How the Passivation Process Works for Aviation & Aerospace Components

Stainless steel brings with it a wide range of different benefits for aviation and aerospace components — chief among them being natural resistance to fire and heat, high strength and impact resistance, sustainability, and more. That doesn't mean that it's a perfect material, however. If left untreated, it can negatively react to its environment in a way that causes rust and corrosion, for example.

Thankfully, solutions exist to help make this something aviation and aerospace organizations don't have to worry about. The passivation process is commonly employed to help make sure that high quality aviation and aerospace components stay that way for as long as possible.

Passivation vs. Anti-Corrosion Plating 

Passivation is a process that is used to increase the corrosion and rust resistance of machined parts, particularly those made from stainless steel. It does this by removing the free irons from the surface, restoring everything to its original corrosion specifications.

Passivation is typically a three step process, starting first with a thorough cleaning of the components in question. At that point, an acid bath is used (which will vary slightly depending on the specific passivation technique being employed). Finally, the material is rinsed and it is ready for further use.

Note that this is different from the use of anti-corrosion plating, though the two techniques do have similar end goals. Passivation treats a material like stainless steel in a way that reduces the way the environment (think: water and air) will have over the long-term. Anti-corrosion plating, however, adds a coat to the surface of the metal in an attempt to slow down oxidation. Both methods provide corrosion resistance, they just go about it in two entirely different ways.

The Kinds of Aerospace Components That Need Passivation

In short, any aviation or aerospace component that is made from stainless steel will need passivation before it can be used. Stainless steel components that are cut during machining or for repair/maintenance purposes would absolutely benefit from this process, for example. Microscopic portions from the blade or bit could easily be left behind, resulting in contamination and rust over time.

For similar reasons, passivation should also be used on components that could see damage from handling or other types of routine maintenance. The same is true of anything that might be exposed to dirt or dust while in a shop.

This is all important because stainless steel is commonly used all across the aviation and aerospace industry. It is used to make components that include but are not limited to ones like:

• Actuators
• Landing gear components
• Control rods for aircraft
• Piston engines
• Jet engines
• Exhaust ducts
• Flash boilers
• Cockpit fasteners
• And more

Premature failure for any reason at any of these points could permanently ground an aircraft (not to mention endanger countless lives), which is why extreme care should always be taken. 

The Various Passivation Methods: An Overview

One of the main types of passivation methods that is commonly employed is called nitric acid passivation. Here, nitric acid is used to remove any free iron from the surface of the material. When the chemical treatment is finished, a protective layer of oxide is produced — thus increasing the corrosion resistant nature of the final product.

Another option is referred to as nitric acid with sodium dichromate passivation. Sodium dichromate is essentially an increased concentration of nitric acid, making the two processes very similar. It's commonly employed with materials that are less naturally resistant to corrosion to help prevent a flash attack. This is when a darkened surface manifests as a result of the process, complete with an (unfortunately) degraded oxide layer. 

Finally, there is citric acid passivation. The major difference is that instead of using nitric acid, the aforementioned citric acid is used. Citric acid is non-toxic and safer to handle, but must often be combined with biocides to prevent organic growth in the solution.

The Benefits of Automated Passivation Systems

In an overarching sense, automated passivation systems can help significantly accelerate the passivation process, helping an organization achieve better results in a faster and more cost-effective manner than if everything were being performed manually.

Not only can automated systems eliminate human error by removing the need for an operator to interact with what is going on, but it also reduces variability as well. By meticulously controlling exposure to chemicals, all components are treated equally. It also frees up the valuable time of human operators so that they can focus on more important matters. 

If you'd like to find out more information about the intricacies of the passivation process and how it works within the context of aviation and aerospace components, or if you'd just like to discuss your upcoming project with someone in a bit more detail, please don't hesitate to contact us today.