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Anodes for use in Electroplating Baths

Anodes for use in electroplating baths

Schloetter can supply a wide range of anodes suitable for use in most electroplating baths. We can supply tin, tin-lead, zinc, nickel, silver and copper anodes.

They can be supplied in various sizes and form factors e.g. dog-bone anodes or slugs, domes, balls etc for use in anode baskets.

All of Schloetter anodes have been sourced for the highest degrees of purity to ensure they give optimum performance during electroplating.

We also supply platinised titanium anodes for use in precious metal plating solutions and a range of anode hooks, plating baskets and anode bags.

Please contact us to discuss your specific requirements.

Types of Anode

Copper Anodes

There are two forms of copper anode:

Electrolytic Copper This is a pure form of copper, suitable for use in cyanide copper plating solutions.
Phosphorous De-Oxidised (PDO)

These anodes contain low traces of phosphorous, typically 0.05% Phosphorous (0.04 - 0.08%). They are essential for use in proprietary acid copper plating solutions that use organic additives. During plating, the anode should form a dark grey / black film consisting of cuprous oxide (CuO).

Causes of Anode Passivation in Acid Copper Electrolytes

Anode passivity in acid copper electrolytes can be caused by any of the following conditions:-

  1. High chloride levels - This normally results in a light grey to white anode film. Confirm by solution analysis.
  2. Over concentrated solution i.e. high levels of copper sulphate or sulphuric acid. Once again, confirm by analysis.
  3. Excessive anode current density. Depending on the degree of solution movement around the anode, anodic current density should not exceed 2.5A/dm². Check anode area and all electrical contacts.
  4. Blocked Anode Bags. This will cause the solution within the bag to become supersaturated.
  5. Incorrect / Poor quality anodes. Insufficient phosphorous content normally results in a reddish brown film being formed on the anodes. The phosphorous content in Schloetter anodes is closely controlled to prevent this problem.
  6. Low Solution Temperature.

In all cases of anode passivation, once the cause has been identified, the passive film must be removed. With bar/oval anodes, this can be done by scrubbing. With anode baskets, this is usually done by soaking in a mild copper etch such as sodium persulphate. The use of nitric acid is not recommended due to hazardous fumes being produced and severe risk of contaminating the copper plating solution.

Nickel Anodes

Electrolytic Nickel Anodes These are the purest (and usually least expensive) type of nickel anode. They are available in strips or small pieces. However, as there are no 'depolarisers' added to aid anode solubility, this type of material is most critical to anodic current density and electrolyte composition (pH and chloride).
Depolarised Nickel Anodes These are made from high purity nickel but additionally contain small amounts of nickel oxide (< 1%). This gives a myriad of fine crystals, separated at the grain boundaries by nickel oxide. The addition of nickel oxide gives improved anode solubility. Usually supplied as rolled oval anodes, their use is generally restricted to dull nickel electrolytes, where the pH should be in the range of 4.0 - 5.8, with a minimum chloride concentration of 8.25 g/l (25 g/l NiCl2.6H2O). During normal operation, a light brown film should be formed on the anodes.
Duvanic Nickel Anodes These are made from high purity nickel, with a small addition of carbon (< 1%). They are available in either rolled or cast formats. The electrolyte must contain a minimum of 4.5 g/l chloride (15 g/l NiCl2.6H2O) and have a pH lower than 4.5. The anode current density is also important and should be kept in the range 1.5 - 3.5 A/dm² (14 - 33 ASF). During normal operation, a tenacious, porous black film is formed on the anode surface.
'S' Nickel Anodes These are available as strips or small pieces of nickel (rounds, pellets etc). They are composed of a very pure form of nickel containing 0.02% sulphur as a depolariser. This ensures a high degree of electrochemical activity, resulting in good solubility and uniform erosion. The high activity makes this type of material ideal for all types of nickel plating solutions, including those that are chloride-free and/or operate at a high pH. They perform well over a wide anodic current density range. They are particularly suitable for use in titanium anode baskets. Though there is no formation of metallic sludge, nickel sulphide is formed and therefore (as with all nickel anode material) the use of anode bags is essential, especially when air agitation is being used.

Mixed Metal Oxide (MMO)

These are titanium anodes that are coated in a mixture of iridium and ruthenium oxide (sometimes combined with tantalum and titanium oxides). They are designed to resist highly acidic conditions. The coating, which has excellent electro-catalytic properties, allows good current flow and evolution of oxygen at low, stable anode potentials.

The coating is typically 20 g/m³ but this can be varied depending upon customer requirements.

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Schloetter Co Ltd

Abbey Works
New Road
Pershore
Worcs, UK
WR10 1BY

Tel:      +44(0)1386 552331

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E-mail:  info@schloetter.co.uk

Registered in England 947371

VAT No. GB 274 7177 31

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