Surface modification of ceramic coating for enhanced hydrophobicity and wear properties

In this paper, a micro–nano structural ceramic coating with good hydrophobicity and wear resistance was successfully prepared by sol–gel method, which is assisted by pore-forming agent and nanoparticles 1H, 1H, 2H, 2H-perfluorodecyltriethoxysilane modified. The surface morphology, hardness, roughness, wettability, and tribological properties of three different surface coatings were characterized. With the complication of the surface structure, the roughness of the coating increases from 1.30 to 2.05 μm. Under the combined effect of roughness and long hydrophobic chains, the contact angles of the coatings before and after modification under saline conditions increased from 56.31 to 140.59° (pH4); from 55.58 to 134.40° (pH7); from 53.80 to 132.26° (pH10). Through the comparison of wear rate and wear morphology, it is found that the micro–nano structure coating has the lowest wear rate (0.705 × 10^–6 mm³·N^–1·s^–1) and the smallest plastic deformation. This means that in addition to the good hydrophobicity and chemical stability, the micro–nano structure on the surface also improves the wear resistance of the coating.     

A novel composite protective coating with UV and corrosion resistance: Load floating and self-cleaning performance

The research in functional materials has been the focus in studying industrial applications, particularly in the field of superhydrophobic functional bionic material. Although many studies of superhydrophobic surfaces have been published at this stage, the performance remain unsatisfactory, especially in a variety of harsh environments in practical applications, such as extremely cold weather, acidic or alkaline environment, prolonged exposure to light, high temperature, or oily wastewater, etc. The mechanical strength and corrosion resistance of coatings in such environments are all mighty challenges. In this study, we propose a fluoro silane-modified zinc oxide (FAS-ZnO) as a nano-filler. A superhydrophobic and oleophobic composite coating was successfully prepared through a single step by spraying suspensions containing attapulgite (ATP), FAS-ZnO, and carboxylated polyphenylene sulfide (PPS–COOH) onto desired substrates. In addition, stearic acid was added as a binder and used to enhance the bonding strength between the filler and the substrate. The composite coatings were characterized by FE-SEM, XRD and FT-IR on substrates, and the corrosion resistance of the coatings was evaluated by electrochemical impedance spectroscopy (EIS) and salt spray chamber experiments. The composite coatings showed excellent corrosion resistance due to the synergistic effect of FAS-ZnO and ATP. It was found that the composite coating had good hydrophobic and oleophobic contact angles of 161 ± 1.5° and 159 ± 1°, respectively, which were mainly attributed to the construction of nano-scale structures. It is worth noting that the composite coating performed excellently in chemical stability, self-cleaning performance, UV resistance, anti-fouling function, mechanical strength, and load-bearing floating ability. The coating maintained its highly hydrophobic surface after being stretched through a universal testing machine. Based on the multiple key properties in the composite coating, it can be expected to be applied to large equipment and instrument surfaces in extreme outdoor environments.     

Role of KOH and NaNO2 on the structural and corrosion properties of anodic spark electrolysis coatings produced on aluminium

Doping light elements into ceramic coatings on different metal substrates by anodic-spark electrolysis (ASE) to improve their properties, such as wear and corrosion resistance, has recently attracted a lot of attention. In this study, nitrogen-doped Al₂O₃ composite ceramic coatings had been fabricated in eco-friendly KOH–NaNO₂ electrolytes using the anodic-spark electrolysis (ASE) method after 9 min at a fixed applied ASE voltage (75 V higher than the breakdown voltages). To deposit a nitrogen-doped coating with high amounts of oxynitride phases possible, we thoroughly studied the ASE coatings deposited in different total variable salts concentrations (KOH+NaNO₂) and NaNO₂/KOH ratios of ASE electrolytes. The coating properties were investigated using X-ray diffraction (XRD), scanning electron microscope (SEM), Fourier-transform infrared spectroscopy (FT-IR), and the electrochemical impedance spectroscopy (EIS) tests. The results indicated that the coating produced in the KOH–NaNO₂ electrolyte with a low total variable salts concentration (2 gr.L⁻¹) and a high NaNO₂/KOH ratio value (3) is optimum in the investigated conditions. It has the highest percentage of nitrogen-doped phases, such as N-doped γ-Al₂O₃ and γ-AlON (γ-Al_2.78O_3.65N_0.35), and a homogeneous morphology of surface with the smallest average size of pores (<14 μm²). This coating showed the significantly higher corrosion resistance with a 4.101104 × 10⁶ Ω cm² value compared to the uncoated aluminium substrate with a corrosion resistance value of 0.094195 × 10⁶ Ω cm² after 48 h of immersion in the 3.5 wt% NaCl solution. The approach presented herein provides an attractive way to modify the surface of aluminium alloys to improve corrosion behaviour.     

Erosive and corrosive wear performance and characterization studies of plasma-sprayed WC/Cr3C2 coating on SS316

Plasma spray coating with ceramic carbide is a promising approach for improving the surface quality of the materials. In this work, the effectiveness of tungsten carbide (WC), chromium carbide (Cr₃C₂), and the composite coating of the two powders in the weight ratio of 50:50 were investigated. In the erosion test, aluminum oxide (Al₂O₃) particles were combined with a high-speed air-jet and impinged at 90° on the top surface of the material. Electrochemical polarization and electrochemical impedance spectroscopy studies were conducted with a 3.5 wt.% of sodium chloride (NaCl) solution as the electrolyte. Using a scanning electron microscope, the surface morphology of powders and coatings, as well as the mechanisms of erosion and corrosion, were studied. Energy-dispersive X-ray analysis and X-ray diffractometry were used to reveal the composition and elemental distribution of the feedstock powders and coatings. Because of the presence of hard phases, the composite coating shows the highest average microhardness of 1350.2 HV. The composite coating exhibits improved erosive wear resistance with an increase in erodent exposure time. The Cr₃C₂ coating has a reduced corrosion current density of 1.404 × 10⁻⁵ mA/cm² and a higher charge transfer resistance of 2086.75 Ω cm² due to passivation.     

Improvement in corrosion resistance of micro-arc oxidation coating on PVD Ti-coated aluminum alloy 7075

Surface treatments are always needed to enhance corrosion-resistant performance of aluminum (Al) alloys when they are used in seawater environments. The paper aimed to prepare the composite oxide ceramic coating on Al alloy 7075 by combining micro-arc oxidation (MAO) and magnetron sputtering technology. The Al substrate was precoated with titanium (Ti) layer by using the magnetron sputtering technology and then treated by MAO in the alkaline aluminate electrolyte, resulting in a composite MAO coating, which is composed of Al₂O₃ and TiO₂ along with the complex oxide (Al₂TiO₅). The potentiodynamic polarization and electrochemical impedance spectroscopy were carried out to evaluate the corrosion performance of the MAO coatings in 3.5 wt% NaCl solution. Better corrosion resistance was observed for composite oxide coating than the reference MAO coating on the bare Al, as evidenced by the higher corrosion potential of −0.664 V versus Ag/AgCl and the lower corrosion current density of 4.41 × 10^-6 A/cm².     

Repair of spline shaft by laser-cladding coarse TiC reinforced Ni-based coating: Process,microstructure and properties

To repair the surface defects of spline shaft and improve wear resistance, the coarse TiC reinforced Ni-based composite coatings were fabricated on the spline shaft surface by laser cladding with six types of precursors containing Ni45, coarse TiC, and fine TiN powder. The effects of ceramic content and fine TiN addition on the formability, microstructure, and mechanical properties of the coatings were studied comprehensively. In TiC reinforced Ni-based coatings 1–3 without fine TiN addition, the porosity decreased from 20.415 % to 0.571 % with the increase of TiC concentration. The coatings mainly consist of CrB, Cr7C3, Cr23C6, coarse TiC, and γ-Ni. With the addition of fine TiN, the length of the ceramic phases in coatings 1#–3# decreased slightly, while volume fraction and porosity increased. Moreover, the ring-shaped Ti (C, N) phases were also detected at the edges of both undissolved TiC and TiN particles, which improved the bonding force between ceramics and matrix. Besides, these ceramics inhibited the generation of columnar crystals and eliminated the heat-affected zone. The performance test results show that the coating 3# with 30 wt% TiC and 6 wt% TiN exhibits the best wear resistance despite slightly decreased hardness, and its friction coefficient of 0.409 and wear rate of 42.44 × 10⁻⁶ mm³ N⁻¹·m⁻¹ are, respectively, 0.667 and 0.307 times those of the substrate. Based on the additive/subtractive hybrid manufacturing technology, the optimized coatings were ground to obtain the finishing surface, which indicates that the coarse TiC reinforced coating can be employed in repairing the damaged parts.     

Study on preparation and anticorrosive performance of a new high hydrophobic anticorrosive coating

Water-based anticorrosive coatings have poor water resistance, which easily lead to coating deterioration and metal corrosion. In order to improve the anticorrosion performance of waterborne coating, herein, the polytetrafluoroethylene/dimethyl siloxane/epoxy resin (PTFE/PDMS/EP) hydrophobic anticorrosive coating was prepared by layer-by-layer construction. The spatial structure and microscopic morphology of the hydrophobic coating were analyzed by XRD, FTIR, and SEM. The hydrophobicity and corrosion resistance of the composite coating were analyzed by hydrophobicity test, electrochemical polarization curve, hydrophobicity and corrosion resistance test of the mixed layer, Tafel polarization curves, and AC impedance spectrum. The results showed that the water contact angle of PTFE/PDMS/EP coating reached 141° and the protection efficiency of PTFE/PDMS/EP coating was 98.62%. After soaking for 7 days, the corrosion process still stays at the initial stage, which was mainly due to the good sealing and barrier properties and high anticorrosion efficiency of PTFE/PDMS/EP coating. The coating has high corrosion protection efficiency and long service life, which is of great significance to metal corrosion protection in harsh marine environments.     

Role of rare-earth Y addition on formation and anticorrosion properties of MAO coating on 2024 aviation aluminum alloy

Different ceramic coatings were prepared on the surface of 2024 aviation aluminum alloy using micro-arc oxidation process in silicate based electrolyte combined with the rare earth based compound Y(NO₃)₃·6H₂O. The thickness, hardness of the coating and conductivity of electrolyte were tested using relative devices, morphology and chemical composition were studied by scanning electron microscope and energy dispersive spectroscope, respectively. The phase composition of the coatings was characterized by X-ray diffraction and X-ray photoelectron spectroscopy. Furthermore, the corrosion resistance of the coating was evaluated by an electrochemical workstation. The results showed that the addition of Y(NO₃)₃·6H₂O could improve the thickness and hardness of the coating. The morphological observation of the coating showed that Y(NO₃)₃·6H₂O was successfully incorporated into the ceramic layer and that the coating had the smallest porosity at 1.5 g/L Y(NO₃)₃. The phase composition of the coating was mainly γ-Al₂O₃, α-Al₂O₃, SiO₂, Y₂O₃, and AlPO₄. The corrosion resistance of coating in simulated seawater with the addition of Y(NO₃)₃·6H₂O was significantly improved, and the values of |Z|_0.01 Hz and corrosion rate of the coating reached the maximum and minimum at 1.5 g/L Y(NO₃)₃, which were 5.63 × 10⁵ Ω cm² and 7.444 × 10⁻⁴ mm/a, respectively.     

Preparation of a thick sponge-like structured amorphous silica ceramic coating on 6061 aluminum alloy by plasma electrolytic oxidation in TEOS solution

Plasma electrolytic oxidation (PEO) was performed on 6061 aluminum alloy in organosilicon electrolyte using a stepwise constant potential control method for 23 min. The resulting coating was a sponge-like structured amorphous silica ceramic with a thickness of about 130 μm. Its exceptional wear resistance was attributed to the high hardness of the silica ceramic and the low elastic modulus of the sponge-like structure. The corrosion resistance was enhanced by a dense layer of approximately 2 μm between the coating and the substrate. Impressively, the indentation depth of the PEO coating during nano-indentation tests was only 50–60% of that of 6061 aluminium alloy under varying loads, while the recovery depth of the PEO coating after unloading was 2.5–3.1 times greater than that of 6061 aluminium alloy. Due to its special composition and structure, the PEO coating caused serious wear to the high hardness Si₃N₄ friction balls during the friction and wear test. In the electrochemical tests, the coating reduced the corrosion current density from 1.056 × 10⁻⁵A·cm⁻² to 1.239 × 10⁻⁷A·cm⁻², while extending the passivation region from 0.322 V to 1.032 V.     

Electrodeposition of graphene oxide-hydroxyapatite composite coating on titanium substrate

In this work, graphene oxide (GO)/hydroxyapatite (HA) composite coatings were successfully prepared on titanium substrate by electrophoretic deposition technology. Subsequently, microstructure, phase composition, adhesion strength, hydrophilicity, corrosion resistance, bioactivity, antibacterial activity and biocompatibility of the coating were evaluated. The adhesion strength of coating increased by 76% from 6.46 MPa to 17.81 MPa with 0 wt% GO to 12 wt% GO and the corrosion rate of coating with 8 wt% GO was achieved at the minima of (1.493 × 10^-3mm/a). Biomineralization experiment indicated the excellent bioactivity of GO/HA composite coatings. The water contact angle of the composite coatings increased from 20.6°(0 wt% GO) to 38.1°(12 wt%GO). The antibacterial rates of coating with 5 wt% GO was 96.7%, while declined to 25% after thermal treatment. In-vitro L929 cell culture experiments indicated the composite coatings with 5 wt% GO exhibited good biocompatibility.     

Effects of graphene content in alkaline silicate electrolyte on AA1060 pure aluminum micro-arc oxidation coating

Ceramic coatings were obtained by micro-arc oxidation (MAO) on the surface of AA1060 pure aluminum in alkaline silicate electrolyte with the addition of graphene. The effects of graphene contents in the range of 0–.30 g/L in the electrolyte on surface morphology, corrosion resistance, and wear resistance of the ceramic coatings were investigated. The outer surface structure, outer surface element content, coating cross-section structure, coating cross-section element content, coating/substrate interface structure, and coating phase were characterized by scanning electron microscope and X-ray diffraction. Potentiodynamic polarization and electrochemical impedance spectroscopy were used to evaluate the corrosion behavior of MAO samples in a 3.5-wt% NaCl solution. In addition, the resistance to sliding and abrasive wear of the oxide coating were studied experimentally. The results show that the alkaline silicate electrolyte with the addition of graphene has a significant effect on the characteristics of MAO coating. The performance of micro-arc oxide coatings is best when the graphene content in the electrolyte is .15 g/L, the average thickness of the film is 7.24 μm, the average pore size is 6.07 μm, the impedance value is approximately 4.01 × 106 Ω, and its friction coefficient is .55.     

A robust quasi-superhydrophobic ceria coating prepared using air-plasma spraying

Hydrophobic coatings that could survive in harsh environment have a wide range of applications from industry to houseware. However, the state-of-the-art polymer-based coatings cannot meet such requirements due to their low melting point and poor wear resistance. In this study, we reported a plasma sprayed ceramic coating made of ceria with exceptional hydrophobicity, high-temperature stability, and good wear resistance. The coating exhibited a water contact angle (WCA) up to 139°, due to the intrinsic hydrophobicity of ceria and unique surface morphology produced by plasma spraying. The WCA only slightly decreased to 131° after annealing at 773 K. In addition, the polished coating (WCA ~ 116°) was still more hydrophobic than the sintered bulk specimen (WCA ~ 95°) with the same composition and roughness, which can be attributed to the surface chemistry change induced by Ar⁺ ion bombing by plasma. It is believed that such robust hydrophobic coating should have great potential in engineering application.     

Comparative Study of Corrosion Protection of Sol–Gel Coatings with Different Organic Functionality on Al-2024 substrate

In this paper we have studied the effect of addition of amino silane and sulfur silane by 2 wt% into a reference coating solution by using two basic silane coupling agents methyl-tri-ethoxy silane (MTEO) and glycidoxy-propyl-tri-ethoxy silane (GPTS) in 1:1 molar ratio by sol–gel technique. The change in hydrophobicity due to the addition of amino group and thiol group was investigated by contact angle study and sol–gel kinetics was studied by Fourier transform infrared spectroscopy. The thermal resistance and surface morphology was analyzed by thermo gravimetric method and scanning electron microscope. The anti corrosion property of all three coatings were evaluated by potentiodynamic polarization study, AC impedance and salt spray method. X-ray photoelectron spectroscopic method was used to monitor the bonding mechanism of coating matrix with the metal surface. All type of investigations revealed that, addition of thiol group containing silane coating to the reference coating solution has caused remarkable improvement in hydrophobicity and corrosion resistance properties where as amine group rendred the surface less hydrophobic and showed no sign of improvement in corrosion protection. The most probable reason behind this improved performance is due to the additional hydrophobicity imparted by much less polar thiol group. But amino silane provided comparatively poor performance due to the presence of polar amine group.     

Effect of graphene on the microstructure and corrosion resistance of PEO coating formed on D16T aluminum alloy

Incorporated graphene coating was successfully prepared on D16T aluminum alloy by plasma electrolytic oxidation (PEO) technology, and the effect of graphene on the microstructure, corrosion resistance, and wettability of the coating was investigated. Microstructure, composition, and morphology were studied by transmission electron microscope, confirming that graphene was successfully incorporated into the coating with pancake-like and embedded mode. The thickness and microhardness of the coating with graphene (G2) increased, whereas roughness and porosity reduced due to the incorporation of graphene, compared to the coating without graphene (G0). The resistive arc radius of G2 is obviously increased. The real impedance value of G2 is four times than that of G0. The resistance (R₁) of G0 and G2 are 3708 and 7533 Ω cm², respectively. The resistance (R₂) of G0 and G2 are 2.508E5 and 7.752E5 Ω cm², respectively. The contact angle of G2 under three liquid droplets was maximum, showing minimal surface-free energy (36.8 mJ/m²). Formation water showed the most obvious effect on the wettability of the coating compared to the distilled water and sodium chloride solution. Results verified that graphene in PEO coating significantly improved the microstructure of the coating and enhanced the hydrophobic performance and corrosion resistance of the coating.     

Hydrophobic benzoxazine-cured epoxy coatings for corrosion protection

A hydrophobic benzoxazine-cured epoxy coating (EPB) was prepared by a dip coating and thermal curing method using benzoxazine monomer (B-TMOS) as curing agent. Fourier transform infrared (FTIR) analyses confirmed the presence of thermal curing reactions and hydrogen-bonding interactions in the epoxy/polybenzoxazine system. The hydrophobicity of epoxy coatings induced by the incorporation of B-TMOS was enhanced significantly, and the water contact angles of resultant EPB coatings were higher than 98°. The corrosion protection ability of epoxy coatings was investigated by open-circuit potentials, potentiodynamic polarization curves and electrochemical impedance spectroscopy (EIS) methods. The results showed that the charge transfer resistance (R_ct) of EPB coatings was increased by about three orders of magnitude compared with bare mild steel, and the protection efficiency values of all EPB samples were more than 98%. This increased corrosion protection property could be attributed to the high hydrophobic performance of EPB coatings.     

Synthesis and characterization of nanosized titanium dioxide and silicon dioxide for corrosion resistance applications

We are reporting the preparation and characterization of nano-titanium dioxide and silica. The corrosion resistance performance of these nanopigments in silicone as well as silicone–polypyrrole Interpenetrating Polymer Network has been evaluated by impedance spectroscopy. The capacitance and resistance exerted by this nanocomposite coating were compared with the microcomposite coating and found that the nanocomposite coatings has the resistance in the order of 10⁸ Ω cm² in 3% sodium chloride solution, which is more than the microcomposite coating. The comparison of heat resistance performance of these composite coatings indicates that nanocomposite coatings exhibit higher heat resistance property than the microcomposite coatings.     

Effect of sub-layer temperature during HFCVD process on morphology and corrosion behavior of tungsten carbide coating

WC coating was deposited on the polished and cleaned 316L stainless steel by Hot Filament Chemical Vapor Deposition (HFCVD) technique at 400°C and 500°C. Field Emission Gun Scanning Electron Microscope (FEG-SEM) was used to study the corrosion morphology of the WC coatings. Energy dispersive spectroscopy (EDS) was used to analyze the chemical composition of the coatings. Coating porosity was measured by immersion in water. Potentiodynamic polarization and electrochemical impedance spectroscopy (EIS) techniques were used to study the corrosion behavior of the coating in the solution of 1 mol/L H₂SO₄. Results showed that the WC coatings have a honeycomb microstructure where its porosity was increased at higher temperature of the sub-layer. Also, the WC coating significantly increases the corrosion resistance of 316L stainless steel. And increasing the sub-layer temperature in the HFCVD method reduces the corrosion resistance of the WC coating. Corrosion morphology was indicative of pitting corrosion of the WC coating.     

Polymer-derived SiOC ceramic coating for corrosion protection

In the present study, a polymer-derived silicon oxycarbide (SiOC) ceramic layer has been coated on stainless steel 304 (SS304) to improve corrosion resistance in a seawater environment. The surface of SS304 is dip-coated with vinyl-functionalized polysiloxane, followed by pyrolysis under argon at 800°C to obtain SiOC layer with a thickness of about 1 μm after two-fold coating/pyrolysis steps. Structural characterization of the samples was performed by fourier transform infrared (FTIR), X-ray diffraction, Raman spectroscopy, and scanning electron microscopy. Electrochemical characterization of SS304 and SiOC-coated SS304 is performed in 0.6 M NaCl solution. Potentiodynamic polarization measurements showed improved corrosion resistance of SiOC-coated SS304 with a very low corrosion current density of 4.14 × 10⁻⁹ A/cm² whereas for uncoated SS304 corrosion current density of 4.56 × 10⁻⁷ A/cm² was measured. Electrochemical impedance spectroscopic study confirmed superior corrosion resistance behavior of SiOC-coated SS304 over uncoated SS304.     

Excellent corrosion protection performance of epoxy composite coatings filled with silane functionalized silicon nitride

Silicon nitride was firstly used as anticorrosive pigment in organic coatings. An effective strategy by combining inorganic fillers and organosilanes was used to enhance the dispersibility of silicon nitride in epoxy resin. The formed nanocomposites were applied to protect Q235 carbon steel from corrosion. The anticorrosive performance of modified silicon nitride with silane (KH-570) was investigated by electrochemical impedance spectroscopy (EIS), water absorption and pull-off adhesion methods. With the increase of immersion time, the corrosion resistance as well as adhesion strength of epoxy resin coating and unmodified silicon nitride coating decreased significantly. However, for the modified silicon nitride coating, the corrosion resistance and adhesion strength still maintained 5.7×10¹⁰ Ω cm² and 7.6 MPa after 2400-h and 1200-h immersion, respectively. The excellent corrosion resistance performance could be attributed to the chemical interactions between KH-570 functional groups and silicon nitride powders, which mainly came from the easy formation of Si-O-Si bonds. Furthermore, the modified silicon nitride coating formed a strong barrier to corrosive electrolyte due to the hydrophobic of modified silicon nitride powder and increased bonds.     

CO2 capture based on Al2O3 ceramic membrane with hydrophobic modification

In this paper, Al₂O₃ ceramic membrane is modified to hydrophobicity by grafting 1 H,1 H,2 H,2 H-perfluorodecyltriethoxysilane. And its properties are characterized in detail. CO₂ capture performance of ceramic membrane is investigated by experiments. Results show that wetting resistance after modification is significantly improved, and contact angle increases from the initial 49.8–130.9°. However, hydrophobic modification has no significant effect on the crystalline phase, surface morphology and pore size distribution of the ceramic membrane. With ethanolamine (MEA) as absorbent, CO₂ mass transfer rate and capture efficiency using modified hydrophobic ceramic membrane are 46.6 × 10⁻³ mol/(m²·s) and 98.0%, showing significantly increase compared to the original membrane. After 72 h immersion in MEA solution, quality of ceramic membrane does not change significantly. And there is almost no change in average pore size. We believe this study will provide a reference for the industrial application for CO₂ capture by gas-liquid membrane contactor with ceramic membrane.