Properties Of Porous Materials Research Articles

Effects of porosity distribution and piezoelectric layers on natural frequencies and unsteady aerodynamic pressure of smart thick porous plates

In this paper, the effects of porosity distribution and piezoelectric layers on the natural frequencies and flutter aerodynamic pressure of smart thick porous plates in supersonic airflow are studied. Based on the third-order shear deformation plate theory and first-order piston theory, thick functionally graded porous plates embedded by piezoelectric layers are investigated. The effective porous material properties, such as Young’s modulus and mass density are considered to vary along the thickness direction. The aeroelastic governing equations of motion are obtained using Hamilton’s principle and Maxwell’s equation. By applying Galerkin’s approach, the partial differential governing equations are transformed into a set of ordinary differential equations. The results indicate that the unsteady aerodynamic pressure and natural frequencies decrease as the porosity coefficient increases. Furthermore, the symmetric porosity distribution predicts the highest unsteady aerodynamic pressure and natural frequencies for porous plates. Besides, the results show that the porous plate enclosed by piezoelectric layers in open circuit condition has higher flutter aerodynamic pressure and natural frequencies than the similar plate in closed circuit condition.

Inorganic Skeleton Reinforcement-A Generic Approach to Improve the Mechanical Properties of Biochar.

Biochar is considered as a promising candidate for emerging sustainable energy systems and environmental technology applications. However, the improvement of mechanical properties remains challenges. Herein, we propose a generic strategy to enhance the mechanical properties of bio-based carbon materials through inorganic skeleton reinforcement. As a proof-of-concept, silane, geopolymer, and inorganic gel are selected as precursors. The composites' structures are characterized and an inorganic skeleton reinforcement mechanism is elucidated. Specifically, two types of reinforcement of the silicon-oxygen skeleton network formed in situ with biomass pyrolysis and the silica-oxy-al-oxy network are constructed to improve the mechanical properties. A significant improvement in mechanical strength was achieved for bio-based carbon materials. The compressive strength of well-balanced porous carbon materials modified by silane can reach up to 88.9 kPa, geopolymer-modified carbon material exhibits an enhanced compressive strength of 36.8 kPa, and that of inorganic-gel-polymer-modified carbon material is 124.6 kPa. Moreover, the prepared carbon materials with enhanced mechanical properties show excellent adsorption performance and high reusability for organic pollutant model compound methylene blue dye. This work demonstrates a promising and universal strategy for enhancing the mechanical properties of biomass-derived porous carbon materials.

Monomer Symmetry-Regulated Defect Engineering: In Situ Preparation of Functionalized Covalent Organic Frameworks for Highly Efficient Capture and Separation of Carbon Dioxide

Developing crystalline porous materials with highly efficient CO2 selective adsorption capacity is one of the key challenges to carbon capture and storage (CCS). In current studies, much more attention has been paid to the crystalline and porous properties of crystalline porous materials for CCS, while the defects, which are unavoidable and ubiquitous, are relatively neglected. Herein, for the first time, we propose a monomer-symmetry regulation strategy for directional defect release to achieve in situ functionalization of COFs while exposing uniformly distributed defect-aldehyde groups as functionalization sites for selective CO2 capture. The regulated defective COFs possess high crystallinity, good structural stability, and a large number of organized and functionalized aldehyde sites, which exhibit one of the highest selective separation values of all COF sorbing materials in CO2/N2 selective adsorption (128.9 cm3/g at 273 K and 1 bar, selectivity: 45.8 from IAST). This work not only provides a new strategy for defect regulation and in situ functionalization of COFs but also provides a valuable approach in the design and preparation of new adsorbents for CO2 adsorption and CO2/N2 selective separation.

Hierarchical Microtubular Covalent Organic Frameworks Achieved by COF‐to‐COF Transformation

AbstractPore environment and aggregated structure play a vital role in determining the properties of porous materials, especially regarding the mass transfer. Reticular chemistry imparts covalent organic frameworks (COFs) with well‐aligned micro/mesopores, yet constructing hierarchical architectures remains a great challenge. Herein, we reported a COF‐to‐COF transformation methodology to prepare microtubular COFs. In this process, the C3‐symmetric guanidine units decomposed into C2‐symmetric hydrazine units, leading to the crystal transformation of COFs. Moreover, the aggregated structure and conversion degree varied with the reaction time, where the hollow tubular aggregates composed of mixed COF crystals could be obtained. Such hierarchical architecture leads to enhanced mass transfer properties, as proved by the adsorption measurement and chemical catalytic reactions. This self‐template strategy was successfully applied to another four COFs with different building units.

Hierarchical Microtubular Covalent Organic Frameworks Achieved by COF-to-COF Transformation.

Pore environment and aggregated structure play a vital role in determining the properties of porous materials, especially regarding the mass transfer. Reticular chemistry imparts covalent organic frameworks (COFs) with well-aligned micro/mesopores, yet constructing hierarchical architectures remains a great challenge. Herein, we reported a COF-to-COF transformation methodology to prepare microtubular COFs. In this process, the C3 -symmetric guanidine units decomposed into C2 -symmetric hydrazine units, leading to the crystal transformation of COFs. Moreover, the aggregated structure and conversion degree varied with the reaction time, where the hollow tubular aggregates composed of mixed COF crystals could be obtained. Such hierarchical architecture leads to enhanced mass transfer properties, as proved by the adsorption measurement and chemical catalytic reactions. This self-template strategy was successfully applied to another four COFs with different building units.

Determining the Geometric Surface Area of Mesoporous Materials

Specific surface area is an important property of porous materials and a crucial index in multiple disciplines, which is mainly measured using nitrogen isotherms and the Brunauer–Emmett-Teller (BET) equation. The BET surface area is remarkably higher than the geometric surface area, which is defined as the surface area of the crystal geometry structure. However, many studies directly use the BET surface area as the geometric surface area. We proposed a simple, general, and accurate method that only needs the nitrogen adsorption isotherm as the input to calculate the geometric surface area of mesoporous materials. The proposed method considers the adsorptive potential influences and the physical state of adsorbed nitrogen in estimating the surface area. We utilized 18 isotherms generated by molecular simulations and actual experiments to cover a wide range of materials, including minerals, catalysts, and carbon-based tubes, and validate the effectiveness of the proposed method. Our results showed that the surface area determined by the proposed method is almost identical to the referenced geometric area. The surface area obtained by the proposed method can be typically considered a geometric surface area.

Study on the effect of modified porous materials on heavy metal remediation in agricultural fields

With the rapid development of modern agriculture, the problem of heavy metal pollution and degradation of soil quality in agricultural soils has become increasingly serious, and the search for efficient, economical and environment-friendly heavy metal passivation materials has become a research hotspot for the solidification and stabilization of heavy metals in agricultural soils. In this paper, we summarize the remediation effect of porous materials on soil heavy metal pollution in view of existing studies, and analyze the changes of porous material properties and the influence on heavy metal remediation ability after modification and aging. Finally, the performance improvement of porous materials and their industrial application in the field of heavy metal pollution remediation are prospected.

Application of modified porous materials and pollution treatment in water

With the continuous development of social economy, water pollution has become one of the key objects of ecological environment governance. It is one of the effective methods to remove heavy metals, nitrogen, phosphorus, antibiotics and other organic pollutants from water by using carbon-based poly porous materials. The physical and chemical properties of porous materials can be improved effectively and the removal effect of target pollutants can be enhanced. The removal of heavy metals, nitrogen, phosphorus and organic matter from water by modified porous materials and its possible mechanism were reviewed. The future research and application of modified porous materials in the field of water pollution control were prospected, which could provide useful reference for related research work and engineering application.

Влияние агрессивных условий на каталитические материалы в системах очистки отработавших газов судовых дизелей

Object and purpose of research. This paper discusses porous permeable catalysts used in converters of marine engines. The purpose of this study was to investigate the effect of aggressive environments upon catalytic properties and parameters of the materials used for catalytic conversion. Subject matter and methods. The paper suggests a procedure for experimental studies intended to investigate the effects of aggressive environments in marine diesels contributing to gas-thermal corrosion. It also presents a test rig for investigation of hot gas flow effects upon corrosion properties of porous permeable catalytic materials. Main results. The study yielded the data on gas-thermal corrosion effects upon properties and parameters of porous permeable catalysts used in exhaust gas converters of marine power plants. Conclusion. The results of the study make it possible to estimate the extent of aggressive environment effects of exhaust gas conversion system upon the properties of its catalysts, as well as to adjust the chemistry of catalytic material in accordance with the requirements to conversion quality of exhaust gases.

Study on efficient and accurate protocols of measuring sorption isotherm of porous building materials using three-dimensional hygrothermal simulation

The sorption property of porous building materials in the hygroscopic region (sorption isotherm) is an important input to hygrothermal simulation. In this study, we proposed efficient and accurate protocols to obtain sorption isotherms using the static desiccator method. We developed a calculation model for three-dimensional simultaneous heat and moisture transfer in a material corresponding to the measurement specified in ISO 12571. Using an international database of the material properties, we conducted numerical simulations of the sorption process for five types of materials. The evolution of the amount of adsorbed moisture in a specimen and the time to reach equilibrium during the measurement were calculated under various humidity levels and specimen dimensions. According to the simulated results, we improved timing and interval for weighting the specimen to confirm the attainment of equilibrium for each type of a material and for each humidity level from the viewpoint of efficiency and accuracy. Meanwhile, the influence of size of a specimen on the time necessary to obtain the results was quantitatively demonstrated. Moreover, it was demonstrated that the method used for the determination of the attainment of equilibrium provided in ISO 12571 can underestimate the moisture content of materials with low moisture content and vapor permeability, and a policy to reduce risks of the underestimation was proposed.

Effects of pore size on the lubrication properties of porous polyimide retainer material

An oil-impregnated porous polyimide (PI) retainer is used in space rolling bearings to improve the lubrication performance, which depends on the release of lubricant from the pores, and therefore is closely related to the pore size. To study the effect of pore size, in this work, PI materials with different pore sizes were prepared by preheating the retainer tube billet during the limit pressing process, and then the friction tests were conducted with the ball-on-ring mode. The results show that the applied load deforms the pores, allowing the lubricant to be squeezed out from the pore; the centrifugal effect induced by rotation also makes the lubricant migrate out of the pore. Therefore, for the same pore sizes, the friction coefficients decrease with the increasing loads and rotation speeds. In addition, it was found that there exists an optimal pore size for the best lubrication properties of porous PI material. Furthermore, the optimal pore size should be larger for lubricants with high viscosity. The microscopic mechanism for lubricant outflow from pores is clarified by molecular dynamic simulations. The insights gained in this study can guide the preparation of oil-impregnated porous retainers under different working conditions.

Porous Alumina-Bentonite Ceramics: Effects of Fillers and Molding Technique

In porous ceramics processing, the green body shaping technique largely determines the control of the final porous structure and material properties. The study is aimed at finding affordable approaches for the shaping of two different narrow-fraction fillers: F240 electro-corundum and hollow alumina microspheres. The results revealed the influence of accessible shaping techniques (semi-dry pressing, direct casting, and slip casting) on the structural and mechanical properties of porous alumina ceramics. The starting materials were characterized by XRD, SEM, EDX, and BET. The manufactured ceramics were studied in terms of microstructure, density, porosity, and flexural strength. Free stacking of the fillers’ particles during the direct and slip casting resulted in a higher porosity of ceramics compared with that of semi-dry pressing, while reducing its mechanical strength. Direct casting appeared preferable for ceramics with hollow microspheres because it maintained the integrity of the filler particles and preserved their inherent porosity in the ceramics. The optimal parameters for porous ceramics processing were determined as follows: pressing at 30 MPa and sintering at 1280–1320 °C with a bentonite content of 15 wt.%. In this case, the average density and open porosity of F240 samples reached 2.22 g cm−3 and 40.4%, while samples containing hollow microspheres reached 2.20 g cm−3 and 36.7%, respectively.

Extended reacting boundary modeling of porous materials with thin coverings for time-domain room acoustic simulations

Modeling of acoustic boundary conditions has a significant impact on the accuracy of room acoustic simulations, which play an important role in the design phase of indoor built environments in order to improve the acoustical comfort. In this work, a numerical framework based on the discontinuous Galerkin (DG) method is presented for modeling extended reacting boundaries of porous absorbers covered by thin materials. The domain decomposition methodology is applied by treating the porous material as a subdomain. Equivalent fluid models are used to depict the acoustic properties of porous materials, whose effective density and compressibility as irrational functions are approximated by multipole rational functions in the frequency domain. By employing the auxiliary differential equation approach to calculate the time convolution, the augmented time-domain governing equations of porous materials can be expressed in the same unified hyperbolic form as the linear acoustic equations, which further enables a consistent upwind numerical flux formulation throughout the whole domain. The numerical coupling across the interface between propagation media is handled by solving the underlying Riemann problem. Compared to existing approaches with the DG method for extended reacting boundaries modeling for room acoustics, the derived upwind numerical flux formulation does not involve the computation of auxiliary variables. The presented framework yield a well-posed linear hyperbolic system with admissible boundary conditions as guided by the “uniform Kreiss condition” (Kreiss, 1970). Acoustic properties of the covering materials are illustrated by considering a limp permeable membrane model. A local time-stepping approach is utilized to improve computational efficiency. Numerical validations against analytical solutions in 1D are performed to verify the desired high-order convergence rate. A 3D case study on modeling spherical wave fronts demonstrates the broadband accuracy of the formulation.

Multifunctional properties and applications of ultra-light porous metal materials

Porous metallic material is a new type of material with a special structure, which undergoes structural changes under certain conditions, thus forming a new structural unit. Due to their unique porosity and pore size structure, ultralight porous metallic materials have unique multifunctional properties, such as absorption and buffering of vibration energy, energy absorption and weight reduction, thermal insulation, vibration and noise reduction, and tunable performance, and thus are widely used in aerospace, energy industry, transportation, and biomedical fields. This paper reviews the research progress of ultra-light porous metal materials at home and abroad in recent years, including the basic structure and main properties of ultra-light porous metal materials, and discusses their application fields. Although China started late in this field, it has taken a place in the international arena with the continuous research work. In the future, we should focus on basic research and engineering application research to lay a solid foundation for China to achieve technological breakthrough in this field.

Recent advances in porous molecular cages for photocatalytic organic conversions.

Photocatalytic organic conversion is considered an efficient, environmentally friendly, and energy-saving strategy for organic synthesis. In recent decades, the molecular cage has emerged as a creative functional material with broad applications in host-guest recognition, drug delivery, catalysis, intelligent materials and other fields. Based on the unique properties of porous molecular cage materials, they provide an ideal platform for leveraging pre-structuring in catalytic reactions and show great potential in various photocatalytic organic reactions. As a result, they have emerged as promising alternatives to conventional molecules or inorganic photocatalysts in redox processes. In this Review, the synthesis strategies based on coordination cages and organic cages, as well as their recent progress in photocatalytic organic conversion, are comprehensively summarized. Finally, we deliver the persistent challenges associated with porous molecular cage compounds that need to be overcome for further development in this field.

RECONSTRUCTION OF RANDOM FIBROUS POROUS MATERIAL AND NUMERICAL STUDY ON ITS TRANSPORT PROPERTIES BY FRACTAL MONTE CARLO METHOD

The microstructures and transport properties of fibrous porous material are significant for chemical catalysts, textile engineering, electronic devices, etc. In this paper, a fractal Monte Carlo method (FMCM) is developed to reconstruct the random microstructure of fibrous porous material based on the fractal scaling laws of fiber columns. And, the two-point correlation function of reconstructed fibrous material is calculated, which shows the effectiveness of the FMCM reconstruction. Also, the single-phase fluid flow through the reconstructed random fibrous porous material is simulated by the finite element method. The predicted permeability indicates good agreement with available empirical formulas. It has been found that the effective permeability of fibrous porous material decreases with the increase of fractal dimensions for fiber column. However, the fractal dimension of fiber column width has a greater influence on the effective permeability of fibrous porous material compared with that of fiber column length. The proposed numerical method provides an effective tool to reconstruct the irregular microstructure and understand the complex transport mechanisms of fibrous porous material.

The effect of fillers’ composition on thermal swelling of silicate materials

The article presents the results of studies of the process of thermal pore formation of materials based on sodium alkaline silicates. The aim of the study is to substantiate fillers composition for liquid glass mixtures. Substandard rocks and technogenic materials were used as fillers. There were determined the temperature intervals of intensive formation of the gas phase during heat treatment of fillers. Comparative analysis of swelling characteristics revealed the preference for a combination of several fillers containing substances with different resistance to temperature transformations. The results of studies of the structure and physical and mechanical properties of porous materials confirmed feasibility of using multicomponent fillers. The cellular material developed is characterized by predominantly closed, high porosity, heat-shielding properties and resistance to mechanical stress.

Effect of Recycled Aggregate and Slag as Substitutes for Natural Aggregate and Cement on the Properties of Concrete: A Review

Using recycled aggregate (RA) and slag instead of natural aggregate (NA) and cement can reduce greenhouse gas emissions (GHGE) and achieve effective waste recovery. In recent years, RA has been widely used to replace NA in concrete. Every year, several researchers conduct investigations on the mechanical performance and durability of recycled aggregate concrete (RAC). Due to the loose and porous material properties of RA, the mechanical properties and durability of RAC, such as strength, carbonation resistance, permeability resistance and chloride ion penetration resistance, are greatly reduced compared with natural aggregate concrete. In contrast, concrete containing slag instead of NA and cement generally improved the strength of concrete and reduced the internal porosity of materials. Herein, we discuss the effects of RA and slag on the workability, compressive strength, splitting tensile strength, ultrasonic pulse velocity (UPV) value, and elastic modulus of concrete. The relationships between the compressive strength and the splitting tensile strength, UPV value, and elastic modulus are discussed, and the optimal substitution method is proposed. In addition, various equations for calculating the compressive strength of concrete based on performance factors related to the compressive strength are summarized.

Peptide-based porous materials and their applications

The porous structure formed by the self-assembly of peptides is a new generation of porous materials with potential applications in the fields of catalysis, sensing, separation, and drug delivery. The pores of the material are filled with amino acid side chains, so the pore size and properties of the peptide-based porous material can be adjusted by rational design or modification of the peptide sequences. The introduction of functional moieties and metal ions has expanded the range of peptide-based porous materials. This review covers the design, synthesis, self-assembly, and properties of peptide-based porous materials, and summarizes their applications in different fields in recent years.

Developing an adaptive FE model to reflect the effective mechanical properties in porous elastomeric materials

Simulation of the microstructure of materials is not usually an efficient approach to estimate the mechanical response in the macro-scale porous components. This paper establishes an adaptive numerical model which reflects the effective mechanical properties of the elastomeric foam materials in the macro-scale, based on the material response in local points. The proposed adaptive model is capable of characterizing the dominant state of stress at each section point and assigning the corresponding mechanical properties from a developed material library. This material library can propose different stress-strain responses of the foam material based on mechanical characterization experiments and using the best-fit energy functions. The material of study is an elastomeric foam with a blend of Polyethylene/Ethylene-vinyl acetate (PE-EVA). The efficiency and performance of the adaptive model were examined using two practical case studies, in which the material was exposed to multiaxial stress conditions (a foam beam and a composite sandwich beam with a foam core under a concentrated loading). The adaptive model accurately predicts the dominant response of the foam beam and composite sandwich beam under flexural loading conditions. However, the uniaxial hyperelastic material models, calibrated by the pure tensile or compressive response of the foam material, dramatically overestimate or underestimate the experimental results.