Flat Nickel Anodes for Plating Tanks

Nickel anodes differ in how readily they dissolve, and that is set by how the nickel was made. Electrolytic nickel is refined by electrowinning or electrorefining and is very pure, but in its plain form it can be slow to dissolve and, in low-chloride baths, may turn passive. Passive anodes stop releasing nickel, the voltage climbs, and nickel content in the bath drifts down.

Depolarised nickel contains a small, controlled amount of nickel oxide. It dissolves at lower potential and stays active where plain nickel would go passive, which is why rolled depolarised anodes have long been popular for bar-type anodes in Watts and bright nickel baths. A third type, sulphur-activated nickel, is mainly used as rounds or pellets in titanium baskets rather than as flats.

When you enquire, tell us your bath type and chloride level, and whether your current anodes are electrolytic or depolarised. Staying with what the bath is already tuned for is usually the safer choice.

Width, thickness and length are the three numbers. Length should keep the bottom of the anode a little above the lowest point of the work, so that the bottom edge of the parts does not get excess current. Width is chosen so that the anodes, hung side by side with a small gap, give enough total surface.

Most bright nickel processes are run with an anode area that matches or exceeds the cathode area, often in a range of about 1:1 to 2:1 anode to cathode. Too little anode area pushes up anode current density, which encourages passivity. Thickness decides how long the anode lasts before it needs replacing.

If you send us the tank length, solution depth and current, we can work out sizes with you.

Nickel dissolves at about 1.095 grams per ampere-hour. Divide the weight of nickel in your anodes by that figure and by your average current to get a rough life in hours. A set of flats weighing 40 kg in a tank drawing 200 amperes would, at full efficiency, last roughly 180 hours of plating time, less if you replace anodes before they are fully used.

Flats tend to dissolve faster along the edges and at the bottom, where current concentrates. Turn or swap anodes during maintenance, and replace them once they become too thin to hold their shape on the hook.

Use titanium hooks, which resist the bath and do not dissolve, and make sure the hook seats fully on a clean anode bar. A poor contact heats up and wastes power. Fit each anode in a polypropylene anode bag that is a little longer than the anode, tied above the solution level, so particles cannot escape over the top.

New anodes should be degreased and given a light acid dip before going into the bath. Some platers also dummy-plate at low current for a while after installing a fresh set. The oval nickel anodes page covers the elliptical alternative if flats are not giving you even dissolution.

• Degrease and acid dip new anodes before use.
• Bag every anode; tie bags above solution level.
• Check hook contact and clean the anode bar regularly.
• Keep anode area at least equal to cathode area.

A test certificate for nickel anodes should show nickel content and the impurities that matter to a plater: copper, iron, zinc, lead, and sulphur and carbon where relevant. Jubilant Impex supplies anodes with a test certificate through a Government-recognised test house on request. More on the wider anode range is on the electroplating anodes page.