Page 101 - 20250602 EEA QM Edition 6.0

Quality Requirements Edition 6.0 European Enamel Association

8.2.1.5 Determination of bivalent iron in the nickel-exchange bath 8.2.1.6 Determination of the nickel deposit on sheet steel

Purpose and scope Purpose and scope

In order to guarantee an even nickel deposition and to avoid a crystallization by It is often desirable to make knowledge of the nickel quantity deposited onto the steel.
cooling, the iron (II) sulphate must be checked.
Analysis instruction
Analysis instructions:
A sample of a defined size (approx. 5 X 5 cm) is to be cut out of a component that is
25 ml of a cooled (20 C) sample of the nickel bath solution is to be diluted with about to be examined. The deposited nickel on its surface has to be taken off by a cold 10%
0
100 ml distilled water in an Erlenmeyer flask and after addition of about 20 ml 20 %- nitric acid, then rinse the sample thoroughly with distilled water. Warm up the nitric
sulphuric acid and 5 drops diphenylaminosulfonic acid to be titrated with 0.02 n acid solution and blend it with about 10 g of tartaric acid in order to mask possible
K2Cr2O7 - solution. Near the end point the green colour of the solution deepens. The dissolved iron. Set up the solution with ammonia whereby iron hydroxide must not
titration is brought to an end when the colour of the solution changes from green to precipitate; in case of this, increase the amount of tartaric acid.
blue-violet.
Precipitate the nickel with 10 ml of a 2% alcoholic dimethylglyoxime solution and pass
ml consumption 0.02 n K 2Cr2O 7 x 0.04 = g Fe / l nickel bath solution the red precipitate through a “white-ribbon” filter, rinse thoroughly with distilled water
2+
and dissolve it in about 5 ml of a 10% nitric acid.
Required reagents:
Dilute the clear solution with water, set it up with ammonia to slight ammoniacal, add
Diphenylaminosulfonic acid: Murexid and titrate with 0.01m Complexion-III solution till the colour changes from
brownish-pink to deep violet.
0.2 g Diphenylaminosulfonic acid to be dissolved in 100 ml n H2SO4

0.02 n K2Cr2O7-solution
ml consumption 0.01m Complexion-III-solution X 5.87 = g Ni/m steel surface
2
2
cm sample surface
List of reagents:
10% nitric acid Tartaric
acid Dimethylglyoxime solution: 2 g dimethylglyoxime are dissolved in alcohol
Murexid: is to blend with NaCl in a proportion 1 : 200

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