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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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Influence of Powder Size of the Vapor Corrosion Inhibitor on Inhibiting Effectiveness Behzad Bavarian, Lisa reiner, and BaBak samimi, California State University Northridge, California, USA Boris a. miksic, Fnace, Cortec Corp., St. Paul, Minnesota, USA The protection effectiveness of com- mercially available vapor corrosion in- hibitor powders with different particle sizes was evaluated. Conventional pow- der size of nanoparticle powder inhibit- ing effectiveness was compared using a vapor-inhibiting ability (VIA) test method. Optical microscopy post VIA corrosion tests revealed that the parti- cle size of inhibitor powder has a signif- icant influence on the degree of protec- tion. The nanoparticle inhibitor showed a corrosion rating of Grade 4 and >41% decrease on the corrosion rate both in electrochemical tests and continuous exposure tests compared with the in- hibitor with coarse particle size. Surface coverage also showed improvement mainly due to an increase of effective surface area and the partial pressure of vapor inhibitors as powder particle size decreased. Adsorption energy was roughly –16,740 J/mol for the nanoparticle-size inhibitor, while ad- sorption energy was roughly –13,660 J/ mol for the coarse-particle-size inhibi- tor. This was indicative of a stronger physical adsorption to the metal surface for the nanoparticle than the coarse in- hibitor, leading to better corrosion pro- tection. Laser Doppler anemometry measurement using the Doppler shift in a laser beam to measure the flow veloc- ity showed a velocity of 6 ft/s for the nanoparticle and uniform flow. The coarse-particle inhibitor had a lower ve- locity of 3 to 4 ft/s and nonuniform flow. Corrosion inhibitors can adsorb to a metal surface, protecting it from the envi- ronment by forming a nonreactive, hydro- phobic layer that prevents corrosion. To be effective, an inhibitor will interact with the anodic or cathodic sites to slow oxida- tion and reduction reactions. Vapor phase corrosion inhibitors (VCIs) rely on vapor pressure for transport of active inhibitor compounds. VCIs form a bond with the metal surface and create a barrier layer to minimize corrosive ions on the surface. VCIs can be used alone or incorporated into packaging materials, oils, chemicals, and coatings. Some applications have been demonstrated for long-term (two years or more) storage of liquefied natural gas pip- ing in Abu Dhabi, United Arab Emirates; power and desalination plant boiler tubes, also in Abu Dhabi; and gas pipe f langes in Wales, United Kingdom. 1 Other applica- tions include aboveground storage tanks with underside corrosion between the tank bottom plate and its concrete foundation. 2 The mechanism of the nanoparticle VCIs involves the transport of the inhibitor to the metal surface and the inhibitor interaction with the metal substrate to form a protec- tive film. When added to a liquid coating, the inhibitors react with water and dissoci- ate. After application, as the liquid coating cures, the charged inhibitors migrate and adsorb onto the bare metal surface. Adsorp- tion occurs as a result of electrostatic forces between the electric charge of the metal and the ionic charges of the inhibitor molecules. Once attached to the metal, the tails of the inhibiting molecules produce a highly hydro- phobic film that repels water and other cor- rosive species, which in turn reduces corro- sion. 3-5 A good level of corrosion protection can be obtained with an inhibitor that forms a passive microphobic layer on the metal surface using micron-size powder particles. However, as a result of the larger particle size, gaps may exist between the particles that are deposited on to the metal surface. This lack of coverage provides an opening for corrosive species to attack the unpro- tected surface (Figure 1). VAPOR PHASE CORROSION INHIBITORS FIGURE 1 Particle size variation can lead to ingress of corrosive species that may attack the surface of the metal. 4 JUNE 2017 MATERIALS PERFORMANCE CORTEC SUPPLEMENT TO MP

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