When looking to increase the longevity, resistance, and performance of a metal or metal alloy through surface treatment, a metal finisher will usually choose between one of the following options: passivation or electropolishing. Each process has its own benefits and disadvantages. However, the process that is eventually chosen will be determined by several factors.
So what is passivation? What is electropolishing? And which is the better choice?
Passivation
Passivation can be defined as treating or coating a metal or metal alloy in order to reduce chemical reactivity on the metal’s surface. For example, a common passivation technique would be to submerge a piece of stainless steel in dilute citric or nitric acid; this acid will react with the free iron on the metal’s surface to form an oxide layer. The free iron, already having been reacted to form an oxide, will no longer be suspect to rusting or further reacting.
The Benefit of Passivation
When an oxide layer is created on the metal by the passivation process, the resulting surface is protected from corrosion and rust. Corrosion, contamination, and rust can destroy the steel. By using a process such as passivation, you can make sure that your metal’s performance will not be affected by chemical degradation.
Are there any Disadvantages?
As with most processes, passivation has disadvantages. Most notably different from electropolishing, it does not smooth out the surface of the metal; it only protects it from corrosion. It also requires a pre-cleaning operation, which will extend the time required to complete the process.
Electropolishing
Electropolishing is a popular way of treating metals, used most notably in the aerospace and medical industries. An electrochemical process also known as electrochemical polishing, electrolytic polishing, or anodic polishing, electropolishing is the act of removing metal from an object’s surface by means of electricity and a conductive electrolyte solution.
The Benefits of Electropolishing
Electropolishing has many benefits, including the elimination of burrs from metal parts, the overall operational improvement, and the cleaning of the surface metal.
In terms of deburring, electropolishing will remove rough surfaces and microscopic debris that would cause problems in the normal course of work for a machine part. This will create a smooth metal piece that is free of contaminants, effectively extending the life of the piece and the machine as a whole.
In medical facilities, sanitation and sterilization are essential. Electropolishing is an excellent method to ensure these metal instruments are free of contaminants. When used in clinical industries, electropolishing ensures that medical instruments remain sanitary, rust-free, and without blemish.
In automotive and aerodynamic applications, electropolishing removes foreign particles and burrs, smoothing metal surfaces and ensuring that metal resistance is kept to a minimum.
This process is used in countless other industries, as nearly any product with a metal component can be benefitted with electropolishing.
Which Process is Better?
As electropolishing smoothens the surface of a metal piece, it would be more beneficial than passivation when applied to either a piece of machinery or a metal whose purpose is to look aesthetically pleasing. The best application of passivation in when a metal piece need only be prevented from reacting to its environment.
Electropolishing is usually the favored process as it is faster, can be controlled, and has a generally wider range of metals it may be applied to. In addition, a metal surface usually becomes passivated over a normal cycle of electropolishing. The main advantage of passivation over electropolishing is that passivation focuses solely on the formation of an oxide layer and will thus usually produce a thicker layer than will electropolishing.
In the end, the process that you choose will depend on the final purpose of the workpiece. If you simply need a piece to resist corrosion and be made unreactive, passivation is a fine process. However, if your piece needs to be polished and efficient as well, electropolishing is the way to go.
