In recent decades, corrosion inhibitors have become widespread application in mitigating or suppressing the corrosion of metals in varying fields, spanning from construction materials and industrial sectors to surface treatment for important cultural heritage. Generally, corrosion inhibitors are unique chemical substances that are added in limited amounts to the environment in which a metallic surface would corrode, to slow down, reduce, or prevent the corrosion process.
These chemical substances are generally effective in low concentrations. This excludes all chemicals that lower the corrosion rate by substantial pH variation or hydrogen sulfide scavengers, facilitating the removal of aggressive species from this solution. Whether you need corrosion inhibitors for steel or any other metal, it's important to consult with an expert who understands the concept of corruption and how this process can be prevented.
Inhibitors reduce or prevent corrosion by creating a solid barrier between the metal and the outside harsh weather elements. Corrosion retardation or the reduction in the oxidation rate of a metallic surface by the addition of some kind of chemical compound is usually caused by corrosion inhibitors.
Note that these inhibitors are usually easy to apply and often offer the benefit of the in-situ application without the inconveniences of disruption to the process. So far, experts believe that corrosion inhibitors are a cost-effective method of converting or preventing corrosion. Having the right corrosion inhibitors can help preserve metallic parts and pieces of equipment for a long time.
The role of corrosion inhibitors
Both organic and inorganic compounds constitute different types of corrosion inhibitors. As mentioned earlier, corrosion inhibitors affect the entire metallic surface when applied at the right concentration level. The inhibitor can be absorbed on the metallic surface, forming a protective layer that prevents weather elements from coming into contact with the metal surface. The absence of elements necessary for corrosion means rusting will not occur and the metal surface will stay intact.
Keep in mind that there are different types of corrosion inhibitors. Each of them works different but their end goal is to control or prevent corrosion. That doesn’t mean you should purchase just any inhibitor. You must first analyze your needs, extend of corrosion, and other relevant factors then choose the most effective corrosion inhibitor. It’s recommended to consult with an expert just to be sure you are choosing the right product to control or prevent corrosion.
Types of corrosion inhibitors
Now that you know what corrosion inhibitors are and their role in preventing corrosion, it's time to learn the different types of corrosion inhibitors. These include:
Interface inhibitors
Accumulating scientific evidence shows that interface inhibitors control corrosion by creating a protective film at the metal-environmental interface. These corrosion inhibitors can be classified into vapor-phase inhibitors and liquid phase-inhibitors. Liquid inhibitors can further be classified into cathodic inhibitors, mixed inhibitors, and anodic inhibitors. These classifications depend on whether they inhibit the cathodic, anodic, or both electrochemical reactions.
Cathodic inhibitors
Cathodic inhibitors slow down the rate of cathodic reaction to reduce the diffusion of the corroding species to the metal surface. The common examples of cathodic inhibitors include oxygen scavengers and cathodic poison. Keep in mind that cathodic poison inhibitors can increase the susceptibility of a specific metal to hydrogen-caused cracking because the metal can easily absorb hydrogen during the process of cathodic charging or aqueous corrosion.
Anodic inhibitors
Generally, anodic inhibitors act by forming a highly protective oxide film on the metal surface. This causes a significant anodic shift in the corrosion potential. These changes force the metal surface into the passivation region. These are also known as passivates. Some of the common examples of anodic inhibitors include tungstate, chromates, nitrates, and molybdates.
Mixed inhibitors
These inhibitors work by slowing down both anodic and candidate reactions. They are simply film-forming compounds that facilitate the formation of precipitate on the metal surface blocking both cathodic and anodic sites indirectly. It is important to mention that hard water that’s high in magnesium and calcium is less corrosive compared to soft water. This is because the salts in hard water usually precipitate on the surface of the metal creating a protective film.
Some of the commonly mixed inhibitors include phosphates and silicates. For instance, sodium silicate is used in most domestic water softeners to prevent instances of rust water. Sodium silicate can also be used in aerated hot water systems to protect copper, brass, and steel. But this protection maybe not always reliable because it depends majorly on pH.
Note that phosphate also requires oxygen to function perfectly as corrosion inhibitors. Phosphates and silicates don't afford the degree of protection offered by nitrates and chromates, but they are very useful in various situations where less toxic additives are necessary.
Summary
Each year, corrosion-related damage amounts to billions of dollars. What most people don’t know is that this damage can be controlled. By understanding the process of corrosion and using the right corrosion inhibitors, you can successfully protect your metallic objects.
