Nickel alloys -- Determination of chromium content -- Potentiometric titration method with ammonium iron(II) sulfate

ISO 7529:2017 specifies a potentiometric titration method for the determination of chromium content in nickel alloys which do not contain insoluble carbides and which have a vanadium content less than a mass fraction of 0,2 %. The method is applicable to chromium contents between a mass fraction of 5 % and a mass fraction of 22 %. Vanadium, which can be present as an impurity in the alloy, will give a positive bias interference. However, at a level of a mass fraction of 0,2 %, this bias is equivalent to a mass fraction of 0,068 % chromium, which is about half the reproducibility of the method.

Alliages de nickel -- Détermination du chrome -- Méthode par titrage potentiométrique avec du sulfate de fer(II) et d'ammonium

General Information

Status
Published
Publication Date
26-Oct-2017
Current Stage
6060 - International Standard published
Start Date
16-Sep-2017
Completion Date
27-Oct-2017
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INTERNATIONAL ISO
STANDARD 7529
Second edition
2017-10
Nickel alloys — Determination of
chromium content — Potentiometric
titration method with ammonium
iron(II) sulfate
Alliages de nickel — Détermination du chrome — Méthode par
titrage potentiométrique avec du sulfate de fer(II) et d'ammonium
Reference number
ISO 7529:2017(E)
ISO 2017
---------------------- Page: 1 ----------------------
ISO 7529:2017(E)
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© ISO 2017, Published in Switzerland

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ii © ISO 2017 – All rights reserved
---------------------- Page: 2 ----------------------
ISO 7529:2017(E)
Contents Page

Foreword ........................................................................................................................................................................................................................................iv

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

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

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

4 Principle ........................................................................................................................................................................................................................ 1

5 Reagents ........................................................................................................................................................................................................................ 1

6 Apparatus ..................................................................................................................................................................................................................... 3

7 Sampling and sample preparation .................................................................................................................................................... 3

8 Procedure..................................................................................................................................................................................................................... 4

8.1 Preparation of the test solution ................................................................................................................................................ 4

8.2 Determination ......................................................................................................................................................................................... 4

8.3 Blank test ..................................................................................................................................................................................................... 5

8.4 Number of determination .............................................................................................................................................................. 5

9 Expression of results ........................................................................................................................................................................................ 5

9.1 Method of calculation ........................................................................................................................................................................ 5

9.2 Precision ....................................................................................................................................................................................................... 5

9.2.1 Interlaboratory tests .................................................................................................................................................... 5

9.2.2 Statistical evaluation .................................................................................................................................................... 6

10 Notes on procedure ............................................................................................................................................................................................ 6

10.1 Alloys containing vanadium ........................................................................................................................................................ 6

10.2 Determination of the end-point ............................................................................................................................................... 6

11 Test report ................................................................................................................................................................................................................... 7

Bibliography ................................................................................................................................................................................................................................ 8

© ISO 2017 – All rights reserved iii
---------------------- Page: 3 ----------------------
ISO 7529:2017(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

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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

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URL: www.iso.org/iso/foreword.html.

This document was prepared by Technical Committee ISO/TC 155, Nickel and nickel alloys.

This second edition cancels and replaces the first edition (ISO 7529:1989), which has been technically

revised with the following changes:
— the scope has been modified;
— Table 1 has been modified.
iv © ISO 2017 – All rights reserved
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INTERNATIONAL STANDARD ISO 7529:2017(E)
Nickel alloys — Determination of chromium content
— Potentiometric titration method with ammonium
iron(II) sulfate
1 Scope

This document specifies a potentiometric titration method for the determination of chromium content

in nickel alloys which do not contain insoluble carbides and which have a vanadium content less than a

mass fraction of 0,2 %. The method is applicable to chromium contents between a mass fraction of 5 %

to a mass fraction of 22 %.

Vanadium, which can be present as an impurity in the alloy, will give a positive bias interference.

However, at a level of a mass fraction of 0,2 %, this bias is equivalent to a mass fraction of 0,068 %

chromium, which is about half the reproducibility of the method.
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 385, Laboratory glassware — Burettes
ISO 648, Laboratory glassware — Single-volume pipettes
ISO 1042, Laboratory glassware — One-mark volumetric flasks
3 Terms and definitions
No terms and definitions are listed 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 Online browsing platform: available at http://www.iso.org/obp
4 Principle

Dissolution of a test portion in a nitric/hydrochloric acids mixture, and evaporation to fumes of

sulfuric acid.

Dissolution of the salts in water and oxidation of chromium to chromium(VI), with ammonium

peroxydisulfate using silver nitrate as a catalyst.

Removal of excess peroxydisulfate by boiling, and reduction of manganese(VII) with hydrochloric acid.

Titration of chromium(VI) with ammonium iron(II) sulfate using potentiometric end-point detection.

5 Reagents

During the analysis, unless otherwise stated, use only reagents of recognized analytical grade and only

distilled water or water of equivalent purity.
© ISO 2017 – All rights reserved 1
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ISO 7529:2017(E)
5.1 Hydrochloric acid, ρ = 1,19 g/ml.
5.2 Hydrochloric acid, ρ = 1,19 g/ml, diluted 1 + 3.
5.3 Nitric acid, ρ = 1,41 g/ml.
5.4 Sulfuric acid, ρ = 1,84 g/ml, diluted 1 + 1.
5.5 Silver nitrate (AgNO ), 15 g/l solution.
5.6 Ammonium peroxydisulfate [(NH ) S O ].
4 2 2 8
5.7 Nitric/hydrochloric acids, mixture.

WARNING — This acid mixture is highly corrosive and unstable. Noxious chlorine gas is

liberated on standing. It shall be prepared and used in a fume hood and shall not be kept in a

closed container.
Carefully mix 25 ml of nitric acid (5.3) and 75 ml of hydrochloric acid (5.1).
This mixture is not stable and shall be prepared just before use.
5.8 Potassium dichromate, standard solution, c(1/6 K Cr O ) = 0,100 mol/l.
2 2 7

Dissolve exactly 4,903 g of potassium dichromate (K Cr O , 99,95 % minimum purity), previously dried

2 2 7
at 105 °C for 1 h, in 500 ml of water.

Transfer to a 1 000 ml one-mark volumetric flask, dilute to the mark with water and mix.

5.9 Ammonium iron(II) sulfate, standard solution, c[(NH ) Fe(SO ) ] = 0,1 mol/l.
4 2 4 2
5.9.1 Preparation

Dissolve 40 g of ammonium iron(II) sulfate hexahydrate [(NH ) Fe(SO ) · 6H O] in 400 ml of water.

4 2 4 2 2
Add slowly, with constant stirring, 100 ml of sulfuric acid (5.4).

Cool, transfer to a 1 000 ml one-mark volumetric flask, dilute to the mark with water and mix.

5.9.2 Standardization

Add, using a burette, 40,0 ml of the potassium dichromate solution (5.8) to 200 ml of water in a 400 ml

tall-form beaker. Add 10 ml of sulfuric acid (5.4), 5 ml of the silver nitrate solution (5.5) and 5 ml of

hydrochloric acid (5.2). Titrate this solution potentiometrically with the ammonium iron(II) sulfate

solution (5.9), as specified in 8.2.

The real concentration, c, of the ammonium iron(II) sulfate solution (5.9), expressed in moles of iron

per lit
...

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