Inorganic Zinc (IOZ) Primer - Chemistry and Purpose of Top Coat? 1

[HotPotato]

I am researching the use of an inorganic zinc primer to protect hot spots on a unit. I did a bit of research into the chemistry behind it but was only able to come up with this: Link

That is a good high level intro. Does anybody have any other information they can provide on the chemistry behind how IOZ primers protect the substrate metal?

Part two of my question is what purpose the top coat of paint (assuming the paired top coat paint from the same vendor) serves? My theory is that besides providing pleasing aesthetics, it serves to protect the primer. This infers that the top coat would not provide any protection to the substrate metal but only protect the primer. Any supporting science would be appreciated too!

 

[SwinnyGG]

I am not a chemist but I have experience with some of these products, specifically Zincanode 304.

I believe the main objective of these primers is to provide galvanic protection. My experience with them has been that when applied correctly (which is tricky) they are mechanically tough and provide good galvanic protection, but are not robust in alkaline environments. So you would use a secondary coating (coal tar epoxy, etc) to protect the zinc primer against the specific conditions it will see in service if necessary.

 

[bimr]

The first zinc rich primers with zinc particles held together with a polymer were utilized in the 1930s. This worked by cathodic protection resulting from the sacrifice of the zinc metal in the coating in preference to oxidation of the carbon steel substrate.

Zinc, under most conditions, is more active than carbon steel and will actively keep carbon steel protected from corrosion provided:
1. There is intimate contact between the zinc and carbon steel.
2. Free zinc available to sacrifice itself. Zinc is somewhat self healing and will bridge small gaps of damaged or uncoated areas.

http://events.nace.org/seminars/ccc_series/2009_SEPT/presentations/Reals.pdf

Zinc-rich primers are topcoated to provide extended exterior durability in severe exposures; to improve color, gloss, and other appearance properties; and to provide resistance to specific conditions such as highly acidic or highly alkaline environments.

http://www.rustbullet.com.au/techni...g-systems/guide-to-zinc-rich-coating-systems/