Properties Of Porous Materials Research Articles

Foam-gelcasting preparation and properties of high-strength mullite porous ceramics

The unique structure and excellent properties of porous materials enhance their prospects for application as catalyst supports, thermal insulation, and liquid filtration, and within biomedicine. In this study, mullite porous ceramics with high apparent porosity were successfully prepared using non-toxic and economical poly-γ-glutamic acid (γ-PGA) gelling system using the foaming method. The effects of the foaming agent (sodium dodecyl sulfate) and sintering temperature on the microstructure, apparent porosity, and mechanical properties of mullite porous ceramics were reported for the first time. The prepared mullite porous ceramics exhibited excellent properties with a porosity of up to 80.23%, corresponding to a bulk density and thermal conductivity of 0.62 g/cm3 and 0.17 W/(m·K), respectively. Moreover, the mullite porous ceramics contained significant amounts of unique near-spherical pores that contributed to a significant increase in compressive strength (6.1 MPa). In addition, the potential use of mullite porous ceramics as catalyst supports was validated by photodegradation of methyl orange solution.

Quantifying Tortuosity in Porous Lithium-Ion Battery Materials Using Ultrasound

Active electrode materials in lithium-ion batteries are porous. These materials are composed of a solid frame containing interconnected pores/channels, in which mass transport follows a tortuous pathway. Tortuosity is defined as the ratio of the average tortuous pathway to the projected straight path, and is a particularly important parameter indicating the diffusivity and conductivity properties of porous battery materials; so quantifying tortuosity is highly desirable to safeguard battery performance. Existing quantification methods are mostly based on impedance and polarisation measurements from specially-fabricated cells and numerical diffusion simulations using the microstructural tomographic images of porous materials. These methods, however, are generally cumbersome and barely applicable to in-production measurement. Here we report a novel alternative quantification method based on ultrasonic Biot waves in porous materials. This method utilises the fundamental fact that in a porous material with a rigid frame (which the electrode sheets are when immersed in the air), the slow Biot wave only travels in the liquid/gaseous phase, through the same tortuous pathway that the diffusion of ions and electrons happens in a finished battery. To achieve the quantification, we first develop a physical model relating the propagation of ultrasonic Biot waves to the tortuosity of porous battery materials. Based on this physical model, we then propose an inversion method to infer tortuosity from ultrasonic readings. The readings are acquired using air-coupled ultrasonic transducers in a non-destructive fashion, thus enabling real-time tortuosity quantification. This ultrasonic method measures the average tortuosity in a range of ~20 mm across the testing material, and can easily scan over a sheet to provide spatially resolved information. With these exciting features, the proposed method could offer a next-generation tortuosity quantification tool for quality control of porous battery material productions and a better understanding of battery performance.

Hygric properties of porous building materials (VIII): Influence of reduced air pressure

Hygrothermal properties of porous building materials are indispensable for understanding and optimizing the hygrothermal performance of building enclosures and the built environment. In high-altitude areas, the influence of reduced air pressure on hygrothermal properties should be considered and, if needed, proper corrections should be adopted. Currently, the impact of reduced air pressure on thermal properties has been thoroughly investigated while that on hygric properties remains unclear. In this research, hygric properties of three representative porous building materials – calcium silicate, autoclaved aerated concrete and ceramic brick – are measured at three different air pressures, namely 1.00, 0.80 and 0.60 atm. The static gravimetric test, psychrometer test, cup test and capillary absorption test are performed to obtain the sorption isotherm, moisture retention curve, vapor permeability, capillary absorption coefficient and capillary moisture content. Results show that the influences of air pressure on the sorption isotherm, moisture retention curve, capillary absorption coefficient and capillary moisture content are limited, while the vapor permeability increases obviously with the decreasing air pressure. Specifically, the vapor diffusion resistance factor remains stable in the dry cup test, and this can be predicted by Schirmer's law. In the intermediate cup and wet cup tests, where liquid water contributes to the moisture transfer, the impact from air pressure becomes smaller.

A robust peridynamic computational framework for predicting mechanical properties of porous quasi-brittle materials

Prediction of the macroscopic mechanical properties and damage evolution of cement paste is significant; however, it poses challenges due to the complex multiphase heterogeneity and porosity of the hydration microstructure. This study presents a robust implicit-explicit hybrid computational framework based on the bond-based peridynamics for predicting crack evolution and macroscopic mechanical properties of porous quasi-brittle materials. Specifically, the prototype micro-elastic brittle (PMB) material model is improved by considering an attenuation kernel function and surface effect correction. Subsequently, an efficient implicit-explicit hybrid approach is developed for the solution of the strong form of peridynamic equation of motion. A critical damage index of the global system is specified to switch the solver from implicit to explicit. CEMHYD3D software is employed to generate the microstructure of hydration under uniaxial tension. Systematic simulations of the microstructure explain the influence of several computational strategies on the results, i.e., the approach of boundary enforcement, the geometry of porous microstructure, the loading rate in the explicit stage, and breaking the bonds across the voids or not. The simulations demonstrate that applying the improved bond-based peridynamic solver on hydration microstructures can capture their cracking behavior and macroscopic mechanical properties, e.g., stress–strain curve, peak stress, maximum tensile strain, Young’s modulus, and fracture energy release rate. This study also paves the way for peridynamic multiscale modeling of cement-based materials.

Tuning Negative Thermal Expansion in AlPO4-17 by Insertion of Guest Molecules.

The very strong negative thermal expansion in the porous aluminophosphate AlPO4-17 with a hexagonal erionite structure was tuned by the insertion of oxygen molecules at high pressure. The structure of the oxygen-filled material was determined in situ at high pressure by synchrotron, single-crystal X-ray diffraction. The thermal expansion of this material was measured precisely at 0.38 GPa by synchrotron X-ray powder diffraction. Whereas the overall volume thermal expansion only exhibits a small change with respect to empty AlPO4-17 at ambient pressure, the expansion along the a direction decreases almost to zero and the expansion along c increases by a factor of 7. Such highly anisotropic thermal expansion properties are of great interest for mechanical and optical applications as in two directions the dimensions of the material are extremely stable, whereas a very strong linear negative thermal expansion of -2.2 × 10-5 K-1 is observed in the perpendicular direction. Guest insertion is thus a very powerful tool for tuning the thermal expansion properties of porous materials.

Investigation of Magnitoelectric Propereties of Composites on the Basу of Fe2O3 Magenic Particles and Bentonite Using a Percolation Theory

The paper presents the results of studies of the electrical and magnetic properties of an inhomogeneous percolated medium based on the theory of percolation. The application of this theory has a wide and varied range. Examples include hopping conductivity in semiconductors, properties of porous materials, and so on. It was found that, with approaching the percolation threshold pc = 0.35, the resistivity decreases, and the electrical conductivity increases accordingly. An increasing number of individual ferromagnetic nanogranules in (p)–Fe2O3–(1–p)MBT composites merge with the formation of individual Fe2O3 clusters in the bentonite matrix, which combine to form a continuous network of clusters. This is due to the fact that the resistivity ρ of the composite is mainly determined by the magnetic component of the latter

Effects of aggregate types and softening effect on multiaxial mechanical properties of lightweight aggregate concrete

Softening effect refers to the inherent property of porous media materials of having their strength decrease over time under water saturation compared with that under dry condition. Typical porous media materials, such as ceramsite and ceramsite-based concrete, exhibit a softening effect. This study investigated the softening effect of shale ceramsite (SC) and different types of lightweight aggregate concrete (LWACs). Mix ratios of LC30 all-lightweight shale ceramsite concrete (also known as all-lightweight concrete, ALWC) whose SC and shale pottery (SP) were selectively or simultaneously replaced with limestone gravel (LSG) and river sand (RS) with the same volume fraction, respectively, were prepared for comparison with gravel lightweight concrete (GLWC), sand lightweight concrete (SLWC) and hybrid aggregate lightweight concrete (HALWC) were formed. The four kinds of LWACs (ALWC, GLWC, SLWC and HALWC) were cast into their corresponding specification and size specimens and demoulded after indoor curing for 24 h, with their target ages (7–180 d) maintained under standard and hydrostatic curing. Then, the strength and initial elastic modulus under uniaxial stress, ultimate compressive strength and stress–strain curves under triaxial stress of the specimens were tested to analyse the influence of aggregate types and curing methods on the mechanical properties and softening effect of LWACs. According to the test results, the cube compression, prism compression, splitting tensile, conventional triaxial compression and elastic modulus decreased after 180 d of hydrostatic curing; the experimental age of the conventional triaxial compression test was after 90 d. ALWC demonstrated the most evident decrease, followed by SLWC, HALWC and GLWC. The trend indicates that normal aggregates can significantly improve the softening effect of LWACs. The failure modes of the triaxial compression specimens changed from splitting failure to shear failure, and a plastic platform phenomenon was apparent on the stress–strain curves, with their descending section appearing gentler than those in the uniaxial compression test with the increase in confining pressure. The relationship between ultimate compressive strength and confining pressure of the LWACs can be accurately described by the Mohr–Coulomb single-parameter failure criterion, Hsieh–Ting–Chen four-parameter failure criterion and Willam–Warnke five-parameter failure criterion. However, the three failure criteria demonstrated application limitations based on meridian equation and deviatoric plane analysis. The extension trend of the compression meridian of the LWACs after 90 d of hydrostatic curing was generally the same, and the types of aggregates exerted a minimal effect on the meridian and deviatoric plane limit trace. The softening effect of LWACs was mainly caused by the softening effect of the SC itself and the influence of pore water on the matrix concrete.

Impact of pearl-necklace-like skeleton on pore sizes and mechanical properties of porous materials: A theoretical view

The structural and mechanical properties of open-porous cellular materials are often described in terms of simple beam-based models. A common assumption in these models is that the pore walls have a constant cross section, which may be in agreement for a vast majority of such materials. However, for many of those materials that are characterized by a pearl-necklace-like network, this assumption seems too idealized. Aerogels are perfect examples of such materials. In this paper, we investigate the effect of such pore walls having a string of pearls-like morphology on the properties of such open-porous materials. First, the pore size is mathematically modeled. Three scenarios are described, where the pore sizes are calculated for cells in 2D, 3D, and 3D with overlapping particles. The dependency of the skeletal features on the resulting pore size is investigated. In the second part, pore walls with 3D overlapping spheres are modeled and subjected to axial stretching, bending, and buckling. The effect of the particle sizes and the amount of overlap between the particles on the mechanical features is simulated and illustrated. The results are also compared with models that assume a constant cross section of pore-walls. It can be observed that neglecting the corrugations arising from the pearl-necklace-like morphology in open-porous cellular materials can result in serious miscalculations of their mechanical behavior. The goal of this paper is not to quantify the bulk mechanical properties of the materials by accounting for the pearl-necklace-like morphology but rather to demonstrate the significant deviations that may arise when not accounted for.

Tailoring centripetal metamaterial with superelasticity and negative Poisson’s ratio for organic solvents adsorption

Graphene metamaterials with a radial-like structure and negative Poisson’s ratio (NPR) were assembled using a unique centripetal freezing technique. Driven by the centripetal temperature gradient, ice crystals were grown toward the center of an aqueous graphene dispersion and form a radially arranged skeleton. A reentrant structure was formed at the diagonal of the monolith as the ice crystals sublimate. The obtained centripetal graphene metamaterial (CGM) was endowed with NPR response. CGM maintained NPR under 50% compression, which reached a minimum (−0.18) at 10% strain. After 50 compressive cycles at 50% strain, CGM retained approximately 96% of the original compressive strength. The radial channels endowed CGM with fast absorption kinetics, and the NPR response effectively accommodated the damage caused by volume shrinkage during repeated adsorption-regeneration cycles. This strategy is an effective method for achieving NPR response and improving the mechanical properties of porous materials.

Introduction of a spiro-linker in triazine-based polymers to enlarge void space and increase IPA adsorbing capacity to 164.7 mg/g at 1000 ppm

BackgroundPorous covalent organic polymers (COPs) are useful and important materials in adsorbing gasses or volatile organic compounds (VOC) due to their thermal stability. Particularly, triazine-based porous polymers consisting of inexpensive starting materials, cyanuric chloride, are noteworthy. To enlarge the void space of triazine-based polymers, a spiro-linker was then used and incorporated in the polymeric framework. MethodsLow-pressure CO2 and N2 adsorption–desorption isotherms of porous materials were measured using a static volumetric system; CO2 as the adsorbate was performed at 195 K, 273 K, and 298 K, respectively, and N2 as the adsorbate was completed at 77 K. Adsorption properties of porous materials were determined using a fixed-bed column (450 mm length and 22 mm inner diameter) linked with an on-line gas chromatograph (GC). Significant findingsThe BET surface areas of the porous materials with spiro-linker increase ∼ 50% of the void space in the polymeric framework, over the corresponding polymer without spiro-linker. In addition, the spiro-linker-containing polymer was also observed to be thermally stable and have good adsorption capacity (165 mg/g) for IPA at 1000 ppm, which is still reasonably good when compared with porous materials such as MOFs or activated carbons. The adsorption capacity for the regenerated IPA after five cycles maintains ∼82% adsorption efficiency.

Fractal Analysis on the Mapping Relationship of Conductivity Properties in Porous Material

The mapping relationships between the conductivity properties are not only of great importance for understanding the transport phenomenon in porous material, but also benefit the prediction of transport parameters. Therefore, a fractal pore-scale model with capillary bundle is applied to study the fluid flow and heat conduction as well as gas diffusion through saturated porous material, and calculate the conductivity properties including effective permeability, thermal conductivity and diffusion coefficient. The results clearly show that the correlations between the conductivity properties of saturated porous material are prominent and depend on the way the pore structure changes. By comparing with available experimental results and 2D numerical simulation on Sierpinski carpet models, the proposed mapping relationships among transport properties are validated. The present mapping method provides a new window for understanding the transport processes through porous material, and sheds light on oil and gas resources, energy storage, carbon dioxide sequestration and storage as well as fuel cell etc.

Heuristic Approaches Based on Modified Three-Parameter Model for Inverse Acoustic Characterisation of Sintered Metal Fibre Materials

Modelling of sound propagation in porous media generally requires the knowledge of several transport properties of the materials. In this study, a three-parameter analytical model that links microstructure properties of sintered metal fibre materials and non-acoustical parameters of the JCAL model is used and modified, and two heuristic approaches based on the established model for inverse acoustic characterisation of fibrous metal felts are developed. The geometric microstructure of sintered fibrous metals is simplified to derive the relationship between pores and fibre diameters. The new set of transport parameters in the modified three-parameter model can cover two controllable parameters during the fabrication process of fibrous metals. With two known transport parameters, six sintered specimens are characterised using a deterministic algorithm, and a satisfactory result is achieved in fitting the normalised surface impedance measured by an acoustic measurement system. Moreover, the forward evaluation shows that our modified three-parameter theoretical model is capable of yielding accurate results for the sintered metal fibre materials. A numerical investigation of the complete inverse acoustic characterisation of fibrous metals by a global non-deterministic algorithm indicates that inversion from two porous material properties is preferable to the normalised surface impedance.

Improvement of mechanical property of biomass-derived porous carbon material through in situ growth of SiCnws and glucose-converted pyrolysed carbon

Biomass porous carbon materials have been widely favoured for their unique structure and properties. At present, most research has mainly focused on improving the functional performance of biomass porous carbon materials without taking into account the mechanical property of biomass porous carbon materials. In this paper, we present a processing method for improving the mechanical property of biomass porous carbon materials. An apple derived porous carbon material (PC) with a low density of 0.167 g/cm3 and compressive strength of 0.59 MPa was prepared by freeze-drying and high-temperature pyrolysis. Subsequently, the in situ growth of SiCnws and glucose-converted pyrolysed carbon were prepared via solid-vapor and PIP method to improve the microstructure and mechanical property of PC. Due to the reinforcing rib structure constructed by SiCnws and pyrolysed carbon, the enhanced porous carbon material displayed a density of 0.316 g/cm3 and a high compressive strength of 3.14 MPa.

Uncertainty analysis of acoustic and non-acoustic parameters derived from four-microphone impedance tube measurements

The uncertainty related to measurements is fundamental for qualifying the method applied to the estimation of the quantities derived from an experimental test. In this paper an uncertainty analysis is given for the estimation of the intrinsic properties of fibrous and porous materials, i.e. the characteristic impedance and the characteristic wavenumber, from measurement data obtained by a four-microphone impedance tube. In addition, an uncertainty analysis is given for some other derived material properties, amongst which the flow resistivity. The uncertainty analysis is based on the principles contained in the Guide to the Expression of Uncertainty in Measurements (GUM) and on its supplement 1, concerning the propagation of distributions using a Monte Carlo (MC) method. The GUM and the MC frameworks are compared with each other in terms of accuracy and in terms of flexibility of use. The uncertainty arising from the process of sampling is also evaluated by testing several samples cut from the same material batch.

Determining Mechanical Moduli of Disordered Materials with Hierarchical Porosity on Different Structural Levels.

The impact of synthesis parameters and structural properties, respectively, on mechanical properties of porous materials on different structural levels provides valuable information for designing materials for specific applications. Within this study, we apply two nonstandard approaches for determining the mechanical properties of the mesoporous backbone phase in a series of disordered SiO2-based monolithic materials possessing hierarchical meso-macroporosity, that is, deformation upon mercury porosimetry and in situ dilatometry during nitrogen adsorption analysis. By using ordered porous model materials, the latter method has been recently proven to provide reliable mechanical moduli. This concept was now applied to a SiO2 monolith developed for high-performance liquid chromatography exhibiting disordered hierarchical meso- and macroporosity, as well as a series of analogue phenyl-modified meso-macroporous SiO2 monoliths with up to 36.1 at% organic modification. The phenyl group was introduced by adding phenyltrimethoxysilane to the sol-gel mixture. The study aimed at investigating in detail the impact of the organic modification on the morphology of the porous solid and the resulting mechanical properties. The study shows that both Hg porosimetry and in situ dilatometry performed during N2 adsorption at 77 K provide similar and reasonable moduli of compression for the mesoporous backbone of the silica materials investigated. These data were compared with moduli of the macroscopic sample as determined from sound velocity measurements by describing the fully connected macroporous backbone with a foam model. The comparison reveals an otherwise overseen side effect of the organic modification of the silica framework: in contrast to the pure reference SiO2 meso-macroporous monoliths, the hybrid material is composed of a more particulate morphology on the mesoscale, that is, mesoporous particles and corresponding necks between them are formed, which results in significant softening of the porous solid on the macroscale.

Improvement and Optimization of a 3D Reconstruction Algorithm for SEM Images of Porous Materials

Porous materials have become increasingly common in people’s daily lives as the industry has advanced. Porous materials have numerous applications in the petroleum and chemical industries, as well as in everyday life. The study of diffusion, thermal conductivity, and percolation properties of porous materials has an important engineering application background and scientific value. The microstructure of materials affects their properties and attributes, so the description and visualization of the microstructure of porous materials is of great importance in the study of materials science. Due to the specificity of the internal structure of porous materials, many scenarios require 3-dimensional reconstruction of porous materials in practical engineering. In order to improve the effect of 3-dimensional reconstruction of porous materials, a 3D reconstruction method based on the improved generative adversarial neural network (GAN) is proposed in this paper for SEM images of porous materials. First, scanning electron microscope (SEM) images of porous materials are acquired, and then the acquired SEM images are preprocessed, including denoising and determining the boundary. Second, an improved GAN-based image super-resolution reconstruction model (ISRGAN) is used, and then the preprocessed images are fed into the ISRGAN model for training. Thus, multiple intermediate layer images are generated. Third, the 3D reconstruction of the intermediate layer images is performed using the slice combination method. The relationship between the unit cell pixels and the porosity is analyzed in the experiments to verify the effectiveness of the 3D reconstruction method used in this paper, and it is concluded that the porosity tends to be stable when the unit cell pixels converge to 110 and converge to the porosity of the real sample. The experimental results validate the feasibility and effectiveness of the method presented in this paper in the 3D reconstruction process.

Strength and Thermophysical Properties of Dense and Porous Materials Based on Silicon Nitride

Strength and Thermophysical Properties of Dense and Porous Materials Based on Silicon Nitride

Study on polyurethane-based porous materials and their adsorption properties

The flexible superhydrophobic thermoplastic polyurethane(TPU) porous material was prepared by heat-induced phase separation method with two cooling steps. The influence of the preparation process on the microstructure of the material was discussed in depth. The microstructure, hydrophobicity and specific surface area of porous TPU materials were analyzed in detail. The surface wettability, separation selectivity, saturated adsorption capacity and adsorption rate, mechanical properties, environmental adaptability and cyclic properties of porous TPU materials were studied.The results show that the TPU-8% porous monolithic material prepared by heat-induced phase separation method shows good performance when the polymer concentration is 8%, the phase separation temperature is 0°C, the phase separation time is 30min, and the mixing solvent ratio is 9:1.

A novel SAXS model for multi-texture systems: application to CaCO3 calcination using in-situ USAXS-SAXS-WAXS

SAXS models, used to calculate the micro-textural properties (porosity, specific surface, correlation length, correlation function) of porous materials, are especially relevant for in-situ material characterization. Certain classes of porous materials, including those generated during solid decompositions, are characterized by distinct regions with different micro-textures. Classical SAXS models cannot be applied directly to such multi-texture systems, thus a novel SAXS model for multi-texture systems is proposed in this work and validated by using measurements of micro-textural properties of a calcined CaCO3 powder, obtained using time-resolved in-situ synchrotron radiation USAXS, SAXS and WAXS data. The proposed model, in contrast to the direct application of classical SAXS models, is capable of correctly predicting the expected linear trend of the particle internal porosity with respect to the CaCO3 conversion and provides a complete description of the micro-textural properties, in very close agreement with experimental data available in the literature. In the reaction product region the correlation function, as well as the other micro-textural properties, is essentially constant during the solid decomposition, and is accurately represented by a two-parameter model. Based on the proposed SAXS model, a simplified expression of the differential scattering cross section, as a product of the CaO mass fraction times a time-independent function of the correlation function, is obtained; such expression can reliably predict the experimental scattering intensity profiles over time.

Prediction of flow properties of granular porous materials for acoustic applications

Johnson-Champoux-Allard, Johnson-Champoux-Allard-Lafarge, and Johnson-Champoux-Allard-Pride-Lafarge are commonly used acoustic models for cellular, fibrous, and granular materials. These models treat the material as homogenous and require non-acoustic fluid flow properties through the porous media. These flow properties can either be directly measured or calculated by inverse techniques. A simple inverse method based on a pore size distribution model developed by Horoshenkov et al, is used. All these acoustic models are programmed in MATELYS AlphaCell code, and once the flow properties are estimated, MATELYS code could be used to predict the acoustic response of a porous material. A new method of fabricating a shaped micro-porous material was developed, prepared several specimens, impedance tested, and test results were used to validate the predictions from MATELYS. The calculated results from the flow properties reported in the literature agree well with the experiment. Results also showed that the ratio of minimum specimen dimension to particle diameter of about 10 or more will provide specimen independent flow properties. This study was conducted for solid spherical beads; for lightweight and multifunctional applications we must use lightweight hollow microbubbles.