Nickel electroplating
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.[1]
Overview
Nickel electroplating is a process of depositing nickel on a metal part. Parts to be plated must be clean and free of dirt, corrosion, and defects before plating can begin.[2] To clean and protect the part during the plating process a combination of heat treating, cleaning, masking, pickling, and etching may be used.[1] 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 in form of nickel ions. The ions travel through the solution and deposit on the cathode.[3]
Types and chemistry
Watts
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.[4][5]
Bath Composition
| Chemical Name | Formula | Bright[4] | Semi-bright[4] | ||
|---|---|---|---|---|---|
| Metric | US | Metric | US | ||
| Nickel sulfate | NiSO4·6H2O | 150–300 g/L | 20–40 oz/gal | 225–300 g/L | 30–40 oz/gal |
| Nickel chloride | NiCl2·6H2O | 60–150 g/L | 8–20 oz/gal | 30–45 g/L | 4–6 oz/gal |
| Boric acid | H3BO3 | 37–52 g/L | 5–7 oz/gal | 37–52 g/L | 5–7 oz/gal |
Operating conditions [3]
- Temperature: 40-65°C
- Cathode current density: 2-10 A/dm2
- PH: 4.7-5.1
Brighteners [3]
- 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.[6]
Bath composition
| Chemical name | Formula | Bath concentration[3] | |
|---|---|---|---|
| Metric | US | ||
| Nickel sulfamate | Ni(SO3NH2)2 | 300-450 g/l | 40–60 oz/gal |
| Nickel chloride | NiCl2·6H2O | 0-30 g/l | 0–4 oz/gal |
| Boric acid | H3BO3 | 30-45 g/l | 4–6 oz/gal |
Operating conditions[3]
- 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.[3]
| Chemical name | Formula | Bath concentration[3] |
|---|---|---|
| Nickel chloride | NiCl2·6H2O | 30–40 oz/gal |
| Boric acid | H3BO3 | 4–4.7 oz/gal |
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-chlorine bath.[3]
| Chemical name | Formula | Bath concentration[3] |
|---|---|---|
| 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.[5]
| Chemical name | Formula | Bath concentration[3] |
|---|---|---|
| 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.[3]
| Chemical name | Formula | Bath concentration[3] | Metric |
|---|---|---|---|
| Nickel sulfate | NiSO4·6H2O | 24 oz/gal | 179.7g/L |
| Ammonium chloride | NH4Cl | 3.3 oz/gal | 24.7 g/L |
| Boric acid | H3BO3 | 4 oz/gal | 29.96 g/L |
Black nickel
Black nickel plating is typically plated on brass, bronze, or steel in order to produce a non-reflective surface.[7] This type of plating is used for decorative purposes and does not offer much protection.[1]
| Chemical name | Formula | Bath concentration[7] |
|---|---|---|
| Nickel ammonium sulfate | NiSO4·(NH4)2SO4·6H2O | 8 oz/gal |
| Zinc sulfate | ZnSO4 | 1.0 oz/gal |
| Sodium thiocyanate | NaCNS | 2 oz/gal |
Applications
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.[4]
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.[4]
See also
References
- ↑ 1.0 1.1 1.2 QQ-N-290A
- ↑ MIL-P-27418
- ↑ 3.00 3.01 3.02 3.03 3.04 3.05 3.06 3.07 3.08 3.09 3.10 3.11 http://www.substech.com/dokuwiki/doku.php?id=nickel_electroplating
- ↑ 4.0 4.1 4.2 4.3 4.4 http://www.pfonline.com/articles/nickel-electroplating
- ↑ 5.0 5.1 NickelElectroplating.pdf
- ↑ http://www.balesmold.com/sulfamate.htm
- ↑ 7.0 7.1 MIL-P-18317
