Organic Coatings Research Articles

Organic Patinas on Small Historical Bronzes: From Mock-Ups to Actual Artworks

This paper deals with the study of organic coatings (patinas) on historical bronzes, specifically those applied on small-size statues in Renaissance workshops. These coatings, often transparent and translucent, contain a mixture of organic and inorganic components and may be still preserved in hidden parts of statues in indoor displays. However, the complexity of the original varnishes, their degradation and alteration over time, and the coexistence of materials added for conservation and maintenance purposes are challenging for their characterization. The often well-preserved surface of varnished bronzes and their small size make it mandatory to make the most of using noninvasive techniques for their investigation. To this end, to simulate the actual historical coatings, we prepared a set of mock-ups following ancient recipes and using materials that were available in the Renaissance. We used the samples to assess to what extent it is possible to disclose the formulation (binders, colourants, and other additives) and the thickness of a Renaissance patina with noninvasive methods. Microprofilometry (MP), optical coherence tomography (OCT), and eddy current (EC) gauge were tested on the samples and the results were combined with reflectance Fourier transform infrared (FT-IR) spectroscopy. The analyses performed on the mock-ups set the ground for investigating a Renaissance bronze featuring reddish semi-transparent varnish layers. The achievements are discussed in this paper, along with the limitations of the use of a noninvasive approach.

Influence of graphene orientation on tribological properties of organic composite coatings from the perspective of energy transfer using molecular dynamics

In this paper, the molecular dynamics was used to analyze the energy transfer behavior of graphene when the angle is 0°, 45° and 90° to the sliding friction direction, and the mechanism of its effect on the tribological performance of the coating was investigated. The angle of graphene orientation increases from 0° to 90°, and both the energy storage and heat dissipation capacities of the coating increase. The coating has the best tribological performance when the graphene orientation angle is 90°, with the lowest friction coefficient of 0.238 and the lowest wear rate of 3.48%. The results show that the coating energy transfer behavior is closely related to graphene orientation and has a significant impact on tribological properties.

Powder organic coatings functionalized with calcium ion-exchanged silica corrosion inhibitors

Powder organic coatings functionalized with calcium ion-exchanged silica corrosion inhibitors

Organic Thin Films Enable Retaining the Oxidation State of Copper Catalysts during CO2 Electroreduction.

A key challenge in electrocatalysis remains controlling a catalyst's structural, chemical, and electrical properties under reaction conditions. While organic coatings showed promise for enhancing the selectivity and stability of catalysts for CO2 electroreduction (CO2RR), their impact on the chemical state of underlying metal electrodes has remained unclear. In this study, we show that organic thin films on polycrystalline copper (Cu) enable retaining Cu+ species at reducing potentials down to -1.0 V vs RHE, as evidenced by operando Raman and quasi in situ X-ray photoelectron spectroscopy. In situ electrochemical atomic force microscopy revealed the integrity of the porous organic film and nearly unaltered Cu electrode morphology. While the pristine thin film enhances the CO2-to-ethylene conversion, the addition of organic modifiers into electrolytes gives rise to improved CO2RR performance stability. Our findings showcase hybrid metal-organic systems as a versatile approach to control, beyond morphology and local environment, the oxidation states of catalysts and energy conversion materials.

Effects of extracellular electron transfer on biomineralization by Shewanella putrefaciens in damaged organic coatings

This study reports the effect of extracellular electron transfer (EET) on biomineralization mediated by Shewanella putrefaciens in damaged coatings under different carbon source conditions. S. putrefaciens was able to obtain energy from metal surfaces to support metabolism via EET when the carbon source was insufficient. Under these conditions, bacteria colonized the coating scratches, resulting in accelerated corrosion instead of mineralization. The EIS results revealed that biomineralization was most significant in the 75% carbon source medium after 7 days of incubation. Interestingly, the pH of the medium increased with an abundance of carbon sources, which promoted biomineralization.

Hybrid inorganic–organic coatings enhancing glass corrosion resistance

This work aims to prepare a functional hybrid organic–inorganic coating on glass using the sol–gel process. The sol–gel coatings are commonly used for changing and/or enhancing optical, chemical and mechanical properties of the substrate glass. The coatings prepared in this work should exhibit high transmittance and good chemical resistance, whereof should be achieved by the combination of default precursor tetraethoxysilane (TEOS) and various functionalized silicon alkoxides 3-(trimethoxysilyl)propyl methacrylate (MEMO) and isobutyl(trimethoxy)silane (IBTMS). Sols were applied on substrate glass via the dip-coating method at different withdrawal speeds. Coatings were dried 1 h at 200 °C in ambient atmosphere. Assessment of transmittance was done by UV-Vis spectrophotometry, chemical resistance was observed by accelerated weathering tests in a humidity chamber, mechanical properties were evaluated with the means of standardized pencil hardness test and cross-cut tape test, and moreover analysis of abrasion resistance was done by model test. The most efficient functionalization was combination of 1% IBTMS + 1% MEMO and functionalization with MEMO up to 2% alone. These coatings showed good resistance against damp heat, they can withstand certain loads of abrasion and concurrently still exhibit high transmittance in the visible spectrum.Graphical

Review of the state of art of Li-based inhibitors and coating technology for the corrosion protection of aluminium alloys

The quest for novel alternatives to hexavalent-chromium-based corrosion inhibitors is of utmost significance and urgency. Strict international health and safety regulations, due to growing concerns regarding the impact of hexavalent chromium on human health and the environment, have pushed the commercial introduction of many alternative inhibitor types, but the implementation of alternative active protective primers for structural parts in the aerospace industry is still pending. This endeavour has proven to be remarkably challenging, as the potential replacement coating types must meet numerous functional requirements encompassing cost-effectiveness and exceptional corrosion protection for intrinsically corrosion susceptible aerospace aluminium alloys. In recent years, considerable attention has been drawn to lithium salts as environmentally friendly corrosion inhibitors forming the basis for a novel active protective coating technology. The involvement of lithium ions has been shown to play a pivotal role in the conversion process of aluminium alloy surfaces by stabilizing the reaction products, thereby facilitating the gradual development of a protective layer with a multi-layered configuration, which exhibits considerable variability in morphology, depending on local chemical and electrochemical conditions. The versatility of the lithium-based corrosion protection extends to their application as corrosion inhibiting pigments in organic coatings or as a pre-treatment, directly forming conversion layers, thereby enhancing their practical implementation. However, previous chromate replacement reviews only introduced the promising outcomes provided by the lithium technology, omitting key details of its development and formation mechanism. This paper critically reviews and summarizes the studies conducted to date on lithium-based inhibitor technologies for the corrosion protection of aluminium alloys as well as topics to be investigated in the future.

Anti-fogging surfaces produced by plasma polymerization of acrylic acid

In this paper, plasma enhanced chemical vapor deposition (PECVD) of acrylic acid (AA) was employed as a one-step and solvent-free technique to prepare durable organic anti-fogging coatings on mirror and glass surfaces. The effects of important PECVD parameters including substrate temperature and plasma power on the deposition kinetics, as well as on the structural and morphological properties of the as-deposited films were investigated. Employing a low substrate temperature (5 °C) and a high plasma power (30 W) combination resulted in the highest observed deposition rate of 27.7 nm/min. Fourier-transform infrared (FTIR) spectroscopy showed high structural resemblance between PECVD-PAA and reference poly(acrylic acid) (PAA). The PAA-deposited surfaces showed excellent and durable anti-fogging performance without any loss in their optical transparencies. Successive antifogging tests showed that the PAA thin film exhibited high functional durability without delamination, indicating that it can be used in real-world applications.

Deposition and corrosion performance of phosphate-polylactic acid composite coatings on WE43 magnesium alloy

The degradation profile of Mg alloys in biomedical environments can be controlled by applying various types of surface coatings. Phosphate chemical conversion coatings (CaP) and polylactic acid (PLA) biopolymer coatings are biocompatible and promising for the corrosion protection of Mg alloys. The aim of this work was to investigate the physicochemical properties and corrosion performance of inorganic, organic, and mixed inorganic-organic coatings. Three types of surface modification, CaP, PLA, and a combined CaP-PLA coating were obtained on the surface of the magnesium alloy WE43. Scanning electron microscopy, X-ray diffraction, X-ray photoelectron spectroscopy, and infrared spectroscopy were employed to characterize the surface and interfacial morphology, along with the composition of the coatings before and after corrosion experiments. The protective performance of obtained coatings was examined by electrochemical impedance spectroscopy and immersion testing in Hank's solution. Coated samples showed significantly improved corrosion resistance. The values of polarization resistance based on impedance measurements were 164; 8688; 69,410; and 228,369 Ω cm2 for WE43 alloy, CaP, PLA, and CaP-PLA coatings, respectively. The results allowed to propose the mechanism of the coatings growth and their further corrosion degradation. A two-component CaP-PLA coating provided reliable corrosion resistance in Hank's solution for 14 days.

Enhancement of anti-microbial corrosion properties through coatings incorporating S2− responsive TCS-MSNs@TA-FeIII nanofillers

In environments susceptible to microbiologically influenced corrosion (MIC), conventional coatings frequently lack antimicrobial properties, resulting in diminished corrosion protection. The direct incorporation of antimicrobial agents into coatings may lead to continuous leakage. In this study, we tackled this challenge by utilizing smart nanofillers known as TCS-MSNs@TA-FeIII, which form mesoporous silica nanoparticles (MSNs) encapsulated by tannic acid-Fe3+ and loaded with triclosan (TCS). These nanofillers exhibited responsiveness to variations in S2− concentration caused by sulfate-reducing bacteria's (SRB) metabolic activities, enabling controlled release of TCS within the low S2− concentration range of 0.05 to 3 mM. Additionally, we evaluated the antimicrobial and anti-corrosion properties of the coating after integrating it into a water-based epoxy coating within an SRB environment. The results showcased exceptional performance of the TCS-MSNs@TA-FeIII coating, characterized by the highest impedance modulus (3.19 × 106 Ω·cm2), lowest corrosion current density (2.04 × 10−8 A·cm−2), and remarkable antimicrobial efficacy. This study offers valuable insights into developing novel coatings with enduring MIC inhibition capabilities while also broadening the potential application range of organic coatings.

Freeze Drying of Organically Modified Layered Silicates as Key Step to Improve the Barrier Properties of Organic Coatings for High Power Electronics Protection

AbstractOrganically modified layered silicates can be used as barrier pigments in organic coating systems to reduce the permeation of water vapor and gases, e.g., oxygen as well as harmful gases that promote corrosion. Unmodified layered silicates are not sufficient to reduce the permeation significantly. However, the arrangement and orientation of the particles have an enormous impact on the later performance in the barrier film. In organic solvents or non‐aqueous polymer matrices the non‐modified layered silicates cannot exfoliate adequately. The organic modification influences the layer spacing and the compatibility to organic solvents. Layered silicates are modified with dodecylamine to enhance the spacing layer. The spacing layer is enhanced by 55% caused by the organic modification as it is commonly known. In contrast to previous work freeze drying of the organically modified layered silicates improved the particle distribution and by this barrier properties significantly. The modified particles reduce the diffusion of water and oxygen by ≈99.6% and 97.2%, respectively. The corrosive gas test of electronic circuit boards shows no growth of dendrites and no failure of the electronics in contrast to protective coating without the layered silicates.

Effect of zinc oxide on the electrochemical properties of micro-arc oxidation coatings in seawater

PurposeThe purpose of this paper is to explore the effect of ZnO on the structure and properties of micro-arc oxidation (MAO) coating on rare earth magnesium alloy under large concentration gradient.Design/methodology/approachThe macroscopic and microscopic morphology, thickness, surface roughness, chemical composition and structure of the coating were characterized by different characterization methods. The corrosion resistance of the film was studied by electrochemical and scanning Kelvin probe force microscopy. The results show that the addition of ZnO can significantly improve the compactness and corrosion resistance of the MAO coating, but the high concentration of ZnO will cause microcracks, which will reduce the corrosion resistance to a certain extent.FindingsWhen the concentration of zinc oxide is 8 g/L, the compactness and corrosion resistance of the coating are the best, and the thickness of the coating is positively correlated with the concentration of ZnO.Research limitations/implicationsToo high concentration of ZnO reduces the performance of MAO coating.Practical implicationsThe MAO coating prepared by adding ZnO has good corrosion resistance. Combined with organic coatings, it can be applied in corrosive marine environments, such as ship parts and hulls. To a certain extent, it can reduce the economic loss caused by corrosion.Originality/valueThe effect of ZnO on the corrosion resistance of MAO coating in electrolyte solution was studied systematically, and the conclusion was new to the common knowledge.

Powder organic coatings functionalized with calcium ion-exchanged silica corrosion inhibitors

Improved durability in organic coatings could partially solve the important problem of metal corrosion. For this reason, this work has sought to manufacture powder organic coatings after their functionalization with inhibitors, particularly calcium ion-exchanged silica microparticles. The objective is to obtain high-performance coatings with better corrosion resistance, as well as to make them more resistant to abrasive and erosive wear to reduce the likelihood of suffering damage during exposure. Different properties of the original epoxy coating and coatings with two different percentages of calcium ion-exchanged silica inhibitors (1 and 2 % by wt.) were analyzed. The corrosion protection of the new organic coatings was evaluated after performing a controlled mechanical damage. The delamination suffered by each coating was measured using scanning Kelvin probe (SKP) for 26 days, after the addition of a 3.5 % NaCl drop on the provoked defect. In addition, scratch resistance, universal hardness, and wear resistance (sliding and erosive) were studied for all organic coatings to evaluate the effect of the additions on their mechanical properties. The results obtained in this work indicate that small additions of these inhibitors manage to reduce the delamination rate of the coating from a defect and improve the results of the scratch test after immersion in NaCl solution. Moreover, 2 % silica particle additions to the epoxy improve the erosive and the sliding wear performances of the coating.

Unraveling the complex infiltration and repairing behaviors in defect coatings

Organic coatings are commonly used to protect the metals or alloys from corrosion. However, defects such as scratches or natural aging of the coating can induce unexpected diffusion paths for the corrosive media, so the wettability of repairing liquids and the selection of suitable repairing liquids are crucial. In this study, we systematically investigated the capillary impregnation phenomenon by using liquids with various surface tensions and glass capillaries with different surface energies. We utilized this regularity to instruct the defects repairing process. By using an ultra-depth field microscope, scanning electron microscope, and electrochemical analysis, two kinds of repairing liquids, high surface tension liquid (HSTL) and low surface tension liquid (LSTL), were investigated for repairing man-made defects of coatings. Our results showed that the substrate and the surface energy of the liquids significantly influence the infiltration of the repair liquid. By effectively leveraging the relationship between the repair liquid and the substrate, the repair agent can not only establish a uniform and dense repairing layer but also notably enhance the corrosion resistance of the defective coating. This study provides valuable insights into the repairing of coating defects, as well as liquids transportation, microfluidic chip design, and surface modification of microporous materials.

Long-term stability of antifouling poly(carboxybetaine acrylamide) brush coatings

A comprehensive understanding how storage conditions affect functional surface properties of antifouling organic coatings remains a persistent challenge across industry and research worldwide. This study investigates the long-term storage stability of state-of-art antifouling functionalizable zwitterionic poly(carboxybetaine acrylamide) (pCBAA) brushes using spectroscopic ellipsometry (SE), infrared reflection-absorption spectroscopy (IRRAS), surface plasmon resonance (SPR), atomic force microscopy (AFM), and X-ray photoelectron spectroscopy (XPS). The pCBAA brushes, prepared by surface-initiated atom transfer radical polymerization (SI-ATRP) on SPR substrates, were subjected to various storage conditions for 43 days: kept in dry state at room temperature or −20 °C, and immersed in water or phosphate-buffered saline (PBS) and kept at 6 °C or −20 °C. The IRRAS, SE and AFM data confirm only negligible release of pCBAA under these storage conditions. However, SE indicated a slightly lower brush swelling ratio depending on storage. The SPR was used to evaluate the resistance of unmodified pCBAA, pCBAA activated by EDC/NHS chemistry and deactivated with 2-(2-aminoethoxy)acetic acid (AEAA), and pCBAA functionalized with anti-E. coli antibodies against fouling from undiluted human blood plasma. The results confirm that pCBAA brushes maintain or may even improve their exceptional antifouling performance after prolonged storage, while displaying a slight deterioration in their binding capacity for anti-E. coli antibodies.

Effect of Phenolic Resin Coating Thickness on Mechanical Properties and Corrosion Resistance of Metal Materials

In the realm of petrochemical and other industries, metal materials face threats such as impact and high-temperature electrochemical corrosion. Consequently, there has been significant attention towards organic coatings that effectively attenuate impact forces while simultaneously providing a barrier against corrosive agents. The thermosetting phenolic resin 2130, known for the facile curing process, exceptional thermal stability, water resistance, corrosion resistance, and superior mechanical properties post-curing, finds extensive applications in the field of coatings. To address the challenge of depositing a complete and uniform resin coating on complex workpieces, coatings with varying thicknesses on the surface of 304 stainless steel were deposited via rotary evaporation combined with long-term low-temperature drying. The relationship between coating thickness and mechanical properties, as well as corrosion resistance, was investigated and analyzed through a comprehensive approach involving mechanical testing, electrochemical analysis, and long-term service weight loss assessment. The results demonstrated that the coatings deposited on the metal surface exhibited excellent integrity and compactness. Moreover, an increase in coating thickness led to a significant reduction in material corrosion rate. The coatings exhibited excellent substrate adhesion and flexibility, thereby providing effective protection against impact on the metal substrate. The relationship between the thickness of the coating and the surface roughness was evident, while the flexibility of the coating first increased and then decreased with the increase of coating thickness. When the coating thickness was 7 μm, the maximum surface roughness of the coating measured 0.44 μm. Under these conditions, the impact toughness of the coating reached the peak, exhibiting a ductile fracture mode and showcasing superior comprehensive mechanical properties. The findings of this study will offer theoretical support for the investigation and formulation of resin coatings in subsequent industrial production.

Hydrophobic phytic acid conversion layers for corrosion protection of steel surfaces

AbstractThe possibility for a good conversion protection based on phytic acid (PA) solutions is described many times in the literature.1,2 The latest results show that PA cannot improve the corrosion protective properties with an organic coating,2 although PA conversion layers without organic coatings have already successfully been applied on different surfaces and the development of layers with enhanced corrosion protective behavior was possible.3,4 The reason why PA does not work together with an organic coating is based on the hydrophilic surface and therefore the low contact angle of the PA conversion layer.2 One solution is to modify PA directly and/or change the solution properties to increase the hydrophobic properties. In this work, a new and innovative way to synthesize a new type of sustainable organic PA-based conversion layers on steel, which works completely without titanium or zirconium and is a new approach for hydrophobic conversion layers, is presented.5 The results prove the formation of a pure PA-based conversion layer on the surface. The infrared (IR), Raman, and nuclear magnetic resonance (NMR) spectroscopy verified the new synthesis products and by means of the vibration spectroscopy, the resulting conversion layers. To analyze the new physical properties, the contact angle of the conversion layers was detected. By means of the electrochemical impedance spectroscopy (EIS), the electrochemical stability of the conversion was studied and with cyclic voltammetry (CV), the solidity ratio was investigated. At last, the corrosion protective performance of the layers in combination with an E-coat in the salt spray test (SST) was examined. All modified PA-based conversion layers in combination with E-coats increased the corrosion protective properties in relation to industrial used phosphate conversion layers of steel surfaces. The overall result is a new kind of hydrophobic phytic acid-based conversion layer which shows advanced anticorrosion and coatability properties compared to other layers based on PA. The results if the EIS measurements show that the resistance of the coating significantly increased, and diffusion could be suppressed by coating the metal surface with PA conversion layers. The comparison of the SST results for the reference and the modified PA underline these observations. The overall SST rating increased by 2 and the delamination went down to 1.9 mm while the corrosion was 0.1, comparable to phosphated steel.

Preparation and anticorrosion performance of graphene-reinforced epoxy powder coating

Existing studies have reported that graphene can enhance the corrosion resistance of solvent-based organic coatings. However, the role of graphene in organic powder coatings remains to be obscure. In the present study, the graphene powder was prepared through liquid-phase exfoliation of graphite followed by freeze drying and the effects of graphene on structures, anticorrosion performance and adhesion strength of epoxy powder coatings were investigated. Scanning electron microscopy (SEM) demonstrated that graphene reduced surface micropores and enhanced structural compactness of the epoxy powder coatings. Electrochemical impedance spectra, Tafel polarization measurement and salt spray test indicated that a small amount (0.0125, 0.025 and 0.05 wt%) of well-dispersed graphene powder would be sufficient to effectively reinforce the anticorrosion performance of the epoxy powder coatings, especially for the coating with 0.025 wt% graphene, of which the impedance modulus maintained the highest values of nearly 107 and 105.8 Ω cm2 after immersion in 3.5 % NaCl solution for 21 and 30 days. Pull-off test confirmed that graphene enhanced the adhesion strength of coatings after salt spray test for 240 h, while the coating with 0.025 wt% graphene exhibited the highest adhesion strength up to 3.88 MPa. In addition, differential scanning calorimetry (DSC) indicated that graphene sheets could improve the thermal conductivity and promote curing reactions of epoxy powder. The mechanism for the reinforcement of epoxy powder coating by graphene has also been proposed.

Surface modification effect on contrast agent efficiency for X-ray based spectral photon-counting scanner/luminescence imaging: from fundamental study to in vivo proof of concept.

X-Ray imaging techniques are among the most widely used modalities in medical imaging and their constant evolution has led to the emergence of new technologies. The new generation of computed tomography (CT) systems - spectral photonic counting CT (SPCCT) and X-ray luminescence optical imaging - are examples of such powerful techniques. With these new technologies the rising demand for new contrast agents has led to extensive research in the field of nanoparticles and the possibility to merge the modalities appears to be highly attractive. In this work, we propose the design of lanthanide-based nanocrystals as a multimodal contrast agent with the two aforementioned technologies, allowing SPCCT and optical imaging at the same time. We present a systematic study on the effect of the Tb3+ doping level and surface modification on the generation of contrast with SPCCT and the luminescence properties of GdF3:Tb3+ nanocrystals (NCs), comparing different surface grafting with organic ligands and coatings with silica to make these NCs bio-compatible. A comparison of the luminescence properties of these NCs with UV revealed that the best results were obtained for the Gd0.9Tb0.1F3 composition. This property was confirmed under X-ray excitation in microCT and with SPCCT. Moreover, we could demonstrate that the intensity of the luminescence and the excited state lifetime are strongly affected by the surface modification. Furthermore, whatever the chemical nature of the ligand, the contrast with SPCCT did not change. Finally, the successful proof of concept of multimodal imaging was performed in vivo with nude mice in the SPCCT taking advantage of the so-called color K-edge imaging method.

Surface treatments on concrete: an overview on organic, inorganic and nano-based coatings and an outlook about surface modification by rare-earth oxides

Typical coatings incorporate organic groups as carrier of hydrophobicity and polar groups at the solid interface, which are weak points in the interaction with water. In contrast, REOs are shielded from interactions with the environment.