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Quality Requirements Edition 5.0 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 cooling, the It is often desirable to make knowledge of the nickel quantity deposited onto the steel.

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 to be
25 ml of a cooled (20 C) sample of the nickel bath solution is to be diluted with about 100 examined. The deposited nickel on its surface has to be taken off by a cold 10% nitric acid,
0
ml distilled water in an Erlenmeyer flask and after addition of about 20 ml 20 %-sulphuric then rinse the sample thoroughly with distilled water. Warm up the nitric acid solution and
acid and 5 drops diphenylaminosulfonic acid to be titrated with 0.02 n K Cr O - solution. blend it with about 10 g of tartaric acid in order to mask possible dissolved iron. Set up the
2 2 7
Near the end point the green colour of the solution deepens. The titration is brought to an solution with ammonia whereby ironhydroxide must not precipitate; in case of this, increase
end when the colour of the solution changes from green to blue-violet. the amount of tartaric acid.

ml consumption 0.02 n K Cr O x 0.04 = g Fe 2+ / l nickel bath solution Precipitate the nickel with 10 ml of a 2% alcoholic dimethylglyoxime solution and pass the
2 2 7
red precipitate through a “white-ribbon” filter, rinse thoroughly with distilled water and dis-
Required reagents: solve it in about 5 ml of a 10% nitric acid.
Diphenylaminosulfonic acid: Dilute the clear solution with water, set it up with ammonia to slight ammoniacal, add

0.2 g Diphenylaminosulfonic acid to be dissolved in 100 ml n H SO Murexid and titrate with 0.01m Complexion-III solution till the colour changes from
2 4
0.02 n K Cr O -solution brownish-
2 2 7
pink to deep violet.

2
ml consumption 0.01m Complexion-III-solution X 5.87 = g Ni/m steel surface
cm sample surface
2

List of reagents:
10% nitric acid Tartaric
acid Dimethylglyoxime
solution
2 g dimethylglyoxime are dissolved in alcohol
Murexid
Murexid is to blend with NaCl in a proportion 1 : 200

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