Improving tribocorrosion performance of chemically bonded ceramic phosphate coating reinforced by GO-ZnO

To enhance the tribocorrosion properties of chemically bonded phosphate ceramic coating (CBPCC), GO-ZnO was prepared and added into CBPCC. And the tribocorrosion behaviour of CBPCC was investigated. Results show that, with the introduction of GO-ZnO, the open circuit potential of CBPCC shifts in a positive direction and corrosion current density decreases. In addition, the total material loss, the total mechanical wear loss and the total electrochemical corrosion loss of CBPCC all decrease with the increase of GO-ZnO. The wear track of CBPCC after tribocorrosion without GO-ZnO is rough and porous, while the wear track becomes smooth and dense with the incorporation of GO-ZnO. The material in wear track is anchored by GO-ZnO due to the strong bond between GO-ZnO and CBPCC, which decreases the wear loss. Because of the extra force from the tribocorrosion experiment, the material anchored by GO-ZnO forms to a dense structure which prevents electrolyte diffusion into CBPCC. Moreover, GO-ZnO can block the electrolyte diffusion pathway and make it more tortuous. The resistance to the electrolyte diffusion decreases the corrosion current density and the increased wear loss due to electrochemical corrosion.     

The long-term effectiveness and failure mechanism of the chemically bonded phosphate ceramic coatings with different thickness

In this study, the chemically bonded phosphate ceramic coatings (CBPCs) with different thickness (100 µm, 200 µm, and 300 µm) are prepared on the mild steel (Q235). Potentiodynamic polarization testing and electrochemical impedance spectroscopy were carried out to study the synthetic effect of coating thickness and etching time (12, 24, 36, and 48 hours) on the corrosion behavior of CBPCs. The surface and cross section microstructure of CBPCs before and after different immersion time in 3.5 wt.% NaCl solution is investigated to better understand the corrosion behavior. Results revealed that the enhanced coating thickness can effectively postpone the corrosive factors infiltration into the substrate and prohibit the corrosion of the mild steel. From the potentiodynamic polarization testing results, the protection efficiency of the coating greatly increases with the increase in etching time. In addition, an increase in 10 000 and 1000 orders of magnitude of impedance value for the CBPCs with 12 hours and 48 hours etching time has been observed, respectively, indicating the CBPCs can effectively protect the mild steel from corrosion damage even with long-term service.     

Effect of silica/PVC composite coatings on steel-substrate corrosion protection

In this paper we focus on the preparation of thin polymer coatings synthetized from 30-nm and 600-nm silica particles dispersed in polyvinyl chloride (PVC) and deposited on two different steel substrates: duplex DSS 2205 and austenitic AISI 316L steel. We show that a silica surface modification with silane IO₇T₇(OH)₃ (trisilanol isooctyl polyhedral oligomeric silsesquioxane, POSS) significantly improves its dispersion properties when mixed with PVC. For comparison, the surface morphology and surface roughness of PVC coatings filled with both silanated and as-received (non-silanated) silica fillers were analyzed with scanning electron microscopy (SEM) and atomic force microscopy (AFM) when sprayed on the steel surface. The effect of the silica silanization is later on reflected in a decreased average surface roughness in the silanated, compared to non-silanated, silica/PVC-coatings. The wetting properties of the silanated and non-silanated silica/PVC-coatings on DSS 2205 and AISI 316L were investigated using contact-angle and surface-energy measurements, indicating an increased surface hydrophilicity in terms of a decreased static water contact angle and an increased total surface energy compared to the uncoated specimens. Finally, the beneficial corrosion resistance of the silica/PVC coatings was confirmed with potentiodynamic polarization spectroscopy in a 3.5% NaCl solution.     

Microstructure and tribological behavior of Ti3C2Tx MXene reinforced chemically bonded silicate ceramic coatings

MXenes – In recent decades, great attention has been paid to the fast-growing two-dimensional (2D) transition metal carbides and nitrides, in terms of their prominent mechanical and electrical properties. The tribological essence of MXene has not yet been entirely investigated, although researches on MXene were conducted in all aspects of its applications. Hence, a newly compound 2D MXene (Ti₃C₂T_x) is exploited to reinforce the wear resistance of the chemically bonded silicate ceramic coatings, which are utilized to protect component surfaces under severe conditions. The structural features, hardness, and tribological behaviors of the targeted coatings are investigated and analyzed. Results show that the micro-hardness of the coatings increases to 156.9 HV_0.5 when added 1.2 wt% MXene. The increment of microhardness extraordinarily reaches 33.3%, compared with the original. The coating with 1.2 wt% MXene also indicates a 31.6% decrement of the coefficient of friction (COF) and a 73% reduction of the wear rate respectively. Furthermore, fatigue is found to be the main reason of the wear mechanism, through exploring the surface morphologies of wear traces and counterpart balls.     

Tribological behavior studies of chemically bonded phosphate ceramic coatings reinforced with modified multi-walled carbon nanotubes (MWCNTs)

To improve the wear resistance of the chemically bonded phosphate ceramic coatings, MWCNTs are selected as the reinforcement after the modification. The high temperature wear experiment is carried out to investigate the wear behavior of the coatings with different temperatures. The results suggest that, when the temperature is below 500℃, MWCNTs can decrease friction coefficient, and the lowest friction coefficient is about 0.28, but MWCNTs lose the lubricant function at 500℃ and the friction coefficient keeps at the level of ~ 0.68. In addition, the wear resistance of coatings is improved with the introduction of MWCNTs at 100℃ and 300℃ (the wear rate is below 15X10^-3mm³/Nm), but keeps similar level at 500℃ (the wear rate is ~ 22 × 10⁻³mm³/Nm). Besides, the wear mechanism of the coatings reinforced by MWCNTs is also investigated based on the wear behavior and microstructural characterizations. MWCNTs improve the fracture toughness by preventing the crack generation and forming the bridge when crack occurs, which leads to smooth wear tracks and good wear resistance of coatings. The coatings with MWCNTs achieve poor wear resistance at 500℃ because MWCNTs lose their strength and resistance to fatigue by oxidizing.     

Synthesis of chemically bonded phosphate ceramic coatings with tailored curing behaviour and enhanced oxidation resistance

The objective of this study was to develop chemically bonded phosphate ceramic (CBPC) coatings with relatively low curing temperature, properly prolonged curing time, and enhanced oxidation resistance. The coating was synthesised using aluminium phosphate as binder, surface modified MgOw/MgO as curing agent, and spherical microscaled Al particle as filler. The MgOw/MgO curing agent was surface coated by an Al₂O₃ layer via sol-gel routes. The Al₂O₃-coated MgOw/MgO agent facilitated a controllable curing process owing to the sustained-release effect of the surrounding microstructure. The weight loss profiles of all CBPCs with a surface modified curing agent exhibited a quasi-parabolic trend. The curing time decreased with the addition of the curing agent, and the Al₂O₃-coated MgOw curing agent was more effective owing to the good dispersion and larger particle number/volume percentage. The thermogravimetric and differential scanning calorimetry curves proved that the Al element exhibited similar effect as Mg²⁺, which could also enhance the curing process via substitution reaction between the basic metal ions with hydrogen in phosphate. Therefore, the addition of Al filler resulted in further curing and densification, exhibiting a decrease in the curing time (30–50 min) and increase in the weight loss (~40%). Proper binder-to-curing agent-to-filler mass (B:C:F) ratio was very important, and the CBPCs with improved surface roughness, hardness, and free of cracks were synthesised at a B:C:F ratio of 10:1:0.05. During oxidation at 800 °C, the Al filler in the CBPCs transformed into a continuous Al₂O₃ layer, which protected the Ti6Al4V alloy from further oxidation.     

Capped inhibitor-loaded halloysite nanoclay-based self-healing silica coatings for corrosion protection of mild steel

The effect of polymeric nanocapsule capping in benzotriazole encapsulated into halloysite nanoclay (HNTs) dispersed into hybrid silica coatings was investigated for corrosion protection of mild steel. Optimization of the amount of inhibitor-loaded halloysite nanotubes with and without capping in the coating sol was carried out. The prepared formulations were dip-coated on mild steel substrates using dip-coater and then cured at 130 °C for 1 h. Surface morphology and elemental analysis of the nanoclay were studied using scanning electron microscopy and energy dispersive X-ray spectroscopy. X-ray diffraction and Fourier Transform Infrared spectroscopy analyses were carried out to confirm the encapsulation and capping of the halloysite nanoclay. The anti-corrosion and autonomic-healing properties of bare and coated substrates in 3.5 wt% NaCl solution were studied using electrochemical impedance spectroscopy, potentiodynamic polarization measurements and scanning vibrating electrode technique for varying exposure times. The coatings generated from the capped inhibitor-loaded HNTs dispersed sol-gel matrix was seen to provide higher corrosion resistance when compared to uncapped HNT based silica coatings. Electrochemical studies carried out for capped inhibitor-loaded HNT based coatings have shown an increase in charge transfer resistance to 10⁸ Ω cm² from 10⁶ Ω cm² of uncapped inhibitor-loaded HNT based coatings.     

The influence of thin benzoate-doped polyaniline coatings on corrosion protection of mild steel in different environments

The corrosion process of mild steel in the presence of benzoate-doped polyaniline coatings exposed to different environments (3% NaCl, atmosphere, and the Sahara sand) has been investigated. This system was also tested for cathodic protection and it has proven more efficient comparing to mild steel alone. Possible mechanisms of the corrosion protection of mild steel in the presence of a polyaniline-based coating in different corrosion media were also proposed.     

Electropolymerized bilayer coatings of polyaniline and poly(N-methylaniline) on mild steel and their corrosion protection performance

Polyaniline (PANI) and poly(N-methylaniline) (PNMA) have been electrodeposited on mild steel from oxalic acid bath using cyclic voltammetric technique. Pretreatments like passivation and primer polymer coatings were required for effective coating. Differently stacked composite polymer layers on the metal surface by layer-by-layer approach have also been obtained and their properties have been compared with their corresponding copolymer coatings. FTIR study confirms the formation of electroactive polymer compounds on mild steel. Evaluation of these coatings in 3.5% NaCl solution by potentiodynamic polarization and electrochemical impedance spectroscopy reveals significant corrosion resistant behavior. Relatively higher corrosion protection is exhibited by copolymer coatings and composite-bilayer coatings than the corresponding homopolymer coatings. The composite metal–PANI–PNMA layer shows higher stability and better protection than the metal–PNMA–PANI layer.     

304不锈钢上纳米TiO2涂层的制备与防腐蚀性能研究

采用溶胶–凝胶法和浸渍提拉法在304不锈钢上制备出均匀致密、彩色透明的纳米TiO2防腐蚀涂层。制备的最佳工艺条件是提拉4次,400°C热处理1h。在w(NaCl)=3%的NaCl溶液中的电化学测试表明,纳米TiO2/304不锈钢在有紫外光照射下其腐蚀电位低于304不锈钢基体。纳米TiO2涂层作为非牺牲性阳极对304不锈钢基体具有阴极保护作用和优异的防腐蚀性能。     

Preparation and corrosion behavior studies of chemically bonded phosphate ceramic coating reinforced with modified multi-walled carbon nanotubes (MWCNTs)

To improve the corrosion resistance of the chemically bonded phosphate ceramic coating, the MWCNTs are selected as the reinforcement after the modification. Through the analysis of TEM, Raman, XRD, and FTIR, it can be shown that MWCNTs are modified with carboxyl groups and the surfactant after treatment, and show good dispersion. In addition, the electrochemical experiments were carried out with 3.5 wt% NaCl solution to investigate the corrosion behavior of the coatings. The results suggest that the corrosion resistance of coatings is improved with the introduction of MWCNTs and the corrosion resistance increases with the increase in MWCNTs. Besides, the corrosion mechanism of MWCNTs reinforced coating corrosion resistance was also investigated based on the corrosion behavior and microstructural characterizations. The gel strength is improved with the addition of MWCNTs because of its strong strength, which can prevent crack occurring and form the bridge when crack happens. Therefore, H₂O, O_2, and Cl⁻ can be prevented from reaching to the substrate, which leads to good corrosion resistance.     

Failure mechanism of thin Al2O3 coatings grown by atomic layer deposition for corrosion protection of carbon steel

Combined analysis by electrochemical impedance spectroscopy (EIS), time-of-flight secondary ion mass spectrometry (ToF-SIMS) and field emission scanning electron microscopy (FESEM) of the corrosion protection provided to carbon steel by thin (50 nm) Al₂O₃ coatings grown by atomic layer deposition (ALD) and its failure mechanism is reported. In spite of excellent sealing properties, the results show an average dissolution rate of the alumina coating of ∼7 nm h⁻¹ in neutral 0.2 M NaCl and increasing porosity of the remaining layers with increasing immersion time. Alumina dissolution is triggered by the penetration of the solution via cracks/pinholes through the coating to the substrate surface where oxygen reduction takes place, raising the pH. At defective substrate surface sites of high aspect ratio and concentrated residual mechanical stress (along scratches) presumably exposing a higher steel surface fraction, localized dissolution of the coating is promoted by a more facile access of the solution to the substrate surface enhancing oxygen reduction. De-adhesion of the coating is also promoted in these sites by the ingress of the anodic dissolution trenching the steel surface. Localized corrosion of the alloy (i.e. pitting) is triggered prior to complete dissolution of the alumina film on the elsewhere still coated surface matrix.     

Development of Poly(aniline-co-o-toluidine)/TiO2 nanocomposite coatings for low carbon steel corrosion in 3.5% NaCl solution

Chemical oxidative polymerization of aniline (AN) and o-toluidine (OT) for the synthesis of copolymer, Poly(AN-co-OT) and its composite with TiO₂ nanoparticles, Poly(AN-co-OT)/TiO₂ employing ammonium persulfate as an oxidant and HCl as an external dopant were carried out. The homopolymers, Polyaniline and Poly(o-toluidine) were also prepared by following similar method. The synthesized polymers were characterized with FTIR spectroscopy, XRD/SEM/TEM analysis. The anticorrosive coatings were synthesized in dimethyl sulfoxide solution by dissolving synthesized polymers, and then were applied on low-carbon steel (LCS) samples using epoxy binder. The anticorrosive potential of the polymer coatings containing copolymer, copolymer-nanocomposite and homopolymers on LCS was evaluated in 3.5% NaCl at a temperature of 30?°C by open circuit potential, electrochemical impedance spectroscopy and potentiodynamic polarization measurements. It was observed that the nanocomposite coating increases the protection efficacy by providing better barrier properties against corrosion as compared with neat copolymer and homopolymers coatings. The morphology of the coatings before and after 60 days LCS immersion in 3.5% NaCl solution was determined using SEM.     

Study on corrosion resistance and roughness of micro-plasma oxidation ceramic coatings on Ti alloy by EIS technique

Micro-plasma oxidation (MPO) technique has been developed quickly in recent years. The produced ceramic coatings are reported to possess fine properties and promising application prospects in many fields. The aim of this work is to study the corrosion resistance and the roughness of the micro-plasma oxidation ceramic coatings on Ti alloy by electrochemical impedance spectroscopy (EIS) technique. Compound ceramic coatings were prepared on Ti-6Al-4V alloy by pulsed bi-polar micro-plasma oxidation in NaAlO₂ solution. The phase composition and element distribution in the coating were investigated by X-ray diffractometry and electron probe micro-analyzer. EIS of the coatings was measured through CHI604 electrochemical analyzer in 3.5% NaCl solution. The ceramic coating is composed of a large amount of Al₂TiO₅ and a little α-Al₂O₃ and rutile TiO₂. The coating is of double-layer structure with the loose outer layer and the dense inner layer. The thickness of the coatings is reduced when the working frequency or the cathode pulse current density is increased, while the thickness is increased when the frequency or the anode current density is increased. The established “equivalent circuit” of the coatings is consistent with the double-layer structure. The electric charge transfer resistance (R_t) in the equivalent circuit can be used to assess the corrosion resistance of the coatings, which is consistent with the result of the polarizing curves test. And the empirical exponent (n₁) of the constant phase element (Q₁) in the equivalent circuit can be used to assess the surface roughness of the coatings, which is consistent with the surface SEM analysis of the coatings.     

无取向硅钢用磷酸盐涂层材料 制备及其防腐性能

系统研究了无取向硅钢用磷酸盐系涂层性能的影响因素。以氢氧化铝和磷酸为原料制备磷酸二氢铝,再添加适量的添加剂酒石酸铵、二氧化硅、环氧树脂,得到的涂液涂布于硅钢表面,并控制合适的烘干温度,通过耐盐雾实验考察各因素对涂液耐腐蚀性能的影响。实验结果表明,在磷酸与氢氧化铝物质的量比为3.4∶1、酒石酸铵用量为2%、二氧化硅用量为1%、环氧树脂用量为5%、烘干温度为300 ℃条件下,所得涂层材料的防（耐）腐蚀效果最佳。     

The effect of mixture of mercaptobenzimidazole and zinc phosphate on the corrosion protection of epoxy/polyamide coating

The protective performance of solvent-borne epoxy/polyamide coatings formulated with zinc phosphate anticorrosion pigment was improved through the addition of 2-mercaptobenzimidazole as an organic corrosion inhibitor. In addition to determining the optimum percentage of mercaptobenzimidazole, the electrochemical impedance spectroscopy data could show the influence of inhibitor concentration on the epoxy behavior within 35 days of immersion in 3.5 wt% NaCl solution. The improved corrosion protection and adhesion strength in the presence of the pigment and inhibitor were connected to the deposition of a protective layer at the coating/substrate interface which might limit active zones for electrochemical reactions. The precipitation was confirmed using electrochemical impedance spectroscopy, polarization curves and SEM/EDX surface analysis.     

Study of the effect of mechanically treated CeO2 and SiO2 pigments on the corrosion protection of painted galvanized steel

The effectiveness of mechanically treated CeO₂ particles and SiO₂ particles as active fillers into an organic coating was investigated. For this purpose, different combinations of CeO₂ and SiO₂ particles were added to an epoxy-polyester polymeric matrix: mechanically treated CeO₂ particles, mechanically treated CeO₂/SiO₂ particles and mechanically treated SiO₂ powders (used for comparison). The particles were dispersed into the polymeric matrix and HDG steel panels were coated with the different paints. A strontium chromates containing paint was used as a reference to compare the performances of the other samples. The salt spray results proved the good performance of coatings containing combinations of ceria and silica especially where these had been mechanically treated in a co-milling operation. The paint containing only the mechanically treated SiO₂ particles showed a fairly good resistance in the salt spray chamber considering the scratched samples. The EIS measurements evidenced the good corrosion protection properties of the paints containing the different combinations of mechanically treated CeO₂ and SiO₂ particles. After about 1000 h of immersion in 0.1 M NaCl solution, the samples containing the mix of mechanically treated CeO₂/SiO₂ particles showed impedance values which were comparable with the chromate control sample. The cathodic polarization tests evidenced the low extent of detachment of the coating containing the mix of mechanically treated CeO₂/SiO₂ particles. The electrochemical characterization and neutral salt spray test results proved the effectiveness of the mechanical treated cerium (IV) oxides treated together with SiO₂ as active pigments to improve the corrosion protection of the substrate. The reasons for the synergistic effect of the milled (together or separately) SiO₂ and CeO₂ particles was not clear at all, but a few hypothesis were discussed.     

A study on the N-, S- and Cl-modified nano-TiO2 coatings for corrosion protection of stainless steel

Nano-titania coatings doped with anions of nitrogen, sulfur and chlorine have been supplied on the surface of 316L stainless steel by a sol-gel process and dip-coating technique. The measurements of XRD, SEM, ATR-IR, Raman and XPS were carried out to characterize the chemical composition and structure for the prepared samples. The corrosion performances of the coating in 0.5 M NaCl were evaluated by electrochemical impedance spectroscopy (EIS) and polarization measurements. According to the measurements of EIS and electrochemical polarization, the N-modified TiO₂ nano-coatings show a highest corrosion resistance among the prepared coatings. It is revealed, from the SEM, XRD and Raman characterizations, that the surface of N-modified TiO₂ nano-coatings are more compact and uniform, relatively well-crystallized and able to act as an optimal barrier layer to metallic substrates. The XPS analysis confirms the presence of low concentration of N element in two forms, atomic β-N (interstitial state) and chemisorbed γ-N₂ on the surface of TiO₂ nano-coatings. It is suggested that the addition of nitrogen is beneficial to improve the compact structure and enhance the hydrophobic property.     

Controlled synthesis of various SrTiO3 morphologies and their effects on photoelectrochemical cathodic protection performance

As an n-type semiconductor with typical perovskite structure, SrTiO₃ has broad research prospects in photochemical cathodic protection because of its suitable energy band structure. However, there is a lack of research on the effect of SrTiO₃ micro morphology on Photoelectrochemical cathodic protection performance. In this paper, a series of SrTiO₃ samples with controllable morphology were designed and prepared by changing the ratio of alcohol to water in the solvent, including nanoparticles (NPs), nano ball (NBs), nano rod (NRs), coral stone-like microspheres (CSLMs) and flower-like microspheres (FLMs). The experimental results show that FLMs samples have better photochemical cathodic protection performance. Under the condition of on light, the photocurrent density of FLMs samples reaches 9.2 μA. The photocurrent density of NPs samples is only 2.5 μA. The former is about 3.6 times that of the latter. The open circuit potential of FLMs samples has shifted from ?0.18 V to ?0.42 V, with a negative shift of 240 mV, while CSLMs samples have only a negative shift of 180 mV. In contrast, FLMs samples have a more negative shift of 60 mV. After four light cycle experiments, the performance of FLMs samples is stable without obvious change.     

Plasma-polymerized coatings of trimethylsilane deposited on cold-rolled steel substrates Part 2. Effect of deposition conditions on corrosion performance

Trimethyl silane (TMS) plasma-polymerized films were deposited on cold-rolled steel (CRS) under different conditions. The films were characterized by angular-dependent X-ray photoelectron spectroscopy (XPS), Auger electron spectroscopy (AES) and time-of flight secondary ion mass spectrometry (TOFSIMS). The complementary information generated by these surface techniques gave detailed information on the film composition. The corrosion performance of the plasma films was estimated by electrochemical impedance spectroscopy (EIS) and by exposure in a humidity test. All films were Si-based and their composition was a function of the deposition conditions and the plasma cleaning of substrate prior to deposition. A reducing plasma for metal surface treatment resulted in a film with the highest impedance. The plasma film surfaces were highly oxidized. The contact angle was the lowest for plasma films deposited from a mixture of TMS and oxygen and their corrosion performance was the poorest.