packing rings ............................................................................................................................................................................................................ 8

7.1 General ........................................................................................................................................................................................................... 8

7.2 Packing A ...................................................................................................................................................................................................... 8

7.3 Packing B ...................................................................................................................................................................................................... 9

8 Test specimens........................................................................................................................................................................................................ 9

9 Procedure..................................................................................................................................................................................................................... 9

10 Expression of results .....................................................................................................................................................................................10

10.1 Total loss in mass per unit area .............................................................................................................................................10

10.2 Corrosion rate .......................................................................................................................................................................................10

11 Boiling citric acid ..............................................................................................................................................................................................11

11.1 General ........................................................................................................................................................................................................11

11.2 Test solution ...........................................................................................................................................................................................11

11.3 Duration of the test ..........................................................................................................................................................................11

11.4 Test report ................................................................................................................................................................................................11

12 Boiling sulfuric acid .......................................................................................................................................................................................11

12.1 General ........................................................................................................................................................................................................11

12.2 Test solution ...........................................................................................................................................................................................11

12.3 Duration of the test ..........................................................................................................................................................................12

12.4 Test report ................................................................................................................................................................................................12

13 Boiling hydrochloric acid ..........................................................................................................................................................................12

13.1 General ........................................................................................................................................................................................................12

13.2 Test solution ...........................................................................................................................................................................................12

13.3 Duration of the test ..........................................................................................................................................................................12

13.4 Test report ................................................................................................................................................................................................13

14 Boiling distilled or demineralized water .................................................................................................................................13

14.1 General ........................................................................................................................................................................................................13

14.2 Test solution ...........................................................................................................................................................................................13

14.3 Duration of the test ..........................................................................................................................................................................13

14.4 Test report ................................................................................................................................................................................................14

15 Standard detergent solution .................................................................................................................................................................14

15.1 General ........................................................................................................................................................................................................14

15.2 Test solution ...........................................................................................................................................................................................14

15.3 Test temperature ................................................................................................................................................................................15

15.4 Duration of the test ..........................................................................................................................................................................15

15.5 Test report ................................................................................................................................................................................................15

16 Other test solutions and/or conditions .....................................................................................................................................15

16.1 General ........................................................................................................................................................................................................15

© ISO 2017 – All rights reserved iii
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ISO 28706-2:2017(E)

16.2 Test solution ...........................................................................................................................................................................................15

16.3 Duration of the test ..........................................................................................................................................................................15

16.4 Test report ................................................................................................................................................................................................16

Bibliography .............................................................................................................................................................................................................................17

iv © ISO 2017 – All rights reserved
---------------------- Page: 4 ----------------------
ISO 28706-2:2017(E)
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 on 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 the following

URL: w w w . i s o .org/ iso/ foreword .html.

This document was prepared by Technical Committee ISO/TC 107, Metallic and other inorganic coatings.

This second edition cancels and replaces the first edition (ISO 28706-2:2008), which has been

technically revised with changes as follows.

— This document can also be used to determine resistance to chemical corrosion using alkaline

liquids. The title of this document has therefore been amended and a section on standard detergent

solutions has been included.

— Additional reagents can be used for testing purposes and these have been included.

A list of all parts in the ISO 28706 series can be found on the ISO website.
© ISO 2017 – All rights reserved v
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ISO 28706-2:2017(E)
Introduction

Corrosion of vitreous and porcelain enamels by aqueous solutions is a dissolution process. The

main component of the enamel, SiO2, forms a three-dimensional silica network. After hydrolysis, it

decomposes and forms silicic acid or silicates. These are released into the attacking medium. Other

components, mainly metal oxides, are hydrolysed as well and form the corresponding hydrated metal

ions or hydroxides. All corrosion products are more or less soluble in the attacking medium. The whole

process results in a loss in mass per unit area.

For some aqueous solutions, the attack on the enamel proceeds linearly during the corrosion time;

for other aqueous solutions, the attack on the enamel proceeds in a logarithmic manner during the

corrosion time. Only for the first series of solutions can a scientifically exact rate of loss in mass per unit

area (g/m2·h) be calculated as well as a corrosion rate (millimetres per year).

The most important parameters influencing aqueous corrosion of the enamel are the enamel quality,

the temperature and the pH value. Inhibition effects resulting from the limited solubility of silica can

also contribute. The following list describes different types of enamel attack for different corrosion

conditions.

a) In aqueous alkali solutions such as 0,1 mol/l NaOH (see ISO 28706-4:2016, Clause 9), the silica

network of the enamel is considerably attacked at 80 °C. Silicates and most of the other hydrolysed

components are soluble in the alkali. Attack proceeds linearly during regular test times. Therefore,

test results are expressed in terms of a rate of loss in mass per unit area (mass loss per unit area

and time) and a corrosion rate (millimetres per year).

b) At room temperature, in weak aqueous acids such as citric acid (see ISO 28706-1:2008, Clause 9) or

also in stronger acids such as sulfuric acid (see ISO 28706-1:2008, Clause 10), there is only minor

attack on the silica network of the enamel. Other constituents are leached to some extent from

the surface. Highly resistant enamels will show no visual change after exposure. On less resistant

enamels, some staining or surface roughening will occur.

c) In boiling aqueous acids (as described in this document), the silica network of the enamel is being

attacked, and silica as well as the other enamel components are released into solution. However,

the solubility of silica in acids is low. Soon, the attacking solutions will become saturated with

dissolved silica and will then only leach the surface. The acid attack is inhibited and the rate of

corrosion drops markedly.

NOTE The glass test equipment also releases silica by acid attack and contributes to the inhibition of

the corrosion.

Inhibition is effectively prevented in vapour phase tests. The condensate formed on the test

specimen is free of any dissolved enamel constituents.

Examples of enamel corrosion proceeding in a logarithmic manner [see 1)] and linearly [see 2)] are

as follows:

1) Boiling citric acid (see Clause 11) and boiling 30 % sulfuric acid (see Clause 12).

Since only minute amounts of these acids are found in their vapours, the test is restricted to

the liquid phase. The attack is influenced by inhibition effects and corrosion depends on the

time of exposure. Therefore, test results are expressed in terms of loss in mass per unit area;

no rate of loss in mass per unit area is calculated.
2) Boiling 20 % hydrochloric acid (see Clause 13).

Since this is an azeotropic boiling acid, its concentration in the liquid and the vapour phase

are identical, and liquid phase testing need not be performed. Vigorous boiling supplies an

uninhibited condensate, and the attack proceeds linearly with time of exposure. Therefore,

vi © ISO 2017 – All rights reserved
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ISO 28706-2:2017(E)

test results are only expressed in terms of rate of loss in mass per unit area (mass loss per unit

area and time) and the corrosion rate (millimetres per year).

d) At high temperatures, with tests in the liquid phase under autoclave conditions (see ISO 28706-5),

aqueous acid attack is severe. To avoid inhibition, the test time is restricted to 24 h and the ratio of

attacking acid to attacked enamel surface is chosen so that it is comparatively high (similar to that

in a chemical reaction vessel). In addition, only low-silica water is used for the preparation of test

solutions. Under these conditions, attack will proceed linearly with time of exposure. Therefore,

test results with 20 % hydrochloric acid (see ISO 28706-5:2010, Clause 8), artificial test solutions

(see ISO 28706-5:2010, Clause 10) or process fluids (see ISO 28706-5:2010, Clause 11) are also

expressed in terms of a rate of loss in mass per unit area (loss in mass per unit area and time).

e) In boiling water (see Clause 14), the silica network is fairly stable. The enamel surface is leached

and silica is dissolved only to a small extent. This type of attack is clearly represented by the vapour

phase attack. In the liquid phase, some inhibition can be observed with highly resistant enamels.

However, if the enamel being tested is weak, leached alkali from the enamel can raise pH values to

alkaline levels, thus increasing the attack by the liquid phase. Both liquid and vapour phase testing

can give valuable information.

f) Since the attack may or may not be linear, the results are expressed only in terms of loss in mass

per unit area and the test time should be indicated.

g) For standard detergent solution (see ISO 28706-3:2008, Clause 9), it will not be certain whether the

linear part of the corrosion curve will be reached during testing for 24 h or 168 h. Calculation of the

corrosion rate is therefore not included in the test report.

h) For other acids (see Clause 15) and other alkaline solutions (see ISO 28706-3:2008, Clause 10 and

ISO 28706-4:2016, Clause 10), it will also not be known if a linear corrosion rate will be reached

during the test period. Calculation of the corrosion rate is therefore not included in the test reports

of those parts of this document.

For vitreous enamels fired at temperatures below 700 °C, the test parameters (media, temperatures and

times) of this document are not appropriate. For such enamels, for example aluminium enamels, other

media, temperatures and/or times should be used. This can be done following the procedures described

in the clauses for “Other test solutions” in ISO 28706-1, ISO 28706-2, ISO 28706-3 and ISO 28706-4.

© ISO 2017 – All rights reserved vii
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INTERNATIONAL STANDARD ISO 28706-2:2017(E)
Vitreous and porcelain enamels — Determination of
resistance to chemical corrosion —
Part 2:
Determination of resistance to chemical corrosion by
boiling acids, boiling neutral liquids, alkaline liquids and/
or their vapours

WARNING — This document calls for the use of substances and/or procedures that may be

injurious to health if adequate safety measures are not taken. This document does not address any

health hazards, safety or environmental matters associated with its use. Is it the responsibility

of the user of this document to establish appropriate health, safety and environmentally

acceptable practices and take suitable actions for any national and international regulations.

1 Scope

This document specifies a test method for the determination of the resistance of flat surfaces of vitreous

and porcelain enamels to boiling acids, boiling neutral liquids, alkaline liquids and/or their vapours.

This method allows the determination of the resistance of vitreous and porcelain enamels to the liquid

and vapour phases of the corrosive medium simultaneously.
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 48, Rubber, vulcanized or thermoplastic — Determination of hardness (hardness between 10 IRHD and

100 IRHD)

ISO 649-1, Laboratory glassware — Density hydrometers for general purposes — Part 1: Specification

ISO 718, Laboratory glassware — Thermal shock and thermal shock endurance — Test methods

ISO 3585, Borosilicate glass 3.3 — Properties
ISO 3696, Water for analytical laboratory use — Specification and test methods
ISO 4788, Laboratory glassware — Graduated measuring cylinders
ISO 4799, Laboratory glassware — Condensers

ISO 28764, Vitreous and porcelain enamels — Production of specimens for testing enamels on sheet steel,

sheet aluminium and cast iron
3 Terms and definitions
No terms and definitions are defined in this document.

ISO and IEC maintain terminological databases for use in standardization at the following addresses:

— IEC Electropedia: available at http:// www .electropedia .org/
© ISO 2017 – All rights reserved 1
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ISO 28706-2:2017(E)
— ISO Online browsing platform: available at http:// www .iso .org/ obp
4 Principle

A set of similarly enamelled test specimens is placed in the liquid zone and/or in the vapour zone of

the test apparatus, as required, and exposed to attack by a boiling acid or boiling neutral liquid, or its

vapour, under specified conditions.

The same design of test apparatus and the same test principle is employed for the different liquids.

The loss in mass is determined and used to calculate the rate of loss in mass per unit area and, if

necessary, the corrosion rate.
5 Reagents

During the determination, use only reagents of recognized analytical grade, unless otherwise specified.

5.1 Water, conforming to the requirements of grade 3 of ISO 3696, i.e. distilled water or water of

equivalent purity.

5.2 Acetic acid solution, volume concentration 50 ml/l, for cleaning the test apparatus and test

specimens.

5.3 Degreasing solvent, such as ethanol, or water containing a few drops of liquid detergent, suitable

for cleaning the test apparatus and test specimens.
5.4 Citric acid monohydrate, (C H O ·H 0), crystalline.
6 8 7 2

5.5 Sulfuric acid, analytical grade, 30 % (by mass) solution, density range 1,217 g/ml to 1,220 g/ml

(measured with a hydrometer; see 6.2.7).

5.6 Hydrochloric acid, analytical grade, 20 % (by mass) solution, density range 1,097 g/ml to

1,099 g/ml (measured with a hydrometer; see 6.2.7).
5.7 Sodium tripolyphosphate (Na P O ).
5 3 10
5.8 Sodium carbonate (Na CO ), anhydrous.
2 3
5.9 Sodium perborate, hydrated (NaBO ·H O ·3H O).
2 2 2 2
5.10 Sodium silicate, containing about 81 % (by mass) of Na SiO .
2 3
5.11 Alkylsulfonate [CH (CH ) – C(SO Na)H – (CH ) – CH ].
3 2 x 2 2 3 3
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ISO 28706-2:2017(E)
6 Apparatus and materials
6.1 Test apparatus

6.1.1 The test apparatus (see Figures 1 and 2) consists of a cylinder (6.1.2; see Figure 3), with an

adjacent support, having a standard socket for holding a reflux condenser (6.1.3) with a graduated

collector (6.1.4) on one side.

Two test specimens shall form the top and bottom of the cylinder. One of them may be replaced by

a glass plate (6.1.14) if required. The cylinder with the specimens shall be supported between two

plates (see Figure 2) locked at the corners by threaded bolts (6.1.8), wing nuts (6.1.7) and hexagonal

nuts (6.1.6). A synthetic-fibre washer (6.1.9) is fixed between the plates (6.1.5) and each specimen. The

specimens are sealed against the ends of the cylinder with packing rings (6.1.10), the material of which

is dependent on the type of test solution. Any uncoated area of the test specimen shall be protected

from exposure to the attacking medium.

When testing specimens cut from an enamelled article, the packing rings (6.1.10) are replaced by

protective envelopes (see Figure 5) in which the specimens are placed.
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ISO 28706-2:2017(E)
Figure 1 — View of assembled test equipment
4 © ISO 2017 – All rights reserved
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ISO 28706-2:2017(E)
Dimensions in millimetres
Key
1 socket for reflux condenser 7 packing ring
2 synthetic-fibre washer 8 heater
3 wing nut 9 electric socket
4 specimen 10 triangular plate
5 socket for thermometer 11 hexagonal nut
6 cylinder
Figure 2 — Test apparatus

The apparatus is heated externally by a heater (6.1.11) placed round the lower half of the cylinder

(6.1.2) such that the lower edge is, at the most, 3 mm above the lower packing ring. The test apparatus is

composed of the parts described in 6.1.2 to 6.1.15.

6.1.2 Cylinder (see Figure 3), made of borosilicate glass 3.3 conforming to the requirements of

ISO 3585, with ground ends. When tested in accordance with ISO 718, the cylinder shall pass the test

without breaking at a difference in temperature of at least 120 °C.

NOTE Cylinders having two sockets can also be used if the smaller socket is closed by a stopper which is

resistant to the boiling solution.
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ISO 28706-2:2017(E)
Dimensions in millimetres
Key
1 ground-glass socket for condenser
2 ground-glass socket for thermometer
3 connecting piece
4 connecting piece
Figure 3 — Cylinder

6.1.3 Liebig-West reflux condenser, or equivalent reflux condenser conforming to ISO 4799, in which

there is no volume change during the test, with a nominal jacket length of 400 mm and standard ground

joint of borosilicate glass 3.3 conforming to the requirements of ISO 3585.

6.1.4 Graduated collector (see Figure 4), with a standard ground joint of borosilicate glass 3.3

conforming to the requirements of ISO 3585, arranged in the apparatus to collect the condensate

produced in the reflux condenser. The graduation interval shall be 0,1 ml.
6 © ISO 2017 – All rights reserved
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ISO 28706-2:2017(E)
Dimensions in millimetres
Figure 4 — Graduated collector
Dimensions in millimetres
Figure 5 — Protective envelope
6.1.5 Two plates of surface-protected steel.
6.1.6 Hexagonal nuts, with a thread fitting the screw bolts.
6.1.7 Wing nuts, with a thread fitting the screw bolts.
6.1.8 Threaded bolts, of corrosion-resistant steel.
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ISO 28706-2:2017(E)
6.1.9 Synthetic-fibre washers, resistant to acid and water at 140 °C.

NOTE Polytetrafluoroethylene (PTFE) is the only plastic material suitable for tests with mineral acids (e.g.

H SO , HCl).
2 4
6.1.10 Packing rings (see Clause 7).
6.1.11 Heater, with an output of 400 W to 500
...

NORME ISO
INTERNATIONALE 28706-2
Deuxième édition
2017-02
Émaux vitrifiés — Détermination de la
résistance à la corrosion chimique —
Partie 2:
Détermination de la résistance à la
corrosion chimique par des acides
bouillants, des liquides neutres
bouillants, ou des liquides alcalins et/
ou leurs vapeurs
Vitreous and porcelain enamels — Determination of resistance to
chemical corrosion —
Part 2: Determination of resistance to chemical corrosion by boiling
acids, boiling neutral liquids, alkaline liquids and/or their vapours
Numéro de référence
ISO 28706-2:2017(F)
ISO 2017
---------------------- Page: 1 ----------------------
ISO 28706-2:2017(F)
DOCUMENT PROTÉGÉ PAR COPYRIGHT
© ISO 2017, Publié en Suisse

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l’internet ou sur un Intranet, sans autorisation écrite préalable. Les demandes d’autorisation peuvent être adressées à l’ISO à

l’adresse ci-après ou au comité membre de l’ISO dans le pays du demandeur.
ISO copyright office
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Tel. +41 22 749 01 11
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copyright@iso.org
www.iso.org
ii © ISO 2017 – Tous droits réservés
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ISO 28706-2:2017(F)
Sommaire Page

Avant-propos ................................................................................................................................................................................................................................v

Introduction ................................................................................................................................................................................................................................vi

1 Domaine d’application ................................................................................................................................................................................... 1

2 Références normatives ................................................................................................................................................................................... 1

3 Termes et définitions ....................................................................................................................................................................................... 2

4 Principe .......................................................................................................................................................................................................................... 2

5 Réactifs ........................................................................................................................................................................................................................... 2

6 Appareillage et matériel ............................................................................................................................................................................... 3

6.1 Appareillage d’essai ............................................................................................................................................................................ 3

6.2 Matériel d’essai ....................................................................................................................................................................................... 8

7 Joints ................................................................................................................................................................................................................................. 8

7.1 Généralités .................................................................................................................................................................................................. 8

7.2 Joint A .............................................................................................................................................................................................................. 9

7.3 Joint B .............................................................................................................................................................................................................. 9

8 Éprouvettes ................................................................................................................................................................................................................ 9

9 Mode opératoire.................................................................................................................................................................................................... 9

10 Expression des résultats............................................................................................................................................................................10

10.1 Perte totale de masse surfacique..........................................................................................................................................10

10.2 Vitesse de corrosion ........................................................................................................................................................................10

11 Acide citrique bouillant ..............................................................................................................................................................................11

11.1 Généralités ...............................................................................................................................................................................................11

11.2 Solution d’essai ....................................................................................................................................................................................11

11.3 Durée de l’essai ....................................................................................................................................................................................11

11.4 Rapport d’essai ....................................................................................................................................................................................11

12 Acide sulfurique bouillant .......................................................................................................................................................................11

12.1 Généralités ...............................................................................................................................................................................................11

12.2 Solution d’essai ....................................................................................................................................................................................12

12.3 Durée de l’essai ....................................................................................................................................................................................12

12.4 Rapport d’essai ....................................................................................................................................................................................12

13 Acide chlorhydrique bouillant ............................................................................................................................................................12

13.1 Généralités ...............................................................................................................................................................................................12

13.2 Solution d’essai ....................................................................................................................................................................................12

13.3 Durée de l’essai ....................................................................................................................................................................................12

13.4 Rapport d’essai ....................................................................................................................................................................................13

14 Eau distillée ou déminéralisée bouillante ..............................................................................................................................13

14.1 Généralités ...............................................................................................................................................................................................13

14.2 Solution d’essai ....................................................................................................................................................................................13

14.3 Durée de l’essai ....................................................................................................................................................................................13

14.4 Rapport d’essai ....................................................................................................................................................................................14

15 Solution détergente normalisée ........................................................................................................................................................14

15.1 Généralités ...............................................................................................................................................................................................14

15.2 Solution d’essai ....................................................................................................................................................................................14

15.3 Température d’essai ........................................................................................................................................................................15

15.4 Durée de l’essai ....................................................................................................................................................................................15

15.5 Rapport d’essai ....................................................................................................................................................................................15

16 Autres solutions et/ou conditions d’essai ...............................................................................................................................15

16.1 Généralités ...............................................................................................................................................................................................15

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ISO 28706-2:2017(F)

16.2 Solution d’essai ....................................................................................................................................................................................15

16.3 Durée de l’essai ....................................................................................................................................................................................16

16.4 Rapport d’essai ....................................................................................................................................................................................16

Bibliographie ...........................................................................................................................................................................................................................17

iv © ISO 2017 – Tous droits réservés
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ISO 28706-2:2017(F)
Avant-propos

L’ISO (Organisation internationale de normalisation) est une fédération mondiale d’organismes

nationaux de normalisation (comités membres de l’ISO). L’élaboration des Normes internationales est

en général confiée aux comités techniques de l’ISO. Chaque comité membre intéressé par une étude

a le droit de faire partie du comité technique créé à cet effet. Les organisations internationales,

gouvernementales et non gouvernementales, en liaison avec l’ISO participent également aux travaux.

L’ISO collabore étroitement avec la Commission électrotechnique internationale (IEC) en ce qui

concerne la normalisation électrotechnique.

Les procédures utilisées pour élaborer le présent document et celles destinées à sa mise à jour sont

décrites dans les Directives ISO/IEC, Partie 1. Il convient, en particulier, de prendre note des différents

critères d’approbation requis pour les différents types de documents ISO. Le présent document a été

rédigé conformément aux règles de rédaction données dans les Directives ISO/IEC, Partie 2 (voir www

.iso .org/ directives).

L’attention est appelée sur le fait que certains des éléments du présent document peuvent faire l’objet de

droits de propriété intellectuelle ou de droits analogues. L’ISO ne saurait être tenue pour responsable

de ne pas avoir identifié de tels droits de propriété et averti de leur existence. Les détails concernant

les références aux droits de propriété intellectuelle ou autres droits analogues identifiés lors de

l’élaboration du document sont indiqués dans l’Introduction et/ou dans la liste des déclarations de

brevets reçues par l’ISO (voir www .iso .org/ brevets).

Les appellations commerciales éventuellement mentionnées dans le présent document sont données

pour information, par souci de commodité, à l’intention des utilisateurs et ne sauraient constituer un

engagement.

Pour une explication de la nature volontaire des normes, la signification des termes et expressions

spécifiques de l’ISO liés à l’évaluation de la conformité, ou pour toute information au sujet de l’adhésion

de l’ISO aux principes de l’Organisation mondiale du commerce (OMC) concernant les obstacles

techniques au commerce (OTC), voir le lien suivant: w w w . i s o .org/ iso/ fr/ avant -propos .html.

Le présent document a été élaboré par le comité technique l’ISO/TC 107, Revêtements métalliques et

autres revêtements inorganiques.

Cette deuxième édition annule et remplace la première édition (ISO 28706-2:2008) qui a fait l’objet

d’une révision technique avec les modifications suivantes.

— Le présent document peut également être utilisé pour déterminer la résistance à la corrosion

chimique en utilisant des liquides alcalins. Le titre du présent document a donc été modifié et un

article relatif aux solutions de détergent normalisées a été inclus.
— D’autres réactifs peuvent être utilisés à des fins d’essais et ont été inclus.

Une liste de toutes les parties de la série de normes ISO 28706 peut être consultée sur le site de l’ISO.

© ISO 2017 – Tous droits réservés v
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ISO 28706-2:2017(F)
Introduction

La corrosion aqueuse des émaux vitrifiés est un processus de dissolution. Le composant principal

de l’émail, SiO , forme un réseau tridimensionnel de silice. Après hydrolyse, celle-ci se décompose

en formant de l’acide silicique ou des silicates. Ceux-ci sont libérés dans le milieu attaquant. D’autres

composants, principalement des oxydes de métal, également soumis à l’hydrolyse, forment les ions

métalliques hydratés ou les hydroxydes correspondants. Tous les produits de corrosion sont plus ou

moins solubles dans le milieu attaquant. Le processus complet entraîne une perte de masse par unité de

surface.

Avec certaines solutions aqueuses, l’attaque de l’émail s’opère de façon linéaire pendant le temps que

dure la corrosion; pour d’autres solutions aqueuses, l’attaque de l’émail s’opère de façon logarithmique

pendant le temps de corrosion. Pour la première série de solutions seulement, un taux de perte de

masse surfacique (g/m ⋅h) scientifiquement exact peut être calculé, ainsi qu’une vitesse de corrosion

(millimètres par an).

Les paramètres les plus importants ayant une incidence sur la corrosion aqueuse de l’émail sont la

qualité de l’émail, la température et la valeur de pH. En outre, les effets d’inhibition résultant de la

solubilité limitée de la silice dans les acides peuvent y contribuer. La liste suivante décrit les différents

types d’attaque de l’émail en fonction de différentes conditions de corrosion.

a) Avec des solutions alcalines aqueuses telles que NaOH à 0,1 mol/l (voir l’ISO 28706-4:2016,

Article 9), le réseau de silice de l’émail est fortement attaqué à 80 °C. Les silicates et la plupart des

autres composants hydrolysés sont solubles dans l’alcali. L’attaque s’opère linéairement pendant

des périodes d’essai régulières. Par conséquent, les résultats des essais sont exprimés en termes de

taux de perte de masse surfacique (perte de masse par unité de surface et temps) et de vitesse de

corrosion (millimètres par an).

b) À température ambiante, les acides aqueux faibles tels que l’acide citrique (voir l’ISO 28706-1:2008,

Article 9) ou également les acides plus forts tels que l’acide sulfurique (voir l’ISO 28706-1:2008,

Article 10) n’attaquent guère le réseau de silice de l’émail. D’autres constituants sont, dans une

certaine mesure, lixiviés de la surface. Les émaux hautement résistants ne présentent aucun

changement visible après exposition. Sur les émaux moins résistants, des taches apparaîtront ou la

surface deviendra rugueuse.

c) Avec des acides aqueux bouillants (tels que décrits dans le présent document), le réseau de silice

de l’émail est attaqué, et la silice ainsi que les autres composants de l’émail sont libérés dans la

solution. La solubilité de la silice dans les acides est néanmoins faible. Les solutions attaquantes,

qui sont vite saturées de silice dissoute, ne feront que lixivier la surface. L’attaque acide est arrêtée

et la vitesse de corrosion diminue de façon marquée.

NOTE L’appareillage d’essai en verre libère également de la silice sous l’effet de l’attaque acide et

contribue à l’inhibition de la corrosion.

L’inhibition est efficacement empêchée avec les essais en phase vapeur. Le condensat formé sur

l’éprouvette est exempt de tout composant d’émail dissous.

Parmi les exemples de corrosion de l’émail s’opérant de façon logarithmique [voir 1)] et linéairement

[voir 2)], on peut citer:

1) Acide citrique bouillant (voir Article 11) et acide sulfurique à 30 % bouillant (voir

Article 12)

Étant donné que l’on ne trouve que des quantités infimes de ces acides dans leurs vapeurs,

l’essai est limité à la phase liquide. L’attaque est influencée par des effets d’inhibition et la

corrosion dépend du temps d’exposition. Par conséquent, les résultats d’essai sont exprimés en

termes de perte de masse par unité de surface; aucun taux de perte de masse surfacique n’est

calculé.
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ISO 28706-2:2017(F)
2) Acide chlorhydrique à 20 % bouillant (voir Article 13)

S’agissant d’un acide bouillant azéotropique, sa concentration est identique en phase liquide

et en phase vapeur; il n’est donc pas nécessaire de réaliser l’essai en phase liquide. Une forte

ébullition fournit un condensat non inhibé et l’attaque se poursuit linéairement pendant le

temps que dure l’exposition. Par conséquent, les résultats des essais ne sont exprimés qu’en

termes de taux de perte de masse surfacique (perte de masse par unité de surface et temps) et

de vitesse de corrosion (millimètres par an).

d) À des températures élevées, lors d’essais en phase liquide en autoclave (voir l’ISO 28706-5), l’attaque

d’acide aqueux est forte. Afin d’éviter l’inhibition, la durée de l’essai est limitée à 24 h et un rapport

relativement élevé est choisi entre l’acide attaquant et la surface d’émail attaquée (analogue à celui

d’une cuve pour réaction chimique). En outre, seule de l’eau à faible teneur en silice est utilisée

pour la préparation des solutions d’essai. Dans ces conditions, l’attaque s’opère de façon linéaire

pendant le temps que dure l’exposition. Par conséquent, les résultats des essais avec de l’acide

chlorhydrique à 20 % (voir l’ISO 28706-5:2010, Article 8), des solutions d’essai artificielles (voir

l’ISO 28706-5:2010, Article 10) ou des fluides de traitement (voir l’ISO 28706-5:2010, Article 11)

sont également exprimés en termes de taux de perte de masse surfacique (perte de masse par unité

de surface et temps).

e) Dans l’eau bouillante (voir Article 14), le réseau de silice est assez stable. La surface d’émail est

lixiviée et la silice n’est que faiblement dissoute. Ce type d’attaque est clairement représenté par

l’attaque en phase vapeur. En phase liquide, on peut observer une certaine inhibition avec les émaux

hautement résistants. Toutefois, si l’émail soumis à essai est peu résistant, l’alcali lixivié dégagé par

l’émail peut relever les valeurs de pH à des niveaux alcalins, augmentant ainsi l’attaque par la phase

liquide. Les essais en phase liquide et en phase vapeur peuvent donner des informations précieuses.

f) Étant donné que l’attaque peut être linéaire ou non, les résultats sont seulement exprimés en termes

de perte de masse par unité de surface et il convient que la durée de l’essai soit indiquée.

g) Pour la solution détergente normalisée (voir l’ISO 28706-3:2008, Article 9), il n’est pas certain que

la partie linéaire de la courbe de corrosion soit atteinte pendant l’essai durant 24 h ou 168 h. Le

calcul de la vitesse de corrosion n’est donc pas inclus dans le rapport d’essai.

h) Pour d’autres acides (voir Article 15) et d’autres solutions alcalines (voir l’ISO 28706-3:2008,

Article 10 et l’ISO 28706-4:2016, Article 10), on ne sait pas non plus si une vitesse de corrosion

linéaire sera atteinte au cours de la période d’essai. Le calcul de la vitesse de corrosion n’est donc

pas inclus dans les rapports d’essais de ces parties du présent document.

Pour les émaux vitrifiés cuits à des températures inférieures à 700 °C, les paramètres d’essai (milieux,

températures et temps) du présent document ne sont pas appropriés. Pour de tels émaux, par exemple

les émaux d’aluminium, il convient d’utiliser d’autres milieux, températures et/ou temps. Pour ce faire,

il suffit de suivre les modes opératoires décrits dans l’article intitulé «Autres solutions d’essai» de

l’ISO 28706-1, l’ISO 28706-2, l’ISO 28706-3 et l’ISO 28706-4.
© ISO 2017 – Tous droits réservés vii
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NORME INTERNATIONALE ISO 28706-2:2017(F)
Émaux vitrifiés — Détermination de la résistance à la
corrosion chimique —
Partie 2:
Détermination de la résistance à la corrosion chimique par
des acides bouillants, des liquides neutres bouillants, ou
des liquides alcalins et/ou leurs vapeurs

AVERTISSEMENT — Le présent document préconise l’utilisation de substances et/ou de modes

opératoires susceptibles d’être dangereux pour la santé si des mesures de sécurité adéquates ne

sont pas prises. Le présent document ne traite pas des dangers pour la santé, ni des questions de

sécurité ou d’environnement associées à son utilisation. Il appartient à l’utilisateur du présent

document d’établir des pratiques appropriées acceptables en termes de santé, de sécurité et

d’environnement et de prendre des mesures adéquates pour satisfaire aux réglementations

nationales et internationales.
1 Domaine d’application

Le présent document spécifie une méthode d’essai permettant de déterminer la résistance de surfaces

planes en émail vitrifié à des acides bouillants, des liquides neutres bouillants, des liquides alcalins

et/ou leurs vapeurs.

La présente méthode permet de déterminer simultanément la résistance des émaux vitrifiés aux phases

liquide et vapeur du milieu corrosif.
2 Références normatives

Les documents suivants cités dans le texte constituent, pour tout ou partie de leur contenu, des

exigences du présent document. Pour les références datées, seule l’édition citée s’applique. Pour les

références non datées, la dernière édition du document de référence s’applique (y compris les éventuels

amendements).

ISO 48, Caoutchouc vulcanisé ou thermoplastique — Détermination de la dureté (dureté comprise entre 10

DIDC et 100 DIDC)

ISO 649-1, Verrerie de laboratoire — Aréomètres à masse volumique d’usage général — Partie 1:

Spécifications

ISO 718, Verrerie de laboratoire — Choc thermique et endurance au choc thermique — Méthodes d’essai

ISO 3585, Verre borosilicaté 3.3 — Propriétés

ISO 3696, Eau pour laboratoire à usage analytique — Spécification et méthodes d’essai

ISO 4788, Verrerie de laboratoire — Éprouvettes graduées cylindriques
ISO 4799, Verrerie de laboratoire — Réfrigérants

ISO 28764, Émaux vitrifiés — Production d’éprouvettes pour l’essai des émaux sur la tôle d’acier, la tôle

d’aluminium et la fonte
© ISO 2017 – Tous droits réservés 1
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ISO 28706-2:2017(F)
3 Termes et définitions
Aucun terme n’est défini dans le présent document.

L’ISO et l’IEC tiennent à jour des bases de données terminologiques destinées à être utilisées en

normalisation, consultables aux adresses suivantes:
— IEC Electropedia: disponible à l’adresse http:// www .electropedia .org/

— ISO Online browsing platform: disponible à l’adresse http:// www .iso .org/ obp

4 Principe

Une série d’éprouvettes émaillées de la même façon est placée selon les exigences dans la zone liquide

et/ou dans la zone vapeur de l’appareil d’essai et exposée à l’attaque par un acide bouillant ou un liquide

neutre bouillant, ou leurs vapeurs, dans des conditions spécifiées.

Un appareil d’essai de conception identique ainsi que le même principe d’essai sont utilisés pour les

différents liquides.

La perte de masse est déterminée et utilisée pour calculer le taux de perte de masse surfacique et, si

besoin, la vitesse de corrosion.
5 Réactifs

Au cours de la détermination, sauf spécification contraire, utiliser uniquement des réactifs de qualité

analytique reconnue.

5.1 Eau, conforme aux exigences de qualité 3 de I’ISO 3696, c’est-à-dire de l’eau distillée ou de l’eau de

pureté équivalente.

5.2 Solution d’acide acétique, de concentration volumique 50 ml/l, pour nettoyer l’appareillage

d’essai et les éprouvettes.

5.3 Solvant de dégraissage, par exemple éthanol ou eau renfermant quelques gouttes de détergent

liquide, convenant pour le nettoyage et le dégraissage de l’appareillage d’essai et des éprouvettes.

5.4 Acide citrique monohydraté, (C H O ⋅H O), cristallisé.
6 8 7 2

5.5 Acide sulfurique, de qualité analytique, solution à 30 % (en masse), de masse volumique comprise

entre 1,217 g/ml et 1,220 g/ml (mesurée à l’aide d’un aéromètre — voir 6.2.7).

5.6 Acide chlorhydrique, de qualité analytique, solution à 20 % (en masse), de masse volumique

comprise entre 1,097 g/ml et 1,099 g/ml (mesurée à l’aide d’un aéromètre — voir 6.2.7).

5.7 Tripolyphosphate de sodium (Na P O ).
5 3 10
5.8 Carbonate de sodium (Na CO ), anhydre.
2 3
5.9 Perborate de sodium, hydraté (NaBO ⋅H O ⋅3H O).
2 2 2 2
5.10 Silicate de sodium, contenant environ 81 % (en masse) de Na SiO .
2 3
5.11 Alkylsulfonate [CH (CH ) – C(SO Na)H – (CH ) – CH ].
3 2 x 2 2 3 3
2 © ISO 2017 – Tous droits réservés
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ISO 28706-2:2017(F)
6 Appareillage et matériel
6.1 Appareillage d’essai

6.1.1 L’appareillage d’essai (voir Figures 1 et 2) est constitué d’un cylindre (6.1.2) (voir Figure 3), avec

un support adjacent, comportant un rodage normalisé pouvant s’adapter à un réfrigérant à reflux (6.1.3)

avec, sur un côté, un collecteur gradué (6.1.4).

Deux éprouvettes doivent constituer le couvercle et le fond du cylindre. L’une d’elles peut, si besoin, être

remplacée par une plaque de verre (6.1.14). Le cylindre et les éprouvettes doivent être maintenus entre

deux plaques (voir Figure 2) serrées aux angles à l’aide de tiges filetées (6.1.8), d’écrous à oreilles (6.1.7)

et d’écrous hexagonaux (6.1.6). Un joint en fibres synthétiques (6.1.9) est fixé entre les plaques (6.1.5) et

chaque éprouvette. Les éprouvettes sont serrées contre le bord du cylindre à l’aide de joints en anneau

(6.1.10) dont la matière dépend du type de solution d’essai. Toute surface non revêtue de l’éprouvette

doit être protégée de l’exposition au milieu attaquant.

Lorsque les éprouvettes sont découpées dans une pièce émaillée, les joints en anneau (6.1.10) sont

remplacés par des enveloppes protectrices (voir Figure 5) dans lesquelles sont placées les éprouvettes.

© ISO 2017 – Tous droits réservés 3
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ISO 28706-2:2017(F)
Figure 1 — Illustration de l’appareillage d’essai assemblé
4 © ISO 2017 – Tous droits réservés
---------------------- Page: 11 ----------------------
ISO 28706-2:2017(F)
Dimensions en millimètres
Légende
1 rodage pour réfrigérant à reflux 7 joint en anneau
2 joint en fibres synthétiques 8 anneau chauffant
3 écrou à oreilles 9 prise électrique
4 éprouvette 10 plaque triangulaire
5 rodage pour le thermomètre 11 écrou hexagonal
6 cylindre
Figure 2 — Appareillage d’essai

L’appareillage est chauffé de l’extérieur par un anneau chauffant (6.1.11) placé sur la demi-hauteur

inférieure du cylindre (6.1.2) de sorte que le bord inférieur soit au maximum à 3 mm au-dessus de

l’anneau d’étanchéité inférieur. L’appareillage d’essai compre
...

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