In this review, several cost-effective thin-film coating methods, which include dip-coating, spin-coating, spray-coating, blade-coating, and roll-coating, are presented. Each method has its own set ...of advantages and disadvantages depending on the proposed application. Not all of them are appropriate for large-scale production due to their certain limitations. That is why the coating method should be selected based on the type and size of the substrate, including the thickness and surface roughness of the required thin films. The sol–gel method offers several benefits, such as simplicity in fabrication, excellent film uniformity, the capacity to cover surfaces of any size and over vast areas, and a low processing temperature. Nevertheless, these coating methods are somewhat economical and well managed in low-budget laboratories. Moreover, these methods offer thin films with good homogeneity and low-surface roughness. Furthermore, some other thin-film deposition methods, for instance, physical vapor deposition (PVD) and chemical vapor deposition (CVD), are also discussed. Since CVD is not restricted to line-of-sight deposition, a characteristic shared by sputtering, evaporation, and other PVD methods, many manufacturing methods favor it. However, these techniques require sophisticated equipment and cleanroom facilities. We aim to provide the pros and cons of thin-film coating methods and let the readers decide the suitable coating technique for their specific application.
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•An overview of zinc rich epoxy primers for cathodic protection of metals is summarized.•Corrosion protection mechanisms and stages involved are presented briefly.•Latest strategies ...and approaches to enhance anticorrosion efficiency of zinc rich epoxy coatings are discussed.•Beneficial and detrimental effects of nano-fillers on cathodic protection of zinc rich epoxy coatings were reviewed.
Zinc rich primer systems are one of the most utilized organic coating systems for corrosion protection of metals designed to operate at moderate to room temperature. Because of this reason, it remains the first choice of researchers for improvements by introducing different innovative functionalities. Nowadays a wide range of highly efficient micro and nano materials have been explored that can be integrated within the organic coatings to enhance their performance. In this review article, we present a comprehensive literature gathered with a view towards assessing the potentiality of zinc rich epoxy primer systems to protect the metal against corrosion. This review is mainly focused on recent progress in zinc rich epoxy coatings embedded with different kinds of filler materials to enhance their corrosion protection efficiency. Several new strategies and approaches have been used by researchers to increase electrical percolation, barrier effect and galvanic longevity so that the coatings provide extended service for a long period of time. Various topics covering fundamentals of protection mechanisms, performance evaluation, challenges and future research directions pertaining to zinc rich epoxy composite coatings are briefly discussed.
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As a prototype tool for slot‐die coating, blade‐coating exhibits excellent compatibility with large‐area roll‐to‐roll coating. A ternary organic solar cell based on PBDB‐T:PTB7‐Th:FOIC blends is ...fabricated by blade‐coating and exhibits a power conversion efficiency of 12.02%, which is one of the highest values for the printed organic solar cells in ambient environment. It is demonstrated that blade‐coating can enhance crystallization of these three materials, but the degree of induction is different (FOIC > PBDB‐T > PTB7‐Th). Thus, the blade‐coated PBDB‐T:FOIC device presents much higher electron mobility than hole mobility due to the very high crystallinity of FOIC. Upon the addition of PTB7‐Th into the blade‐coated PBDB‐T:FOIC blends, the crystallinity of FOIC decreases together with the corresponding electron mobility, due to the better miscibility between PTB7‐Th and FOIC. The ternary strategy not only maintains the well‐matched crystallinity and mobilities, but also increases the photocurrent with complementary light absorption as well as the Förster resonant energy transfer. Furthermore, small domains with homogeneously distributed nanofibers are observed in favor of the exciton dissociation and charge transport. This combination of blade‐coating and ternary strategies exhibits excellent synergistic effect in optimizing morphology, showing great potential in the large‐area fabrication of highly efficient organic solar cells.
A balanced crystallinity of donor and acceptor is finely controlled by combining blade‐coating and ternary strategies in a PBDB‐T:PTB7‐Th:FOIC‐based organic solar cell, resulting in well‐matched hole and electron mobilities with a power conversion efficiency of 12.02%.
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Blade‐coating serving as a prototype tool for slot‐die coating can be very compatible with large‐area roll‐to‐roll coating. Using blade‐coating in an ambient environment, an average power conversion ...efficiency (PCE) of 10.03% is achieved in nonfullerene organic solar cells, which is higher than that of the optimal spin‐coated device with a PCE of 9.41%. It is demonstrated that blade‐coating can induce a higher degree of molecular packing for both conjugated polymer donors and small‐molecular acceptors as it helps to produce a seeding film containing numerous crystal grains, subsequently providing nucleation sites for the residual solution when the motion of the blade exposes a liquid front. Due to this effect, blade‐coating can partially replace the role of the additive 1,8‐diiodooctane (DIO) and thus achieves the optimized morphology with fewer additives. Moreover, it is found that the blade‐coated film with 0.25% DIO possesses not only a smaller domain size but also higher domain purity, suggesting more D/A (donor/acceptor) interfaces and a purer phase domain as compared to the spin‐coated film with 1% DIO. Encouragingly, the blade‐coated device with less DIO (0.25%) exhibits much better stability than the spin‐coated device with 1% DIO, showing excellent prospects.
A blade‐coated device with a lower amount of 1,8‐diiodooctane (DIO) (0.25%) based on PBDB‐T:ITIC blends exhibits a higher power conversion efficiency of 10.03% and better stability than the optimal spin‐coated device with 1% DIO, because blade‐coating can induce a higher degree of molecular packing and partially replace the role of DIO, showing excellent prospects.
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Corrosion is a significant issue in many industrial fields. Among other strategies, coatings are by far the most important technology for corrosion protection of metallic surfaces. The Special Issue ...“Advanced Coatings for Corrosion Protection” has been launched as a means to present recent developments in any type of advanced coating for corrosion protection. This book compiles 15 contributions on metallic, inorganic, polymeric and nanoparticle enhanced coatings that provide corrosion protection as well as other functionalities.
In this paper, an environmentally-friendly pretreatment has been used for electroless NiP on AZ31 magnesium alloy. Saturated aqueous NaHCO3 solution was used to form carbonate compounds on the ...surface of the substrate prior to Ni-P/nano-SiC electroless plating. Various amounts of nano-SiC particles were used to enhance the hardness, corrosion and wear resistance of the coatings. The coatings were characterized by using scanning electron microscopy (SEM) equipped with energy dispersion spectroscopy (EDS), and via X-ray diffraction (XRD). Polarization tests were carried out for investigating the corrosion resistance of the coatings. Pin on disk tests were used to study wear behavior of the coatings. The effect of heat treatment temperatures on the coatings structure, hardness and corrosion behavior were studied. However, the hardness of the substrate decreased due to the growth of Mg grains at high temperatures. Moreover, heat treated NiP coatings at 300 °C exhibited better corrosion resistance compared to other heat treatment temperatures. As a result, the temperature of 300 °C was chosen as the optimum temperature. Results also indicated that 1 g L−1 nano-SiC in plating bath provided a uniform composite NiP electroless coating with high hardness (795 HV) and corrosion resistance. Adding more nano-particles to the bath resulted in agglomeration of the particles and did not have positive effect on properties. The wear behavior of coatings were investigated using steel pin (AISI 52100) as the counterpart in pin-on-disk wear test. The optimum as-plated composite coating (Ni-P/1SiC) produced the best wear resistance at a rate of 4.2 × 10−5 mm3 N−1 m−1 wear rate and the highest corrosion resistance belonged to Ni-P/1SiC after annealing at 300 °C.
•Carbonate conversion coating inhibited the corrosion of AZ31 in electroless bath.•Ni-P/1SiC coating revealed the best hardness results among composite coatings.•The optimum heat treatment temperature was 300 °C to improve hardness of coatings.•The best corrosion resistance was for Ni-P/1SiC annealed at 300 °C.•The best wear resistance was for as-deposited composite coating.
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In this work, a series of low temperature zinc phosphate conversion coatings formed on mild steel. The surface treatment was carried out at different pHs in the phosphate solutions containing Mn2+. ...An epoxy/polyamide coating was then applied on the phosphated substrates. Potentiostatic polarization test was carried out in order to evaluate the corrosion protection properties of the phosphated samples in 3.5wt.% NaCl solution. The microstructure and morphology of the coatings were studied by X-ray diffraction (XRD), energy-dispersive X-ray spectroscopy (EDS), scanning electron microscopy (SEM) and atomic force microscopic (AFM). The adhesion strengths of the epoxy coatings applied on the surface treated samples were measured before and after 30days of immersion in 3.5wt.% NaCl solution by a pull-off test. Results showed that the corrosion resistance of the phosphate coating was significantly enhanced using Mn2+ (especially at 7g/L). A less porous and more compact phosphate coating formed on the metal surface in the presence of Mn2+ compared with the one without additive. Adhesion properties were enhanced by addition of Mn2+ to the phosphate coating composition.
•A low temperature zinc phosphate coating containing Mn2+ formed on steel substrate.•Mn2+ enhanced the corrosion resistance of the phosphate coating.•A less porous and more compact phosphate coating formed in the presence of Mn2+.•Mn2+ reduced adhesion loss of epoxy coating in 3.5wt.% NaCl solution.
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Zn-coated advanced high strength steels are popular in the automotive industry due to their excellent combination of mechanical strength and ductility as well as superior corrosion resistance ...provided by the Zn-coating – with hot-dip galvanized and galvannealed coatings being the most popular. Gas metal arc brazing technology is a non-fusion joining method, proposed as an alternative to the gas metal arc welding process due to several advantages: The arc-brazing process delivers significantly lower heat input to the substrate, which minimizes the Zn-coating burn-off leading to higher corrosion protection for the joined parts, and reduces the HAZ softening phenomenon which affects the mechanical integrity of the substrate, while at the same time reduces welding defects such as porosity and blowholes. The strength of an arc-brazed joint depends on the spreading of the molten filler material over the joint to create a bond between the parts as the molten braze solidifies. Existing literature on the subject suggests that heat input is the main driving factor controlling the wettability of the molten braze material with the type of shielding gas used also having an effect. However, the influence of different types of Zn-coatings and their respective surface condition (i.e., clean, or unclean) on the wettability of Cu-based molten braze materials during arc-brazing has not been investigated. The present work investigates the effect of surface morphology of galvanized and galvannealed DP600 steel in the as-received and plasma cleaned conditions on the wettability of molten Si-Bronze (CuSi3Mn1) brazing filler material in the bead-on-plate configuration. The findings of this work clearly demonstrate that the type of coating and its surface condition has a significant effect on the spreading of the molten filler material and on the growth of the intermetallic compound layer at the joint interface and therefore, should be taken into consideration as a factor that can impact the efficacy of an arc-brazed joint.
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•Evaluating surface morphology of different Zn-coatings to calculate their surface free energy.•Establishing a clear link between the surface roughness of Zn-coated steels on the wettability of molten Si-Bronze filler material.•The study shows that the wettability of the molten filler material is also affected by the presence of organic contaminants on the coating surface.•This work shows the relevance of surface morphology in controlling the wetting length of weld brazed joints.•The thickness of the intermetallic compound layer at the braze interface can be controlled by using oxygen plasma cleaning.
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Zinc (Zn) has recently emerged as a promising biodegradable metal thanks to its critical physiological roles and promising degradation behavior. However, cytocompatibility and ...antibacterial property of Zn is still suboptimal, in part, due to the excessive Zn ions released during degradation. Inspired by the calcium phosphate-based minerals in natural bone tissue, zinc phosphate (ZnP) coatings were prepared on pure Zn using a chemical conversion method in this study. The coating morphology was then optimized through controlling the pH of coating solution, resulting in a homogeneous micro-/nano-ZnP coating structure. The ZnP coating significantly increased the cell viability, adhesion, and differentiation of pre-osteoblasts and vascular endothelial cells, while significantly reduced the adhesion of the platelets and E. coli. Additionally, ZnP coating significantly reduced the Zn ion release from the bulk material during degradation process, resulting in a much lower Zn2+ concentration and pH change in the surrounding environment. The improved hemocompatibility, cytocompatibility and antibacterial performance of ZnP coated Zn biomaterials could be mainly attributed to the controlled Zn ion release and micro-/nano-scaled coating structure. Taken together, ZnP coating on Zn-based biomaterial appears to be a viable approach to enhance its biocompatibility and antibacterial property as well as to control its degradation rate.
Statement of Significance
Zn and its alloys are promising biodegradable implant materials for orthopedic and cardiovascular applications. However, notable cytotoxicity has been reported due to degradation products accumulated in the local environment, largely overdosed Zn2+. Thus, controlling burst Zn2+ release is the key to minimize the toxicity of Zn implants. To achieve this goal, we prepared a homogenous ZnP coating on Zn metals thanks to its easy synthesis, stable chemical property, and good biocompatibility. Results showed that ZnP not only improved the cell viability, adhesion and proliferation, but also significantly reduced the attachment of platelet and bacterial. Therefore, ZnP could be a promising approach to improve the functional performance of Zn-based implants, and potentially be applied to many other medical implants.
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Magnetic graphene was prepared by modified polyol methods. Gallic acid-based epoxy resin was synthesized and adopted to enhance the dispersion of graphene. Four kinds of coating were prepared, and ...they were graphene coatings (G), magnetic graphene coatings (MG), magnetic graphene coatings oriented by magnetic field (MG-MF), magnetic graphene zinc-rich coatings (MG/Zn), magnetic graphene zinc-rich coatings oriented by magnetic field (MG/Zn-MF). Magnetic graphene has a larger size than the graphene, which reduced its delamination in the coatings and weakened the protective ability. After the oriented treatment by magnetic field, the parallel hierarchical arrangement of magnetic graphene significantly increased the diffusion resistance of corrosive medium and improved the corrosion resistance of the coatings. The diffusion kinetics of corrosive media in the coatings was established. However, the orientation of magnetic graphene attenuated the cathodic protection of zinc-rich coatings, due to the reduction of effective electron transport path and active interfacial zinc. The electrons lost by the anode sacrifice of zinc needed to cross two types of potential barriers in the process of migrating to the protected metal. They were metal-graphene potential barrier and graphene-graphene potential barrier. According to the calculation and modeling of electrodynamics and quantum mechanics, electron penetration through the latter barrier was less difficult than the former and graphene facilitated the transfer of electrons between metals. This was also the microscopic mechanism of graphene improving the cathodic protection of zinc-rich coatings.
•The magnetic graphene is oriented in the coatings.•Gallic acid is used to disperse graphene.•The effect of graphene alignment on coating properties is clarified.•The electronic transfer equations in zinc-rich coatings are established.
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