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IS0
IN TERN AT1 ON AL ORGANIZATION FOR STA N DA RDlZATl ON
IS0 RECOMMENDATION
R 671
CHEMICAL ANALYSIS OF STEEL AND CAST IRON
DETERMINATION OF SULPHUR
(METHOD AFTER COMBUSTION IN A CURRENT OF OXYGEN,
AND TITRATION WITH SODIUM BORATE)
1st EDITION
February 1968
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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 671, Chemical analysis of steel and cast iron - Determination of
sulphur (Method after combustion in a.current of oxygen, and titration with sodium borate), 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 1958 and led. in 1965, to the
IS0 Recommendation.
adoption of a Draft
in February 1966, this Draft IS0 Recommendation (No. 915) was circulated to all IS0 Member
Bodies for enquiry. It was approved, subject to a few modifications of an editorial nature, by the
following Member Bodies :
Argentina
Hungary Romania
Australia India
South Africa,
Austria Israel Rep. of
Belgium Italy Spain
Brazil Japan Sweden
Canada Korea, Rep. of Switzerland
Chile Netherlands Turkey
Czechoslovakia New Zealand U.A.R.
Denmark Norway United Kingdom
Germany Poland Yugoslavia
Three Member Bodies opposed the approval of the Draft :
France
Portugal
U.S.A.
The Draft IS0 Recommendation was then submitted by correspondence to the IS0 Council.
which decided, in February 1968, to accept it as an IS0 RECOMMENDATION.
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ISO/R 671 -1968 (E
IS0 Recommendation R 671 February 1968
CHEMICAL ANALYSIS OF STEEL AND CAST IRON
DETERMINATION OF SULPHUR
(METHOD AFTER COMBUSTION IN A CURRENT OF OXYGEN,
AND TITRATION WITH SODIUM BORATE)
1. SCOPE
This IS0 Kecommendation describes methods of combustion and titration for the determination of
sulphur in steel and cast iron.
2. PRINCIPLE OF THE METHOD
2. I Combustion
Metal chips are burnt in a small refractory boat introduced into a tube heated by an electric
furnace and through which is passed a current of oxygen of known rate of flow. The tempera-
ture of the metal can be attained either by the temperature of the furnace itself (general case)
or by the addition of a metal flux (particular case of refractory steels).
2.2 Titration
The gases resulting from combustion, freed from oxide dust. are absorbed by a solution of
potassium sulphate and hydrogen peroxide and then titrated with standard sodium borate
solution (see Note 8.h).
3. REAGENTS
3.1 Oxygen. Minimum purity 09 free from sulphur-bearing compounds
3.2 Soda asbestos (particle size : approximately 2 mm) and magnesium perchlorate (particle size :
approximately 2 mm).
3.3 Absorbent solution. Dissolve 5 g of potassium sulphate in 300 ml of boiled and cooled distilled
water. Add 100 mi of hydrogen peroxide 100 volumes (30 and dilute to 2500 ml with
boiled and cooled distilled water.
3.4 Standard sodium borate solution. Weigh 2.3839 g of sodium borate, Na, B,O, .tOH,O, analy-
tical reagent quality, dissolve in boiled and cooled distilled water and make up the volume to
2000 mi with the same water.
1 ml = 0.010 of sulphur for 1 g of test sample.
3.5 Mixed indicator (see Note 8.1). Dissolve 0.1 g of methylene blue and 0.3 g of methyl red (salt
form) in water and dilute to 500 ml with water.
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ISOlR 671 -1968 (E
4. APPARATUS
Dimensions in millimetres
U
FIG. 1 - Example of apparatus for the determination of sulphur.
(Method after combustion in a current of oxygen)
A. Source ofoxygen (3.1) fitted with a sensitive regulating valve and a pressure gauge.
B. Purifying und dtying column containing soda asbestos and magnesium perchlorate (3.2).
Flow meter capable of measuring a current of oxygen of 0.2 to 3 litres per minute.
C.
D. Electric furnace capable of maintaining the combustion tube (E) at 1430 "C in continuous
operation.
E. Combustion tube in refractory material capable of ensuring continuous operation at 1450 OC.
having a wide part of inside diameter 27 mm and length 450 mm, and a narrow part of inside
diameter 3 mm and length 250 mm (see Notes 8.2 rind 8.3).
F. Oxygen inlet tap.
G. Oxygen inlet device with a window permitting visual observation of the progress of combustion
(see Fig. 2 as an example).
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ISO/R 671 -1968 I
Dimen sions in millimetres
Water chamber
\ Water outlet
Knurled section to _1 IIu 0;;~gen iniet itji wati0in/et iIJ1
facilitate tightening
@ and @ = Pressure-tight rubber joints
@ = Toroidal joint
= Coloured glass mounted in epoxy resin
@
@ = Combustion tube
13G. 2 - Water-cooled tube closure
Phtinumlplatinum-rhodium thermocouple in which the hot junction is placed near the external
H.
surface of the tube close to the boat and cartridge assembly. The relationship between the inner
temperature of the tube (E) and the indications of the pyrometer should be established and
checked periodically.
I. Boat oj refractory material with a wide flat base capable of withstanding two heatings at
1420 "C (length 80 to 100 mm, height 8 to 9 mm, width 15 to 16 mm) (see Fig. 3).
06 Dimensions in millimetres
'-
i'
BLat Cartridge
FIG. 3 - Boat and cartridge
J. Refractory filter-cartridge (inside diameter 14 mm, outside diameter 16 mm, length 50mm)
(silica content 12 to 15 the remainder being alumina). The porosity of the cartridge is
defined by the flow of gas through the whole surface at a given pressure : 4 to 5 litres of gas p
...