As-prepared Coatings Research Articles

Electrospun highly corrosion-resistant polystyrene\u2013nickel oxide superhydrophobic nanocomposite coating

A key challenge in producing superhydrophobic coatings (SHC) is to tailor the surface morphology on the micro-nanometer scale. In this work, a feasible and straightforward route was employed to manufacture polystyrene/nickel oxide (PSN) nanocomposite superhydrophobic coatings on aluminum alloys to mitigate their corrosion in a saline environment. Different techniques were employed to explore the influence of the addition of NiO nanoparticles to the as-prepared coatings. PSN-2 composite with ~ 4.3 wt% of NiO exhibited the highest water contact angle (WCA) of 155° ± 2 and contact angle hysteresis (CAH) of 5°.Graphic abstractEIS Nyquist plots of 3 g of electrospun polystyrene coatings (a) without and with (b) 0.1, (c) 0.15, and (d) 0.2 g of NiO.

Multi-type nanoparticles in superhydrophobic PU-based coatings towards self-cleaning, self-healing and mechanochemical durability

Mechanochemical durability is a key limited factor for superhydrophobic coatings to produce the real applications in some important fields. Herein, the superhydrophobic PU-based coatings were firstly synthesized with silica particles (F-SiO2) and carbon nanotube (F-CNT) as the main fillers and the reinforced mediums, respectively. The superhydrophobic coatings showed excellent water repellency with higher water contact angle of 154.3° and lower sliding angle of only 5°. Also, the impacting droplets could rapidly bounced off the superhydrophobic coatings with the contact time of 11 ms. The superhydrophobic coatings exhibited the excellent self-cleaning property. Furthermore, the as-prepared superhydrophobic coatings (F-CNT to F-SiO2 mass ratio was 3:3) possessed the robust mechanochemical durability with higher bonding strength to the aluminum substrates, and the coatings could retain their high superhydrophobicity after over 100 cycles of sand abrasion under a load condition of 1.1 kPa. In strongly acidic and alkaline solutions for 6 h, the composite coatings were intact and showed high ability to resist the chemical erosion. Even though the superhydrophobic coatings suffered the UV damage, the water repellency could be restored under thermal treatment at 135 °C for 3 h. All these excellent performances were attributed to the rational regulation of nanoparticles in superhydrophobic PU-based composite coatings.

Effect of Al2O3 addition on the microstructure and oxidation behavior of SiC coating prepared by pack cementation on C/C composites

The study addresses the effects of Al2O3 on the SiC coating fabricated by pack cementation by preparing coatings with different Al2O3 contents on C/C composite. After the in-depth analysis of various characterization results, including XRD, SEM, EDS, and XPS, the competition brought by Al2O3 between enhancing coatings qualities and affecting oxidation behaviors was revealed. One insight into the microstructure of as-prepared coatings is that Al2O3 could boost internal exchange and the diffusion of parent materials, which is conducive to resisting oxidation by improving the qualities of the layers. Another insight about the coating oxidation is obtained from the SiC–Al2O3 volatility diagram, where the multiple roles of Al2O3 plays in the transition of oxidative mechanisms are elucidated. The beneficial impact that stables the oxide layer and reduces the coating consumption takes the upper hand comparing to the adverse effect, including breaking the structure of SiO2.

Silk fibroin-Ti3C2TX hybrid nanofiller enhance corrosion protection for waterborne epoxy coatings under deep sea environment

The complex and harsh deep sea environment is the main reason for the failure of the protective coating of marine equipment. However, excellent protective coating is the key to prolong the service life of the equipment under deep sea environment. Ti3C2TX, with high aspect ratio, abundant surface functional groups and excellent mechanical properties, is the suitable candidate nanofiller for coating reinforcement. Herein, we synthesized a novel silk fibroin-Ti3C2TX (SF-Ti3C2TX) hybrid nanofiller as reinforced-additives for improving the anti-corrosion ability of waterborne epoxy coating. Due to the rough surface of SF-Ti3C2TX nanosheets, they have excellent compatibility with the resin matrix and could fill the inherent defects of the coating. The anticorrosion behaviors of as-prepared composite coatings under both of atmospheric pressure and simulated deep sea environment were investigated in detail. Particularly, the composite coating with 0.5 wt% SF-Ti3C2TX sheets showed outstanding corrosion protection (impedance value remained 1.31 × 108 Ω⋅cm2, four orders of magnitude higher than pure EP) after 240 h immersion under 20 MPa hydrostatic pressure. In addition, the interface of coating/steel was not damaged and the coating remained the favorable adhesion strength (3.16 MPa, but that of pure EP only 0.88 MPa) even in the harsh high hydrostatic pressure. Based on the experiment data, we discussed and analyzed the failure process of coatings and explained the corrosion protection mechanism of SF-Ti3C2TX hybrid under simulated deep sea environment.

Comparison of plasma sprayed NbB2-NbC coatings obtained by ex-situ and in-situ approaches

NbB2-NbC composite coatings were fabricated on the surface of TC4 by plasma spraying NbB2-NbC and Nb-B4C composite powders. The microstructure and properties of the as-prepared coatings were investigated, and the reaction mechanism of the Nb-B4C composite powder in the plasma jet and the formation mechanism of the NbB2-NbC coatings were revealed. During the plasma spraying process, NbB2-NbC composite powder underwent melting-depositing and no phase transformation occurred. The formation mechanism of the coating by plasma spraying Nb-B4C composite powder was solid phase diffusion-reaction-melting-deposition, and NbB2 and NbC were formed in situ by the solid phase diffusion reaction between Nb and B4C in the plasma jet. The coating obtained by reactive plasma spraying Nb-B4C composite powder has obvious lamellar structure, low porosity, high density, higher microhardness, good toughness, and better wear resistance compared with the coating prepared by NbB2-NbC composite powder, which is attributed to the exothermic reaction between Nb and B4C.

Long-term protective mechanism of poly(N-methylaniline)/phosphate one-step electropolymerized coatings for copper in 3.5% NaCl solution

Cauliflower-like phosphate-intercalated poly(N-methylaniline) (PNMA) composite coatings were electropolymerized on copper surface in a facile one-step procedure for preventing the substrate from corrosion in 3.5% NaCl solution. The composite (PNMA-5P) with 5 mM phosphate in supporting electrolyte exerted superior properties in thickness, conductivity and adhesive strength. Long-term anti-corrosion capacity of PNMA-5P coating was evaluated by morphological, electrochemical, wettability and solution analyses. Multi-scale simulations were employed to distinguish the deposition and protection mechanism of as-prepared coatings for copper in the corrosive solution. Morphological observation indicated that PNMA-5P coating is stable with hydrophobic characteristic during 30 days immersion in NaCl solution. Electrochemical analyses revealed that PNMA and PNMA-5P coatings behaved as a barrier against mass/charge exchange, and therefore impeded copper corrosion effectively. Phosphate reinforced the anodic protection of composite, for which PNMA-5P coating earned the superior anti-corrosion ability for copper in the long-term immersion as compared to the pristine control. Theoretical calculations in electron- and atom-scale evidenced that phosphate was stabilized among PNMA chains via electrostatic force and facilitated the stretched deposition of polymer on copper surface. Time-dependent diffusion trajectories supported that in-situ ions were confined in local region for the compact structure, favorable barrier and anodic protection effects of composite coating.

Microstructure, electrochemical and tribocorrosion behaviors of CrCN nanocomposite coating with various carbon content

The CrCN nanocomposite coatings with various carbon content were firstly synthesized via mid-frequency magnetron sputtering to seek the possibility of application in marine corrosion environment. The microstructure of the CrCN coatings were characterized systematically. In particular, the mechanical, electrochemical as well as tribocorrosion performances of the resulting coatings were evaluated in detail. The results showed that the CrCN coatings were polycrystalline structures composed of CrN phase, Cr7C3 phase and amorphous carbon. The carbon content of the CrCN coating significantly influenced its mechanical, electrochemical and tribocorrosion properties. The hardness and elastic modulus of the CrCN coating increased initially and then gradually decreased as the raising of the carbon content in the coating. And the CrCN coating with 20.3% carbon content exhibited maximum hardness of 14.7 GPa and the highest elastic modulus of 197.7 GPa among all coatings. However, the adhesion strength of the prepared coatings gradually deteriorated as the carbon element doping into CrN coating. The CrN coating with many defects exhibited poor electrochemical performances compared with the dense CrCN coatings. The CrCN coating with 20.3% carbon content presented the lowest wear rate of 3.85 × 10−7 mm3(Nm)−1 and minimum OCP value of −0.19 V, revealing its excellent tribocorrosion properties. This could ascribe to its high hardness and the obvious graphitization of the wear surface. Finally, the possible tribocorrosion mechanisms of the as-prepared coatings were proposed according to the analyzed results of their microstructure, electrochemical behaviors and wear surfaces.

Investigations on the thermal control properties and corrosion resistance of MAO coatings prepared on Mg-5Y-7Gd-1Nd-0.5Zr alloy

In this paper, the micro arc oxidation (MAO) method was utilized to prepare the ceramic coatings on Mg-5Y-7Gd-1Nd-0.5Zr substrate. Effects of different reaction time and NH4VO3 concentration on the morphology, composition, absorptance, emissivity, corrosion resistance and adhesion strength of coatings were investigated. These results show that the as-prepared coatings were mainly composed of Mg, Si, P, V, O and Na elements, and all of them existed as amorphous state. With the increases of reaction time and NH4VO3 concentration could improve the thickness, roughness and reduce the lightness (L value), and so the absorptance and emissivity of prepared coatings increased. Meanwhile, the corrosion resistance of coatings was much better than that of Mg alloy, exhibiting an increasing tendency as the reaction time and NH4VO3 concentration. However, too more NH4VO3 might cause many pores and micro-cracks generated on the surface of coatings, which slightly reduced the corrosion resistance. Although scratch tests denote that the adhesion strength of coatings decreased with the increase of thickness, T4/N4 with the maximum thickness still had good adhesion to the substrate and remained stable after thermal shock experiments. In general, T4/N4 possessed the optimal comprehensive performances, which would expand the application range of Mg-5Y-7Gd-1Nd-0.5Zr in aerospace and optics.

Epoxy thermoset coatings with fine controllable hierarchical structures prepared from bio-inspired photo-/colloidal lithography technique for anticorrosion application

Several epoxy thermoset (ET) composite coatings with artificial fine controllable micro/nano hierarchical structures were prepared through photolithography/colloidal lithography and subsequently applied in anticorrosion field. Firstly, several silicon wafers with fine controllable interspacing and width of micro-scaled cylindrical structures were fabricated through conventional photolithography. Subsequently, nano-scaled tips were fabricated upon a smooth clean surface on the previous silicon wafer with micro-scaled cylinders to generate nano-scaled tips through colloidal lithography. Moreover, ET coatings were duplicated by nano-casting technique with polydimethylsiloxane (PDMS) as a soft negative template. Surface morphology and contact angle (CA) of as-prepared hard silicon template and ET coatings were identified. The CA of water droplets on ET coating with bio-inspired micro/nano hierarchical structures (denoted by BET) was 160°, which meant that this coating was more hydrophobic than ET coatings with distinctive surface structures. Anticorrosion studies of as-prepared ET coating with/without distinctive structures showed that cold rod steel (CRS) electrode coated with BET had better anticorrosion performance than other ET coating for short- and long-term studies. This procedure of fine controllable micro/nano structure coatings opens the door for further innovative investigations of corrosion protection methods and material designs.

Cathode electrolytic plasma deposition of (Al0.9Cr0.1)2O3/γ-Al2O3 composite coatings onto Ti45Al8.5Nb0.1Y0.2W alloys for high-temperature applications

The anti-oxidation properties of TiAl-based alloys at above 900 °C are of particular interesting for high-temperature applications. Here, novel (Al0.9Cr0.1)2O3/γ-Al2O3 composite coatings have been fabricated on the surface of Ti45Al8.5Nb0.1Y0.2W alloys by cathode electrolytic plasma deposition technique (CEPDT). The effects of as-prepared composite coatings on the microstructure and long-term oxidation behavior of Ti45Al8.5Nb0.1Y0.2W alloys are investigated through X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM), energy dispersion spectrometry (EDS), and isothermal oxidation measurements. Benefited from Cr3+ doping at the Al3+ sites of Al2O3, there shows a much denser structure for the (Al0.9Cr0.1)2O3/γ-Al2O3 composite coatings than single γ-Al2O3 coatings. This favors the decrease of weight gain into 0.773 mg/cm2 for CEPDT-modified alloys with the composite coatings after overall oxidation of 720 h at 900 °C, as compared to mass gains of 3.213 mg/cm2 and 2.331 mg/cm2 for pristine alloys and CEPDT-modified alloys with γ-Al2O3 coatings. It is also found that the microstructural characteristics of the composite coatings after oxidation shows much favorable impact on high-temperature application of TiAl-based alloys in a protective way.

Tribological properties and corrosion behavior of AC-HVAF sprayed nanostructured NiCrCoAlY-TiB2 coatings

In this paper, agglomerated and dense nanostructured NiCrCoAlY-TiB2 composite powders prepared by spray drying and plasma spheroidization were used for activated combustion high velocity air fuel (AC-HVAF) spray. The effect of sprayed powders on the microstructure, tribological properties and corrosion behavior of the AC-HVAF sprayed coatings was systematically investigated. The present results demonstrate that plasma spheroidized powders are beneficial for dense microstructure and can effectively enhance coating's wear and corrosion resistance in turn. The coating sprayed by plasma spheroidized powders exhibits good wear resistance with the coefficient of friction of 0.48 ± 0.01 and wear rate of 1.6 ± 0.2 × 10−5 mm3 N−1 m−1. The good wear resistance is mainly due to the uniformly distributed nanostructured TiB2, which can work as the hard-skeleton support. The electrochemical polarization tests and electrochemical impedance spectroscopy (EIS) analysis show that the good corrosion resistance can be attributed to the TiO2 and B2O3 oxide films formed on the surface and dense microstructure of as-prepared coatings.

TiC-TiSi2-Al2O3 composite coatings prepared by spray drying, heat treatment and plasma spraying

An innovative approach to improve the quality of TiC-TiSi2-Al2O3 composite coating was demonstrated. In-situ synthesis is one of the most economical methods for preparing refractory composite coatings, but the problems of low reaction degree and poor quality of the as-prepared coatings still exist. In the present investigation, TiC-TiSi2-Al2O3, Al-TiO2-SiC and heat-treated Al-TiO2-SiC composite powders were plasma sprayed on the surface of TC4 titanium alloy to prepare TiC-TiSi2-Al2O3 composite coatings, respectively. The phase composition and microstructure of the three kinds of composite powders and as-prepared coatings were analyzed, and the porosity, microhardness and fracture toughness of the coatings obtained by the three kinds of composite powders were comparatively studied. The results show that the heat-treated Al-TiO2-SiC composite powders had higher density and smoother surface than that of Al-TiO2-SiC composite powders. The pre heat treatment of Al-TiO2-SiC feedstock could avoid the inadequate reaction during the plasma spraying process. The coating obtained by plasma spraying heat-treated Al-TiO2-SiC composite powders had the highest bonding strength, microhardness (51.8% higher than Al-TiO2-SiC coating) and fracture toughness among the three coatings.

Recycle of magnesium alloy scrap for improving fire resistance, thermal stability, and water tolerance of intumescent fire-retardant coatings

The rapid development and widespread application of magnesium alloy bring about a significant amount of magnesium alloy scrap. Thus, we offer a feasible and simple way to realize the recycling of magnesium scrap in this work, applying it as a synergist in the intumescent fire-retardant coatings for steel structure. With the introduction of magnesium scrap, the fire resistance, thermal stability, and water tolerance of the as-prepared coatings significantly improved. According to ASTM E119 standards, the fire resistance of coatings was investigated in our laboratory. Adding only ~ 0.48 wt% of the scrap decreased the backside temperature of the coated steel from 310°C to 171°C, with a ~ 44.8% reduction, indicating obvious synergy. Moreover, the coating containing ~ 0.48 wt% scrap exhibited excellent thermal stability and water resistance, and its char yield at 800°C and water contact angle reached up to 27% and 80.6°, respectively. Based on the analysis of flame-retardant mechanism, the scrap and intumescent fire-retardant system jointly promoted the formation of an intumescent and compact char residue, thus suppressing the heat transfer and protecting the steel. Hence, using magnesium alloy scrap as a synergist contributed to realizing the recycling of waste and providing practical intumescent fire-retardant coatings for structural steel.

Harmonizing mechanical responses of nanostructured CrN coatings via Ni additions

CrN coatings are often brittle and prone to abrupt failure. Incorporation of Ni is known to have significant effects on the chemical composition, microstructure and mechanical behaviour of chromium nitride coatings synthesised by PVD, and thus imparting toughness. In this study, a series of NiCrN coatings, with varying Ni concentrations, were deposited onto AISI M2 tool steel substrates through closed-field unbalanced magnetron sputtering ion plating (CFUMSIP). The phase compositions, microstructure, mechanical properties and deformation behaviour of the coatings were characterised by XRD, AFM, FIB, TEM/EDS and indentation testing. Residual stresses of these as-prepared coatings were measured by the XRD-sin2ψ method. A columnar structure was observed in all coatings, although grain refinement at higher NiCr target currents was noted. High hardness values of ~20 GPa were found in the coatings with the lower Ni (~5–14 at%) contents, associated with the effects of solid solution hardening, high compressive residual stress and grain refinement. Moreover, significant damage-tolerance, coupled with good hardness values (greater than ~12 GPa), was found in the NiCrN coatings deposited at INiCr ≥ 2 A. The presence of a metallic nickel-rich phase, together with nanoscale porosity, may contribute to stress dissipation and help maintain structural integrity.

Preparation of titania-reduced graphene oxide composite coatings with electro- and photosensitive properties

Smooth and optically transparent titania (TiO2) and TiO2-reduced graphene oxide (RGO) composite films were successfully prepared here. A nanocrystalline anatase suspension was initially prepared by combining the sol-gel process and hydrothermal treatment. Graphene oxide (GO) nanosheets were prepared following a route similar to the Hummers method. Glass slides were then dip-coated using mixtures of TiO2 and GO suspensions. The concentration of GO in the prepared coatings ranged from 1 to 5 wt%. The coated samples were air-dried, and then either calcined or irradiated with UVA light. It was observed that UVA light promoted the reduction of GO to RGO, which increased both the electrical conductivity and hydrophilicity of the composites. The heat treatment of as-prepared coatings also decreased the water contact angle (WCA) with its surface, which is related to the removal of organics residues, graphene burning, and the increase in surface energy. The superhydrophilicity of the prepared samples was investigated after keeping them in air for up to 60 days, followed by UVA illumination. It was also demonstrated that a hydrophilic behavior can be induced in the samples prepared here by applying a direct current (DC) voltage, which could allow their use as smart materials in several applications.

Anti-corrosive mechanism of poly (N-ethylaniline)/sodium silicate electrochemical composites for copper: Correlated experimental and in-silico studies

Poly (N-ethylaniline) (PNEA) composites with varying silicate content were fabricated on copper through a novel electropolymerized strategy in acidic solution. Thickness, compactness, conductivity and adhesive strength of the composite (PNEA-10Si) were optimized as silicate content reached 10 mM. Electrochemical, morphological and solution analyses were employed to evaluate the protective performance of PNEA and PNEA-10Si coatings for copper in 3.5 % NaCl solution. Results of electrochemical analyses indicated that as-prepared coatings retarded the oxygen reduction process efficiently for copper in 3.5 % NaCl solution, drained corrosion current density and elevated interfacial charge transfer resistance. Due to favorable barrier effect, compact structure and low porosity index, PNEA-10Si composite exhibited superior anti-corrosive performance, which was more tolerant than PNEA during long-time immersion. PNEA-10Si coated sample exhibited a stable topography after 144 h immersion with the minimum concentration of released ions revealing the improved protection capacity. Electronic/atomic-multiscale calculations were conducted to clarify the deposition and protection mechanism of as-prepared coatings. Outcomes of density functional theory corroborated that silicate is stabilized in the PNEA layer via electrostatic force; and immobile silicate positively contributed to the charge transfer barrier of the composite. Molecular dynamics simulations evidenced that the favorable compatibility between PNEA and silicate facilitated polymer deposition and confined in-situ ions diffusion.

Microstructure and properties of in-situ composite coatings prepared by plasma spraying MoO3–Al composite powders

MoO3–Al composite powders were used for preparing in situ composite coatings. Effects of the composition of MoO3–Al composite powder on the microstructure and properties of the as-prepared coatings were investigated. The results show that the main phases of the as-prepared coatings were γ-Al2O3 and Mo. An optimal composition (63 wt%) of MoO3 in MoO3–Al composite powder was demonstrated. The porosity of the as-prepared composite coatings decreased first and then increased with the increase of MoO3. This is attributed to the fact that the melting state of the powder during plasma spraying is closely involved in the content of MoO3. The coating prepared by composite powder with 63 wt% MoO3 had the most Al2O3 and the highest microhardness. The wear resistance of 63 wt% MoO3 composite coating was the best among four coatings with different content of MoO3, which is attributed to its high hardness and good toughness.

Self-cleaning material based on superhydrophobic coatings through an environmentally friendly sol–gel method

Recently, there has been increasing interest in developing artificial superhydrophobic surfaces, especially in the field of self-cleaning application. However, the poor robustness and high-cost preparation of these surfaces have always been some issues for their industrial development. Herein, we describe an environmentally friendly way to prepare stable, robust, and transparent superhydrophobic coatings through the deposition of a rough substructure of TiO2 film followed by chemical modification using octadecyltrichlorosilane (OTS), a fluorine-free organic silane. The as-prepared coatings exhibited a great superhydrophobic property and ultralow adhesion (with a static water contact angle of 158 ± 2° and sliding angle of 4 ± 1°). It was found that the superhydrophobic coatings can still maintain good performance after UV irradiation, chemical immersion, and physical abrasion. More importantly, the coated surfaces showed an excellent self-cleaning ability against dirt particles after rinsed with water droplets.

A novel TiC-TiN based spectrally selective absorbing coating: Structure, optical properties and thermal stability

A novel TiC-TiN/Al2O3 tandem solar selective absorbing coating was successfully deposited on Si (1 0 0) and stainless steel (SS) substrates by reactive RF magnetron sputtering deposition. The spectral characteristics, microstructure, thermal stability and solar-thermal conversion efficiency of the coating before and after a long annealing in vacuum were investigated systematically. The optical constants of the coating are measured by an Ultraviolet–visible-near-infrared (UV/Vis/NIR) spectrometer, and the chemical composition analysis, structure information and surface morphology are investigated using XRD, XPS and FESEM. An excellent absorptance (α = 0.92) and a low emittance (ε = 0.11) at 82 °C are obtained by the as-prepared coatings. After annealed at 500 °C for 100 h in vacuum, there is no significant change in micromorphology and optical properties of the coating, which produces a good solar-thermal conversion efficiency. These results indicate that it can be applied as a potential coating material to a high temperature concentrated solar power (CSP) system.

Effect of the Ni(NO3)2 additive on the electrophoretic deposition of NiO nanoparticles

In this work, we report the electrophoretic deposition of NiO nanoparticles on aluminum plates, as well as the effect of the nickel nitrate salt used as additive for coating deposition. First, the Ni(OH)2 nanoparticles were synthesized by a precipitation route with NaOH in a conventional microwave oven. This precursor was submitted to a heat treatment at 300 °C for 3 h in order to obtain the nickel oxide without any secondary phase. The NiO nanoparticles with mean crystallite size of 2.79 nm were dispersed in isopropanol and deposited by an electrophoretic procedure on aluminum substrates with 1 cm of distance and under 10 V of DC voltage for 30 min. XPS analysis of the as-prepared coatings reveals that metallic Ni is produced during the EPD process. Moreover, the presence of Ni(NO3)2 as additive on the electrophoretic procedure leads to changes in the morphological features of the coatings. In this sense, a compact and homogenous coating was formed without the presence of nickel salt, whereas a coating with porous and cavities was obtained with a 0.5 mM concentration of Ni(NO3)2. Moreover, a 1.0 mM concentration of the additive results in a poor coverage of the electrode surface. The porous structure of the coatings in combination with the formation of metallic Ni could be useful for electrochemical applications such as capacitors or electrochromic devices.