The passivation of stainless steel is done to enhance its corrosion resistance properties. The passivation treatment helps to perk up the surface state of stainless steel by dissolving iron that has been engrafted on the surface during the process of forming or machining. If these contaminations are left on the surface, the iron can oxidize and give the appearance of rust spots on the stainless steel. The passivation process for stainless steel helps bring back the original corrosion-resistant surface by cr
Passivation in general can be defined as a process in which a material is made "passive", often by depositing on it a coating of oxide that stick to the surface of the metal. In air, the passivation has an effect on the properties of almost all kind metals–some of the prominent example being aluminum, zinc, titanium, and silicon which is a metalloid. In the context of corrosion, passivation is the self generated creation of a tough non-responsive coating on the surface of the object that arrests the further corrosion. This film is often an oxide or nitride which has thickness of only few nanometers.
Passivation of Stainless Steel
The passivation of stainless steel
is a method which is carried out to make its surface passive, i.e., a coating on surface is created which forces the surface to drop its chemical reactivity. In other words, passivation of stainless steel is done to make its surface non-reactive. It also helps to make the stainless steel surface corrosion resistant.
The passivation process for stainless steel aims at removing the compounds of iron from the surface of the stainless steel by means of a chemical disintegration. In most cases, the chemical disintegration involves treating stainless steel with an acid solution that will get rid of contamination on the outer layer without affecting the stainless steel itself. Additionally, the process of stainless steel passivation can also be described as the chemical treatment of stainless steel with a gentle oxidant, like a solution of nitric acid which is carried out to increase the spontaneous creation of a protective passive coating on its surface. The passivation of stainless steel is known to provide a much desired low corrosion rate of the metal.
In simple terms, the passivation process for stainless steel takes away the free iron pollutants which are left behind on the outer layer of the steel from machining and fabricating. These pollutants are possible corrosion places that usually result in early corrosion and in due course lead to the weakening of the component if not removed. The passivation process also eases the creation of a thin, transparent oxide layer that defends the stainless steel from selective corrosion. Thus, the process of passivation of stainless steel is a process that not only cleans the surface of stainless steel but also forms a protective coating on its surface to safeguard it against corrosion or oxidation.
How Passivation of Stainless Steel Is Performed
The passivation process of stainless steel usually starts with a complete cleaning cycle in which all the contaminations are removed from its surface which are present there during the fabrication and machining procedures. The main types of contaminations which are generally present on the stainless steel surface includes oils, compounds, coolants, cutting fluids and other kind of organic as well as metallic remains. There are different ways through which the general cleaning can be done.
When the cleaning process is done, the stainless steel object is dipped into the suitable passivation solution. Although there are various kinds of solutions which are used for passivation of stainless steel, the most preferred and commonly used one are the nitric-acid-based solutions.
The most important variables that need to be considered and maintained for the selection of proper passivation process are time, temperature and concentration. Vigilant solution control which includes water purity, parts per million concentrations of metallic impurities and chemical maintenance are quite decisive elements to obtain success and desired results. Additional, the quality of stainless steel also plays an important role in deciding the most effective passivation process for stainless steel.
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