ISO 7529:2017

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
• ICS: 77.120.40 - Nickel, chromium and their alloys
• Technical Committee: ISO/TC 155 - Nickel and nickel alloys
• Drafting Committee: ISO/TC 155/WG 10 - Nickel alloys analysis
• Current Stage: 9093 - International Standard confirmed
• Start Date: 16-May-2023
• Completion Date: 13-Dec-2025

Relations

• Revises: ISO 7529:1989 - Nickel alloys - Determination of chromium content - Potentiometric titration method with ammonium iron(II) sulfate
• Effective Date: 21-Nov-2015

Overview

ISO 7529:2017 is an international standard specifying a precise potentiometric titration method for determining chromium content in nickel alloys. This method is designed specifically for nickel alloys without insoluble carbides and with vanadium content below 0.2% by mass. The standard covers chromium contents ranging from 5% to 22% by mass fraction.

The method uses ammonium iron(II) sulfate as the titrant and requires careful sample preparation, reagent handling, and potentiometric end-point detection for accurate analysis. This approach offers a reliable and reproducible technique essential for quality control and material verification in various industrial applications involving nickel alloys.

Key Topics

• Scope and Applicability

  • Suitable for nickel alloys with ≤0.2% vanadium
  • Chromium content detection between 5% and 22%
  • Vanadium presence causes slight positive bias, minimal impact at specified levels

• Analytical Principle

  • Dissolution of sample in nitric/hydrochloric acid mixture followed by sulfuric acid evaporation
  • Oxidation of chromium to chromium(VI) using ammonium peroxydisulfate and silver nitrate catalyst
  • Removal of excess oxidant with hydrochloric acid and boiling
  • Potentiometric titration of chromium(VI) with ammonium iron(II) sulfate detecting end-point using platinum indicator and silver/silver chloride or calomel reference electrodes

• Reagent Details

  • Standard reagents of analytical grade: hydrochloric acid, nitric acid, sulfuric acid, silver nitrate, ammonium peroxydisulfate, potassium dichromate, and ammonium iron(II) sulfate
  • Preparation and standardization protocols ensure titrant accuracy

• Apparatus Requirements

  • Potentiometric titration setup including platinum indicator electrode, reference electrode, magnetic stirrer, burettes conforming to ISO standards, and a high impedance voltmeter or pH-meter
  • Use of Class A volumetric glassware for precise measurement

• Sampling and Sample Preparation

  • Use of millings or drillings without insoluble carbides
  • Cleaning samples contaminated with oil or grease using acetone
  • Ensuring sample homogeneity through riffling if particle size varies

• Precision and Reproducibility

  • Interlaboratory tests validated reproducibility of results
  • Chromium content calculation formula provided for accurate reporting

Applications

• Quality Control in Nickel Alloy Production Manufacturers use ISO 7529:2017 to assess chromium concentration during alloy fabrication to ensure material meets specified standards.

• Metallurgical Analysis Laboratories conducting chemical analysis of nickel alloys employ this potentiometric titration method for precise chromium determination, critical for alloy characterization and certification.

• Materials Inspection in Aerospace and Chemical Industries Given the importance of chromium in corrosion resistance and mechanical properties, this standard supports inspection protocols in highly demanding industries such as aerospace and chemical processing.

• Research and Development Researchers analyzing elemental composition in novel nickel alloys leverage the method for chromium quantification as part of material innovation and testing.

Related Standards

• ISO 385: Laboratory Glassware - Burettes Ensures the accuracy and quality requirements of burettes used in titration processes.

• ISO 648: Laboratory Glassware - Single-Volume Pipettes Defines requirements for pipettes crucial in precise liquid handling during sample preparation.

• ISO 1042: Laboratory Glassware - One-Mark Volumetric Flasks Specifies volumetric flasks used for accurate solution preparation critical in titrant standardization and dilution steps.

• ISO 5725: Accuracy (Trueness and Precision) of Measurement Methods and Results Provides guidelines for evaluating measurement precision and reproducibility, relevant for validating this titration method.

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Keywords: ISO 7529, nickel alloys, chromium determination, potentiometric titration, ammonium iron(II) sulfate, nickel alloy analysis, chromium content measurement, metallurgical testing, nickel alloy standards, chemical analysis nickel chromium, analytical method for chromium, ISO nickel alloy standards.

Standards Content (Sample)

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 2017
© 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
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written permission. Permission can be requested from either ISO at the address below or ISO’s member body in the country of
the requester.
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ii © ISO 2017 – All rights reserved

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
Foreword
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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

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.
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
...