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IS0
O RG A N IZ AT1 O N FOR STA N DA RD I2 AT1 ON
I N TERN AT1 ON A L
I SO R ECO M M EN DATI O N
R 798
CHEMICAL ANALYSIS OF ALUMINIUM AND ITS ALLOYS
GRAVIMETRIC DETERMINATION OF ZINC IN ALUMINIUM ALLOYS
(Zinc content between 0.50 and 6.5
1st EDITION
July 1968
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The copyright of IS0 Recommendations and IS0 Standards
belongs to IS0 Member Bodies. Reproduction of these
documents, in any country, may be authorized therefore only
by the national standards organization of that country, being
a member of ISO.
For each individual country the only valid standard is the national standard of that country.
Printed in Switzerland
Also issued in French and Russian. Copies to be obtained through the national standards organizations.
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BRIEF HISTORY
The IS0 Recommendation R 798, Chemical analysis of aluminium and its alloys - Gravimetric
determination of zinc in aluminium alloys (Zinc content between 0.50 and 6.5 'Io), was drawn up by
Technical Committee ISO/TC 79, Light metals and their alloys, the Secretariat of which is held by the
Association Française de Normalisation (AFNOR).
Work on this question by the Technical Committee began in 1956 and led, in 1963, to the
adoption of a Draft IS0 Recommendation.
In June 1966, this Draft IS0 Recommendation (NO. 971) was circulated to all the IS0 Member
Bodies for enquiry. It was approved, subject to a few modifications of an editorial nature, by the
following Member Bodies :
Argentina India Sweden
Austria
Ireland Switzerland
Belgium
Israel Turkey
Brazil Italy U.A.R.
Bulgaria Japan United Kingdom
Canada Netherlands U.S.A.
Chile
Norway U.S.S.R.
Czechoslovakia
Poland Yugoslavia
Germany South Africa,
Hungary
Rep. of
Korea, Rep. of
Spain
One Member Body opposed the approval of the Draft :
France
The Draft IS0 Recommendation was then submitted by correspondence to the IS0 Council,
which decided, in July 1968, to accept it as an IS0 RECOMMENDATION.
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ISO/R 798-1968 (I
IS0 Recommendation R 798 July 1968
CHEMICAL ANALYSIS OF ALUMINIUM AND ITS ALLOYS
GRAVIMETRIC DETERMINATION OF ZINC IN ALUMINIUM ALLOYS
(Zinc content between 0.50 and 6.5 'l,)
1. SCOPE
1.1 This IS0 Recommendation describes a gravimetric method for the determination of zinc in
aluminium alloys.
1.2 The method is applicable to the determination of zinc content between 0.50 and 6.5
1.3 The method does not apply completely to the special case of alloys with high nickel contents,
for which it should be modified as described in the Annex.
2. PRINCIPLE
2.1 Attack with oxidizing acid.
2.2 Filtration and volatilization of the silica after dehydration in a sulphuric medium. Recovery of
any zinc retained in the residue.
2.3 Precipitation of Group II metals by treatment with hydrogen sulphide in an acid medium.
2.4 Precipitation of zinc with hydrogen sulphide in a formic buffer medium after complexing the
aluminium with tartaric acid.
2.5 Dissolution of the zinc sulphide with dilute hydrochloric acid. Removal of any traces of heavy
metals by means of sodium hydrosulphide.
2.6 Oxidation and complexing of the iron with phosphoric acid, followed by precipitation of the zinc
as zinc mercuric thiocyanate.
2.7 Filtration, washing, drying and weighing of the precipitate.
3. REAGENTS
3.1 Mixed acids :
Sulphuric acid, d = 1.84 (approximately 35.6 N) 250 ml
made up to 'Ooo ml
Hydrochloric acid, d = 1.19 (approximately 12 N)
200 ml
200 ml with water
Nitric acid, d = 1.40 (approximately 15 N)
1
Carefully add the sulphuric acid to about 300 ml of water, while cooling. Add the hydrochloric
acid, then the nitric acid, and make up the volume to 1000 ml with water.
3.2 Sulphuric acid, d = 1.26 (approximately 9 N).
Carefully add 250 ml of sulphuric acid, d = 1.84, to water, cool and make up the volume to
1000 ml,
3.3
Sulphuric acid, d = 1 .O1 (approximately 0.35 N).
Carefully add 10 ml of sulphuric acid, d = 1.84, to water, cool and make up the volume to
1 O00 ml.
3.4 Sulphuric acid, d = 1.48 (approximately 17.5 N).
Carefully add 50 ml of sulphuric acid, d = 1.84, to water, cool and make up the volume to
1 O0 ml.
3.5
Hydrofluoric acid, 40 d = approximately 1.15.
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ISO/R 798-1968 (E
3.6 Nitric acid, d = 1.23 (approximately 7.4 N).
Take 50 ml of nitric acid, d = 1.40, and make up the volume to 1 O0 ml with water.
3.7 Hydrogen sulphide wash solution.
Saturate cold sulphuric acid (3.3) with hydrogen sulphide.
Prepare just before use.
3.8 Tartaric acid solution, 300 g per litre.
Dissolve 300 g of tartaric acid (C,H,O,) in water and make up the volume to 1000 ml.
3.9 Ammonia solution, d = 0.95 (approximately 7 N).
Take 50 ml of ammonia solution, d = 0.90, and make up the volume to 100 ml with water.
3.10 Formic mixture
Formic acid, d = 1.20 (approximately 24 N) 2oo ml
made up to 1000 ml
Ammonium sulphate
25og } with water
Ammonia solution, d = 0.90 (approximately 14.4 N) 30 ml
Dissolve 250 g of ammonium sulphate [(NH,), SO,] in about 600 ml of water, add 200 ml of
formic acid (HCOOH), then 30 ml of ammonia solution, and make up the volume to 1000 ml
with water.
3.11 Gelatine solution, 0.20 g per litre.
Dissolve 0.020 g of pure gelatine (with ash content of less than 0.1
in about 80 ml of warm
water while heating gently. Cool and make up the volume to 100 ml.
Renew weekly.
3.12 Formic wash solution.
Dilute 25 ml of formic mixture (3.10) to 1000 ml with water and saturate the cold solution
with hydrogen sulphide.
3.13 Hydrochloric acid, d = 1.05 (approximately 3 N).
Take 25 ml of hydrochloric acid, d = 1.19, and make up the volume to 100 ml with water.
3.14 Nitric acid, d = 1.40 (approximately 15 N).
3.15 Sodium hydrosulphide solution.
Dissolve 0.25 g of sodium hydroxide (NaOH) in 100 ml of water and saturate with hydrogen
sulphide at room temperature.
3.16 Hydrogen peroxide, 6
(approximately 20 volumes).
Add 5 ml of hydrogen peroxide, 36
d = 1.1 2,to 25 ml of water.
3.17 Phosphoric acid, d = 1.35 (approximately 22.5 N).
Take 50 mi of phosphoric acid, d = 1.71 (approximately 45 N), and make up the volume to
100 ml with water.
3.18 Mercuric thiocyanate reagent.
Dissolve 27 g of mercuric chloride (HgCl,) in about 800 ml of water, while heating gently. After
cooling, add 39 g of potassium thiocyanate (KSCN) [or, alternatively, 33 g of sodium thio-
cyanate (NaSCN)]and make up the volume to 1000 ml with water.
NOTE. - If neither potassium thiocyanate nor sodium thiocyanate is available, proceed as follows :
Dissolve 31 g of ammonium thiocyanate (NH,SCN) and 20 g of sodium hydroxide in 200 ml of water in a
500 ml conical flask. Boil to the disappearance of ammoniacal vapours,,make up the volume to 200 ml with
water and neutralize (against litmus paper) with dilute sulphuric acid. Dissolve 27 g of mercuric chloride
(HgCl,) in 300 ml of lukewarm water. Mix the two solutions and make up the volume to 1000 ml with water.
3.19 Mercuric thiocyanate wash solution.
Take 10 ml of mercuric thiocyanate reagent (3.18) and make up the volume to 500 ml with
water.
3.20 Lead acetate paper.
3.21 Methyl red solution.
Dissolve 0.10 g of methyl red in 100 ml of ethanol, 95
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ISO/R 798-1968 (E)
4. APPARATUS
Ordinary laboratory equipment
All volumetric apparatus should comply with national standards.
5. SAMPLING
Laboratory sample
5.1
See the appropriate national standard on sampling.
5.2 Test sample
Chips not more than 1 mm thick should be obtained from the laboratory sample by drilling or
milling.
6. PROCEDURE
Test portion
6.1
Mass of test portion : 2 * 0.001 g.
6.2 Blank test
Carry out a blank test in parallel with the determination, following the same procedure and
using the same quantities of all reagents.
6.3 Determination
6.3.1 Attackof thetest portion and preparation of the main solution. Place the test portion in a
beaker of suitable capacity (400 mi), provided with a watch-glass, and carefully add 70 ml of
mixed acids (3.1) in small portions, while cooling.When the reaction subsides, heat moderate-
ly to complete the reaction. Place a glass triangle between the watch-glass and the beaker,
then increase the heating and evaporate to copious white fumes which should bemaintained
for about 15 to 20 minutes.
Allow to cool sufficiently, then take up with 20 ml of sulphuric acid (3.2) and 100 to 150 ml
of hot water. He
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