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UDC 669.14 Ref. No. : ISO/R 437 - 1965 (E)
IS0
FOR STA N DA RDl ZATl O N
1 N TERN AT ION A L ORGAN IZATl O N
IS0 RECOMMENDATION
R 437
CHEMICAL ANALYSIS OF STEELS
DETERMINATION OF TOTAL CARBON
(GRAVIMETRIC METHOD AFTER COMBUSTION
IN A STREAM OF OXYGEN)
1st EDITION
May 1965
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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 437, Chemical Analysis of Steels-Determination of Total
Carbon (Gravimetric Method after Combustion in a Staeam of Oxygen), was drawn up by
Technical Committee ISO/TC 17, Steel, the Secretariat of which is held by the British Standards
Institution (BSI).
Work on this question by the Technical Committee began in 1957, and led in 1962, to the
adoption of a Draft IS0 Recommendation.
In February 1963, this Draft IS0 Recommendation (No. 528) 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 :
Australia India Romania
Austria Iran Spain
Sweden
Canada Italy
Switzerland
Chile Japan
Czechoslovakia Netherlands Turkey
France Norway U.A.R.
United Kingdom
Denmark Poland
U.S.S.R.
Finland Portugal
Yugoslavia
Hungary Republic of South Africa
Three Member Bodies opposed the approval of the Draft:
Belgium
Germany
U.S.A.
The Draft IS0 Recommendation was then submitted by correspondence to the IS0
Council, which decided, in May 1965, to accept it as an IS0 RECOMMENDATION.
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IÇO/R 437 - 1965 (E)
IS0 Recommendation R 437 May 1965
CHEMICAL ANALYSIS OF STEELS
DETERMINATION OF TOTAL CARBON
(GRAVIMETRIC METHOD AFTER COMBUSTION
IN A STREAM OF OXYGEN)
1. SCOPE
1.1 The purpose of this IS0 Recommendation is to describe the gravimetric method of deter-
mining total carbon in steel after combustion of the sample in a stream of oxygen.
1.2 The method is applicable to carbon contents of not less than 0.10 per cent.
2. PRINCIPLE OF THE METHOD
2.1
The sample is heated to combustion at high temperature (1200 to 1350 OC) in a stream of
pure oxygen and the carbon is converted to carbon dioxide. If it is necessary a flux may be
added.
2.2 The carbon dioxide, carried by oxygen, is passed through and absorbed by soda asbestos in
a tared bulb, the increase in mass of which is proportional to the quantity of carbon dioxide
formed.
f
c + O, = CO,
2 NaOH + CO, = Na,CO, + H,O
3. REAGENTS
3.1 Ogjgen, at least 99 per cent purity.
3.2 Anhydrous magnesium perchlorate, Mg (ClO,),.*
3.3 Fluxes: lead dioxide, analytical reagent grade; copper oxide, tin, pure iron, etc.
3.4 Manganese dioxide or silver orthovanadate, prepared as follows :
3.4.1 Manganese dioxide. When a suitable chemically active grade is not available, it may be
prepared as follows :
To prepare about 50 g of manganese dioxide, dissolve in a 4-litre beaker 200 g of man-
ganous sulphate MnSO,, 4 H,O in 2.5 litres of demineralized water. After making this
solution clearly ammoniacal, add 1 litre of ammonium persulphate solution (225 g per
litre) freshly prepared, bring the whole to boiling point. Continue boiling for 10 min
and add ammonia solution as frequently as is necessary to maintain the solution ammo-
niacal. Allow the precipitate to settle.
If the supernatant liquid is not clear, or if the precipitate does not settle quickly, add
50 to 100 ml of ammonium persulphate solution and boil again for 10 min keeping the
solution constantly ammoniacal.
When precipitation appears to be complete, allow the manganese dioxide to settle
completely, carefully siphon off the supernatant liquid and wash the precipitate by
decantation with 3 or 4 litres of warm water in portions of 500 to 600 ml. Stir the
manganese dioxide well in the water and allow to settle after each washing and before
decantation. Finally wash twice in the same way with very dilute sulphuric acid.
In the meantime, prepare a 15 cm diameter funnel fitted with a 5 cm filter disc filled
with a thin layer of purified asbestos pulp (in place of the latter, it is also permitted
to use a porcelain funnel of the Buchner type).
* Contact with organic substances should be avoided because of the potential hazard of an explosion.
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ISO/R 437 - 1965 (E)
After the last washing, transfer the manganese dioxide onto the filter and wash with
warm water until it is freed from ion sulphates. Then place this on a porcelain dish and
dry it in an oven at 105 C.
Grind the manganese dioxide in a mortar so that it will pass through a sieve with aper-
tures of 0.8 mm and dry again completely at 105 C.
3.4.2 Silver orthovanadate
Reaction: Na,VO, + 3 AgNO, -f Ag,VO, + 3 NaNO,
Dissolve 60 g of sodium orthovanadate in 400 ml of demineralized water. Boil for 15
min. Also dissolve 170 g of silver nitrate in 200 ml of demineralized water.
Add the silver nitrate solution dropwise to the warm solution of sodium orthovanadate.
An abundant yellow orange precipitate should form.
Filter on a Buchner funnel and wash with water until free from positive silver ions
(Ag +), verify with negative chloride ions (Cl-).
Dry the precipitate overnight at about 80 C. It may darken slightly.
Grind and store protected from light.
NOIE. - Ammonium orthovanadate is not sufficiently soluble for it to be specified.
Soda asbestos, asbestos impregnated with sodium hydroxide, in granules of about 2 mm
3.5
diameter. Avoid contact with air.
4. APPARATUS
The apparatus consists of a source of oxygen and the unit for purifying it, the furnace with the
combustion tube, the purification train and the carbon dioxide absorptio
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