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Equimolar mixtures composed of isomers were firstly used to investigate the molecular branching effect on thermal diffusion behavior, which was not disturbed by factors of molecular mass and composition in this work. Eight heptane isomers, including n-heptane, 2-methylhexane, 3-methylhexane, 2,2-dimethylpentane, 2,3-dimethylpentane, 2,4-dimethylpentane, 3,3-dimethylpentane and 3-ethylpentane, were chosen as the researched mixtures. A non-equilibrium molecular dynamics (NEMD) simulation with enhanced heat exchange (eHEX) algorithm was applied to calculate the Soret coefficient at T = 303.15 T=303.15 K and P = 1.0 atm P=1.0\hspace{0.1667em}\text{atm} . An empirical correlation based on an acentric factor was proposed and its calculation coincides with the simulated results, which showed the validity of the NEMD simulation. It is demonstrated that the isomer with higher acentric factor has a stronger thermophilic property and tends to migrate to the hot region in the heptane isomer mixture, and the extent of thermal diffusion is proportional to the difference between the acentric factors of the isomers.

For high-temperature, sand-bearing, and high-pressure water injection pipelines, failure of commonly used organic epoxy coatings occurs frequently, which needs to be solved urgently. Ceramic coating is excellent alternative to solve this problem, attributed to its high hardness, high temperature resistance, and corrosion resistance. However, ceramic coatings prepared till date suffer from some problems, such as high porosity, and poor toughness. To improve overall performance of composite ceramic coating, herein, ceramic-lined composite steel pipes were synthesized by centrifugal self-propagating high-temperature synthesis (centrifugal-SHS), via doping different concentrations of SiO2 in the Al/Fe2O3 reaction system. The microstructure and phase of composite ceramic coatings after addition of SiO2 were analyzed by optical microscopy with super depth of focus, scanning electron microscopy, energy dispersive spectroscopy, and X-ray diffraction. Effects of SiO2 on the density and porosity, microhardness and fracture toughness, compression-shear strength and crushing strength of composite ceramic coatings were investigated by Archimedes method, Vickers indentation microfracture method, shearing test, and squeezing test, respectively. Results showed that the introduction of appropriate amount of SiO2 reduced cooling rate of reaction system, thus improving the densification level and strength of coatings. Furthermore, in reaction system, FeAl2O4 phase disappeared, owing to excessive Al, which could improve corrosion resistance of composite ceramic coatings. The optimum doping concentration of SiO2 was found to be 4 wt%, in which composite ceramic coating showed excellent properties.

The effect of the temperature gradient on the Soret coefficient in n-pentane/n-decane (n-C5/n-C10) mixtures was investigated using non-equilibrium molecular dynamics (NEMD) with the heat exchange (eHEX) algorithm. n-Pentane/n-decane mixtures with three different compositions (0.25, 0.5, and 0.75 mole fractions, respectively) and the TraPPE-UA force field were used in computing the Soret coefficient ( S T {S_{T}} ) at 300 K and 1 atm. Added/removed heat quantities (ΔQ) of 0.002, 0.004, 0.006, 0.008, and 0.01 kcal/mol were employed in eHEX processes in order to study the effect of different thermal gradients on the Soret coefficient. Moreover, a phenomenological description was applied to discuss the mechanism of this effect. Present results show that the Soret coefficient values firstly fluctuate violently and then become increasingly stable with increasing ΔQ (especially in the mixture with a mole fraction of 0.75), which means that ΔQ has a smaller effect on the Soret coefficient when the temperature gradient is higher than a certain thermal gradient. Thus, a high temperature gradient is recommended for calculating the Soret coefficient under the conditions that a linear response and constant phase are ensured in the system. In addition, the simulated Soret coefficient obtained at the highest ΔQ within three different compositions is in great agreement with experimental data.

To investigate the effect of hydrogen atoms on the size of the plastic deformation zone, molecular dynamics (MD) simulations were performed on a single crack model. The model uses pre-charged hydrogen to quantify the compression effect of hydrogen atoms on the plastic zone during cyclic loading. The results show that stress release at the crack tip occurs mainly in the form of plastic deformation, and the degree of compression in the plastic zone increases with increasing hydrogen concentration. A compression factor, which considers hydrogen concentration, is found with the help of the simulation results. A modified fatigue crack growth rate (FCGR) model, combined with the compression factor, was then used to predict the hydrogen-assisted fatigue crack growth rate. The proposed model shows excellent agreement with the experimental data for X100 steel, and it provides a new framework to describe hydrogen-assisted cracking.

Nowadays corrosion has become an urgent problem to be solved. Scientists are committed to finding various ways to restrain the corrosion of metals. The anticorrosion coating is considered to be an economical and effective method. However, the conventional anticorrosion coating is vulnerable to be damaged. The external self-healing coating can release the active healing agent when destroyed and prevent the corrosion spontaneously, which has been the subject of increasing interest. In this paper, the anticorrosion application of external self-healing coatings was described in detail, including organic micro/nanocontainer-based, inorganic micro/nanocontainer-based, and microvascular network-based self-healing coatings. First, the present article introduced the development, preparation, and self-healing properties of the external self-healing coating. In the successive chapter, the anticorrosion performance of the coating was highlighted. Also, some open problems and future challenges were also investigated. Finally, special attention was dedicated to the prospect of the external self-healing coating. This review provides readers with an overview of achievements to date and insights into the future development of engineering applications to promote the large-scale application of external self-healing anticorrosion coatings.

Graphene has attracted significant attention for applications in many industrial fields due to its excellent anti-corrosion properties, and a series of satisfactory results have been achieved. In recent years, the scope of research into graphene-based anti-corrosive applications has been extremely diversified and encompasses two aspects: pure graphene coatings and graphene composite coatings. In this study, the application of graphene coatings to metal anti-corrosion is comprehensively reviewed. First, the preparation methods for graphene and pure graphene coatings are described in detail. Second, the corrosion resistance, existing problems, and optimizations of pure graphene coating are presented. Third, methods for improving the dispersibility of graphene, such as chemical modification and surface decoration nanoparticles, are introduced. Next, the corrosion resistance, anti-corrosion mechanism, existing problems, and optimization measures of graphene composite coatings are summarized. Finally, future development directions for graphene anti-corrosive coatings are proposed, and their viability in near-future applications is discussed.

Hydrogen embrittlement has been extensively studied for decades; however, the atomistic origins of hydrogen embrittlement remain debated. Here, we studied the role of body-centered cubic (bcc) to face-centered cubic (fcc) phase transition at the crack tip on hydrogen embrittlement in alpha iron at room temperature. Molecular dynamics simulations were performed to examine the propagation of [10 1 ¯ ](101) crack. The results indicate that in the absence of hydrogen atoms, the phase transition could release the strain energy and postpone the crack propagation. Hydrogen atoms would form a nanosize hydrogen-rich region ahead of the crack tip and inhibit phase transition, thus enhancing brittle crack growth. A general expression is provided to predict the hydrogen concentration beyond which the phase transition does not occur. In addition, a simplified crack growth model is proposed to predict the risk level during the operation.

To obtain nanocomposite coating resistant to CO2 corrosion, new idea is proposed in this paper. First, based on first-principle method, adsorption characteristics of CO2 on different nanocomposite coatings were studied, and coating structure with CO2 corrosion resistance was optimized. Then, relevant experiments were carried out to verify corrosion resistance of coating and evaluate CO2 corrosion resistance. Results indicate that coating structure resistant to CO2 corrosion is Ni-W alloy as matrix metal; Y2O3 and ZrO2 nanoparticles are added with mass ratio of 1:1. In this case, adsorption energy of CO2 reaches the minimum, and corrosion resistance is optimal. Theoretical result was confirmed by scanning electron microscopy observation and electrochemical test of coating. When the coating is placed in CO2 environment with different partial pressures and temperatures, after a period of time, it is still dense, and no corrosion pits appear on the surface. Electrochemical test results show that the resistance of coating after CO2 corrosion is high, and corrosion resistance is still good. Above simulation and experimental results provide new idea for the structural optimization of nanocomposite coatings.

Purpose When hydrogen evolution reaction occurs on a metal surface, on the one hand, the generated hydrogen atom may penetrate into the metal that causes the hydrogen embrittlement failure of materials; on the other hand, the hydrogen generation may increase the local pressure in the coating and cause coating blistering. The purpose of this study is to study the effect of NaCl concentration and pH on hydrogen evolution reaction of X60 steel. Design/methodology/approach A cathodic polarization curve 257E-2V vs OCP and EIS was obtained by conventional three-electrode system in different NaCl concentrations, 257E3.5 and pH. Second, various parameters such as hydrogen evolution, over-potential current–density polarization resistance and capacitance of double electric layer were obtained based on fitting of the experimental data. Finally, the reaction mechanism was determined by Tafel curves. Findings It was concluded that in different NaCl concentrations, diffusion layer induced by concentration polarization affects the diffusion process of H+ ions, which makes over-potential increase. Under great effect of concentration polarization, the reaction is different in acid and alkaline environments, and the dielectric layer shows the characteristic of meta-alkaline adsorption, which makes difference in mechanism. Originality/value This research not only has theoretical significance but also gains utilization prospect. Ultimately, this research could be applied to clear hydrogen evolution process and protect long-distance pipeline against delamination.

In this work, nickel-based composite coatings were deposited using ultrasonic electrodeposition under pulse current condition at different current densities, temperatures and concentrations of Y2O3 and/or ZrO2 dispersed in the plating solution. The morphology and electrochemical properties were investigated. The electrochemical test methods (such as chronopotentiometry, potentiodynamic polarisation and electrochemical impedance spectroscopy) were used to investigate the stability of electrode potential during deposition and the corrosion resistance of Ni-based coating reinforced using Y2O3 and ZrO2. It was demonstrated that, when the deposition current density was 1.5 A dm−2, the temperature was 60°C and the added amount of Y2O3 and ZrO2 nanoparticles was 10 g L−1 each, the coating was compact, stable and free of cracks. The results of electrochemical tests showed that, under the optimal deposition parameters, the deposition process was stable, while the corrosion current density decreased by an o...

Graphene in anticorrosive composite coatings has broad application prospects because of its excellent physical, electrical, mechanical, and chemical properties. Due to the comprehensive performance advantages of graphene-composite coatings, they can better meet protection requirements in complex and changeable environments and will gradually replace the traditional single coatings used in industry. Herein, the excellent protective properties of anticorrosive graphene-composite coatings are reviewed. First, the dispersion methods of graphene in composite coatings are introduced. Second, the comprehensive anticorrosion performance of graphene-composite coatings is introduced. The positive effect of graphene on the performance of anticorrosive composite coatings is expounded from the aspects of its basic anticorrosion mechanism and multi-functional cooperative protection. Third, specific optimization measures are put forward according to the shortcomings of graphene in its application in anticorrosive coatings. Finally, the development trend of graphene in the field of anticorrosive materials is analyzed from many aspects, and some research suggestions are provided.

The study of combustion in the plateau environment has gradually aroused the interest of scholars. Due to the particularity of the plateau environment, these plateau combustion experiments are usually carried out in artificial low-pressure chambers. The image processing of continuous flames has recently been widely used in scientific research and detection applications for various thermal and power devices. In this paper, three methods for selecting the optimal threshold for flame binarization images were investigated by using a flame video of horizontal diesel spray combustion in a low-pressure chamber. The results show that the binarization image with the threshold value selected by the two-peak method came closer to the actual flame's morphology. The maximum class difference method greatly increases the binarization area at the bottom of the flame, while the minimum error method significantly reduce the binarization area of the flame, especially with regard to the flame length. Finally, the mechanism of influence of the threshold selection method was analyzed from the perspective of the flame luminance and buoyancy of the horizontal jet flame. This work provides a better method of threshold selection for scientific research into simulating plateau combustion flames in low-pressure chambers, which has important engineering value and significance.

Compared with the common self-healing coating, the self-healing polymer/graphene composite coating has better self-repairing ability and anti-corrosion performance. This is attributed to the superior physical and chemical properties of graphene, which can be used as the energy conversion center, energy transfer medium or corrosion medium shield in coatings. And according to different healing mechanisms, graphene can play different roles. In this paper, the function of graphene in self-healing coating and the application status of self-healing polymer/graphene composite coating are discussed in detail. First, the function of graphene is introduced from the intrinsic and extrinsic self-healing mechanisms. Second, the optimization measures of graphene properties and self-healing polymer/graphene composite coatings are summarized. And for graphene, the effects of its structure, size, electrical conductivity and dispersion on the self-healing properties are analyzed in detail. Finally, the current application problems of self-healing polymer/graphene composite coatings are analyzed, and the future development direction of self-healing polymer/graphene composite coatings is discussed.

In the current research, the dependence of hydrogen embrittlement (HE) on the temperature in X90 steel is studied through experimental tests and molecular dynamics simulations. Slow strain rate tests (SSRT) were applied to X90 specimens in the air and the simulated groundwater solution (called NS4), respectively. The fracture morphologies of the specimens were observed by scanning electron microscope (SEM). The results indicate that the temperature threshold of hydrogen embrittlement (HE) in X90 steel is 313 K, beyond which the HE would be weakened with the rise of temperature, and below which the HE would be enhanced with the rise of temperature. To illustrate the underlying mechanism of this phenomenon, molecular dynamics simulations were applied to quantify the correlation of temperature with hydrogen diffusivity, and the results of Devanathan-Stachurski tests were used to quantify the bulk hydrogen concentration at different temperatures. A theoretical model was thus developed based on hydrogen potential thermodynamics to predict the threshold temperature. The predictive model matches well with experimental results, revealing the promoting effect of hydrogen diffusion and accumulation on the crack growth, which is fundamental for understanding hydrogen-induced damage in structural materials.

In recent years, superhydrophobic materials have shown tremendous industrial application value in many fields. Especially in the field of anti-corrosion, the superhydrophobic coating can capture the air to form many "air bags" on the surface of the substrate, so it has a strong water-repellent ability, thus isolating the corrosion media and achieving remarkable anti-corrosion performance. Various preparation technologies of superhydrophobic coatings have been proposed, but each has its own defects. As a relatively mature industrial processing method, electrodeposition shows unique advantages. However, there are few reviews on the preparation of anticorrosive superhydrophobic coatings by electrodeposition till now. In this paper, the general theory of superhydrophobic surface, including factors affecting wettability and theoretical wetting models, is firstly reviewed. Secondly, the mechanism, application status and anti-corrosion performance of superhydrophobic coatings prepared by metal electrodeposition, non-metallic electrodeposition, and composite electrodeposition are summarized in detail, respectively. The internal mechanism of process conditions, especially crystal modifiers, to regulate the coating morphology is described. Moreover, new developments over the years in electrodeposition such as pulse electrodeposition, magnetic field-induced electrodeposition, ultrasonic-assisted electrodeposition for the fabrication of superhydrophobic coatings are also presented. Finally, the deficiency of this technology is pointed out, and the future research directions of improving the durability of superhydrophobic coatings are proposed.

Smart anticorrosive coatings have better anticorrosion ability than traditional anticorrosive coatings. This is attributed to the development of active protection performance in the smart anticorrosive coating based on the passive barrier of the traditional coating. Smart anticorrosive coating can effectively respond to environmental changes, heal coating defects, and prevent further corrosion. In this study, the application prospects of smart anticorrosive coatings for protection of metal corrosion are reviewed from two aspects of extrinsic and intrinsic self-healing. First, the related concepts of healing due to coating are introduced. Second, the development of nano-container, anticorrosion performance, existing problems, and optimization measures of the extrinsic healing smart anticorrosive coating are introduced. Third, the mechanism, anti-corrosion performance, existing problems, and optimization measures of intrinsic healing smart anticorrosive coating are summarized. Finally, the development direction of smart anticorrosive coating is put forward, and the possible application prospects of these smart coatings to attain a long-term effect in the future are discussed.

Functionally graded Ni-graphene coatings with both graphene content and grain size increasing in the thickness direction are electrodeposited by altering the duty cycle in a one-pot plating bath. X-ray diffraction (XRD) and energy dispersive spectroscopy (EDS) are used to investigate the microstructure and element content. The prepared coatings are tested in synthetic seawater, CO2-structured synthetic seawater, and a simulated condition of gathering pipelines (temperature: 40 °C, partial pressure of CO2: 2 MPa, flow rate: 0.5 m/s). The corrosion resistances of the coatings are studied using potentiodynamic polarization, electrochemical impedance spectroscopy (EIS), and surface observations. These results demonstrate the excellent corrosion resistance of functionally graded Ni-graphene coatings, which potentially provides a promising pathway to mitigate the corrosion problems in the oil and gas industry.

Carbon capture and storage (CCS) is the most effective way to reduce CO2 emissions. In CCS, CO2 transportation plays an important role for the transmission of CO2 from the capturing facility to the location of permanent storage. In order to increase the CO2 density and avoid two-phase flow, CO2 needs to be transformed into the supercritical state. The supercritical CO2 environment poses a threat to pipeline safety because it is a high pressure environment with gaseous impurities. In this paper, the influencing factors of pipeline corrosion under supercritical CO2 environment and the current prevention and control methods for SC CO2 corrosion are reviewed. To begin, the supercritical CO2 corrosion environment and corrosion evaluation methods are introduced. Then, the effects of some factors, such as the water content, gaseous impurities, acids, alkalis, salts, temperature, pressure, flow rate, exposure angle, and pipeline steel, on corrosion are comprehensively reviewed. New research areas, such as the use of coatings and inhibitors, are also reviewed. Finally, future development directions for studying corrosion in a supercritical CO2 environment are proposed.