Nickel electroplating is a technique of electroplating a thin layer of nickel onto a metal object. The nickel layer can be decorative, provide corrosion resistance, wear resistance, or used to build up worn or undersized parts for salvage purposes.
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Overview
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.
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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 nickel where a high luster is not desired.
Bath Composition
Operating conditions
- Temperature: 40-65 °C
- Cathode current density: 2-10 A/dm2
- pH: 4.7-5.1
Brighteners
- Carrier brighteners (e.g. paratoluene sulfonamide, benzene sulphonic acid) in concentration 0.75-23 g/l. Carrier brighteners contain sulfur providing uniform fine grain structure of the nickel plating.
- Levelers, second class brighteners (e.g. allyl sulfonic acid, formaldehyde chloral hydrate) in concentration 0.0045-0.15 g/l produce (in combination with carrier brighteners) brilliant deposit.
- Auxiliary brighteners (e.g. sodium allyl sulfonate, pyridinum propyl sulfonate)in concentration 0.075-3.8 g/l.
- Inorganic brighteners (e.g. cobalt, zinc) in concentration 0.075-3.8 g/l. Inorganic brighteners impart additional luster 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, 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.
Sulfate-chloride
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.
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.
Hard nickel
A hard nickel solution is used when a high tensile strength and hardness deposit is required.
Black nickel
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 purposes and does not offer much protection.
Applications
Decorative coating
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.
Source of the article : Wikipedia
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