Electroplating & Surface Treatment Anti-Rust Applications
Pre-plating pickling protection · In-process rust prevention · Cl/P free, no plating bath contamination
Corrosion Control in Electroplating & Surface Treatment
Pre-plating treatment (degreasing, pickling, activation) directly determines coating quality. Without inhibitor protection during pickling, common problems include:
- ⚠️ Substrate over-corrosion: surface roughening and loss of gloss, affecting coating uniformity and adhesion
- ⚠️ Hydrogen ingress and embrittlement: hydrogen evolved during pickling diffuses into the substrate, a notable risk for high-strength fasteners and springs
- ⚠️ Flash rusting between process steps: the activated surface after pickling and rinsing rusts quickly during transfer/holding, risking blistering and mottling in the coating
Imidazoline in Pre-Plating Treatment
| Process Step | Recommendation |
|---|---|
| Pre-plating pickling / activation | BXH-101 Water-Soluble Imidazoline at 0.1-0.5% of acid volume |
| Short-term in-process rust protection | Dip in a water-based rust preventive, or a rust-preventive oil containing BXH-102 (0.3-1%) |
| System compatibility | Free of Cl, P and metal ions; thorough rinsing keeps it out of the plating bath |
BXH-101 is a nonionic imidazoline polyoxyethylene ether surfactant with active content ≥98%, soluble in water and alcohol. It stays in the aqueous phase and rinses off easily, making it suitable for plating lines sensitive to bath cleanliness.
FAQ
Q: Why add an inhibitor before plating pickling?
Pre-plating pickling/activation removes the oxide film and activates the surface, but over-attack of the substrate causes roughening and hydrogen ingress, directly affecting coating adhesion and post-plating performance. Adding 0.1-0.5% imidazoline inhibitor dissolves the oxide film while protecting the substrate and reducing hydrogen penetration.
Q: Will the inhibitor affect coating adhesion?
The imidazoline adsorption film is a physicochemical adsorption layer and, after thorough rinsing, does not leave stubborn residue on the surface. Under standard practice (two or more countercurrent rinses after pickling) it generally does not affect coating adhesion; for processes with extremely high adhesion requirements, we recommend a coupon plating comparison test before adopting it in production.
Q: How should in-process rust protection be handled for plated parts?
Ferrous substrates flash-rust very easily after pickling and rinsing, so transfer and holding time should be minimized. If parts must sit, dip them in a diluted water-based rust preventive. After plating (if further processing is needed), a short-term rust-preventive oil containing oil-soluble imidazoline (BXH-102, 0.3-1%) can be used.
Q: Can imidazoline reduce hydrogen embrittlement in plating?
It reduces one source of hydrogen at the pickling stage — the inhibitor film suppresses the hydrogen evolution reaction during pickling, lowering hydrogen ingress. However, the plating process itself (especially acidic plating baths) also introduces hydrogen, so high-strength steel parts still require post-plating hydrogen baking per standard.
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