Elektrolessiin

Elektrolessiin, or electroless deposition, is a chemical method for depositing a metal coating on a substrate without applying external electrical current. The process relies on a redox reaction in an aqueous bath, where a chemical reducing agent converts metal ions in solution into metal that deposits on a catalytically active surface.

Substrates are typically pretreated to be clean and activated, so they present catalytic sites for initiation of deposition. Activation often involves etching and a sensitization step or palladium activation, enabling auto-catalytic growth of the coating.

Common electroless coatings include nickel–phosphorus (Ni-P) and nickel–boron (Ni-B), electroless copper, and, less widely, coatings of gold, palladium, cobalt and tin alloys. The Ni-P system is the most widespread in industrial use, with phosphorus content that influences hardness, wear resistance and corrosion protection. Bath compositions use a nickel salt, a reducing agent (typically hypophosphite for Ni-P), complexing agents, stabilizers and surfactants; operations occur at elevated temperature, around 80–95 C.

Advantages include uniform coating thickness on complex shapes, good corrosion and wear resistance, and the ability to deposit on nonconductive substrates after activation. Drawbacks include slower deposition rates compared with electroplating, stringent bath controls, and environmental and health considerations related to nickel compounds and phosphorus content.

Applications span electronics (PCB metallization and connectors), automotive and aerospace components, corrosion protection for manifolds and fittings, decorative coatings, and bearing surfaces where conformal coverage is required.

Safety and environmental aspects require proper handling of chemical baths, waste treatment and regulatory compliance due to nickel compounds and other additives. See also electroless nickel plating, electroless copper plating, and electroplating.