All About Passivation

What is Passivation?

Passivation is a way to make metal stronger. It helps metal not get bad. It makes a thin layer on top of the metal. This layer keeps the metal safe.

Many big places use passivation. Airplanes need it. Doctors use it. Cars need it too.

Did you know? Passivation can make stainless steel last 50% longer! That is a lot!

How Passivation Works

When we do passivation, we make a oxide layer. This layer stops corrosion. Corrosion is what makes metal get bad.

We use acid to make this layer. We can use two kinds of acid:

• Nitric acid (strong but not nice to earth)
• Citric acid (better for earth)

After the acid bath, we wash the metal. Then we dry it. Then we check if it worked.

Types of Passivation

There are two big types of passivation:

1. Chemical Passivation
   • Uses ASTM standards
   • Can use nitric acid or citric acid
   • Most shops use this kind
2. Electrochemical Passivation
   • Used for small parts
   • Needs more tools
   • Makes very good layers

Materials & Places That Use Passivation

Many metals can be passivated:

• Stainless steel (like 304 and 316)
• Titanium
• Aluminum

These places use passivation a lot:

In medical devices, helps make parts that can then be passivated for safety.

Step-by-Step Passivation Process

Here is how we do passivation:

1. Clean the Metal
   • Take off all dirt and oil
   • Use good soap and water
2. Acid Bath
   • Put metal in acid
   • Keep it in for right time
   • Make sure acid is not too hot or cold
3. Wash Off Acid
   • Use clean water
   • Make sure all acid is gone
4. Test It Worked
   • Use salt spray test
   • See if metal stays good

For parts that need special shapes before passivation, CNC milling makes them just right.

Why Passivation is Good

Passivation helps in many ways:

• Stops metal from getting bad in rain or sea water
• Makes things last longer
• Keeps medical devices safe to use in the body
• Meets rules that big groups make

Did you know? In food places, 80% of stainless steel problems come from not doing passivation right!

Mistakes People Make

Some people think wrong things about passivation:

Wrong Idea: “Passivation fixes rust.” Truth: It stops rust from starting, but can’t fix old rust.

Big Mistakes to Not Make:

• Not cleaning the metal first
• Using tap water to wash (it has stuff that’s bad)
• Not following rules about where to put used acid

Passivation vs. Other Things Like It

Passivation is not the same as these:

• Pickling: Takes off scale but can hurt the metal
• Anodizing: For aluminum only, uses electricity
• Electropolishing: Makes metal smooth and also passivates

For parts that need both smooth surfaces and passivation, Swiss machining can be a good first step.

How to Pick a Good Passivation Shop

When you need to find a shop to do passivation, ask:

• “Do you follow ASTM standards?”
• “Have you worked on parts like mine before?”
• “Can you show me test results?”
• “How do you take care of used acid?”

For aerospace parts, make sure they know all about aerospace CNC machining too.

Big Facts About Passivation

Here are some big facts about passivation:

• Citric acid passivation makes 30% less bad waste than nitric acid
• Good passivation can cut fix costs by 25% in chemical plants
• 40% of do-it-yourself passivation fails because of wrong acid mix
• Passivated car parts last 2-3 times longer in places with salt on roads

Questions People Ask

End Words

Passivation is very good for metal parts. It makes a thin oxide layer that stops corrosion. Many big places like medical, aerospace, and automotive need it.

The two main types use nitric acid or citric acid. The ASTM standards tell us how to do it right.

If you want your metal parts to last long, think about passivation!