1. Core Principle of Chemical Patina Acceleration
Introducing corrosion-promoting ions (e.g., Cl⁻, SO₄²⁻) to speed up the electrochemical oxidation reaction on the steel surface.
Providing Cu²⁺ ions (matching the alloy content of weathering steel) to promote the formation of copper-rich oxide phases-these phases are the core of the dense, protective patina.
Regulating the oxidation rate to ensure uniform color across the entire surface, avoiding spotty or uneven rusting caused by natural environmental differences.
2. Common Chemical Accelerator Formulations
| Accelerator Type | Key Components | Target Patina Color | Application Scenario |
|---|---|---|---|
| Standard Type | 2–5% ferric chloride + 1–3% copper sulfate + trace organic acid | Rich reddish-brown (classic weathering steel patina) | Building facades, landscape signs |
| Dark Type | 3–6% sodium chloride + 2–4% potassium permanganate | Deep brown to blackish-brown | Art installations, decorative furniture |
| Light Type | 1–2% ammonium sulfate + 0.5–1% copper chloride | Light orange-brown | Indoor decorative panels |
3. Standard Chemical Acceleration Process
Remove mill scale, oil stains, and contaminants via sandblasting (for hot-rolled plates) or alkaline degreasing (for cold-rolled plates). The ideal surface roughness is Ra 1.5–3.0 μm to provide nucleation sites for patina.
Rinse the surface with clean water and dry it completely (no residual moisture).
Apply the solution evenly via spraying or brushing-avoid dripping or missed areas (critical for color uniformity).
For large plates, use a low-pressure spray gun to ensure a thin, uniform coating (wet film thickness: 10–20 μm).
Place the treated steel in an environment with temperature 20–30°C and relative humidity 70–90% (use a humidity chamber for industrial production).
Maintain the environment for 2–5 days: the surface will gradually develop the target patina color. Turn the plates over every 24 hours to ensure uniform oxidation on both sides.
Rinse the surface with clean water to remove residual accelerator ions (prevents over-corrosion).
Dry the plate thoroughly, then apply a transparent breathable fluorocarbon sealant to lock in the color and enhance corrosion resistance. The sealant does not alter the patina appearance but prevents color fading due to UV exposure.
