Today's KNOWLEDGE Share ; Zinc dispersion in zinc-rich Epoxy

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Today's KNOWLEDGE Share

Effective zinc dispersion in zinc-rich epoxy (ZRE) coatings requires over 80 wt% zinc, ensuring electrical contact between particles and the steel substrate for cathodic protection. Standards like ISO 12944 define ZREs as having high zinc content, but effective dispersion and continuous electrical paths are critical for performance, often achieved through careful application and sometimes aided by additives like graphene to create conductive networks that prevent isolation of zinc particles.


Importance of Zinc Dispersion


Cathodic Protection:

The primary mechanism of ZREs is cathodic protection, where zinc particles act as sacrificial anodes, corroding preferentially to protect the steel.


Electrical Contact:

For effective cathodic protection, a continuous electrical pathway must exist between the zinc particles and the steel substrate.


Barrier Protection:

The corrosion products from the zinc also fill micropores in the coating, providing a secondary physical barrier effect against corrosive substances.


Standards and Specifications


High Zinc Content:

ISO 12944 defines a zinc-rich coating as having more than 80 wt% of zinc dust in the dry film to facilitate effective cathodic protection.


Active Electric Channels:

The dispersion must ensure that the zinc particles are not isolated by non-conductive binders or corrosion products, which would hinder the formation of active electronic channels to the metal substrate.


Achieving Effective Dispersion


Pigment Grinding:

The manufacturing process involves a grinding stage to ensure uniform dispersion of zinc pigments, often using bead mills.


Binder and Pigment Ratio:

The correct proportion of binder (epoxy resin) to zinc is crucial. An excess of binder can lead to isolated zinc particles, reducing the coating's effectiveness.


Surface Preparation:

A properly prepared, clean, and often sandblasted steel surface is essential for the zinc-rich coating to adhere properly and form the necessary electrical contact with the substrate.


Factors Affecting Dispersion and Performance


Zinc Particle Size:


While not explicitly a dispersion metric, the particle size of zinc dust is relevant.


Coating Additives:

Materials like graphene can enhance dispersion by promoting the formation of conductive networks within the coating, which improves electrical contact and extends the lifespan of the sacrificial protection.


Curing:

Proper curing conditions after application are necessary for the coating to fully harden and form the necessary barrier and conductive properties.


source : Hussien Elkaluoby

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