Impact of TiO2 nanoparticles and nanowires on corrosion protection performance of chemically bonded phosphate ceramic coatings

The impact of the addition of TiO₂ nanoparticles and nanowires on the morphology, phase characteristics, contact angle, and electrochemical performance of chemically bonded phosphate ceramic coatings (CBPCs) was investigated. The chemical composition and surface morphology of the TiO₂ nanoparticle and nanowire modified with and without (heptadecafluoro-1,1,2,2-tetradecyl) trimethoxysilane were characterized. Results indicated that the hydrophobic –CF₂– and –CF₃ groups were successfully introduced into the TiO₂ nanoparticles and nanowires after modification. Corrosion resistance of CBPCs with TiO₂ was evidently improved compared with that without TiO₂. Such improvement was mainly due to the combined effects of low surface energy materials and micro/nano structures. In addition, CBPCs with TiO₂ nanowires exhibited higher hydrophobicity and corrosion resistance than those with TiO₂ nanoparticles because of the special columnar structure of the nanowires.     

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.     

Microstructural characteristics and long-term stability of wollastonite-based chemically bonded phosphate ceramics

The microstructure of a wollastonite chemically bonded phosphate ceramic (WCPC) and its long-term stability can be characterized in terms of functions over time and at intermediate temperatures (RT, 40°C, 60°C, and 80°C). As seen through SEM images and EDX analysis, the ceramic microstructure comprises brushite, wollastonite and an amorphous heterogeneous phase. Electron backscatter diffraction (EBSD) mapping shows the amorphous phase in this chemically bonded phosphate ceramic to have a uniform distribution of Ca and P elements. The transformation of brushite and the amorphous matrix in its solid state to a more stable CaP phase takes place over a long period. The mechanical performance of the ceramic is therefore improved by thermal aging. Chemical changes are accompanied by denser, more stable phases leading to increased stiffness. The primary disadvantage associated with using this new material in construction would be its relatively high shrinkage as a result of chemical and physical factors.     

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.     

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.     

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.     

Fabrication of ZnO–GO hybrid for enhancement of chemically bonded phosphate ceramic coatings corrosion protection performance on AISI304L stainless steel

In this paper, a solvothermal method is used to prepare nano-sized zinc oxide-graphene oxide (ZnO–GO) hybrid, and the ZnO–GO hybrid is characterized by X-ray diffraction analysis, Raman, Fourier transform infrared spectroscopy, and scanning electron microscopy. In addition, chemically bonded phosphate ceramics coatings with different content of ZnO–GO hybrid are prepared on the stainless steel through the sol-gel method. The corrosion performance of the coatings is evaluated by electrochemical properties and the analysis of the surface and cross morphology of the coating. Results indicate ZnO–GO hybrid significantly enhances the compactness and corrosive behavior of the coating because the overlapping structure of GO flake improves the barrier performance of the coating. Besides, ZnO nanoparticles on the surface of GO can react with aluminum dihydrogen phosphate binder, in that case the adhesion between GO and the coating is improved.     

金属陶瓷涂层耐蚀性能研究

采用溶胶－凝胶浸渍提拉法在不锈钢、纯铜及铝合金基体上制备具有保护性的ＳｉＯ２、ＺｒＯ２、ＴｉＯ２、Ａｌ２Ｏ３及ＳｉＯ２－ＴｉＯ２陶瓷涂层,利用阳极极化曲线的、循环动电位极曲线、点蚀电位的测量以及三氯化铁和５％硫酸介质中的腐蚀试验研究了所得陶瓷涂层的耐蚀性。结果表明,这些陶瓷涂层能大幅芳提高金属基体在各种腐蚀介的耐蚀性。     

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.     

粘接剂对热化学反应陶瓷涂层结构与性能的影响

采用相同的陶瓷骨料(SiO2+Al)、添加剂(MgO+CrO3)和固化工艺,分别以磷酸铝和水玻璃为粘接剂,在Q235钢上制备陶瓷涂层,对其相成分、微观形貌、热震性能以及耐蚀性能进行了分析测试,讨论了粘接剂对涂层耐蚀性的影响。结果表明,尽管以磷酸铝为粘接剂的陶瓷涂层在固化过程中产生少量孔隙,但仍具有比以水玻璃为粘接剂的陶瓷涂层更优异的抗热震性能以及耐酸、碱、盐腐蚀性能。     

Behaviour of intact and scratched phosphate coatings on zinc, zinc–nickel and mild steel in dilute sodium phosphate solution

Impedance measurements were performed at room temperature in a 0.005 M Na₂HPO₄ solution on steel and on electrodeposited Zn and Zn–12%Ni before and after phosphating. It was found that potential and impedance parameters (R _ct and C _d) for phosphated materials attained nearly steady values within about 20 min, indicating that this solution did not cause meaningful changes in phosphate coatings and that it could therefore be used for the quality evaluation of these coatings. On scratches in phosphate coatings on Zn or Zn–12%Ni phosphate deposits rapidly formed, probably owing to enhanced dissolution of the locally exposed substrates at the nobler potentials of the coated materials. This demonstrates that damaged coatings can easily recover on Zn substrates in a non-aggressive phosphate solution. It is suggested that the formation of phosphate deposits on bare metal amidst phosphate coatings should be taken into account in the porosity determination by chemical or electrochemical methods.     

The effects to the structure and electrochemical behavior of zinc phosphate conversion coatings with ethanolamine on magnesium alloy AZ91D

This paper discussed a zinc phosphate conversion coating formed on magnesium alloy AZ91D from the phosphating bath with varying amounts of ethanolamine (MEA). The effects of MEA on the form, structure, phase composition and electrochemical behavior of the phosphate coatings were examined using an scanning electron microscopy (SEM), X-ray diffraction (XRD) potentiodynamic polarization curves and electrochemical impedance spectroscopy (EIS) measurements. Interpretations of the electrical elements of the equivalent circuit were obtained from the SEM structure of the coatings, assumed to be formed of two layers: an outer porous crystal layer and an inner flat amorphous layer. The result showed that adding MEA refined the microstructure of the crystal layer and that the phosphate coating, derived at the optimal content of 1.2 g/L, with the most uniform and compact outer crystal layer provided the best corrosion protection.     

Deposition of Al2O3 ceramic film on copper-based heterostructured coatings by aluminizing process: Study of the electrochemical responses and corrosion mechanism of the coating

The effect of deposition of the Al₂O₃ ceramic film by the aluminizing method on electrochemical responses and corrosion mechanism of copper-based heterostructured coatings was studied. The single layer coatings of Cu and Al₂O₃ and Cu/Al₂O₃ double layers were produced using reverse pulsed current electroplating process followed by powder cementation of aluminum on a substrate made of Inconel 600 superalloy. The produced coatings were then characterized using Scanning Electron Microscope (SEM), Energy Dispersive Spectroscopy (EDS), and X-ray Diffraction (XRD) methods. In order to evaluate the behavior and corrosion mechanism of the produced coatings, potentiodynamic polarization and electrochemical impedance spectroscopy methods were also used in 1 mol/L HCl solution at immersion times of 1, 12, 24, and 48 hours. The results of the study showed that the mechanism of the formation of Cu/Al₂O₃ copper-based coatings is that in the aluminizing step, first, the diffusion of Al from the surface layers to the interior occurs and then the diffusion of Cu from the plating layer to the exterior takes places. It was also found that the deposition of the Al₂O₃ ceramic film resulted in the formation of α-Al₂O₃ and CuAl₂O₄ phases and increased corrosion resistance in Cu/Al₂O₃ copper-based coatings at all immersion times and the corrosion mechanism has changed from uniform to localized state.     

The fertilizer effectiveness of calcined Christmas Island C-grade aluminium-iron phosphate rock and superphosphate during the early stages of plant growth

A glasshouse trial with wheat (Triticum aestivum L. cv. Gamenya) in which harvests were taken at intervals up to 24 days has shown that the effectivness of calcined Christmas Island C-grade aluminium-iron phosphate rock (C500) relative to superphosphate remained low. Relative growth rates did not change despite a decrease in the concentration of bicarbonate extractable phosphorus in soil fertilized with superphosphate. Different numerical values of relative effectiveness based on plant yield and phosphorus uptake respectively may be attributed to different internal efficiencies of phosphorus use for the two fertilizers.     

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.     

河南省广播电视发射塔涂装方案

分析了河南省广播电视发射塔所处环境特点。参照国内外类似钢结构的涂装方案,确定了该发射塔的配套涂料体系和涂装方案。介绍了该涂装方案的性能与效果,以及涂装要点。     

耐高温隔热涂料的隔热性与涂层厚度相关性探讨

探讨了耐高温隔热涂料的隔热性与涂层厚度的相关性,利用相关性指导选择适宜的涂层厚度,达到保温隔热的目的。