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Ref. No. : ISO/R 808-1968 (E)
J
IS0
I N TER N AT I O N A L ORGAN IZATl O N FOR STAND AR D IZATl O N
IS0 RECOMMEN
DATION
R 808
CHEMICAL ANALYSIS OF ALUMINIUM AND ALUMINIUM ALLOYS
PHOTOMETRIC DETERMINATION OF SILICON
(Silicon content between 0.02 and 0.4 'l,)
1st EDITION
August 1968
COPYRIGHT RESERVED
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 808, Chemical analysis of aluminium and aluminium alloys -
Photometric determination of silicon (Silicon content between 0.02 and 0.4 'la), was drawn up by
Technical Committee ISO/TC 79, Light metals und 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 1957 and led, in 1965, to the
adoption of a Draft IS0 Recommendation.
L
In December 1966, this Draft IS0 Recommendation (No. 1129) 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 South Africa,
Austria Ireland Rep. of
Belgium Israel Spain
Sweden
Bulgaria Italy
Switzerland
Canada Japan
Chile Korea, Rep. of Turkey
Czechoslovakia Netherlands United Kingdom
France New Zealand U.S.A.
Germany Norway U.S.S.R.
Hungary Poland Yugoslavia
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 August 1968, to accept it as an IS0 RECOMMENDATION.
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ISO/R 808-1968 (E
IS0 Recommendation R 808 August 1968
CHEMICAL ANALYSIS OF ALUMINIUM AND ALUMINIUM ALLOYS
PHOTOMETRIC DETERMINATION OF SILICON
(Silicon content between 0.02 and 0.4 'L)
1. SCOPE
This 1SO Recommendation describes a photometric method for the determination of silicon in
aluminium and in aluminium alloys.
The method is applicable to the determination of silicon content between 0.02 and 0.4 O/'.
The method does not apply to the special cases of aluminium alloys containing tin or bismuth. In
this IS0 Recommendation these special cases are not treated.
2. PRINCIPLE
2.1 Attack of the sample with sodium hydroxide and oxidation with hydrogen peroxide.
2.2 Acidification with nitric and hydrochloric acids.
2.3 Formation of the yellow silico-molybdic complex (at a pH of approximately 0.9) on an aliquot
of the principal solution.
2.4 lncrease of the acidity with sulphuric acid and reduction to the blue silico-molybdic complex
(using a reducing solution based on l-amino-2-naphthol-4-sulphonic acid or, alternatively,
ascorbic acid solution).
2.5 Photometric measurement at a wavelength of about 810 nm.
3. REAGENTS
For the preparation of solutions and during analysis use doubly distilled water.
3.1 Hydrogen peroxide, 6 'k (approximately 20 volumes).
17 ml of hydrogen peroxide 36 (d = 1.12) with water and make up the volume to
Dilute
100 ml.
3.2 Sulphurous acid solution
Pass a current of sulphur dioxide (SOz) in water until saturation point is reached.
3.3 Basic solution for plotting the calibration graph
Into a plastic vessel (e.g. polythene) of suitable capacity (e.g. 400 ml), introduce 40.0 ml of
sodium hydroxide solution (3.7), add approximately 200 ml of water, and acidify by means of
54.0 ml of nitric acid (3.8) and 40.0 ml of hydrochloric acid (3.9). After cooling, transfer the
solution to a 500 ml volumetric flask and make up to volume with water.
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ISOlR 808-1968 (E
3.4 Molybdate solution
Either :
3.4.1 Sodium molybdate solution, 145 g per litre.
Dissolve 145 g of sodium molybdate (NazMo04.2Hz0) in approximately 700 ml of warm
water. Cool, filter if necessary through a medium texture filter, collect the filtrate in a
1000 ml volumetric flask and wash with cold water. Make up to volume with water and
transfer to a polythene vessel. Check the pH of this solution; if it is higher than 8, discard
the solution and prepare a fresh one using purer sodium molybdate.
Or :
3.4.2 Ammonium molybdate solution, 106 g per litre, stabilized at pH 7.2.
In a vessel of suitable capacity (e.g. 600 ml glass beaker), dissolve 53 g of ammonium molyb-
date [(",),Mo, Oz, .4Hz O] in approximately 250 ml of water. Add approximately 30 ml
of sodium hydroxide solution (3.7), mix, cool to room temperature, if necessary, and make
up the volume to approximately 350 ml with water. Add, dropwise and while stirring,
sufficient sodium hydroxide solution (3.7) to bring the pH to about 7.2, using a pH meter.
Filter through a sintered giass filter, collect the filtrate in a 500 ml volumetric flask and
wash with water. Make up to volume with water, mix and transfer to a polythene vessel.
3.5 Tartaric acid solution, 200 g per litre.
Dissolve 200 g of tartaric acid (C4H606) in water and make up the volume to 1000 ml.
3.6 Reducing solution
Either
3.6.1 Solution of I -amino-2-naphthol-Csulphonic acid
Dissolve 7 g of anhydrous sodium sulphite (NaZSO3) in 100 ml of water, then add 1.5 g of
i-amino-2-naphthol4sulphonic acid and stir the solution until dissolution is complete.
Dissolve separately 90 g of sodium metabisulphite (NazSz05) in approximately 800 ml of
water. Mix the two solutions, then filter through a medium texture filter, collecting the
filtrate and the washings in a 1000 ml volumetric flask. Make up to volume with water, mix
and transfer the solution to a flask of amber glass. Use a solution less than one month old.
Or :
3.6.2 Ascorbic acid solution, 20 g per litre.
ml. Use a freshly pre-
Dissolve 2 g of ascorbic acid in water and make up the volume to 100
pared solution.
Sodium hydroxide solution, 8 N
3.7
Dissolve 320 g of sodium hydroxide with water in a container not attacked by sodium hydrox-
ide (e.g. a nickel basin).
NOTE. - Make sure that the sodium hydroxide contains as little silica as possible. For this reason the use of
sodium hydroxide supplied in plastic containers is recommended.
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ISO/R 808-1968 (E
Cool and transfer to a polythene bottle provided with a mark at 1000 mi; make up to volume
with water and mix. Check the concentration of the solution by titrating it with nitric acid
solution 8 N (3.8), using methyl red solution (3.14) as indicator.
If necessary, adjust the concentration of the sodium hydroxide solution so that 10.0 mi of
this solution corresponds to 10.0 * 0.1 mi of nitric acid (3.8).
3.8 Nitric acid, 8 N
Dilute 540 mi of nitric acid, d = 1.40 (approximately 15 N), to 1000 ml with water. Check the
strength of the solution by titrating 10.600 g of anhydrous sodium carbonate (Naz CO,) prev-
iously dried in a hot air oven (at approximately 110 OC) and using methyl red solution (3.14) as
indicator.
The theoretical quantity of 8 N nitric acid for the above quantity of anhydrous sodium carbon-
ate is 25 ml. If necessary, adjust the concentration of the nitric acid solution by adding water or
acid so that the solution corresponds to the strength of 8 N,
3.9 Hydrochloric acid, 4.4 N
Dilute 352 ml of hydrochloric acid, d = 1.19 (approximately 12.5 N), to 1000 ml with water.
Check the strength by titrating it with sodium hydroxide solution (3.7) and, if necessary, adjust
the concentration so that 20.0 mi of the hydrochloric acid solution corresponds to 1 1 .O it O. 1 ml
of sodium hydroxide solution (3.7).
3.10 Sulphuric acid, 8 N
Carefully add 225 ml of sulphuric acid, d = 1.84 (approximately 35.6 N), to water, cool and
make up the volume to 1000 mi. Check the strength by titrating it with sodium hydroxide
solution (3.7) and if necessary adjust the concentration so that 10.0 mi of the sulphuric acid
solution corresponds to 10.0 it 0.1 mi of the sodium hydroxide solution (3.7).
3.1 1 Standard silicon solution, O. 1 g per litre (1 mi contains 0.1 mg of silicon).
Either :
3.11.1 In alarge platinum crucible with a lid, fuse 0.2140 g of pure silica (Sioz), previously calcined
at 1000 OC to constant mass, with 2 g of a mixture of equal parts of sodium carbonate
(Naz CO3) and potassium carbonate (Kz CO3).
NOTE. - Avoid contact between the platinum crucible and refractory materials (for example use triangles
or supports of platinum or nickelchromium).
Continue the fusion until a clear melt is obtained. Cool, dissolve the fused mass with warm
water, transfer the solution to a 1000 ml volumetric flask, make up to volume with water
and mix.
Or :
3.11.21n a plastic beaker of suitable capacity (e.g. approximately 500 mi) place 0.6702 g of sodium
fluoroslicate (Naz %Fa) and add approximately 400 ml of warm water. Cover with a plastic
lid and heat on a water bath until the salt appears dissolved. Continue heating for another
30 minutes, stimng occasionally with a polythene rod. Then cool to room temperature,
transfer to a 1 O00 mi volumetric flask, make up to volume with water and mix.
Immediately transfer the solution (3.1 1.1 or 3.1 1.2) to a polythene bottle.
3.12 Standard silicon solution, 0.01 g per litre (1 mi contains 0.01 mg of silicon).
Take 50.0 ml of standard silicon solution (3.1 1), place this in a 500 mi volumetric flask and
make up to volume with water. Prepare just before use.
Transfer the solution to a polythene vessel.
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