Materials Performance Supplements


Materials Performance is the world's most widely circulated magazine dedicated to corrosion prevention and control. MP provides information about the latest corrosion control technologies and practical applications for every industry and environment.

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VAPOR PHASE CORROSION INHIBITORS The use of traditional corrosion inhibi- tors in paints and coatings continues to be challenged from both an environ- mental and performance aspect. End users are demanding better corrosion performance and in many formulations this cannot be achieved with traditional zinc or chromate-type inhibitors. The use of vapor corrosion inhibitors in coat- ing formulations has shown that in many systems, they can replace the older technology or signifi cantly improve the performance of the system by working in synergy with the existing inhibitors. Vapor phase corrosion inhibitors (VCIs) are a corrosion inhibitor technology that is comprised of very small particles that are attracted to a metal substrate. Once the par- ticles attach to the metal substrate through adsorption, they prevent a corrosion cell from forming. They come in various for- mulations that are dependent on the type of system they will be used in; for example, films, oils, coatings, cleaners, etc. There are also a variety of formulations that provide The Use of VCIs in Conjunction with or Replacement of Traditional Corrosion Inhibitors MARKUS BIEBER, Cortec Corp., St. Paul, Minnesota, USA protection in ferrous, nonferrous, or multi- metal applications. Other variables include the amount of vapor phase compared to con- tact phase inhibitors. 1 VCIs are widely used throughout a broad range of industries and applications ranging from automotive to processing to preservation and have saved billions of dollars of corrosion-expenses. VCIs as Alternative Corrosion Inhibitor Technologies The use of VCIs as alternative corrosion inhibitor technologies in coatings is not a new concept. In the last few years, however, with the growing environmental pressures to reduce the use of traditional inhibitors containing heavy metals, they have gained in popularity. 2 VCIs as a category are very broad and can be made up of thousands of combinations of raw materials that can have varying rates of effectiveness. Commonly used terms, such as amine carboxylates, cover a broad range of potential formulations. Depending on the formulation, they can vary in their function- ality as far as contact vs. vapor phase inhibi- tion. When choosing the right VCI package to formulate into a coating, it is critical to find not only the package that is compatible with the coatings carrier (solvent or water) but also the resin system. Choosing the wrong inhibitor package can lead to a variety of issues in the coating itself, which include gelling, phase separa- tion, and flocculation. Once these issues have been eliminated, the next stage is testing to determine at which level there is an improve- ment in the corrosion performance, which is typically done using the salt fog test standard (ASTM B117 3 ). Since VCI particles have a polar attrac- tion to the metal substrate, this allows them to work in the coating without negatively impacting other components of the coating such as defoamers, wetting agents, level- ing agents, etc. VCIs are typically added to the formulation in very small amounts by weight of the overall formula. The typical range is from 0.5% to 3%. The particle size of the VCIs is ver y small in comparison to the traditionally used inhibitors (Figure 1). This allows the VCIs to migrate into the smaller voids more effectively. Once the VCIs have adsorbed onto the surface of the metal, they provide an effec- tive barrier that is hydrophobic and pre- vents moisture from getting through to the metal surface. Consequently, this prevents the for - mation of a corrosion cell and renders the moisture ineffective. 4 Experimental Procedure These studies examine the effectiveness of various types of corrosion inhibitors in single-component, waterborne acrylic coat- ings, based on salt fog results (ASTM B117). FIGURE 1 Microscopic surface view. 3 CORTEC SUPPLEMENT TO MP MATERIALS PERFORMANCE JUNE 2019

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