In the nickel electroplating process, "nickel sealing" usually refers to the sealing treatment of the nickel plating layer to improve its corrosion resistance, wear resistance or improve its appearance.
Author: Marisa
In the nickel electroplating process, "nickel sealing" usually refers to the sealing treatment of the nickel plating layer to improve its corrosion resistance, wear resistance or improve its appearance.
Commonly used sealing treatment solutions include passivation solution, rust inhibitor, organic sealer, etc. The specific choice depends on the application requirements (such as rust prevention, wear resistance, decoration, etc.)
1. Chromate passivation (traditional corrosion resistant sealing)
Use: Improve the corrosion resistance of nickel plating (such as salt spray test performance).
Potion composition:
Hexavalent chromium passivation (gradually eliminated, strict environmental protection restrictions):
Chromic anhydride (CrO₃): 2-10 g/L
Sulfuric acid (H₂SO₄): 0.5-2 mL/L
Temperature: 20-40℃, time: 10-60 seconds
Trivalent chromium passivation (environmentally friendly alternative, mainstream choice):
Trivalent chromium salt (such as Cr₂(SO₄)₃): 5-20 g/L
Coordinating agent (such as formate, citrate)
pH: 3.5-4.5, temperature: 30-50℃, time: 30-120 seconds
Features:
Form a dense passivation film, significantly improve corrosion resistance (salt spray test can reach 24-96 hours).
Hexavalent chromium is toxic and requires strict wastewater treatment, while trivalent chromium is more environmentally friendly.
2. Chromium-free passivation (environmentally friendly sealing)
Use: Replace chromate to meet environmental protection requirements such as RoHS.
Potion ingredients:
Molybdate/tungstate system:
Sodium molybdate (Na₂MoO₄): 5-20 g/L
Phosphate or silicate as auxiliary film-forming agent
Organosilanes:
Silane coupling agent (such as KH-550) hydrolyzate to form a hydrophobic film.
Rare earth metal salts (such as cerium salts):
Cerium nitrate (Ce(NO₃)₃): 1-5 g/L, pH 3-5
Features:
Non-toxic, but corrosion resistance is slightly lower than chromate, and other sealing processes are required.
3. Organic sealant (wear-resistant, decorative)
Use: Improve wear resistance, anti-fingerprint or give a special appearance (such as matte, glossy).
Type of solution:
Acrylic or epoxy resin sealant:
Water-soluble or solvent-based, formed by dipping or spraying, and cured by baking (80-150℃).
Wax-based sealant:
Such as microcrystalline wax emulsion, suitable for short-term rust prevention or transportation protection.
Silicone oil:
Forms a hydrophobic layer and prevents fingerprints (commonly used in nickel plating of electronic products).
Features:
Simple operation, but may fail at high temperature or long-term exposure.
4. Anti-rust oil/anti-rust water (temporary protection)
Use: short-term rust prevention (such as during storage or transportation).
Solution ingredients:
Mineral oil + corrosion inhibitor (such as sodium petroleum sulfonate).
Water-soluble rust inhibitor (such as sodium nitrite + triethanolamine).
Features:
Low cost, but requires subsequent cleaning and removal.
Selection suggestions
High corrosion resistance requirements: trivalent chromium passivation is preferred.
Environmental requirements: chromium-free passivation or organic sealant.
Decoration/wear resistance: acrylic resin sealing.
Temporary protection: anti-rust oil.
Note: Before sealing, make sure the nickel plating is thoroughly cleaned (rinsed with deionized water) to avoid residual plating solution affecting the sealing effect.