SIST EN ISO 28706-4:2016

SLOVENSKI STANDARD
01-april-2016
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SIST EN ISO 28706-4:2012
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Vitreous and porcelain enamels - Determination of resistance to chemical corrosion -
Part 4: Determination of resistance to chemical corrosion by alkaline liquids using a
cylindrical vessel (ISO 28706-4:2016)
Emails und Emaillierungen - Bestimmung der Beständigkeit gegen chemische Korrosion
- Teil 4: Bestimmung der Beständigkeit gegen chemische Korrosion durch alkalische
Flüssigkeiten unter Verwendung eines Gerätes mit zylindrischem Gefäß (ISO 28706-
4:2016)
Émaux vitrifiés - Détermination de la résistance à la corrosion chimique - Partie 4:
Détermination de la résistance à la corrosion chimique par des liquides alcalins dans un
récipient cylindrique (ISO 28706-4:2016)
Ta slovenski standard je istoveten z: EN ISO 28706-4:2016
ICS:
25.220.50 Emajlne prevleke Enamels
2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.

EN ISO 28706-4
EUROPEAN STANDARD
NORME EUROPÉENNE
January 2016
EUROPÄISCHE NORM
ICS 25.220.50 Supersedes EN ISO 28706-4:2011
English Version
Vitreous and porcelain enamels - Determination of
resistance to chemical corrosion - Part 4: Determination of
resistance to chemical corrosion by alkaline liquids using a
cylindrical vessel (ISO 28706-4:2016)
Émaux vitrifiés - Détermination de la résistance à la Emails und Emaillierungen - Bestimmung der
corrosion chimique - Partie 4: Détermination de la Beständigkeit gegen chemische Korrosion - Teil 4:
résistance à la corrosion chimique par des liquides Bestimmung der Beständigkeit gegen chemische
alcalins dans un récipient cylindrique (ISO 28706- Korrosion durch alkalische Flüssigkeiten unter
4:2016) Verwendung eines Gerätes mit zylindrischem Gefäß
(ISO 28706-4:2016)
This European Standard was approved by CEN on 7 November 2015.

CEN members are bound to comply with the CEN/CENELEC Internal Regulations which stipulate the conditions for giving this
European Standard the status of a national standard without any alteration. Up-to-date lists and bibliographical references
concerning such national standards may be obtained on application to the CEN-CENELEC Management Centre or to any CEN
member.
This European Standard exists in three official versions (English, French, German). A version in any other language made by
translation under the responsibility of a CEN member into its own language and notified to the CEN-CENELEC Management
Centre has the same status as the official versions.

CEN members are the national standards bodies of Austria, Belgium, Bulgaria, Croatia, Cyprus, Czech Republic, Denmark, Estonia,
Finland, Former Yugoslav Republic of Macedonia, France, Germany, Greece, Hungary, Iceland, Ireland, Italy, Latvia, Lithuania,
Luxembourg, Malta, Netherlands, Norway, Poland, Portugal, Romania, Slovakia, Slovenia, Spain, Sweden, Switzerland, Turkey and
United Kingdom.
EUROPEAN COMMITTEE FOR STANDARDIZATION
COMITÉ EUROPÉEN DE NORMALISATION

EUROPÄISCHES KOMITEE FÜR NORMUNG

CEN-CENELEC Management Centre: Avenue Marnix 17, B-1000 Brussels
© 2016 CEN All rights of exploitation in any form and by any means reserved Ref. No. EN ISO 28706-4:2016 E
worldwide for CEN national Members.

Contents Page
European foreword . 3
European foreword
This document (EN ISO 28706-4:2016) has been prepared by Technical Committee ISO/TC 107
“Metallic and other inorganic coatings” in collaboration with Technical Committee CEN/TC 262
“Metallic and other inorganic coatings” the secretariat of which is held by BSI.
This European Standard shall be given the status of a national standard, either by publication of an
identical text or by endorsement, at the latest by July 2016, and conflicting national standards shall be
withdrawn at the latest by July 2016.
Attention is drawn to the possibility that some of the elements of this document may be the subject of
patent rights. CEN [and/or CENELEC] shall not be held responsible for identifying any or all such patent
rights.
This document supersedes EN ISO 28706-4:2011.
According to the CEN-CENELEC Internal Regulations, the national standards organizations of the
following countries are bound to implement this European Standard: Austria, Belgium, Bulgaria,
Croatia, Cyprus, Czech Republic, Denmark, Estonia, Finland, Former Yugoslav Republic of Macedonia,
France, Germany, Greece, Hungary, Iceland, Ireland, Italy, Latvia, Lithuania, Luxembourg, Malta,
Netherlands, Norway, Poland, Portugal, Romania, Slovakia, Slovenia, Spain, Sweden, Switzerland,
Turkey and the United Kingdom.
Endorsement notice
The text of ISO 28706-4:2016 has been approved by CEN as EN ISO 28706-4:2016 without any
modification.
INTERNATIONAL ISO
STANDARD 28706-4
Third edition
2016-01-15
Vitreous and porcelain enamels —
Determination of resistance to
chemical corrosion —
Part 4:
Determination of resistance to
chemical corrosion by alkaline liquids
using a cylindrical vessel
Émaux vitrifiés — Détermination de la résistance à la corrosion
chimique —
Partie 4: Détermination de la résistance à la corrosion chimique par
des liquides alcalins dans un récipient cylindrique
Reference number
ISO 28706-4:2016(E)
©
ISO 2016
ISO 28706-4:2016(E)
© ISO 2016, Published in Switzerland
All rights reserved. Unless otherwise specified, no part of this publication may be reproduced or utilized otherwise in any form
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ii © ISO 2016 – All rights reserved

ISO 28706-4:2016(E)
Contents Page
Foreword .iv
Introduction .v
1 Scope . 1
2 Normative references . 1
3 Principle . 1
4 Reagents . 2
5 Apparatus and material . 2
6 Test specimens. 7
7 Procedure. 7
8 Expression of results . 8
8.1 Total loss in mass per unit area . 8
8.2 Corrosion rate . 8
9 Hot 0,1 mol/l sodium hydroxide test . 9
9.1 General . 9
9.2 Test solution, c(NaOH) = 0,1 mol/l . 9
9.3 Test temperature . 9
9.4 Duration of the test . 9
9.5 Test report . 9
10 Hot 1,0 mol/l sodium hydroxide test .10
10.1 General .10
10.2 Test solution, c(NaOH) = 1,0 mol/l .10
10.3 Test temperature .10
10.4 Duration of the test .10
10.5 Test report .10
11 Other test solutions .11
11.1 General .11
11.2 Test solution .11
11.3 Test temperature .11
11.4 Duration of the test .11
11.5 Test report .11
Bibliography .12
ISO 28706-4:2016(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 meaning of ISO specific terms and expressions related to conformity
assessment, as well as information about ISO’s adherence to the WTO principles in the Technical
Barriers to Trade (TBT) see the following URL: Foreword - Supplementary information.
The committee responsible for this document is ISO/TC 107, Metallic and other inorganic coatings.
This third edition cancels and replaces the second edition (ISO 28706-4:2008), of which it constitutes a
minor revision.
ISO 28706 consists of the following parts, under the general title Vitreous and porcelain enamels —
Determination of resistance to chemical corrosion:
— Part 1: Determination of resistance to chemical corrosion by acids at room temperature
— Part 2: Determination of resistance to chemical corrosion by boiling acids, boiling neutral liquids and/or
their vapours
— Part 3: Determination of resistance to chemical corrosion by alkaline liquids using a hexagonal vessel
— Part 4: Determination of resistance to chemical corrosion by alkaline liquids using a cylindrical vessel
— Part 5: Determination of resistance to chemical corrosion in closed systems
iv © ISO 2016 – All rights reserved

ISO 28706-4:2016(E)
Introduction
Corrosion of vitreous and porcelain enamels by aqueous solutions is a dissolution process. The
main component of the enamel, SiO , 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/m ⋅h) be calculated as well as a corrosion rate (mm/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 like 0,1 mol/l NaOH (see Clause 9 of this part of ISO 28706), 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 like citric acid (see ISO 28706-1:2008, Clause 9) or also
in stronger acids like 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 (see ISO 28706-2), 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:
1) Boiling citric acid (see of ISO 28706-2:2008, Clause 10) and boiling 30 % sulfuric acid (see
ISO 28706-2:2008, Clause 11)
Since only minor 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 ISO 28706-2:2008, Clause 12)
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,
ISO 28706-4:2016(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
...