Alloyed steels -- Determination of manganese -- Potentiometric or visual titration method

This document specifies a potentiometric or visual titration method for the determination of manganese content in alloyed steels. The method is applicable to manganese mass fractions between 2 % and 25 %. Vanadium and cerium interfere with the determination. If the mass fraction of cerium in the sample is less than 0,01 %, or the mass fraction of vanadium in the sample is less than 0,005 %, the interference is negligible, otherwise theoretical corrections are necessary.

Aciers alliés -- Détermination du manganèse -- Méthodes par titration visuelle ou potentiométrique

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Status
Published
Publication Date
07-Aug-2018
Current Stage
6060 - International Standard published
Start Date
01-Jul-2018
Completion Date
08-Aug-2018
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INTERNATIONAL ISO
STANDARD 18632
Second edition
2018-08
Alloyed steels — Determination of
manganese — Potentiometric or
visual titration method
Aciers alliés — Détermination du manganèse — Méthodes par
titration visuelle ou potentiométrique
Reference number
ISO 18632:2018(E)
ISO 2018
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ISO 18632:2018(E)
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© ISO 2018

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ii © ISO 2018 – All rights reserved
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ISO 18632:2018(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 ..................................................................................................................................................................................................................... 4

7 Sampling ........................................................................................................................................................................................................................ 4

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

8.1 Test portion ................................................................................................................................................................................................ 4

8.2 Determination ......................................................................................................................................................................................... 5

8.2.1 Preparation of test solution .................................................................................................................................... 5

8.2.2 Titration................................................................................................................................................................................... 5

8.2.3 Theoretical correction of vanadium and cerium .................................................................................. 5

9 Expression of results ........................................................................................................................................................................................ 6

9.1 Method of calculation ........................................................................................................................................................................ 6

9.1.1 Visual titration ................................................................................................................................................................... 6

9.1.2 Potentiometric titration ............................................................................................................................................. 6

9.2 Precision ....................................................................................................................................................................................................... 7

10 Test report ................................................................................................................................................................................................................... 7

Annex A (informative) Additional information on the international interlaboratory test..........................8

Annex B (informative) Graphical representation of precision data .................................................................................10

Annex C (informative) Main redox reactions and correction of vanadium and cerium contents ......11

Bibliography .............................................................................................................................................................................................................................12

© ISO 2018 – All rights reserved iii
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ISO 18632:2018(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: www .iso .org/iso/foreword .html.

This document was prepared by Technical Committee ISO/TC 17, Steel, Subcommittee SC 1, Methods of

determination of chemical composition.

This second edition cancels and replaces the first edition (ISO 18632:2010), which has been technically

revised. The following changes have been made:

— a procedure has been added for the removal of the oxidized layer when the manganese standard

solution is prepared;
— superfluous figures have been deleted in Table A.2;

— Annex C has been added to explain the main redox reaction and the correction of vanadium and

cerium content in the document.
iv © ISO 2018 – All rights reserved
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INTERNATIONAL STANDARD ISO 18632:2018(E)
Alloyed steels — Determination of manganese —
Potentiometric or visual titration method
1 Scope

This document specifies a potentiometric or visual titration method for the determination of manganese

content in alloyed steels.

The method is applicable to manganese mass fractions between 2 % and 25 %. Vanadium and cerium

interfere with the determination. If the mass fraction of cerium in the sample is less than 0,01 %, or the

mass fraction of vanadium in the sample is less than 0,005 %, the interference is negligible, otherwise

theoretical corrections are necessary.
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
ISO 3696, Water for analytical laboratory use — Specification and test methods

ISO 14284, Steel and iron — Sampling and preparation of samples for the determination of chemical

composition
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:

— ISO Online browsing platform: available at https: //www .iso .org/obp
— IEC Electropedia: available at https: //www .electropedia .org/
4 Principle

Dissolution of a test portion in appropriate acids. Addition of phosphoric acid. Oxidation of manganese

to manganese(III) in phosphoric acid medium by ammonium nitrate. Visual titration of manganese(III)

with a ferroammoniumdisulfate standard solution with N-phenylanthranilic acid as indicator, or

potentiometric titration with a ferroammoniumdisulfate standard solution. If the sample contains

vanadium and/or cerium, the manganese content shall be corrected.
5 Reagents

During the analysis use only reagents of recognized analytical grade and only grade 2 water in

accordance with ISO 3696.
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ISO 18632:2018(E)
5.1 Ammonium nitrate, NH NO .
4 3
5.2 Urea.
5.3 Phosphoric acid, ρ approximately 1,69 g/ml.
5.4 Nitric acid, ρ approximately 1,42 g/ml.
5.5 Hydrochloric acid, ρ approximately 1,19 g/ml.
5.6 Sulfuric acid, diluted 1 + 3.
5.7 Sulfuric acid, diluted 5 + 95.
5.8 N-phenylanthranilic acid solution, C H NHC H COOH, approximately 2 g/l.
6 5 6 4

Dissolve 0,20 g of N-phenylanthranilic acid and 0,20 g of sodium carbonate in 100 ml of water and filter.

5.9 Potassium dichromate solution, K Cr O , 0,002 5 mol/l.
2 2 7

Weigh 0,735 5 g of high purity potassium dichromate, previously dried at 150 °C for at least 2 h and

cooled in a desiccator. Introduce it into a 250 ml beaker and dissolve in some water. Transfer the solution

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

5.10 Manganese standard solution, corresponding to 1,00 g/l of manganese.

Weigh, to the nearest 0,1 mg, 1,000 g of pure manganese [ purity ≥ 99,9 % (mass fraction)].

When the surface of manganese seems oxidized, the oxide layer should be removed before weighing as

follows:

a) introduce several grams of manganese into a beaker containing sulfuric acid (5.7) and stir;

b) decant, discard the sulphuric acid solution and immediately rinse the metal several times, firstly

with water and then with ethanol or acetone;
c) dry the metal for about 2 min at 100 °C and cool in a desiccator.

Introduce it in a 250 ml beaker and add 40 ml of hydrochloric acid (5.5). Cover with a watch glass and

heat gently to complete dissolution. Cool and transfer the solution quantitatively to a 1 000 ml one-

mark volumetric flask, dilute to the mark with water and mix.
1 ml of this standard solution contains 1,00 mg of manganese.

5.11 Ferroammoniumdisulfate standard solution, [(NH ) Fe(SO ) ⋅6H 0] 0,015 mol/l.

4 2 4 2 2
5.11.1 Preparation of the solution

Dissolve 5,9 g of ferroammoniumdisulfate in 1 000 ml sulfuric acid (5.7) and mix.

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ISO 18632:2018(E)
5.11.2 Standardization of the solution (to be carried out just before use)
5.11.2.1 Visual titration method
5.11.2.1.1 Titration

Transfer three aliquots of 20,0 ml of the potassium dichromate solution (5.9) to three 250 ml

conical flasks.

Add 20 ml of sulfuric acid (5.6), 5 ml of phosphoric acid (5.3) and water up to a volume of approximately

150 ml. Proceed as specified in 8.2.2.1.

Calculate the mean (V ) of the three volumes values of the ferroammoniumdisulfate solution. The

difference between the values should not exceed 0,05 ml.
5.11.2.1.2 Correction for N-phenylanthranilic acid

Transfer three aliquots of 5,0 ml of the potassium dichromate solution (5.9) to three 250 ml conical

flasks. Add 20 ml of sulfuric acid (5.6), 5 ml of phosphoric acid (5.3). Titrate the solution with the

ferroammoniumdisulfate solution (5.11) until the end point is approached (i.e. when the purplish

red colour of the solution becomes lighter). Add two drops of N-phenylanthranilic acid solution (5.8),

continue the titration until the purplish red colour disappears and record the volume added. Add

another 5,0 ml of potassium dichromate solution (5.9), titrate with the ferroammoniumdisulfate

solution (5.11) until the end point and record the volume added again. The mean of the differences

between the volumes of the two titrations is the corrected value, V .
5.11.2.1.3 Calculation

The corresponding concentration, c, expressed in moles per litre, of the ferroammoniumdisulfate

solution (5.11) is given by Formula (1):
0,015×20,0
C= (1)
VV−
where

V is the mean volume, expressed in millilitres, of the ferroammoniumdisulfate solution

(5.11) used for the titration;

V is the mean volume, expressed in millilitres, of the ferroammoniumdisulfate solution

(5.11) used for the correction of N-phenylanthranilic acid titration;

0,015 is the molar concentration, expressed in moles per litre, of the potassium dichromate

solution (5.9) times six;

20,0 is the volume, expressed in millilitres, of the potassium dichromate solution (5.9) used for

the standardization.
5.11.2.2 Potentiometric titration method
5.11.2.2.1 Titration

Transfer three aliquots of 20,0 ml of the manganese standard solution (5.10) to three 300 ml conical

flasks. Add 15 ml of phosphoric acid (5.3). Heat until the surface of the solution calms down (i.e. a state

where no bubble is observed on the surface of the solution) and white fumes are just given off (at this

stage the temperature should be about 200 °C to 240 °C). Remove the flask from the heater, add 2 g of

ammonium nitrate (5.1) immediately and shake the conical flask for removing nitrogen oxide. Nitrogen

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ISO 18632:2018(E)
oxide shall be eliminated thoroughly by
...

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