Key Takeaway
Our Diver Magnets use a multi-layer Epoxy-HDPE coating because bare NdFeB oxidises rapidly in saltwater and permanently loses magnetic strength. Without proper protection, the iron content in NdFeB (neodymium-iron-boron) alloy oxidises rapidly, causing irreversible loss of magnetic strength and structural deterioration. Our diver magnets use a multi-layer Epoxy-HDPE coating system specifically engineered to provide a durable barrier against saltwater, pressure, abrasion, and UV exposure.
Why Neodymium Magnets Corrode
Neodymium magnets corrode because roughly 65% of the NdFeB alloy is iron, which oxidises in moisture and far faster in saltwater. The iron component — which makes up approximately 65% of the alloy by weight — is highly susceptible to oxidation when exposed to moisture. In saltwater, the corrosion process accelerates dramatically due to the electrolytic properties of dissolved salts.
When corrosion occurs, it does not just affect the surface. Oxidation penetrates through the grain boundaries of the sintered magnet material, causing:
- Loss of magnetic strength: Oxidised regions lose their magnetic alignment permanently
- Structural crumbling: Corroded magnets become brittle and can fragment
- Coating failure cascade: Once a coating is breached, corrosion spreads rapidly beneath the surface
Standard Coatings vs Marine-Grade Coatings
Standard 8–25 µm nickel, zinc or epoxy-only coatings suit dry indoor use and fail quickly in marine conditions. These coatings provide adequate protection for dry indoor environments but fail rapidly in marine conditions:
- Nickel plating (10–15 µm): Offers basic scratch resistance but is porous at the microscopic level; salt spray penetrates within weeks
- Zinc plating (8–12 µm): Provides sacrificial corrosion protection but dissolves quickly in saltwater
- Epoxy-only coating (15–25 µm): Better moisture barrier, but brittle and prone to chipping on impact
The Epoxy-HDPE Coating System
Our diver magnets use a multi-layer Epoxy-HDPE coating system designed specifically for prolonged saltwater immersion:
- Surface preparation: The NdFeB magnet is cleaned, degreased, and acid-etched to create a microscopically rough surface for maximum coating adhesion
- Epoxy primer layer: A chemical-resistant epoxy is applied as the primary moisture barrier, bonding directly to the prepared neodymium surface
- Polyethylene outer layer: A tough, flexible polyethylene coating is applied over the epoxy, providing mechanical protection against impact, abrasion, and UV degradation
This multi-layer system creates a continuous, pinhole-free barrier that prevents saltwater from reaching the magnet core.
Why Two Layers?
Two layers are needed because epoxy bonds well and resists chemicals but cracks on impact, while polyethylene is tough but bonds poorly to neodymium.
- Epoxy provides excellent chemical resistance and adhesion to the magnet surface, but is relatively brittle and can crack under impact
- Polyethylene provides flexibility and impact resistance, but does not bond as well directly to neodymium
Together, they create a coating system that is both chemically resistant and mechanically durable — essential for the demanding conditions of commercial diving operations.
Marine-Grade Hardware
Every wetted metal part is corrosion-resistant: 316 stainless steel eye nut, handle and screws in a plated A3 steel pot. Every metal component that contacts saltwater must also be corrosion-resistant. Our diver magnets use:
- 316 stainless steel eye nut: The most corrosion-resistant common stainless steel grade, suited to continuous marine exposure
- 316 stainless steel handle: Provides controlled attachment and detachment without exposing unprotected metal
- 316 stainless steel screws
- Plated A3 steel pot: Holds the sealed magnet and concentrates its magnetic flux while resisting deformation
Maintenance Best Practices
Rinse after every dive, inspect the coating, store dry, remove iron filings and avoid impacts to extend coating life.
- Rinse after every dive: Fresh water removes salt crystals that can gradually degrade the coating surface
- Inspect the coating regularly: Look for chips, scratches, or wear that could allow moisture ingress
- Store dry: Keep magnets in a low-humidity environment between uses
- Remove iron filings: Small metal particles trapped on the surface can create scratches that damage the coating over time
- Avoid impacts: Do not drop magnets onto hard surfaces — impacts can crack the coating and damage the neodymium core
For more maintenance and safety guidance, read our safety rules for neodymium magnets or visit our FAQ page.
