What Is the Difference between Pickling & Passivation?

 

The key difference between Pickling and Passivationis that pickling is the process we use to remove impurities on a metal surface, while passivation is the protection of a metal surface against corrosion. We also use the term pickling when it comes to food. Here, pickling is a form of surface treatment of metals. On the other hand, passivation is making a material "passive" to corrosion. Unlike pickling, here we protect the surface of the metal before it becomes impure.

What is Pickling?

Pickling is the process of treating metal surfaces to remove any impurities on the surface. Impurities can include stains, rust, scale, inorganic contaminants, etc. Iron and its alloys, silver, copper, aluminium, brass are a few examples of metals that undergoes this process.The chemical agent we use in this process is "pickle". It usually contains acids. It also contains other ingredients, such as wetting agents, corrosion inhibitors, etc.This pickling process is common in cleaning steel surfaces in steel making processes. The need for this process is to remove substances on the metal surface that can affect further metal processing such as plating and painting. De-scaling is an important step in this process. Many hot working processes leave a layer of discolouring oxide on the metal surface. We can remove this layer of encrustation by immersing it in a vat of brine.

Pickling techniques

In general, most Pickling Companies use three different techniques: the mechanical pickling, the chemical pickling and pickling electrolytic or electrochemical. Mechanical pickling involves the mechanical removal of impurities present on the surface of metals by abrasion. Chemical pickling is carried out by means of spray, brush or immersion pickling agents by putting the surfaces in contact with ad hoc chemical solutions. The electrolytic or electrochemical pickling involves the use of chemical solutions together with the supply of electric current with an appropriate waveform, which optimizes and speeds up the treatment of the metal.

Some information on passivation

Corrosion is the main enemy of all metals. It is formed when common steels react with the environment creating a surface containing iron oxide. This very porous surface allows the oxidation process to continue, penetrating into the steel. The corroded surface will produce what is usually referred to as rust.The term passivation refers to an electrochemical phenomenon aimed at slowing down or preventing the corrosion of metallic materials and metal alloys.

ALT=Pickling and Passivation

The company specializing in passivation leads to the passivity of the metal material. In particular, the phenomenon of corrosion is stopped. The final result is a metal with zero corrosion speed. This is a phenomenon caused by the continuous dissolution and regeneration of the passivation film.The passivation layer formed by the use of baths with a content of 15% -20% nitric acid are more homogeneous and have oxides-hydroxides more rich in chromium.Passivation brings several advantages –

·         Improves corrosion resistance

·         Gives a uniform and smooth finish / appearance

·         Makes the surface shiny

·         Allows easier cleaning

·         Helps to give the product a greater life.

Comparison and characteristics

In the industrial sector, the surface of the stainless steel work piece must be machined to improve its quality. There are many processes of surface treatment of stainless steel, such as passivation, pickling, rust proofing, polishing, galvanizing, electrophoresis, etc. The most commonly used is the Pickling and Passivation solution. The surface treatment of stainless steel pickling passivation is very convenient. Of course, different manufacturers will choose a suitable surface treatment based on their manufacturing process.

First, we explain the role and characteristics of the solution. When working with the surface of stainless steel parts, the whole stainless steel part is mainly immersed in the passivation solution until the surface of the stainless steel parts is completely uniform. After this process, the stainless steel part then rinse with clean water. In this way, the surface of the machined work piece will achieve a uniform colour and a beautiful surface will be obtained. This type of processing method is increasingly extended in the application. And the stainless steel pickling and passivation solution can be recycled and used without evaporation, non-volatile, no yellow smoke and hydrogen embrittlement, so the operating environment is good and does not require special equipment.

Conclusion

Metals are most of the time very reactive when we expose them to normal air. And, through proper Chemical Cleaning it is possible to protect the entire metal surface. Pickling and Passivation are two techniques we can use to protect the metal surface. Pickling is the process of treating metal surfaces to remove any impurities on the surface. We can do this using pickled liqueur. In this way it protects a metal surface from impurities on the metal surface. Passivation is the process of making a material "passive" to corrosion. Furthermore, passivation is sometimes spontaneous and natural, or we can do it through a chemical reaction. Furthermore, it protects the metal surface even before it is exposed to normal air.