EN 24937-1990 pdf download.Steel and iron-Determination of chromium content Potentiometric or visual method.
5 Apparatus
Ordinary laboratory apparatus (see the note) and
5.1 Potentiornetric titration device, which permits a difference in potential to he measured with platinum-saturated calomel electrodes.
NOTE All volumetric glassware shall be clasa A. in accordance with ISO 385-1. ISO 648 or ISO 1042 as appropriate.
6 Sampling
Carry out sampling in accordance with ISO 377 or the appropriate national standards for iron.
7 Procedure
WARNING: Perchioric acid vapour may cause explosions in the presence of ammonia, nitrous fumes or organic material in general.
7.1 Test portion
According to the presumed chromium content, weigh, to the nearest 0,000 1 g, the following mass (rn) of the test portion:
a) for chromium contents between 0.25 and 2 % (rn/rn), rn approximately 2 g;
b) for chromium contents between 2 and 10 % (rn/rn), rn approximately I g;
c) for chromium contents between 10 and 25 % (rn/rn), rn approximately 0,5 g;
d) for chromium contents between 25 and 35 % (rn/rn), rn approximately 0.25 g.
7.2 Blank test
Carry out a blank test in parallel with the determination, by the same procedure, using the same reagents, as in the determination, but omitting the test portion.
7.3 Determination
7.3.1 Preparation of the test solution
7.3.1.1 Unalloyed steel and iron Place the test portion (7.1) in a 600 ml beaker, add 60 ml of sulfuric acid (4.9) and 10 ml of orthophosphoric acid (4.4), and heat to dissolve, then oxidize with 15 ml of nitric acid (4.5). Heat until dense white fumes are given off. cool and then add 100 ml of water.
To accelerate the dissolution of a test portion which has a high silicon content, a few drops of hydrofluoric acid (4.3) may be added (see note 1).
7.3.1.2 Chromium and/or nickel alloyed steel and iron
Place the test portion (7.1) in a 600 ml beaker, add 25 ml of hydrochloric acid (4.6) and heat to dissolve, then oxidize with 15 ml of nitric acid (4.5). If dissolution proves to be particularly difficult. add 1 to 2 ml of hydrofluoric acid (4.3). Then add 20 ml of sulfuric acid (4.8) and 10 ml of orthophosphoric acid (4.4), and heat until dense white fumes appear.
After cooling, add a further 15 ml of nitric acid (4.5) to the fuming solution, if necessary making further additions, until the carbides have completely decomposed. Continue fuming to remove completely oxides of nitrogen then cool and add 100 ml of water (see note 1).
7.3.1.3 Steel containing tungsten Place the test portion (7.1) in a 600 ml beaker, add 25 ml of hydrochloric acid (4.6) then 20 ml of sulfuric acid (4.8) and 10 ml of orthophosphoric acid (4.4) and heat until effervescence has ceased. If dissolution proves to he particularly difficult add I to 2 ml of hydrofluoric acid (4.3). Oxidize with 15 ml of nitric acid (4.5) then heat until dense white fumes appear.
After cooling, add a further 15 ml of nitric acid (4.5) to the fuming solution, if necessary making further additions, until the carbides have completely decomposed. Continue fuming to remove completely oxides of nitrogen then cool and add 100 ml of water (see note 1).
7.3.1.4 High alloyed steel and iron, or steel and iron with high silicon content
Place the test portion (7.1) in a 750 ml conical flask, and add 20 ml of hydrochloric acid (4.6), 10 ml of nitric acid (4.5) and 1 ml of hydrofluoric acid (4.3). When effervescence has ceased, add 30 ml of perchioric acid (4.2). Heat until white fumes are given off, cover with a watch.glass and continue to heat until the alloy has completely dissolved (the white fumes being retained in the flask). Allow to cool.
Add 30 ml of water, boil for 5 mm, and allow to cool (see note 1). Transfer quantitatively into a 600 ml beaker and add 20 ml of sulfuric acid (4.8). 10 ml of orthophosphoric acid (4.4) and 70 ml of water.
7.3.2 Oxidation of chromium and preparation for titration
If necessary, to remove graphite, filter the test solution through a cellulose-pulp-lined filter and wash with sulfuric acid (4.10). Dilute to about 350 ml with warm water, and add 20 ml of silver sulfate solution (4.11) and 10 ml of ammonium peroxydisulfate solution (4.12). Cover the beaker with a watch-glass and boil for 10 mm (see note 2).
Then, break down the permanganic acid by adding to the solution, after it has been brought to the boil. firstly 15 ml of hydrochloric acid (4.7), then, after about 3 mm, if necessary a further amount of hydrochloric acid (4.7), drop by drop, until the violet colour disappears (see note 3). Boil for 10 mm until the odour from the chlorine compounds formed disappears (see note 4). Cool rapidly to room temperature.
NOTE 1 The dissolution procedures (7.3.1) may be incomplete for particular samples (for example samples with high contents of chromium and carbon). In such cases a fusion of the residue is required. and the result of this fusion shall be added to the test solution.
NOTE 2 The violet colour of the permanganic acid will be observed, if the test portion contains only a very small amount of manganese, add about 5 ml of manganese sulfate solution (4.13). so that the pernianganic acid is visible.
NOTE 3 The addition of hydrochloric acid (4.7) must be made after complete oxidation, visible by the violet colour-formation of the permanganic acid.
NOTE 4 In the case of a visual titration (7.3.3.2). after the decomposition of the permanganic acid and after boiling for tO mm. it is necessary to add 4 ml of manganese sulfate solution (4.14). then boil for a further 3 mm.EN 24937-1990 pdf download.
EN 24937-1990 pdf download
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