Here we prepared PEO coatings on Mg alloys in silicate-NaOH-phosphate electrolyte containing different concentrations of NaF addition.The detailed microstructural characterizations combining with potentiodynamic polar...Here we prepared PEO coatings on Mg alloys in silicate-NaOH-phosphate electrolyte containing different concentrations of NaF addition.The detailed microstructural characterizations combining with potentiodynamic polarization and electrochemical impedance spectra(EIS)were employed to investigate the roles of fluoride in the growth and corrosion properties of PEO coating on Mg.The result shows the introduction of NaF led to a fluoride-containing nanolayer(FNL)formed at the Mg/coating interface.The FNL consists of MgO nanoparticles and insoluble MgF_(2)nanoparticles(containing rutile phase and cubic phase).The increase in the NaF concentration of the electrolyte increases the thickness and the MgF_(2)content in the FNL.When anodized in the electrolyte containing 2 g/L NaF,the formed FNL has the highest thickness of 100-200 nm along with the highest value of x of∼0.6 in(MgO)_(1-x)(MgF_(2))x resulted in the highest corrosion performance of PEO coating.In addition,when anodized in the electrolyte containing a low NaF concentration(0.4-0.8 g/L),the formed FNL was thin and discontinuous,which would decrease the pore density and increase the coating's uniformness simultaneously.展开更多
In this paper, five factors, namely the HF （hydrofluoric acid） concentration, field strength, illumination intensity as well as the oxidizing-power and conductivity of electrolytes were found to strongly affect the ...In this paper, five factors, namely the HF （hydrofluoric acid） concentration, field strength, illumination intensity as well as the oxidizing-power and conductivity of electrolytes were found to strongly affect the fast pore etching. The oxidizing power of aqueous HF electrolyte of different concentrations was especially measured and analysed. A positive correlation between optimal bias and HF concentration was generally observed and the relationship was semiquantitatively interpreted. Pore density notably increased with enhanced HF-concentration or bias even on patterned substrates where 2D （two-dimensional） nuclei were densely pre-textured. The etch rate can reach 400μm/h and the aspect ratio of pores can be readily driven up to 250.展开更多
Amorphous carbon materials play a vital role in adsorbed natural gas(ANG) storage. One of the key issues in the more prevalent use of ANG is the limited adsorption capacity, which is primarily determined by the porosi...Amorphous carbon materials play a vital role in adsorbed natural gas(ANG) storage. One of the key issues in the more prevalent use of ANG is the limited adsorption capacity, which is primarily determined by the porosity and surface characteristics of porous materials. To identify suitable adsorbents, we need a reliable computational tool for pore characterization and, subsequently, quantitative prediction of the adsorption behavior. Within the framework of adsorption integral equation(AIE), the pore-size distribution(PSD) is sensitive to the adopted theoretical models and numerical algorithms through isotherm fitting. In recent years, the classical density functional theory(DFT) has emerged as a common choice to describe adsorption isotherms for AIE kernel construction. However,rarely considered is the accuracy of the mean-field approximation(MFA) commonly used in commercial software. In this work, we calibrate four versions of DFT methods with grand canonical Monte Carlo(GCMC) molecular simulation for the adsorption of CH_4 and CO_2 gas in slit pores at 298 K with the pore width varying from 0.65 to 5.00 nm and pressure from 0.2 to 2.0 MPa. It is found that a weighted-density approximation proposed by Yu(WDA-Yu) is more accurate than MFA and other non-local DFT methods. In combination with the trapezoid discretization of AIE, the WDA-Yu method provides a faithful representation of experimental data, with the accuracy and stability improved by 90.0% and 91.2%, respectively, in comparison with the corresponding results from MFA for fitting CO_2 isotherms. In particular, those distributions in the feature pore width range(FPWR)are proved more representative for the pore-size analysis. The new theoretical procedure for pore characterization has also been tested with the methane adsorption capacity in seven activated carbon samples.展开更多
Osmotic power generation in biomimetic nanofluidic systems has attracted considerable research interest owing to the enhanced performance and long-term stability. Towards practical applications, when extrapolating the...Osmotic power generation in biomimetic nanofluidic systems has attracted considerable research interest owing to the enhanced performance and long-term stability. Towards practical applications, when extrapolating the materials from single-nanopore to multi-pore membranes, conventional viewpoint suggests that, to gain high electric power density, the porosity should be as high as possible. However, recent experimental observations show that the commonly-used linear amplification method largely overestimates the actual performance, particularly at high pore density. Herein, we provide a theoretical investigation to understand the reason. We find a counterintuitive pore-density dependence in high porosity nanofluidic systems that, once the pore density approaches more than lx109 pores/cm2, the overall output electric power goes down with the increasing pore density. The excessively high pore density impairs the charge selectivity and induces strong ion concentration polarization, which undermines the osmotic power generation process. By optimizing the geometric size of the nanopores, the performance degradation can be effectively relieved. These findings clarify the origin of the unsatisfactory performance of the current osmotic nanofluidic power sources, and provide insights to further optimize the device.展开更多
The tight oil formation develops with microfractures and matrix pores,it is important to study the influence of matrix physical properties on flow characteristics.At first,the representative fracture and matrix sample...The tight oil formation develops with microfractures and matrix pores,it is important to study the influence of matrix physical properties on flow characteristics.At first,the representative fracture and matrix samples are selected respectively in the dual media,the fracture and matrix digital rocks are constructed with micro-CT scanning at different resolutions,and the corresponding fracture and matrix pore networks are extracted,respectively.Then,the modified integration method is proposed to build the dual network model containing both fracture and matrix pore-throat elements,while the geometric-topological structure equivalent matrix pores are generated to fill in the skeleton domain of fracture network,the constructed dual network could describe the geometric-topological structure characteristics of fracture and matrix pore-throat simultaneously.At last,by adjusting the matrix pore density and the matrix filling domain factor,a series of dual network models are obtained to analyze the influence of matrix physical properties on flow characteristics in dual-media.It can be seen that the matrix system contributes more to the porosity of the dual media and less to the permeability.With the decrease in matrix pore density,the porosity/permeability contributions of matrix system to dual media keep decreasing,but the decrease is not significant,the oil-water co-flow zone decreases and the irreducible water saturation increases,and the saturation interval dominated by the fluid flow in the fracture keeps increasing.With the decrease in matrix filling domain factor,the porosity/permeability contributions of matrix system to dual media decreases,the oil-water co-flow zone increases and the irreducible water saturation decreases,and the saturation interval dominated by the fluid flow in the fracture keeps increasing.The results can be used to explain the dual-media flow pattern under different matrix types and different fracture control volumes during tight oil production.展开更多
Micro-disturbance grouting is a recovery technique to reduce the excessive deformation of operational shield tunnels in urban areas.The grout mass behaves as a fluid in the ground before hardening to form a grout–soi...Micro-disturbance grouting is a recovery technique to reduce the excessive deformation of operational shield tunnels in urban areas.The grout mass behaves as a fluid in the ground before hardening to form a grout–soil mixture,which highlights the necessity of using fluid–solid coupling method in the simulation of grouting process.Within a discrete element modeling environment,this paper proposes a novel fluid-solid coupling method based on the pore density flow calculation.To demonstrate the effectiveness of this method,it is applied to numerical simulation of micro-disturbance grouting process for treatment of large transverse deformation of a shield tunnel in Shanghai Metro,China.The simulation results reveal the mechanism of recovering tunnel convergence by micro-disturbance grouting in terms of compaction and fracture of soil,energy analysis during grouting,and mechanical response of soil-tunnel interaction system.Furthermore,the influence of the three main grouting parameters(i.e.,grouting pressure,grouting distance,and grouting height)on tunnel deformation recovery efficiency is evaluated through parametric analysis.In order to efficiently recover large transverse deformation of shield tunnel in Shanghai Metro,it is suggested that the grouting pressure should be about 0.55 MPa,the grouting height should be in the range of 6.2–7.0 m,and the grouting distance should be in the range of 3.0–3.6 m.The results provide a valuable reference for grouting treatment projects of over-deformed shield tunnel in soft soil areas.展开更多
基金Zhu.L.and Li.H.contributed equally to this work.This work is supported by the National Natural Science Foundation of China(Grant No.51901121)the Natural Science Foundation of Shaanxi Province(Grant No.2021JM-203,2019JQ-433,2020zdzx04-03-02)the Fundamental Research Funds for the Central Universities(Grant No.GK202103022).
文摘Here we prepared PEO coatings on Mg alloys in silicate-NaOH-phosphate electrolyte containing different concentrations of NaF addition.The detailed microstructural characterizations combining with potentiodynamic polarization and electrochemical impedance spectra(EIS)were employed to investigate the roles of fluoride in the growth and corrosion properties of PEO coating on Mg.The result shows the introduction of NaF led to a fluoride-containing nanolayer(FNL)formed at the Mg/coating interface.The FNL consists of MgO nanoparticles and insoluble MgF_(2)nanoparticles(containing rutile phase and cubic phase).The increase in the NaF concentration of the electrolyte increases the thickness and the MgF_(2)content in the FNL.When anodized in the electrolyte containing 2 g/L NaF,the formed FNL has the highest thickness of 100-200 nm along with the highest value of x of∼0.6 in(MgO)_(1-x)(MgF_(2))x resulted in the highest corrosion performance of PEO coating.In addition,when anodized in the electrolyte containing a low NaF concentration(0.4-0.8 g/L),the formed FNL was thin and discontinuous,which would decrease the pore density and increase the coating's uniformness simultaneously.
基金supported by Chinese National ‘863’ Project (Grant No 2006AA04Z312)‘973’ Project (Grant No 2006CB300403)the National Natural Science Foundation of China (Grant No 60772030)
文摘In this paper, five factors, namely the HF （hydrofluoric acid） concentration, field strength, illumination intensity as well as the oxidizing-power and conductivity of electrolytes were found to strongly affect the fast pore etching. The oxidizing power of aqueous HF electrolyte of different concentrations was especially measured and analysed. A positive correlation between optimal bias and HF concentration was generally observed and the relationship was semiquantitatively interpreted. Pore density notably increased with enhanced HF-concentration or bias even on patterned substrates where 2D （two-dimensional） nuclei were densely pre-textured. The etch rate can reach 400μm/h and the aspect ratio of pores can be readily driven up to 250.
基金Supported by the National Sci-Tech Support Plan(2015BAD21B05)China Scholarship Council(201408320127)
文摘Amorphous carbon materials play a vital role in adsorbed natural gas(ANG) storage. One of the key issues in the more prevalent use of ANG is the limited adsorption capacity, which is primarily determined by the porosity and surface characteristics of porous materials. To identify suitable adsorbents, we need a reliable computational tool for pore characterization and, subsequently, quantitative prediction of the adsorption behavior. Within the framework of adsorption integral equation(AIE), the pore-size distribution(PSD) is sensitive to the adopted theoretical models and numerical algorithms through isotherm fitting. In recent years, the classical density functional theory(DFT) has emerged as a common choice to describe adsorption isotherms for AIE kernel construction. However,rarely considered is the accuracy of the mean-field approximation(MFA) commonly used in commercial software. In this work, we calibrate four versions of DFT methods with grand canonical Monte Carlo(GCMC) molecular simulation for the adsorption of CH_4 and CO_2 gas in slit pores at 298 K with the pore width varying from 0.65 to 5.00 nm and pressure from 0.2 to 2.0 MPa. It is found that a weighted-density approximation proposed by Yu(WDA-Yu) is more accurate than MFA and other non-local DFT methods. In combination with the trapezoid discretization of AIE, the WDA-Yu method provides a faithful representation of experimental data, with the accuracy and stability improved by 90.0% and 91.2%, respectively, in comparison with the corresponding results from MFA for fitting CO_2 isotherms. In particular, those distributions in the feature pore width range(FPWR)are proved more representative for the pore-size analysis. The new theoretical procedure for pore characterization has also been tested with the methane adsorption capacity in seven activated carbon samples.
文摘Osmotic power generation in biomimetic nanofluidic systems has attracted considerable research interest owing to the enhanced performance and long-term stability. Towards practical applications, when extrapolating the materials from single-nanopore to multi-pore membranes, conventional viewpoint suggests that, to gain high electric power density, the porosity should be as high as possible. However, recent experimental observations show that the commonly-used linear amplification method largely overestimates the actual performance, particularly at high pore density. Herein, we provide a theoretical investigation to understand the reason. We find a counterintuitive pore-density dependence in high porosity nanofluidic systems that, once the pore density approaches more than lx109 pores/cm2, the overall output electric power goes down with the increasing pore density. The excessively high pore density impairs the charge selectivity and induces strong ion concentration polarization, which undermines the osmotic power generation process. By optimizing the geometric size of the nanopores, the performance degradation can be effectively relieved. These findings clarify the origin of the unsatisfactory performance of the current osmotic nanofluidic power sources, and provide insights to further optimize the device.
基金This work was supported by National Natural Science Foundation of China(No.51704033,No.51804038)PetroChina Innovation Foundation(No.2018D-5007-0210).
文摘The tight oil formation develops with microfractures and matrix pores,it is important to study the influence of matrix physical properties on flow characteristics.At first,the representative fracture and matrix samples are selected respectively in the dual media,the fracture and matrix digital rocks are constructed with micro-CT scanning at different resolutions,and the corresponding fracture and matrix pore networks are extracted,respectively.Then,the modified integration method is proposed to build the dual network model containing both fracture and matrix pore-throat elements,while the geometric-topological structure equivalent matrix pores are generated to fill in the skeleton domain of fracture network,the constructed dual network could describe the geometric-topological structure characteristics of fracture and matrix pore-throat simultaneously.At last,by adjusting the matrix pore density and the matrix filling domain factor,a series of dual network models are obtained to analyze the influence of matrix physical properties on flow characteristics in dual-media.It can be seen that the matrix system contributes more to the porosity of the dual media and less to the permeability.With the decrease in matrix pore density,the porosity/permeability contributions of matrix system to dual media keep decreasing,but the decrease is not significant,the oil-water co-flow zone decreases and the irreducible water saturation increases,and the saturation interval dominated by the fluid flow in the fracture keeps increasing.With the decrease in matrix filling domain factor,the porosity/permeability contributions of matrix system to dual media decreases,the oil-water co-flow zone increases and the irreducible water saturation decreases,and the saturation interval dominated by the fluid flow in the fracture keeps increasing.The results can be used to explain the dual-media flow pattern under different matrix types and different fracture control volumes during tight oil production.
基金supported by the Natural Science Foundation of Henan,China(Grant No.242300421646)the Key Laboratory of Geotechnical and Underground Engineering of Ministry of Education,Tongji University,China(Grant No.KLE-TJGE-B2205).
文摘Micro-disturbance grouting is a recovery technique to reduce the excessive deformation of operational shield tunnels in urban areas.The grout mass behaves as a fluid in the ground before hardening to form a grout–soil mixture,which highlights the necessity of using fluid–solid coupling method in the simulation of grouting process.Within a discrete element modeling environment,this paper proposes a novel fluid-solid coupling method based on the pore density flow calculation.To demonstrate the effectiveness of this method,it is applied to numerical simulation of micro-disturbance grouting process for treatment of large transverse deformation of a shield tunnel in Shanghai Metro,China.The simulation results reveal the mechanism of recovering tunnel convergence by micro-disturbance grouting in terms of compaction and fracture of soil,energy analysis during grouting,and mechanical response of soil-tunnel interaction system.Furthermore,the influence of the three main grouting parameters(i.e.,grouting pressure,grouting distance,and grouting height)on tunnel deformation recovery efficiency is evaluated through parametric analysis.In order to efficiently recover large transverse deformation of shield tunnel in Shanghai Metro,it is suggested that the grouting pressure should be about 0.55 MPa,the grouting height should be in the range of 6.2–7.0 m,and the grouting distance should be in the range of 3.0–3.6 m.The results provide a valuable reference for grouting treatment projects of over-deformed shield tunnel in soft soil areas.
