Iron electrolyte

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Iron electrolytes are used in the plating for the coating of metal surfaces with iron used, commonly known as "Verstahlen" or Verstählung mentioned.

The electrolyte consists of an aqueous solution of readily water-soluble iron (II) salts . The metal surface to be coated is connected as a cathode . The anodes are made of pure iron (99.99%), so-called arm iron anodes. The dissolved Fe 2+ ions migrate to the cathode, where they are reduced to elemental iron and form a thin iron layer on the metal surface.

In contrast to other galvanic electrolytes, iron electrolytes are only used in a few special areas, for example

How the components work

Iron electrolytes have a relatively simple structure. As early as 1887, A. Watt investigated the deposition of iron from solutions of a large number of iron salts and wrongly concluded that only sulphate baths could be used in practice. Iron (II) sulfate , iron (II) chloride or iron (II) tetrafluoroborate, for example, are used as iron sources today . Through organic additives, such as glycerin , dextrin and sugar to porous layers can be produced that are suitable because of their good emergency running properties for the treatment of details (pores as lubricants stop). High concentrations of halogens in the electrolyte increase the anode solubility. Additions of aluminum sulfate increase the hardness of the precipitates. Ammonium and manganese ions cause grain refinement of the layer. The addition of AlCl 3 , BeCl 2 or CrCl 2 in low concentrations should make the layer softer and more flexible. The presence of AlCl 3 should also increase the stability of the layer. Conductive salts such as potassium or sodium chloride can further increase conductivity. Hydrazine acts as an anodic depolarizer and prevents the formation of oxygen at the anode.

Basic ingredients Bath parameters
Iron source Conductive salt PH value temperature Current density
Iron (II) chloride (200 ... 600 g / l) Manganese (II) chloride (4 ... 60 g / l) 1.5 ... 2 65… 95 ° C 3… 20 A / dm²
Iron (II) sulfate (250 ... 400 g / l)

Iron (II) fluoroborate (40 ... 80 g / l)

Ammonium chloride (20 ... 60 g / l) 3… 4 40 ... 70 ° C 3… 6 A / dm²
Iron (II) fluoroborate (200 ... 300 g / l) Sodium chloride (8 ... 20 g / l) 2… 4 40 ... 70 ° C 3… 6 A / dm²

Error table for iron electrolytes

Visible errors Possible Cause remedy
Precipitations peel off lack of degreasing;
high internal stress
carefully degrease and pickle
fragile precipitation pH too low;
Temperature too low
increase to pH 3;
Increase temperature
brittle precipitation Iron (III) ions in the electrolyte;
organic pollution;
Foreign metals
acidify and hang in chemically pure iron plate for reduction
Activated carbon treatment; Selective cleaning
warty rainfall;
The electrolyte becomes cloudy
Iron (III) ions in the electrolyte acidify and hang the chemically pure iron plate for reduction
rough rainfall Mud on the anodes filter;
Use anode bags
hydrogen-containing precipitation pH too low blunt to pH 2.9 ... 3.2
Current yield too low pH too low blunt to pH 2.9 ... 3.2
budding precipitation Current density too high Lower current density, use current screens; Movement of goods

Individual evidence

  1. a b c Wilhelm Pfanhauser: The electrolytic metal precipitates textbook of electroplating with consideration of the treatment of metals before and after electroplating . Springer-Verlag, 2013, ISBN 978-3-662-29050-7 , pp. 536 ( limited preview in Google Book search).
  2. a b c d e f Mordechay Schlesinger, Milan Paunovic: Modern Electroplating . John Wiley & Sons, 2011, ISBN 1-118-06314-7 , pp. 310 ( limited preview in Google Book search).
  3. A. Watt, Electrician, 20,6 (1887-1888).