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1. Post-Fire Analysis of Thermally Sprayed Coatings: Evaluating Microstructure, Mechanical Integrity, and Corrosion Behavior

   https://doi.org/10.3390/pr11051490  

   Yasoda, Ratna Divya; Hakim, Nour; Huang, Ying; Qi, Xiaoning (May 2023, Processes)

   This paper examines the impact of fire on the microstructural, mechanical, and corrosion behavior of wire-arc-sprayed zinc, aluminum, and Zn-Al pseudo-alloy coatings. Steel plates coated with these materials were subjected to temperatures in increments of 100 °C, starting from 300 °C and progressing until failure. Microstructural characterization, microhardness, abrasion resistance, and electrochemical impedance studies were performed on the post-fire coatings. The findings from this study show that heat had a positive impact on the performance of zinc and Zn-Al pseudo-alloy coatings when they were exposed to temperatures of up to 400 °C, while aluminum coatings maintain their performance up to 600 °C. However, above these temperatures, the effectiveness of coatings was observed to decline, due to increased high-temperature oxidation, and porosity, in addition to decreased microhardness, abrasion resistance, and corrosion protection performance. Based on the findings from this study, appropriately sealed thermal-spray-coated steel components can be reused after exposure to fire up to a specific temperature depending on the coating material. 

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2. Improvement of Wear, Pitting Corrosion Resistance and Repassivation Ability of Mg-Based Alloys Using High Pressure Cold Sprayed (HPCS) Commercially Pure-Titanium Coatings

   https://doi.org/10.3390/coatings11010057  

   Daroonparvar, Mohammadreza; Kasar, Ashish K.; Farooq Khan, Mohammad Umar; L. Menezes, Pradeep; Kay, Charles M.; Misra, Manoranjan; Gupta, Rajeev K. (January 2021, Coatings)

   null (Ed.)

   In this study, a compact cold sprayed (CS) Ti coating was deposited on Mg alloy using a high pressure cold spray (HPCS) system. The wear and corrosion behavior of the CS Ti coating was compared with that of CS Al coating and bare Mg alloy. The Ti coating yielded lower wear rate compared to Al coating and Mg alloy. Electrochemical impedance spectroscopy (EIS) and cyclic potentiodynamic polarization (CPP) tests revealed that CS Ti coating can substantially reduce corrosion rate of AZ31B in chloride containing solutions compared to CS Al coating. Interestingly, Ti-coated Mg alloy demonstrated negative hysteresis loop, depicting repassivation of pits, in contrast to AZ31B and Al-coated AZ31B with positive hysteresis loops where corrosion potential (Ecorr) > repassivation potential (Erp); indicating irreversible growth of pits. AZ31B and Al-coated AZ31B were most susceptible to pitting corrosion, while Ti-coated Mg alloy indicated noticeable resistance to pitting in 3.5 wt % NaCl solution. In comparison to Al coating, Ti coating considerably separated the AZ31BMg alloy surface from the corrosive electrolyte during long term immersion test for 11 days. 

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3. Corrosion Behavior Evaluation of Coated Steel Using Fiber Bragg Grating Sensors

   https://doi.org/10.3390/coatings9010055  

   Deng, Fodan; Huang, Ying; Azarmi, Fardad (January 2019, Coatings)

   Coatings, either soft or hard, are commonly used to protect steel against corrosion for longer service life. With coatings, assessing the corrosion behavior and status of the substrate is challenging without destructive analysis. In this paper, fiber Bragg (FBG) grating sensors were proposed to nondestructively evaluate the corrosion behavior of steel coated with two popular coatings, including the polymeric and wire arc sprayed Al-Zn coating. Laboratory accelerated corrosion tests demonstrated that the embedded FBG sensors inside both the soft and hard coatings can effectively quantify the corrosion rate, monitor the corrosion progress, and detect the coating damages and crack propagation of coated steel in real time. The laboratory electrochemical corrosion test on the wire arc sprayed Al-Zn coating validated the proposed embedded FBG sensor method with a good agreement in comparison. The proposed sensing platform provides an alternative nondestructive real-time corrosion assessment approach for coated steel in the field. 

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4. Multi-functional low-cost epoxy based nanocomposite corrosion resistant coatings

   Nawani, Pranav; Gese, Natalie (June 2017, MegaRust 2017 Organized by the American Society of Naval Engineers)

   Corrosion is a significant global issue, resulting in high maintenance and repair costs. Long term structural integrity of metal and its products is directly dependent on its anti-corrosive properties. Surfaces exposed to marine environments are prone to microbial attachment followed by biofilm formation, resulting in bio-fouling. Hence coatings are used to protect the surfaces against corrosion and biofilm formation. Currently various organic coatings are used to protect metals and the cost of these coatings is directly dependent upon the cost of the fillers used to impart specific properties. Conventionally fillers such as zinc, Titanium and Silver based compounds are used in coatings for corrosion and/or microbial protection of surfaces, which are expensive. The underlying issue with using these compounds as fillers is that they can adversely effect mechanical and barrier properties, due to which they are used as a base coat and additional fillers are used to compensate for such property losses. Most of these coatings need an enhanced anti-microbial surface and improvement in their barrier efficacy against water/moisture, oxygen, and chloride ions. Hence it is imperative to develop low-cost fillers that will enhance both active & passive corrosion resistance properties, prevent microbial attachment on the surfaces and will not degrade any polymeric properties. In this work, ASL is developing a multi-functional low cost epoxy-clay nanocomposite coating, for microbial and corrosion resistance. Multi-functional coatings are developed using a multi-component approach, where the innovation lays in deriving the benefits of various fillers through a combinatorial approach to synergistic harvesting of functionality and vigor. The primary filler is a naturally abundant clay material and, owing to their sheet like morphology and layered structures, their surface can be modified to achieve the desired property enhancements. Sheet like morphology enhances polymer filler interactions, resulting in enhanced mechanical and reduced barrier properties. The presence of clay in the coating materials will mitigate the impact of moisture and chloride ions (in marine environment) providing passive protection to the coated surface. Modification of clay with transition metal ions (TMI) enhances corrosion resistance properties of coatings. 

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5. Corrosion Protective Coatings from Poly(heterocyclic diphenylamine): Polyaniline Analogues

   https://doi.org/10.1021/acsapm.3c02347  

   Awoyemi, R. F.; Almtiri, M.; Giri, H.; Scott, C. N.; Wipf, D. O. (March 2024, ACS applied polymer materials)

   This study explores conducting polymers with side chains containing long, branched alkyl groups as candidates for corrosion suppression coatings. These polymers, containing carbazole, phenothiazine, and phenoxazine cores, may be considered as analogues to polyaniline, which is often employed in corrosion control applications. The polymers are prepared from the corresponding dibrominated carbazole, phenothiazine, and phenoxazine monomers with 2,5-dimethyl-1,4-phenylenediamine by the Buchwald−Hartwig coupling reaction. The effectiveness of these coatings for corrosion suppression was tested by potentiodynamic polarization studies and electrochemical impedance spectroscopy. The morphology of the coatings was characterized by scanning electron microscopy (SEM) and atomic force microscopy (AFM). Corrosion testing of coated AISI 4130 steels in 3.5 wt % NaCl showed that the phenothiazine- and carbazole-containing polymers display excellent corrosion resistance. The protection efficiency (PE) of 95.9% for phenothiazine outperformed the other polymers, including polyaniline coating. SEM images indicate that the polymers are still uniformly coated with stable morphology after 24 h of exposure to corrosive media. These results suggest that phenothiazine and carbazole-based PANI analogues may be candidates for protective organic coatings in transportation, aviation, marine, and oil and gas industrial applications. 

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