Alkaline washing

Alkaline cleaning is a critical pre-treatment step in electroplating, used to remove oils, greases, dirt, and light oxides from metal surfaces. This ensures proper adhesion and uniformity of the subsequent plating layers.

 

Author: Marisa

1. Introduction 

Alkaline cleaning is a critical pre-treatment step in electroplating, used to remove oils, greases, dirt, and light oxides from metal surfaces. This ensures proper adhesion and uniformity of the subsequent plating layers.

2. Purpose

• Removes organic contaminants (oil, grease, fingerprints).

• Eliminates light surface oxides and particles.

• Improves wettability for better electroplating adhesion.

• Prepares the surface for subsequent steps (e.g., acid pickling, electrocleaning).

3. Common Alkaline Cleaning Agents 

• Sodium Hydroxide (NaOH) – Strong alkali, effective for heavy grease.

• Sodium Carbonate (Na₂CO₃) – Milder, used for light cleaning.

• Sodium Silicate (Na₂SiO₃) – Acts as a corrosion inhibitor.

• Surfactants & Chelators – Added to improve cleaning efficiency.

4. Process Methods 

• Soak Cleaning – Parts are immersed in a heated alkaline solution (typically 50–80°C).

• Spray Cleaning – High-pressure alkaline spray for faster cleaning.

• Electrocleaning – Uses electrical current (anodic or cathodic) to enhance cleaning.

5. Typical Process Parameters 

Parameter	Range/Example
Concentration	5–10% (NaOH-based cleaners)
Temperature	50–80°C (122–176°F)
Time	3–10 minutes (varies with contamination)
Agitation	Mechanical or ultrasonic for better cleaning

6. Key Considerations

• Material Compatibility: Aluminum, zinc, and other amphoteric metals may corrode in strong alkalis.

• Rinsing: Thorough water rinsing is required to avoid alkaline residues.

• Waste Treatment: Neutralization (e.g., with acid) before disposal.

7. Common Defects & Solutions

• Poor Adhesion → Check cleaning time/temperature, increase agitation.

• White Stains → Improve rinsing to remove residual alkali.

• Surface Etching → Reduce alkali concentration or temperature for sensitive metals.

8. Comparison with Acid Cleaning 

Feature	Alkaline Cleaning	Acid Cleaning (Pickling)
Main Use	Organic contaminants	Oxides, rust, scale
Chemicals	NaOH, Na₂CO₃, etc.	HCl, H₂SO₄, HNO₃
Metal Impact	May etch amphoteric metals	Can corrode most metals

9. Example Process Flow

1. Alkaline Cleaning → 2. Water Rinse → 3. Acid Activation → 4. Electroplating

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Summary

Alkaline cleaning is essential in electroplating to ensure a contaminant-free surface. Proper selection of chemicals, temperature, and time ensures optimal plating quality.