Passive corrosion protection: Self-healing and flexible adhesion lead to success
Passive corrosion protection is a critical measure for preserving the integrity and functionality of metal structures. It involves the use of coatings and other protective measures that create a physical barrier between the metal and corrosive environments. In contrast, active corrosion protection, through techniques such as cathodic protection, electrochemically reduces the corrosion rate without completely blocking the metals’ direct exposure to corrosive substances.
What is passive corrosion protection?
Passive corrosion protection works by forming a continuous, impermeable barrier that keeps corrosive substances at bay. This barrier can consist of various materials, such as corrosion-inhibiting wax, coatings like paints, or specially treated surface layers that either physically cover the metal or chemically react with it to form resistant layers. The surfaces must have high electrical resistance so that they prevent direct contact between the metal and corrosive elements, such as more noble metals in the electrochemical series. It is crucial that the driving force—the electrochemical potential—does not lead to an electrochemical reaction. This is particularly important in combating galvanic corrosion and contact corrosion in aluminum, where electrochemical processes would otherwise progress rapidly.
Self-healing & Adhesion
The core of passive corrosion protection lies in creating a continuous, impermeable barrier that prevents corrosive substances from coming into contact with the metal surface. Corrosion protection wax and a few other coatings enable minor damage to the barrier to be repaired automatically, thereby keeping the protective barrier intact. This effect is called self-healing.
For passive corrosion protection, good adhesion is also crucial to ensure that the barrier remains intact under various operating conditions, such as mechanical stress or thermal fluctuations, and thus no gaps form in the barrier. Good adhesion also reduces the rate of corrosive penetration. With corrosion protection wax and oil, the adhesion strength cannot be determined via a cross-cut test as with paints. The key factor is the wetting of the surface. This naturally applies to cavities in the bodywork or gaps, such as in a bolted joint.
Specific protective measures for passive corrosion protection
- The simplest barriers are conversion coatings, which cause a chemical transformation of the surface on metals such as aluminum to increase their resistance to corrosion. Some conversion coatings have self-healing properties, but their protective effect is far less effective than that of organic barriers
- Paints are the best-known corrosion protection barriers. Their adhesion and resistance to damage are crucial for corrosion protection of steel and aluminum.
- Corrosion protection wax can be used for cavity preservation—that is, for protecting hard-to-reach interior spaces, such as those commonly found in vehicle bodies. It protects against the accumulation of moisture and corrosive substances that could otherwise cause serious damage. It can also be applied to sealing surfaces, such as screw connections.
Passive vs. active (or cathodic) corrosion protection
Unlike active or cathodic corrosion protection, which directly influences the electrochemical process of corrosion through the use of sacrificial anodes or sacrificial coatings, passive corrosion protection works by physically isolating the metal surface from the corrosive medium, thereby preventing the corrosion process. While active corrosion protection alters the metal’s electrochemical environment to reduce the corrosion rate, passive corrosion protection effectively blocks any contact between the metal and potential corrosion triggers. This property makes passive corrosion protection particularly valuable in environments where maintenance is difficult or impossible, as it provides long-lasting protection without requiring regular monitoring or an energy supply.
Conclusions
The use of passive protection techniques, supported by the latest advances in materials science and chemistry, offers a reliable method for extending the service life and ensuring the functionality of metal components. By creating an effective barrier that repels corrosive substances, passive corrosion protection ensures the long-term preservation of metal structures without the need for constant maintenance or energy input, as required by active corrosion protection.
PFINDER KG’s products, including oil-based, paint-like, and long-term flexible corrosion protection agents, exemplify this approach. Thanks to their excellent adhesion and ability to self-heal minor damage, they provide durable and reliable corrosion protection. These properties make them ideal for a wide range of applications, from the automotive industry to agricultural and construction machinery, where effective corrosion prevention is critical.