Post 14 September

Stainless Steel Passivation: What It Is & How It’s Done

Steel contains a significant amount of iron, which makes it susceptible to rust and wear when in contact with water and other chemicals. Steel needs to be safeguarded in order to stop these negative consequences. Using a method known as passivation is one of the most popular ways to accomplish this.

Why Passivation Happens?
Fundamentally, passivation is a well-liked and successful method of finishing metals like steel. In stainless steel, the free iron is removed from the surface material using acid during the passivation process. The finished product is steel that has a passivation layer applied to it, making it less prone to react with water and more resistant to rust and erosion.

How was it found?
Christian Schönbein, a chemist, made the discovery of passivation in 1800. As he submerged steel in highly concentrated nitric acid, he noticed that the iron’s chemical reactivity had been significantly diminished or eliminated. This steel byproduct was thought to be in a “passive” state at this point.

Throughout the course of the next century, as this method grew more widely, additional harmful environmental and safety complaints regarding nitric acid became well-known. Fortunately, a German brewing company discovered citric acid as a safer and more efficient substitute. In recent years, businesses have opted to utilise citric acid instead of nitric acid to safeguard the environment and the health of their employees.

Gains from Passivation
The benefits of this approach are extensive. For instance, by using nitric or citric acid to finish your steel, you may expect a longer lifespan for your steel, a strong barrier against rust and corrosion, the removal of pollutants from the steel’s surface, and a reduction in long-term maintenance expenses.

Tips for Passivation
It’s crucial to correctly complete each step of the passivation process to achieve the optimum results. Deep cleaning the steel is the first crucial step. By doing this, the product is cleaned of contaminants like grease, coolant, and iron flakes that have accumulated on the piece and might subsequently reduce the acid’s efficacy.

While acid does remove some impurities, it is unable to properly dissolve fats present on the metal, such as grease and oil. Instead, it only adheres to the material’s outside, preventing the steel from properly passivating.

The steel can then be placed into an acid bath, particularly one containing citric acid. As a result, the bottom layers of metal alloys like chromium will remain intact while the free iron is removed. After finishing, allow the steel to dry for one to two days so that the oxygen in the air can build a chromic coating on its surface.

The modification and optimization of chromium oxide will have a protective impact. With the addition of this new layer of metal and the removal of the free iron, steel will become more robust, nearly rust-proof, and less chemically reactive.

Keep in mind that you might need to repeat this procedure if the steel is mechanically damaged, exposed to new chemicals, or heated above the recommended temperature. Fortunately, by repeating this easy technique, the advantages can be rapidly obtained whenever necessary.