ISO 8424:2023
(Main)Raw optical glass — Resistance to attack by aqueous acidic solutions — Test method and classification
Raw optical glass — Resistance to attack by aqueous acidic solutions — Test method and classification
This document specifies two methods for testing the resistance of raw optical glasses to attack by aqueous acidic solutions and defines a classification of optical glasses according to the acid resistance determined by these methods. The surface method tests the resistance of the polished plate-shaped optical glass to attack by aqueous acidic solutions at 25 °C for a specified time and indicates the class determined by this method as “SR-S”. The powder method tests the resistance of crushed granular optical glass to attack by an acidic aqueous solution at above 98 °C for 1 h, and indicates the class determined by this method as “SR-P”.
Verre d'optique brut — Résistance à l'attaque par des solutions acides aqueuses — Méthode d'essai et classification
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Standards Content (Sample)
INTERNATIONAL ISO
STANDARD 8424
Third edition
2023-07
Raw optical glass — Resistance to
attack by aqueous acidic solutions —
Test method and classification
Verre d'optique brut — Résistance à l'attaque par des solutions acides
aqueuses — Méthode d'essai et classification
Reference number
ISO 8424:2023(E)
© ISO 2023
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ISO 8424:2023(E)
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© ISO 2023
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Published in Switzerland
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ISO 8424:2023(E)
Contents Page
Foreword .iv
Introduction .v
1 Scope . 1
2 Normative references . 1
3 Terms and definitions . 1
4 Principle of measurement .1
4.1 Surface method . 1
4.2 Powder method . 2
4.3 Selection help for the methods . 2
5 Reagents . 2
6 Surface method . 3
6.1 Apparatus . 3
6.2 Preparation of the samples . . 6
6.2.1 General . 6
6.2.2 Lapping . 6
6.2.3 Polishing . 6
6.2.4 Calculation of total surface area . 6
6.2.5 Cleaning . 7
6.3 Procedure . 7
6.3.1 General . 7
6.3.2 Testing unknown glasses . . 8
6.3.3 Testing known glasses . 8
6.4 Expression of results . . 9
6.5 Classification and designation . . 9
7 Powder method .10
7.1 Apparatus . 10
7.1.1 Sieve . 10
7.1.2 Basket for corrosion test . 10
7.1.3 Apparatus for corrosion test . 11
7.1.4 Heating bath .12
7.2 Preparation of the specimen of the glass to be tested .12
7.3 Procedure .12
7.4 Classification and designation . .13
8 Test report .13
Annex A (informative) Acid resistance correlation between class SR-S and class SR-P .15
Annex B (informative) Method for glass polishing and processing .16
Bibliography .17
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ISO 8424:2023(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 of the voluntary nature of standards, the meaning of ISO specific terms and
expressions related to conformity assessment, as well as information about ISO's adherence to
the World Trade Organization (WTO) principles in the Technical Barriers to Trade (TBT), see
www.iso.org/iso/foreword.html.
This document was prepared by Technical Committee ISO/TC 172, Optics and photonics, Subcommittee
SC 3, Optical materials and components.
This third edition cancels and replaces the second edition (ISO 8424:1996), which has been technically
revised.
The main changes are as follows:
— a new measurement procedure, the powder method, was added;
— Annex A was added;
— Annex B was added;
— the surface method is technically revised.
Any feedback or questions on this document should be directed to the user’s national standards body. A
complete listing of these bodies can be found at www.iso.org/members.html.
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ISO 8424:2023(E)
Introduction
This document specifies methods for testing the resistance of optical glasses to the attack by aqueous
acidic solutions and provides corresponding classifications according to the resistance determined.
Two different methods are provided: A surface method and a powder method. Both methods are
described side by side so that the user can select a suitable or convenient method for the application.
The surface method is applied to polished glass samples. The results are comparable to application
conditions.
The powder method uses small amounts of crushed granular glass for testing. It is easy to apply, and
provides test results quickly.
The acid resistance classes determined by the two different methods show a correlation, but they
cannot be converted into each other unambiguously. Therefore, different notations are introduced for
the acid resistance classes referring to the determining method to avoid misunderstandings.
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INTERNATIONAL STANDARD ISO 8424:2023(E)
Raw optical glass — Resistance to attack by aqueous acidic
solutions — Test method and classification
1 Scope
This document specifies two methods for testing the resistance of raw optical glasses to attack by
aqueous acidic solutions and defines a classification of optical glasses according to the acid resistance
determined by these methods.
The surface method tests the resistance of the polished plate-shaped optical glass to attack by aqueous
acidic solutions at 25 °C for a specified time and indicates the class determined by this method as “SR-
S”.
The powder method tests the resistance of crushed granular optical glass to attack by an acidic aqueous
solution at above 98 °C for 1 h, and indicates the class determined by this method as “SR-P”.
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 2768-1, General tolerances — Part 1: Tolerances for linear and angular dimensions without individual
tolerance indications
ISO 3310-1, Test sieves — Technical requirements and testing — Part 1: Test sieves of metal wire cloth
ISO 3585, Borosilicate glass 3.3 — Properties
ISO 4797, Laboratory glassware — Boiling flasks with conical ground joints
ISO 4799, Laboratory glassware — Condensers
ISO 10110-8, Optics and photonics — Preparation of drawings for optical elements and systems — Part 8:
Surface texture
3 Terms and definitions
No terms and definitions are listed in this document.
ISO and IEC maintain terminology databases for use in standardization at the following addresses:
— ISO Online browsing platform: available at https:// www .iso .org/ obp
— IEC Electropedia: available at https:// www .electropedia .org/
4 Principle of measurement
4.1 Surface method
A polished glass sample is exposed to a test solution with a pH of 0,3 (nitric acid Solution 0,5 mol/l) or
4,6 (buffer solution) at 25 °C for specified durations. The sample is weighed before and after immersion
to determine the loss in material. From this result the duration required to remove a surface layer of
0,1 µm depth is determined and categorized into the acid resistance class SR-S.
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ISO 8424:2023(E)
4.2 Powder method
The glass is ground into particles with diameters in the range of 425 µm to 600 µm. A powder sample
equivalent to the specific gravity in grams is placed in a platinum basket. The basket is placed in a flask
of silica glass and boiled for 60 min. The degree of the acid resistance is determined by measuring the
mass loss (in percentage) and is categorized into the acid resistance class SR-P.
4.3 Selection help for the methods
The pros and cons of both methods are listed in Table 1.
Annex A gives an informative overview on the comparability of the results of both methods.
Table 1 — Pros and cons of both methods
Pros Cons
Surface method — The acid resistance class can be — The test shall be repeated until the
categorized "in detail" through several mass loss achieved is within the
test steps. specified value.
— Appearance can be judged. — Test duration cannot be predicted in
advance for unknown glasses.
— It can be tested in the same condition as
a polished product since the glass sample — Tying is bothersome work when the
is polished on all 6 faces. wire has been damaged.
— Closer to real application as in terms of
surface tested.
Powder method — The acid resistance class can be — Appearance evaluation is not possible.
categorized "simply".
— A specific Pt basket is required.
— The test duration is constant and short
for all glasses.
— The test procedure (method) is simple.
5 Reagents
Use only reagents of recognized analytical grade.
5.1 Nitric acid
a) surface method: solution [c(HNO ) = 0,5 mol/l], pH 0,3 + 0,05.
3
b) powder method: solution [c(HNO ) = 0,01 mol/l], pH 2,2 ± 0,05.
3
3
5.2 Acetic acid [CH COOH =1,05 g/cm ], 100 % [mass fraction].
3
5.3 Sodium hydroxide, solution [c(NaOH) = 1 mol/l].
5.4 Alcohol
a) surface method: 2-propanol (C H OH) is used. After evaporation of 100 ml of the alcohol, no residue
3 7
shall be visible. If residue is still visible, re-distill 2-propanol;
b) powder method: ethanol, methanol and 2-propanol can be used, but water-containing alcohol
cannot be used.
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ISO 8424:2023(E)
5.5 Buffer solution, pH 4,6 ± 0,05.
In glass vessels with graduated volumes (e.g. volumetric flask, beaker, conical beaker), mix 11,8 ml of
the acetic acid (5.3), 200 ml of water and 100 ml of the sodium hydroxide solution (5.4). Fill up to the
mark with water. Store in a plastic or borosilicate glass bottle.
6 Surface method
6.1 Apparatus
Usual laboratory equipment, together with the following.
6.1.1 Beaker, flat flange, made of borosilicate glass 3.3, in accordance with the requirements
of ISO 3585, having a capacity of 2 000 ml, an internal diameter of 150 mm, an external diameter of
153 mm and a height of 200 mm (see Figure 1).
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ISO 8424:2023(E)
Dimensions in millimetres
Key
1 polyethylene foam 5 sample
2 flat flange beaker (capacity of 2 000 ml) 6 surface of the liquid
3 stirrer (See Figure 3) 7 polymethyl methacrylate (PMMA) plate
4 sample
Permissible variations in dimensions without tolerance indication shall be in accordance with the coarse series in
ISO 2768-1.
Figure 1 — Test apparatus
6.1.2 Stirrer, approximately 350 mm long, having a 10 mm diameter glass shaft, or a 15 mm diameter
polytetrafluoroethylene (PTFE) shaft (see Figure 2) or the shaft made of similar material in workability,
chemical stability and mechanical strength, e.g. polyether ether ketone (PEEK).
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ISO 8424:2023(E)
Dimensions in millimetres
a) Glass b) PTFE
a
3 for glass stirrer, 5 for PTFE stirrer.
Permissible variations in dimensions without tolerance indication shall be in accordance with the coarse series in
ISO 2768-1.
Figure 2 — Stirrers
6.1.3 Acid resistant wires (e.g. platinum, nylon, etc.)
Less than 0,15 mm in diameter used to entwine the sample and hold it in the bath in such a way that
the area that is not in contact with the test liquid is less than 1 %. It is also possible to use a different
material as long as it is resistant to the test solution.
6.1.4 Heating bath
Gas or electrically heated, with a capacity of 30 l to 40 l, thermostatically controlled to maintain the
temperature of 25,0 °C ± 0,2 °C.
6.1.5 Analytical balance
Accurate to ±0,1 mg or better.
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ISO 8424:2023(E)
6.1.6 Desiccator
Using a 2:1 mixture of silica gel (for H O absorption) and soda lime (a mixture of CaO and NA O, for CO
2 2 2
absorption) with indicator for regeneration.
6.1.7 Tongs
Protected with inert smooth material, for example plastics.
6.1.8 Measuring instruments
Suitable for measuring lengths and diameter to an accuracy of ±1 %.
6.1.9 Ultrasonic equipment for laboratory use
Filled with water, which can be heated to at least 50 °C.
6.1.10 Beakers, made of borosilicate glass 3.3 in accordance with the requirements of ISO 3585,
having a capacity of 100 ml.
6.1.11 pH meter, it shall be calibrated with pH standard buffer before use.
6.2 Prepar
...
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