Application Of Hydrotalcites As Corrosion Inhibiting Pigments In Organic Coatings

Abstract: High strength aluminum alloys typically used in the aerospace industry are provided with coatings for corrosion protection. One of the coating layers is the primer, containing corrosion inhibiting pigments. Conventionally chromate pigments have been used but they are carcinogenic; so there is a need to develop environment-friendly alternatives that can match the corrosion inhibition of chromates. In this study, the use of hydrotalcites as corrosion-inhibiting pigments in organic coatings has been explored. Hydrotalcites are anion clays with excellent ion-exchange capabilities, and for this reason they have been used in industry as anion scavengers. Vanadates are excellent inhibitors of Al alloy corrosion. A Zn-Al-decavanadate hydrotalcite (HT-V) was synthesized and its ion exchange properties characterized. From instrumental neutron activation studies, it was determined that inhibitor release was a small fraction of the total inhibitor in the pigment. However, this was sufficient to provide appreciable corrosion inhibition to Al alloys during potentiodynamic polarization. Additionally, inhibitor release occurred even when these pigments were dispersed in epoxy resins and applied to Al alloys. A bare surface in close proximity to the coating was also inhibited from corrosion. Lastly, coatings containing the HT-V pigment performed well in a salt spray environment, protecting scribe corrosion up to [approx.] 1000 h exposure. Blistering problems encountered during this test were overcome by silane additions to the coating, which improved adhesion and controlled blistering.

"These proceedings represent contributions to the Symposium on the Corrosion and Protection of Light Metals, held at the 204th Meeting of the Electrochemical Society, October 12th through 17th, 2003, in Orlando, Florida."--P. iii.

Abstract: High strength aluminum alloys are used in aerospace industry and are normally coated to prevent corrosion. The corrosion protection of the coatings is mainly provided by pigmented-primer layer. Strontium chromate pigments are widely used, but they are toxic and carcinogenic. The objective of the current study is to develop and characterize the ion exchange compounds bentonite and hydrotalcite as corrosion inhibiting pigments. These compounds were synthesized with different cations and anions, and were used either alone or in mixtures as particulate additive in organic coatings. In coating applications as well as bulk solution, the inhibitor release mechanism is based on ion exchange. To evaluate corrosion inhibition, pigments extract solutions were used in potentiodynamic polarization as well as electrochemical impedance spectroscopy (EIS) experiments on bare aluminum alloy 2024-T3. Cathodic polarization showed that zinc- and cerium-containing filtrate solutions modestly inhibited cathodic current density. These solutions also decreased the extent of pitting damage formed on the surface, as compared to uninhibited 0.5 M NaCl solution. Pigments were also added as primer additives, and painted on AA2024-T3. The coated panels were then subjected to salt spray exposure testing. The possibility of sensing inhibitor exhaustion by means of X-ray diffraction interrogation of the pigment in a coating is demonstrated and discussed on cerium bentonite-pigmented coatings. Although cerium bentonite-pigmented coatings did not show behavior indicative of self-healing, the combination of bentonite and hydrotalcite that released Ce3, Zn2, and PO43− showed potent scribe protection even after 3000 h exposure in salt spray. Promising self-healing was also demonstrated by pigments that consisted of decavanadate-hydrotalcite and zinc pyrovanadate, as indicated by a shiny scribed area after 1000h exposure in salt spray. When these pigments are used, blistering is minimized.

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Smart Composite Coatings and Membranes: Transport, Structural, Environmental and Energy Applications provides the latest information on the increase in demand for new smart materials for a wide array of different technological applications. The book comprehensively reviews the latest developments in smart composite materials used as membranes, barriers, and coatings, with a special focus on corrosion protection, transportation, structure, and the wide range of applications. Part one examines the properties, processing, and manufacture of smart composite materials, along with techniques for modeling the behavior of these materials, while other sections review the use of smart composite coatings in aerospace, marine, and metal structural applications, examine the protective properties and applications of smart composite coatings, and introduce specific low environmental impact and energy efficient applications, such as energy generation and storage, water management, and stone conservation. Explores the use of smart composite materials for coatings, barriers and membranes Comprehensively reviews the latest developments in smart composite materials, with a special focus on corrosion protection, transportation, structure, and the wide range of applications Examines the properties, processing, manufacture and behavior modeling of smart composite materials Focuses on applications that have an impact on more effective energy savings and efficiency, green-house emissions, and environmental protection

Furthermore, synthetic hydrotalcite anion exchange clay pigments were synthesized with vanadates and other possible inhibitor anions. Hydrotalcites allow the use of inhibitors that are too soluble for direct use in organic coatings without leading to coating blistering. A number of hydrotalcite pigments were synthesized and compared to a SrCrO4 standard using electrochemical impedance spectroscopy and salt spray exposure of scribed organically coated panels. Typically, vanadate pigmented PVB coatings were observed to have total impedance within an order of magnitude of SrCrO4 (2 x 107 ohms·cm2). Further, all vanadate coatings were observed to provide some scribe protection during 750 hours of salt spray exposure, however, these coatings also had a tendency to blister. Release from vanadate hydrotalcites was characterized using neutron activation analysis. Interestingly, vanadate hydrotalcite pigments that released relatively small total concentrations of vanadium resulted in the best performance. Low concentrations of vanadium may promote the formation of tetrahedrally coordinated species which were shown to act as inhibitors earlier in this study.

Intelligent Coatings for Corrosion Control covers the most current and comprehensive information on the emerging field of intelligent coatings. The book begins with a fundamental discussion of corrosion and corrosion protection through coatings, setting the stage for deeper discussion of the various types of smart coatings currently in use and in development, outlining their methods of synthesis and characterization, and their applications in a variety of corrosion settings. Further chapters provide insight into the ongoing research, current trends, and technical challenges in this rapidly progressing field. Reviews fundamentals of corrosion and coatings for corrosion control before delving into a discussion of intelligent coatings—useful for researchers and grad students new to the subject Covers the most current developments in intelligent coatings for corrosion control as presented by top researchers in the field Includes many examples of current and potential applications of smart coatings to a variety of corrosion problems

This ACS symposium book is focused on polymer synthesis, materials development, advanced applications for coatings and techniques for measuring a coatings performance in various environments. This book addresses current coating technologies geared for an organic-polymer chemist and chemical engineers perspective. The book would add to an academic, industrial or government laboratory inventory of coatings books.

Provides comprehensive coverage of organic corrosion inhibitors used in modern industrial platforms, including current developments in the design of promising classes of organic corrosion inhibitors Corrosion is the cause of significant economic and safety-related problems that span across industries and applications, including production and processing operations, transportation and public utilities infrastructure, and oil and gas exploration. The use of organic corrosion inhibitors is a simple and cost-effective method for protecting processes, machinery, and materials while remaining environmentally acceptable. Organic Corrosion Inhibitors: Synthesis, Characterization, Mechanism, and Applications provides up-to-date coverage of all aspects of organic corrosion inhibitors, including their fundamental characteristics, synthesis, characterization, inhibition mechanism, and industrial applications. Divided into five sections, the text first covers the basics of corrosion and prevention, experimental and computational testing, and the differences between organic and inorganic corrosion inhibitors. The next section describes various heterocyclic and non-heterocyclic corrosion inhibitors, followed by discussion of the corrosion inhibition characteristics of carbohydrates, amino acids, and other organic green corrosion inhibitors. The final two sections examine the corrosion inhibition properties of carbon nanotubes and graphene oxide, and review the application of natural and synthetic polymers as corrosion inhibitors. Featuring contributions by leading researchers and scientists from academia and industry, this authoritative volume: Discusses the latest developments and issues in the area of corrosion inhibition, including manufacturing challenges and new industrial applications Explores the development and implementation of environmentally-friendly alternatives to traditional toxic corrosion inhibitors Covers both established and emerging classes of corrosion inhibitors as well as future research directions Describes the anticorrosive mechanisms and effects of acyclic, cyclic, natural, and synthetic corrosion inhibitors Offering an interdisciplinary approach to the subject, Organic Corrosion Inhibitors: Synthesis, Characterization, Mechanism, and Applications is essential reading for chemists, chemical engineers, researchers, industry professionals, and advanced students working in fields such as corrosion inhibitors, corrosion engineering, materials science, and applied chemistry.

The interaction of metal with its environment that results in its chemical alteration is called metallic corrosion. According to the literature, corrosion is classified to two types: uniform and localized corrosion. Intervention in either in the alloy environment or in the alloy structure can provide the corrosion protection of metallic materials. Furthermore, the interference in the metal alloy environment can be conducted with the utilization of cathodic or anodic protection via the corresponding inhibitors. Therefore, the most common categorization is cathodic, anodic, and mixed-type inhibitors, taking into account which half-reaction they suppress during corrosion phenomena. The majority of the organic inhibitors are of mixed type and perform through chemisorption. In order to update the field of the corrosion protection of metal and metal alloys with the use of organic inhibitors, a Special Issue entitled "Advances in Organic Corrosion Inhibitors and Protective Coatings" is introduced. This book gathers and reviews a collection of ten contributions (nine articles and one review), from authors from Europe, Asia, and Africa, that were accepted for publication in this Special Issue of Applied Sciences.