Zinc Passivation and
Zinc Nickel Passivation


The Zinc Passivation Layer typically has Two Functions…





1) The Passivation Coating / Layer increases the Corrosion Protection of Your Parts / Components (which are usually Steel and sometimes Zinc Die Castings).

2) Depending upon the type of Passivate used… we can essentially "Color" the Parts / Components. Example… if we use a "Black Passivate" we create a Black Finish. If we use a "Yellow Passivate" we create a Yellow Finish. If we use a “Blue” Passivate, we create a Clear to Blue "Chrome-Like" Finish.

Chromates… 

In the past (and also even today), we used Chromates instead of Passivates. Chromates contain Hexavalent Chromium - Cr (VI), and have been essentially phased out by many Governments and OEMs.

The Hexavalent Chromium is supposedly / probably Carcinogenic. Therefore, these Chromates have been replaced with Passivates.

 

Passivates contain Trivalent Chromium - Cr (III), which is normally Specified by OEMs, and is considered Non-Carcinogenic (or at least much, much less Carcinogenic than Hexavalent Chromium).

Okay… enough of this discussion… what you need to know is that Passivates are the "Norm" for today's Zinc Plating and Zinc Nickel Plating.


Let's talk about the Corrosion Protection Function of the Zinc  and Zinc Nickel Passivation Coating / Layer...



As we have discussed elsewhere within our Website… the PRIMARY PURPOSE of Zinc and Zinc Nickel Plating is to Protection Your Parts / Components (the Base Material) from Corrosion.

And normally we can say that we want to Protect Your Parts / Components from Red Rust, because this is the Corrosion that actually begins to “EAT” and Destroy the Part (the actual Base Material) and therefore will eventually cause the Failure of the Part and it's Function (example… the bolt gets so rusty that the bolt breaks and no longer holds the tire on the wheel).

Now (I hope you are still following me! : )), it is the Zinc Coating (or Zinc Nickel Coating) that protects the Steel Part from Red Rust. So… how does the Zinc or Zinc Nickel Passivation Coating / Layer help in Corrosion Protection???

The Passivate Coating / Layer protects the Zinc or Zinc Nickel Coating from the formation of White Rust.

White Rust normally forms before Red Rust. So… logically (and in reality)… if we can protect the Zinc or Zinc Nickel Coating from White Rust… we will therefore Increase the Overall Protection against the Formation of Red Rust.

 

A Clear Example...

Let us give a clear example…

If we have two Steel Parts (let us say we have two similar Bolts).

One Bolt is plated with 8 microns (315 microinches) of Zinc ONLY (NO Passivate Coating / Layer)...

And the othe Bolt is plated with 8 microns (315 microinches) of Zinc AND has a Passivation Coating / Layer...

We put both of these Bolts into the Salt Spray Chamber and perform a Neutral Salt Spray Test... the Bolt that is plated with Zinc ONLY will immediately begin to Form White Rust... Our Bolt that has BOTH Zinc Plating and a Passivation Coating / Layer does NOT immediately Form White Rust.

Now… we know that we will get about 15 hours of Neutral Salt Spray Protection against Red Rust for every 1 micron (39 microinches) of Zinc Plating Thickness. Therefore, our Zinc ONLY Plated Bolt will probably begin to show Red Rust after about 120 hours.

Now… with our Zinc Plated AND Passivated Bolt… the Passivation Coating / Layer (depending upon the type of Passivate) will give us around 96 Hours of Corrosion Protection to White Rust and therefore our TOTAL PROTECTION to Red Rust will be 216 hours to Red Rust.

Therefore, you can see that by adding a Passivation Process Step we are dramatically able to increase the Overall Corrosion Protection of the Customer’s Parts.


The "Cosmetic / Decorative" Function of Passivation...



Okay… now let us begin discussing Point Number 2 (if you even remember???)…

The Second "Possible" Purpose of the Zinc Passivation Coating / Layer is for "Cosmetic / Decorative / Identification" Purposes…

It is simple to state that Customers normally want their Parts / Components to look "right". Both the "End Application" of the Part / Component...  and the Requirements of the Customer will have a large influence upon the "Cosmetic / Decorative / Identification" Requirements.

 



Let us explain this last sentence in more detail…



1) If we are Zinc Plating Shopping Carts (the Shopping Carts we use at Walmart for example), then there are certain Decorative Effects that Walmart is looking for.

First of all, Walmart doesn't want the Shopping Cart to Rust!

AND Walmart wants the Shopping Cart to be bright and shiny for as long as possible!

Probably a Nice "Blue Bright / Chrome-Like Passivation Coating" on top of an Acid Zinc Coating / Deposit will help us fulfill this requirement!

Imagine if we had NO Passivation Coating / Layer… we would Plate the Shopping Cart with Zinc (to protect it from Red Rust) and after a few months (maybe a few weeks) in use at Walmart… and the Shopping Cart would begin to Form White Rust.

While the Function of the Shopping Cart is still GOOD, with the Formation of White Rust… the Shopping Cart begins to look like CRAP (grey, not bright, and formations of White Rust all over the place).

So… in this particular Application, a Passivate Coating / Layer allows the Shopping Cart to maintain its “Bright, Shiny, Decorative Chrome-Like” Appearance for a longer time. 

 

2) There are also a large number of Parts / Components that will NEVER be seen by an End-User Customer.

A good example is Automotive Parts / Components, that will at best, only be seen by mechanics.

Here, the Main Requirement of the Passivation Coating / Layer is to provide the Expected Corrosion Resistance so that the Part / Component will fulfill it's Function for the longest amount of time possible.

 

3) We can also use the Passivation Coating / Layer to help with Identification Purposes.

By using the various "Colors" available (Black, Olive Drab, Yellow, Iridescent, or "Clear - Colorless - Transparent to Blue" we can Differentiate between Various Parts (example... different Screws for different purposes). This can help in Assembly and Maintenance Issues.

 

Passivates as an Adhesion Promoter...

Passivates can also help in promoting (making better) the Adhesion of Powder Coatings (great choice is ENTHONE's PERMA PASS ULTRA III), rubber fittings, or laquer.


 

Sources Of More Information...



Click here for information on Thin Film Passivates.

Click here for information on Thick Film Passivates.




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Available Colors are Black...


And Yellow...


And "Clear" / Transparent"...