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
- for reinforcement of printing plates ,
- for reconditioning worn or undersized machine parts,
- in electroforming due to the easy removal by hydrochloric or sulfuric acid
- in the production of pure iron for magnetic cores ,
- as a primer for less common base metals such as niobium or molybdenum and
- in special cases due to the good emergency running properties .
- Coating of soldering tips to prevent the alloying of tin into the copper body
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)
||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;
|brittle precipitation||Iron (III) ions in the electrolyte;
|acidify and hang in chemically pure iron plate for reduction
Activated carbon treatment; Selective cleaning
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|
- ↑ 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).
- ↑ 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).
- ↑ A. Watt, Electrician, 20,6 (1887-1888).