The term “Passivation” is derived from the adjective ‘passive’ which loosely refers to a state wherein the body or material in concern is non reactive or non responsive to any outside influence.
Process of Metal Passivation:
The main purpose of metal passivation is to enable the metal to be less prone to corrosion when exposed to environmental conditions such as water and air. Passivity involves the formation of a shield over the base metal. The technique involves the use of a light coat of a protective material such as metal oxide to create a guard against corrosion. This technique is more specifically used to enhance and strengthen the outer appearance of metals, thereby increasing their durability.
Materials Used for Passivation:
Silicon –Various forms of Silicon such as silicon nitride, silicon dioxide, titanium dioxide can be successfully used to reduce surface recombination that rapidly occurs on metals exposed to the atmosphere.
Aluminium– Aluminium in its pure form works wonderfully to create a thin layer of protection known as Aluminium Oxide, over the metal, when it is exposed to oxygen. This occurs naturally through the process of oxidation (the chemical process by which any substance such as chemicals, wood or metals etc is combined with oxygen in the air). This Aluminium Oxide works as a superb physical barrier and prevents further reduction or corrosion of the substance.
While Aluminium works well for passivation, aluminium alloys provide no protection from corrosion.
Stainless Steel- Materials and substances made from Stainless steel are usually non corrosive and hence may not necessarily require going through the passivation process. However, certain stainless steel products may need some amount of treating to ensure longevity in usage and durability.
Passivated Stainless Steel
Passivation is a critical step in maximizing the essential corrosion resistance of parts and components machined from stainless steels. It can lead to a major difference between satisfactory performance and premature failure of products and machinery made from stainless steel. If it is performed incorrectly, passivation can actually induce corrosion.
Passivation is an essential process that is conducted on the stainless steel alloy (the fusion of two or more metals or a metal with a non metal to create another unique and new substance), thereby increasing the durability and performance scale of the machine whose part or parts have been manufactured using stainless steel components. It is not a scale removal treatment nor is it like a coat of paint.
Expert opinions vary on the precise mechanics of how passivation works towards protecting the substance. But it is certain that a protective oxide film is present on the surface of passive stainless steel. This invisible film is considered to be extremely thin, less than 0.0000001 inch thick, which is about 1/100,000 the thickness of a human hair!
A clean, brand new and freshly polished and manufactured stainless steel part naturally acquires this thin film of oxide on exposure to the oxygen in the air. This further goes into the machining process.
Understanding the meaning of Passivity:
‘Passivation’ mainly refers to a process in Metallurgy wherein a metal is treated in such a way so as to render the surface less reactive chemically.