Nickel electroplating is a process of depositing nickel onto a metal part. Parts to be plated must be clean and free of dirt, corrosion, and defects before plating can begin. To clean and protect the part during the plating process, a combination of heat treating, cleaning, masking, pickling, and etching may be used. Once the piece has been prepared it is immersed into an electrolyte solution and is used as the cathode. The nickel anode is dissolved into the electrolyte to form nickel ions. The ions travel through the solution and deposit on the cathode.
Types and chemistry
Watts baths
Watts nickel plating baths can deposit both bright and semi-bright nickel. Bright nickel is typically used for decorative purposes and corrosion protection. Semi-bright deposits are used for engineering applications where high corrosion resistance, ductility or electrical conductivity is important, and a high luster is not required.
Carrier brighteners in concentration 0.75-23 g/l. Carrier brighteners contain sulfur providing uniform fine grain structure of the nickel plating.
Levelers, second class brighteners in concentration 0.0045-0.15 g/l produce brilliant deposit.
Auxiliary brighteners in concentration 0.075-3.8 g/l.
Inorganic brighteners in concentration 0.075-3.8 g/l. Inorganic brighteners impart additional lustre to the coating.
Type of the added brighteners and their concentrations determine the deposit appearance: brilliant, bright, semi-bright, satin.
Nickel sulfamate
Sulfamate nickel plating is used for many engineering applications. It is deposited for dimensional corrections, abrasion and wear resistance, high efficiency coating and corrosion protection. It is also used as an undercoat for chromium.
Bath composition
Operating conditions
Temperature: 40-60 °C
Cathode current density: 2-25 A/dm2
pH: 3.5-4.5
All-chloride
All-Chloride solutions allow for the deposition of thick nickel coatings. They do this because they run at low voltages. However, the deposition has high internal stresses.
A Sulfate-Chloride bath operates at lower voltages than a Watts bath and provide a higher rate of deposition. Although internal stresses are higher than the Watts bath, they are lower than that of an all-chloride bath.
Chemical name
Formula
Bath concentration
Nickel sulfate
NiSO4·6H2O
20–30 oz/gal
Nickel chloride
NiCl2·6H2O
20–30 oz/gal
Boric acid
H3BO3
4–6 oz/gal
All-sulfate
An all-sulfate solution is used for electro-depositing nickel where the anodes are insoluble. For example, plating the insides of steel pipes and fittings may require an anode.
Chemical name
Formula
Bath concentration
Nickel sulfate
NiSO4·6H2O
30–53 oz/gal
Boric acid
H3BO3
4–6 oz/gal
Hard nickel
A hard nickel solution is used when a high tensile strength and hardness deposit is required.
Black nickel plating is typically plated on brass, bronze, or steel in order to produce a non-reflective surface. This type of plating is used for decorative and military purposes and does not offer much protection.
Decorative bright nickel is used in a wide range of applications. It offers a high luster finish, corrosion protection, and wear resistance. In the automotive industry bright nickel can be found on bumpers, rims, exhaust pipes and trim. It is also used for bright work on bicycles and motorcycles. Other applications include hand tools and household items such as lighting and plumbing fixtures, wire racks, firearms, and appliances.
Engineering applications
Engineering nickel is used where brightness is not desired. Non decorative applications provide wear and corrosion protection as well as low-stress buildups for dimensional recovery. The method can be used for making nanocomposite wear resistance coatings.
