BS EN ISO 4938:2016 pdf free

BS EN ISO 4938:2016 pdf free.Steel and iron – Determination of nickel content – Gravimetric or titrimetric method
The following applies to test portions containing cobalt and high concentrations of copper.
To the test portion prepared in 7.2.1, add hydrazine dihydrogen sulphate solution (4.21) drop by drop until the chromium is completely reduced.
Remove the copper by electrolysing the solution at controlled potential, commencing the deposition with a cathode potential of -0,15 V (against standard calomel electrode) and gradually reducing to -0,30 V (against standard calomel electrode). Copper deposition should be complete after about 40 min when the current remains constant at a very low value.
Completion of deposition can be checked by adding about 20 ml of water to the test solution and continuing the electrolysis. Deposition is complete if no copper is deposited on the freshly submerged portion of the cathode after 5 min. Switch off the current to the calomel electrode circuit. Remove the calomel electrode, then remove the platinum electrodes and rinse with water.
Add about 5 ml of nitric acid (4.5) and evaporate the solution until copious white fumes are evolved.
Cover the beaker with a dry watch-glass and continue heating until the chromium is completely oxidized. Remove the beaker from the heat source and allow to cool. Dilute the solution with 100 ml of water, heat to dissolve the salts and boil for about 5 min to eliminate chlorine compounds.
The second nickel precipitation may be omitted for test portions containing less than 20 mg of copper and less than 25 mg of cobalt if the titrimetric determination is to be used, in which case, proceed as described in 7.2.5.
Place the filter and precipitate obtained in 7.2.2 in the precipitation beaker and cover with a watch glass. Add 15 ml of nitric acid (4.5), 10 ml of sulphuric acid (4.7) and 4 ml of perchloric acid (4.6), and then heat. Increase the temperature to evaporate the solution until there is a strong emission of white fumes (see Note 1). Cool and dilute with water to about 400 ml.
NOTE 1 The elimination of the organic content of the precipitate and filter normally takes 20 min to 30 min.BS EN ISO 4938 pdf download.