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IS0
I NT ERN AT1 O N A L ORGAN IZ AT1 O N FOR S TA N DA R D IZATl ON
IS0 RECOMMENDATION
R 797
CHEMICAL ANALYSIS OF ALUMINIUM AND ITS ALLOYS
GRAVIMETRIC DETERMINATION OF SILICON
(Silicon content greater than or equal to 0.30
1st EDITION
July 1968
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belongs to IS0 Member Bodies. Reproduction of these
documents, in any country, may be authorized therefore oniy
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 797, Chemical analysis of aluminium and its alloys-Gravimetric
determination of silicon (Silicon content greater than or equal to 0.30 yo), 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. 970) 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 :
Korea, Rep. of Spain
Argentina
India Sweden
Austria
Ireland Switzerland
Belgium
Brazil Israel Turkey
Bulgaria Italy U.A.R.
Japan United Kingdom
Canada
Netherlands U.S.A.
Chile
Czechoslovakia Norway U.S.S.R.
France Poland Yugoslavia
Germany South Africa,
Hungary Rep. of
No Member Body opposed the approval of the Draft.
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 797-1968 (I
IS0 Recommendation R 797 July 1968
CHEMIÇAL ANALYSIS OF ALUMINIUM AND ITS ALLOYS
GRAVIMETRIC DETERMINATION OF SILICON
(Silicon content greater than or equal to 0.30
1. SCOPE
1.1 This IS0 Recommendation describes a gravimetric method for the determination of silicon in
aluminium and its alloys.
1.2 The method is applicable to silicon content greater than or equal to 0.30 'Io.
1.3 The method does not apply completely to the following special cases for which it should be
modified as described in Annex A and Annex B :
aluminium-silicon alloys (silicon content greater than 3 O/') and aluminium-magnesium
(a)
alloys (see Annex A);
aluminium alloys containing tin or antimony (see Annex B).
(b)
2. PRiNCIPLE
2.1 Attack with sodium hydroxide.
2.2
Acidification with perchloric acid; dehydration of the silica.
2.3 Filtration, drying, calcination and weighing of the silica.
2.4 Volatilization of the silica, by means of hydrofluoric acid, and weighing of the residue.
2.5 Determination of the silica by difference in mass.
3. REAGENTS
3.1 Sodium hydroxide pellets. (Store in a plastics container).
3.2 Hydrobromic acid, 48 'l0,d = approximately 1.49.
3.3 Hydrochloric acid, d = 1 .O1 (approximately 0.62 N).
Take 5 mi of hydrochloric acid, d = 1.19 (approximately 12 N), and make up the volume to
100 mi with water.
3.4 Hydrofluoric acid, 40 '/,,d = approximately 1.1 5.
3.5 Nitnc acid, d = 1.40 (approximately 15 N).
3.6 Perchloric acid, d = 1.67 (approximately 11.7 N). *
3.7 Perchloric acid, d = 1.22 (approximately 4 N).
Take 35 mi of perchloric acid, d = 1.67, and make up the volume to 100 ml with water.
3.8 Sulphuric acid, d = 1.48 (approximately 17.5 N).
Carefully add 50 mi of sulphuric acid, d = 1.84 (approximately 35.6 N), to water, cool and
make up the volume to 100 mi.
Perchloric acid, d = 1.54 (approximately 9 N), may also be used. (1000 ml of perchloric acid, d = 1.67, is
of perchloric acid, d = 1.54).
equivalent to 1270 ml
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ISO/R 797-1968 (E)
3.9 Bromine water. saturated solution.
3.10 Hydrogen peroxide, 6 (about 20 volumes).
Take 17 ml of hydrogen peroxide, 36 d = 1.12, and make up the volume to 100 ml with
water.
3.1 1 Sodium hydroxide solution, d = 1 .O5 (approximately 1.25 N).
Dissolve 50 g of sodium hydroxide (NaOH) in a little water and, after cooling, make up the
volume to 1000 ml. (Store in a plastics container).
4. APPARATUS
Ordinay laboratory equipment '
All volumetric apparatus should comply with national standards.
5. SAMPLING
Laboratory sample
5.1
See the appropriate national standard on sampling.
1
5.2 Test sample
Chips not more than 1 mm thick should be obtained from the laboratory sample by drilling or
milling.
6. PROCEDURE
6.1 Test portion
Weigh the test portion with an accuracy of k 0.001 g, in accordance with the quantities shown
in Table 1, below.
For the hypereutectic aluminium-silicon alloys, the masses of coarse and fine particles in the
test portion should be taken in the same proportion as in the test sample.
6.2 Blank test
Carry out a blank test in parallel with the determination, following the same procedure and
using the same quantities of ail reagents.
6.3 Determination
6.3.1 Attack of the test portion. In accordance with the assumed silicon content, take the size of
test portion shown in Table 1 and use the corresponding quantities of the reagents.
TABLE 1
Assumed silicon Mass of test sodium
content portion
h y droxid] ' [,,,::er nitric acid (3.5) acid
(3.6)
(3.1)
g g+ml ml ml+ ml
-
5 1st 30 5 110+ 60
0.30 to 1
2 8+ 15 5 60+ 30
over 1 to 3
1 6+ 10 * 5 45+ 20
over 3 to 7
over 7 0.5 to 1 IO+ 20 * 5 60+ 30
*
Alternatively, for the two-stage attack method, see Annex A and the following Note.
i
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ISO/R 797-1968 (E)
NOTE. - It is possible to use the normal single-stage attack method as described in the procedure, even for
the analysis of aluminium-silicon alloys (silicon content greater than 3 'A) and aluminium-magnesium
alloys.
Place the test portion in a nickel or silver basin of suitable capacity (e.g. about 250 ml and of
120 to 150 mm diameter) fitted with a nickel or silver lid, add the appropriate quantity of
sodium hydroxide (3.1) (see Table l), then carefully add, in small portions, the correspond-
ing volume of water.
When the attack is complete, rinse the cover and the wall of the basin with the smallest
possible quantity of hot water, place the covered basin on a hot-plate (or sand bath) and
evaporate the solution to a syrupy consistency, avoiding spattering.
After cooling, add dropwise 5 to 6 ml of hydrogen peroxide (3.10) and again evaporate to a
syrupy consistency. If necessary, repeat the treatment by hydrogen peroxide (3.1 O).
6.3.2 Dehydration of the silica. Add 100 ml of hot water, washing the wall of the basin, boil to
dissolve the salts, cool and transfer the contents of the basin into a vessel (e.g. a porcelain
basin) of suitable capacity containing nitric acid (3.5), perchloric acid (3.6) and water in the
quantities shown in Table 1 for the corresponding size of test portion.
Carefully wash the basin and the cover with hot water, then with a small quantity of
L
perchloric acid (3.7), about 10 ml in all, removing any particles adhering to the basin and to
the cover (using, for example, a glass rod fitted with a ribbed thimble of para rubber). Rinse
lastly with hot water and add the washings to the main solution.
Stir with a glass rod and, if the solution has a brown colour owing to the presence of
manganese dioxide, add a few drops of hydrogen peroxide (3.10). Cover the basin with a
watch-glass and evaporate to the release of copious white fumes of perchloric acid until the
solution begins to crystallize (duration of white perchloric acid fumes about 15 to 20
minutes). Allow to cool, then take up in hot water and make up the volume of the solution
to about 200 ml for a tèst portion of 0.5 to 1 g, 400 ml for a test portion of 2 g, and about
600 ml for a test portion of 5 g.
to bring the salts into complete solution, and
Stir carefully with a glass rod, heat in order
dissolve any manganese dioxide that may have separated by adding a few drops of hydrogen
peroxide (3.10).
6.3.3 Filtration and washing. Bring the particles of silica in
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