ISO 15355 pdf download.Steel and iron — Determination of chromium content — Indirect titration method
1 Scope
This International Standard specifies a potentiometric titration method for the determination of chromium content in steel and iron. The method is applicable to chromium contents between 1 % (m/m) and 35 % (m/m). Vanadium contents in steel and iron should be less than 1 % (m/m) for chromium contents higher than 1 0 % (m/m) and less than 0,2 % ( m / m ) for chromium contents less than 1 0 % (m/m).
2 Normative references
The following normative documents contain provisions which, through reference in this text, constitute provisions of this International Standard. For dated references, subsequent amendments to, or revisions of, any of these publications do not apply. However, parties to agreements based on this International Standard are encouraged to investigate the possibility of applying the most recent editions of the normative documents indicated below. For undated references, the latest edition of the normative document referred to applies. Members of ISO and IEC maintain registers of currently valid International Standards. ISO 385-1 :1 984, Laboratory glassware — Burettes –– Part 1 : General requirements . ISO 648:1 977, Laboratory glassware — One-mark pipettes . ISO 1 042:1 998, Laboratory glassware — One-mark volumetric flasks . ISO 3696:1 987, Water for analytical laboratory use — Specification and test methods . ISO 4942:1 988, Steel and iron — Determination of vanadium content — N-BPHA spectrophotometric method . ISO 4947:1 986, Steel and cast iron — Determination of vanadium content — Potentiometric titration method . ISO 5725-1 :1 994, Accuracy (trueness and precision) of measurement methods and results — Part 1 : General principles and definitions . ISO 5725-2:1 994, Accuracy (trueness and precision) of measurement methods and results — Part 2: Basic method for the determination of repeatability and reproducibility of a standard measurement method . ISO 5725-3:1 994, Accuracy (trueness and precision) of measurement methods and results
3 Principle
Fusion of the sample with sodium peroxide followed by acidification with sulfuric acid. Oxidization of chromium (III) to dichromate with peroxodisulfate using silver as a catalyst. Reduction of the dichromate with an excess of a solid iron (II) salt and potentiometric back titration of the excess with a dichromate solution. Any interference from vanadium is corrected mathematically.
4.10 Ferroammonium disulfate, (NH 4 ) 2 Fe(SO 4 ) 2 6H 2 O The reduction grade of the salt shall be determined for each batch that is to be used. Thoroughly grind a portion of 300 g to 400 g of the salt so that no large crystals are left. Store the salt in a jar that can be tightly closed. Transfer, to five 400 ml glass beakers, about 300 mg (to the nearest 0,01 mg) of the potassium dichromate (4.8) and dissolve in 200 ml of water and 35 ml of sulfuric acid (4.2). Add to each beaker about 2 700 mg (to the nearest 0,01 mg) of the ground iron salt. Stir with a glass rod to dissolve all crystals. Titrate the solutions with the dichromate solution (4.9).
5 Apparatus
All volumetric glassware shall be class A, in accordance with ISO 648 or ISO 1 042 as appropriate. Ordinary laboratory apparatus, and 5.1 Potentiometric titration device , consisting of 5.1.1 Redox electrode , combination Pt-Ag/AgCl 5.1.2 Titration assembly , consisting of a 400 ml beaker, a 1 0 ml burette complying with the requirements of ISO 385-1 , class A and a magnetic stirrer 5.1.3 High impedance electronic voltmeter. Normally a pH-meter can be used as a voltmeter but commercial automatic titrators or potentiographs have an advantage over manual systems in that the titration curve is plotted and the end-point can be evaluated by interpolation of the curve rather than by calculation from the first or second derivative. See clause 9. 5.2 Muffle furnace, able to provide a constant temperature of 650 C and an argon atmosphere 5.3 Zirconium crucible The crucible shall be clean and not worn in order to avoid zirconium interference. 5.4 Zirconium lid The lid shall be clean and not worn in order to avoid zirconium interference. 5.5 Glass granules, for anti-bumping