In electroplating production, alkali (alkaline substance) is mainly used for oil removal, activation, plating solution pH adjustment, neutralisation treatment and so on. The following are the bases commonly used in the plating process and their functions, properties and precautions:
What are the bases commonly used in electroplating production?
Author: Robby
In electroplating production, alkali (alkaline substance) is mainly used for oil removal, activation, plating solution pH adjustment, neutralisation treatment and so on. The following are the bases commonly used in the plating process and their functions, properties and precautions:
1. Sodium hydroxide (NaOH, caustic soda)
Uses
Chemical degreasing: Used in pre-treatment for electroplating to remove grease and organic matter from metal surfaces (saponification reaction).
Alkaline galvanising: As a main component of galvanising baths (e.g. zincate galvanising).
De-plating: Used to strip certain plating layers (e.g. to remove undesirable nickel plating).
Characteristics
Strongly alkaline (pH > 13), highly corrosive, easily absorbs moisture.
Dissolves amphoteric metals such as aluminium and zinc (reaction generates hydrogen, explosion-proof).
Precautions
Wear protective gloves and goggles to avoid skin contact.
Waste liquid should be neutralised and treated (if it contains heavy metals, it should be recycled separately).
2. Sodium carbonate (Na₂CO₃, soda ash)
Uses
Weak alkaline degreasing: milder than NaOH, suitable for precision parts or aluminium parts cleaning.
Buffer: adjust the pH of plating solution (e.g. chemical nickel plating).
Neutraliser: treating acidic wastewater (adjusting pH to neutral).
Characteristics
Weak alkalinity (pH ~11), not easy to damage the substrate.
Reacts with calcium and magnesium ions to produce scale (caution in hard water areas).
Cautions
Long-term use may affect the stability of the plating solution due to the accumulation of carbonate.
3. Trisodium phosphate (Na₃PO₄)
Uses
Metal surface treatment: Enhance the effect of oil removal (compounded with NaOH).
Water softening: prevent hard water scaling.
Characteristics
Strong alkaline (pH ~12), with some emulsifying effect.
Cautions
Wastewater containing phosphorus needs to be treated to avoid eutrophication of the water body.
4. Potassium hydroxide (KOH)
Use
Alkaline plating solution: such as gold plating, tin plating, etc. (better conductivity than NaOH).
Chemical polishing: alkaline etching of aluminium and aluminium alloy.
Characteristics
Strongly alkaline, easily soluble in water, highly corrosive.
Higher price than NaOH, generally used for special plating.
Precautions
Similar to NaOH, corrosion-resistant storage (plastic containers) is required.
5. Ammonia (NH₄OH)
Uses
pH adjustment: used for weak alkaline plating solution (such as chemical copper plating, silver plating).
Complexing agent: forming complexes with copper, zinc and other metal ions (e.g. ammonia sulfonic acid nickel plating).
Characteristic
Highly volatile, irritating odour (good ventilation required).
Weakly alkaline (pH ~11), dissolving effect on some metals (e.g. copper).
Precautions
Avoid mixing with acids (produces toxic NH₃ gas).
Storage should be sealed to prevent volatilisation and loss.
6. Sodium silicate (Na₂SiO₃, water glass)
Uses
Metal cleaning: used as corrosion inhibitor to prevent over-corrosion of metal during alkaline cleaning.
Passivation treatment: for surface treatment of aluminium and magnesium alloys.
Characteristics
Alkaline (pH ~11), film-forming.
Precautions
Excessive use may result in decreased adhesion of the plated layer.
7. Organic alkali (e.g. ethanolamine, EDTA)
Uses
Complexing agent: Replace cyanide in cyanide-free gold and silver plating.
pH adjustment: Used in environmentally friendly plating solution (e.g. chemical nickel plating).
Characteristics
Weak alkalinity, good environmental protection, easy to treat wastewater.
Cautions
Higher cost, need to optimise the formula.
Safety and environmental protection points
Ventilation protection: NaOH, KOH, ammonia and other volatile and irritating gases, need to be equipped with an air extraction system.
Waste liquid treatment:
Alkaline waste liquid containing heavy metals (e.g. zinc, nickel) needs to be treated separately (precipitation method).
High pH waste water needs to be neutralised to 6~9 before discharge.
Storage Requirements:
Solid NaOH/KOH needs to be sealed against moisture to avoid caking.
Ammonia needs to be stored away from light and at low temperature.
Summary
Alkalis Main applications pH range Caution
NaOH Degreasing, alkaline galvanising, de-plating 13~14 Strong corrosiveness, explosion-proof is required.
Na₂CO₃ Weak degreasing, pH buffering, wastewater neutralisation 10~11 Use with caution in hard water areas.
Na₃PO₄ Enhanced oil removal, scale prevention 11~12 Phosphorus-containing wastewater needs to be treated.
KOH Special plating solution (gold plating, tin plating) 13~14 High cost, better conductivity than NaOH
NH₄OH pH adjustment, complexation (copper plating, silver plating) 10~11 High volatility, need ventilation
Na₂SiO₃ corrosion inhibition, passivation 10~11 may affect the adhesion of plating layer
Organic alkali Environmentally friendly plating solution (cyanide-free plating) 8~10 High cost, but waste water is easier to treat
In electroplating process, the selection of alkali needs to consider the decontamination ability, pH stability, cost and environmental requirements. With the tightening of environmental regulations, low-toxicity, easily degradable organic bases (e.g. ethanolamine) are gradually replacing traditional strong bases.