Degradation Behaviors of Two Epoxy Coatings After Dry/Wet-Accelerated Fog Exposure of Different Solutions

Applying organic coating is an important and effective approach for the protection of metal from corrosion. Weathering degradation and under-film corrosion are the two major important factors that cause the failure of organic coatings. In this work, the degradation investigation of two epoxy coatings (clear and pigmented coatings) was carried out under the dry–wet circulation of three different water fog solutions (deionized water, 0.5 wt% NaCl, 0.05 wt% NaCl + 0.35 wt% (NH4)2SO4) in 35 days. The apparent performance (pull-off adhesion and surface potentials) and electrochemical features [electrochemical noise and electrochemical impedance spectroscopy (EIS)] of the coating samples were monitored after dry–wet fog exposure. In our three accelerating systems of the fog atmosphere, the time that the detectable defects appeared on the surface of coating samples was far ahead in the mixed salt solution than that in the deionized water or 0.5 wt% NaCl solution. For a defective or damaged coating surface, the derived results by using the standard deviation method (SDM) or Fourier power spectrum (FPS) were rather higher than those obtained from EIS as a whole, while for the same coating, the degradation trend with time derived from EIS, SDM, FPS, and scanning Kelvin probe was consistent with each other.

CuZn and ZnO Nanoflowers as Nano-Fungicides against Botrytis cinerea and Sclerotinia sclerotiorum: Phytoprotection, Translocation, and Impact after Foliar Application

Inorganic nanoparticles (INPs) have dynamically emerged in plant protection. The uptake of INPs by plants mostly depends on the size, chemical composition, morphology, and the type of coating on their surface. Herein, hybrid ensembles of glycol-coated bimetallic CuZn and ZnO nanoparticles (NPs) have been solvothermally synthesized in the presence of DEG and PEG, physicochemically characterized, and tested as nano-fungicides. Particularly, nanoflowers (NFs) of CuZn@DEG and ZnO@PEG have been isolated with crystallite sizes 40 and 15 nm, respectively. Organic coating DEG and PEG (23% and 63%, respectively) was found to protect the NFs formation effectively. The CuZn@DEG and ZnO@PEG NFs revealed a growth inhibition of phytopathogenic fungi Botrytis cinerea and Sclerotinia sclerotiorum in a dose-dependent manner with CuZn@DEG NFs being more efficient against both fungi with EC50 values of 418 and 311 μg/mL respectively. Lettuce (Lactuca sativa) plants inoculated with S. sclerotiorum were treated with the NFs, and their antifungal effect was evaluated based on a disease index. Plants sprayed with ZnO@PEG NFs showed a relatively higher net photosynthetic (4.70 μmol CO2 m−2s−1) and quantum yield rate (0.72) than with CuZn@DEG NFs (3.00 μmol CO2 m−2s−1 and 0.68). Furthermore, the penetration of Alizarin Red S-labeled NFs in plants was investigated. The translocation from leaves to roots through the stem was evident, while ZnO@PEG NFs were mainly trapped on the leaves. In all cases, no phytotoxicity was observed in the lettuce plants after treatment with the NFs.

Sorption of Uranium (VI) From Aqueous Solution Using Nanomagnetite Particles; Singly and Coated With Humic Acid

Magnetite nanoparticles (Fe3O4) and humic acid coated magnetite nanoparticles (Fe3O4/HA) were investigated for the removal of U(VI) from aqueous solution. Batch sorption experiments were studied as a function contact time, adsorbent mass, U(VI) concentration and pH. The sorption kinetic data follow the pseudo-second order while the isotherms are found to obey Langmuir model with maximum capacity (Qmax) of 230, 196 mg/g for Fe3O4 and Fe3O4/HA, respectively. The study reveals that humic acid decreases the sorption capacity due to the formation of a polyanionic organic coating and thus altering the surface properties of the particles and reduces the magnetite aggregation and stabilizes the magnetite suspension.

Comparison between Accelerated Tests and Natural Exposures for Organic Coating Protective Systems Based on EIS Parameters

The equivalent relationship between accelerated tests and natural exposures has been extensively studied over the past several years to estimate the service life of a barrier organic coating protective system. Herein, based on the probability density function (PDF) theory, a mathematical expression that describes the limit value of the low-frequency impedance (RL) of a barrier organic coating protective system as a function of the elapsed time is proposed in form of Arrhenius formula under certain assumptions, and the degradation coefficient is defined. This expression was consistent with the results of the accelerated tests. The equivalent relationship between accelerated tests and natural exposures, established based on the equivalence principle, was utilized to predict the service life of the coated Al alloy in an ocean atmospheric environment.

Aggressiveness of Different Ageing Conditions for Three Thick Marine Epoxy Systems

Three different coated steel systems were aged in natural or artificial seawater, in neutral salt spray (NSS), and using alternate immersion tests in order to evaluate the aggressiveness of the different ageing conditions. Commercial epoxy coatings were applied onto steel (S355NL), hot-galvanized steel (HDG), and Zn-Al15 thermal spraying coated steel. The defect-free systems were immersed in artificial seawater at 35 °C for 1085 days and in natural seawater for 1200 days and were characterized by electrochemical impedance spectroscopy (EIS). Panels with artificial defects were immersed for 180 days in artificial seawater and, regarding adhesion, were evaluated according to ISO 16276-2. In parallel, the three coated systems were submitted to cyclic neutral salt spray (NSS) for 1440 h: defect-free panels were regularly evaluated by EIS, while the degree or corrosion was measured onto panels with artificial defect. After NSS, defect-free panels were immersed in artificial seawater at 35 °C for further EIS investigations. Finally, alternate immersion tests were performed for 860 days for the three defect-free coated systems and for 84 days for panels with a defect. The results showed that, for defect-free panels, immersions in natural or artificial seawater and NSS did not allowed us to distinguish the three different systems that show excellent anticorrosion properties. However, during the alternate immersion test, the organic coating system applied onto HDG presented blisters, showing a greater sensitivity to this test than the two other systems. For panels with a defect, NSS allowed to age the coatings more rapidly than monotone conditions, and the coating system applied onto steel presented the highest degree of corrosion. Meanwhile, the coating systems applied onto HDG and the thermal spray metallic coating showed similar behavior. During the alternate immersion test, the three coated systems with a defect showed clearly different behaviors, therefore it was possible to rank the three systems. Finally, it appeared that the alternate immersion test was the most aggressive condition. It was then proposed that a realistic thermal cycling and an artificial defect are needed when performing ageing tests of thick marine organic coating systems in order to properly rank/evaluate the different systems.

Analysis the Performance of Hydrophilic and Corrosion Resistant Coatings on the Distillation Desalination Tube in High Temperature Seawater

Distillation desalination can use solar energy and other renewable energy, it is one of the most potential technologies for desalination. However, distillation desalination system pervades problems such as low desalination efficiency and poor corrosion resistance. Based on our preliminary study (i.e., apply hydrophilic modification on the surface of distillation desalination tube can effectively improve desalination efficiency), this paper introduces a composite functional coating with the micro-arc oxidation (MAO) coatings sealed with hydrophilic organic coating-TiO2 hybrid sols (OT-MAO) by sol-gel process. Through contact angle measurement, scanning electron microscopy (SEM) and potentiodynamic polarization test to analyze and compare the performance of hydrophilicity and corrosion resistance of the MAO coatings and the OT-MAO composite coatings in high temperature seawater environment. The corrosion mechanism of the OT-MAO composite coatings was analyzed by electrochemical impedance spectroscopy (EIS). The results show that the OT-MAO composite coatings in high temperature seawater has much better hydrophilicity and corrosion resistance than the MAO coatings. This paper provides theoretical and technical reference for developing a new type of surface modified distillation desalination tube.

Enhancing adhesion and anti-corrosion performance of hot-dip galvanized steels by sandblasting/phosphating co-treatment

The substations outdoor steel structures employed in aggressive marine environments can accelerate corrosion damage and cause incredible degradation of performance. Hot-dip galvanizing and organic coating dual-coated anticorrosion system is currently the most effective and efficient protection strategy. In present paper, sandblasting and phosphating technique were applied to the surface of zinc plating, the effect of various grit-blasting and phosphating technology conditions on the adhesion performance and corrosion resistance of duplex-coated system were systematically investigated. Results revealed that the bonding strength of the duplex coating after grit-blasting and phosphating pretreatment was 3.25 and 2.71 times higher than that of the untreated, respectively. In particular, sandblasting and phosphating coprocessing of duplex coating could furtherly improve the adhesion behavior and corrosion resistance, which mainly due to their synergistic effect. Sandblasting can rough the surface of galvanized coating and generate many pits and scratches. Thus, phosphating can form more needle-like zinc phosphate crystals in those positions, anchoring and pinning firmly the interface between galvanized coating and organic coating. Meanwhile, the phosphating film still acted as an anti-corrosion physical barrier to hinder the intrusion of corrosive medium and protect galvanized steels from storage rust before painting for a long time.