A Universal Theoretical Framework in Material Characterization for Tailored Porous Surface Design

The sound radiation caused by tyre/road noise can be reduced significantly by the use of porous road surfaces. A hybrid analytical/numerical modelling approach has been developed to predict the sound absorption coefficient of such road surfaces. Furthermore, the modelling approach has been used as a design tool to optimise the sound absorption of porous road surfaces in the design phase. Using this design tool, two porous surfaces have been developed and constructed at a special test area. These road surfaces have been measured extensively for both sound absorption and for noise radiation in combination with different tyres. This research is carried out within the project `Silent and Safe Road Traffic'. The goal of this project was to find methods and measures to reduce the noise from tyre/road interaction while ensuring (wet) grip. The developed hybrid analytical/numerical modelling approach is based on the combination of the solutions of two subsystems: an analytically described background sound field and a numerically solved scattered sound field describing the scattering of the sound waves on the (assumed rigid) porous structure. Furthermore, the sound absorption caused by viscothermal effects inside the air-filled pores is included analytically in the modelling approach. Also, the sound absorption coefficient for oblique incidence can be predicted using this modelling approach. This is an important property when considering tyre/road noise, since most traffic noise is received at oblique incidence. Therefore, the sound absorption for oblique incidence should be considered when predicting the noise reduction by porous road surfaces. The main advantage of the developed hybrid modelling approach compared to a full numerical model is the low computation time, because (1) no mesh refinement is needed for the mesh of the structure inside the air-filled pores, since the viscothermal effects inside the pores are included analytically, and (2) the air domain surrounding the structure can be relatively small, since the scattering problem is localised around the porous structure and the background sound field is included analytically. In addition, the developed modelling approach can be applied to predict the sound absorption for any three-dimensional porous structure. The work presented here focuses on structures of tube resonators and on granular structures. Both types of porous structures are used for the validation of the modelling approach. For normal incidence, the modelling approach is validated using the impedance tube technique. The correlation between the measured sound absorption coefficient and the predicted sound absorption coefficient was extremely good for both the tube resonators and structures of stacked glass marbles. To validate the modelling approach for oblique incidence, a large sound hard box filled with glass marbles was measured using a small cubic microphone array. This validation was more complex, since the measurement technique introduced various uncertainties. However, the model results and measurement results showed good correlation. Furthermore, the developed modelling approach was adjusted in such a way that structures made from sound absorbing materials can be modelled as well. To demonstrate this, a structure of coupled tube resonators has been designed and manufactured with the 3D printing technique, an upcoming technique suitable for manufacturing complex sound reducing panels. The measured sound absorption coefficient of this sample showed an influence of the material properties on the sound absorption coefficient, which could be predicted fairly well with the adjusted modelling approach.

Various electrode materials have been developed over the years for use in the electrochemical double layer capacitors (EDLCs) or supercapacitors. Among all, activated carbon materials are widely studied and used due to their pore structure, very high specific surface area, low cost and ease of processing. It is known that the electrochemical performance of supercapacitors highly depends upon surface area, pore size/shape, overall pore volume, pore size distribution, surface functionality and electrical conductivity. In addition, microstructure and surface chemistry have significant influence on their electrochemical performance. In order to enhance the performance, stability and cycle life of the supercapacitors fabricated from activated carbon materials, their pore structure, surface area, microstructure and surface chemistry need to be controlled and modified via various processing routes. This study investigated the influence of processing routes on the properties of the activated carbon materials, and also electrochemical performance and stability of the fabricated supercapacitors. Lignocellulosic biomass can be easily, and cost effectively processed to produce activated carbon materials with unique microstructure and surface properties as electrodes. The aim of this study was to utilize different processing routes to understand their effect on the pore structure, microstructure, surface chemistry and final electrochemical performance. Therefore, three major processing techniques, which are air torrefaction (or oxidative thermostabilization), pyrolysis and chemical activation, were used in this study. The air torrefaction pretreatment was performed at low temperature regime (200°-300°C) and in air to stabilize and control the microstructure at the initial stage. Selected samples were also pyrolyzed at 450°C under nitrogen to achieve biochar samples. Chemical activation process was conducted using potassium hydroxide (KOH) to further modify the pore structure and surface chemistry of the biomass-derived carbon. Prior to fabrication of the supercapacitors, properties of the activated biomass and biochar samples were characterized by BET, SEM, TGA, XPS and Raman spectroscopy. Activated carbon materials with ultra-high specific surface area (up to 3265 m2/g), high cumulative pore volume (1.99 cm3/g) and controlled microstructure were successfully obtained. The results also demonstrated significant changes in the relative concentration of oxygen- and carbon-containing surface functional groups depending upon the processing route. To fabricate supercapacitors, activated biomass and biochar samples were mixed with polyvinylidene fluoride (PVDF) binder and carbon black for 24 h to prepare electrode inks. The electrodes were then casted on a stainless steel sheet using a doctor blade. The supercapacitors were then fabricated using a typical CR-2032 parts, KOH as an electrolyte, and nafion as a separator. Constant-current charge-discharge and self-discharge tests were conducted at the range of 0.1-1.0 V and 0.1 A/g, up to 1000 and 50 cycles, respectively. The activated biochar samples showed higher specific capacitance (107-123 F/g) compared to activated biomass (70-92 F/g), presenting the positive influence of the pyrolysis process. Initial air torrefaction process substantially increased the electrochemical performance, since there was a 22-25 F/g increase in the specific capacitance. This may be related to better microstructural control and further change in surface chemistry. All supercapacitors fabricated from the activated biomass and biochar samples showed high electrochemical stability up to 1000 cycles. The average capacitive loss after 1000 cycles was found to be around 2.0%. Acknowledgements: The U.S. Department of Agriculture (USDA), McIntire Stennis Grant Program supported this work under accession number of 1007044 and project number of WVA00118. The authors also would like to acknowledge the West Virginia University Shared Research Facilities for support through materials characterization. Dr. Yumak acknowledges financial support from the Scientific and Technological Research Council of Turkey (TUBITAK) BIDEB-2219 Postdoctoral Research Program.

Pool boiling heat transfer and simplified one-dimensional model for prediction on coated porous surfaces with vapor channels

Pickering high internal-phase emulsions (HIPEs) and porous materials derived from the Pickering HIPEs have received increased attention in various research fields. Nevertheless, nondegradable inorganic and synthetic stabilizers present toxicity risks, thus greatly limiting their wider applications. In this work, we successfully developed nontoxic porous materials through the Pickering HIPE-templating process without chemical reactions. The obtained porous materials exhibited appreciable absorption capacity to corn oil and reached the state of saturated absorption within 3 min. The Pickering HIPE templates were stabilized by gliadin-chitosan complex particles (GCCPs), in which the volume fraction of the dispersed phase (90%) was the highest of all reported food-grade-particle-stabilized Pickering HIPEs so far, further contributing to the interconnected pore structure and high porosity (>90%) of porous materials. The interfacial particle barrier (Pickering mechanism) and three-dimensional network formed by the GCCPs in the continuous phase play crucial roles in stabilization of HIPEs with viscoelastic and self-supporting attributes and also facilitate the development of porous materials with designed pore structure. These materials, with favorable biocompatibility and biodegradability, possess excellent application prospects in foods, pharmaceuticals, materials, environmental applications, and so on.

Natural porous materials such as nanoporous clays are used as green and low-cost adsorbents and catalysts. The key factors determining their performance in these applications are the pore morphology and surface activity, which are typically represented by properties such as specific surface area, pore volume, micropore content and pH. The latter may be modified and tuned to specific applications through material processing and/or chemical treatment. Characterization of the material, raw or processed, is typically performed experimentally, which can become costly especially in the context of tuning of the properties towards specific application requirements and needing numerous experiments. In this work, we present an application of tree-based machine learning methods trained on experimental datasets to accelerate the characterization of natural porous materials. The resulting models allow reliable prediction of the outcomes of experimental characterization of processed materials (R2 from 0.78 to 0.99) as well as identification of key factors contributing to those properties through feature importance analysis. Furthermore, the high throughput of the models enables exploration of processing parameter–property correlations and multiobjective optimization of prototype materials towards specific applications. We have applied these methodologies to pinpoint and rationalize optimal processing conditions for clays exploitable in acid catalysis. One of such identified materials was synthesized and tested revealing appreciable acid character improvement with respect to the pristine material. Specifically, it achieved 79% removal of chlorophyll-a in acid catalyzed degradation.

We report synthesis and characterization of a macroporous polymeric material containing a covalently immobilized pore-surface phase of well-defined thickness, gel-phase porosity and organic functional group content. The pore surfaces of otherwise inert macroporous (32 μm mean pore size) ultrahigh-molecular-weight polyethylene (UHMWPE) are aminated throughout using a low-pressure flowing-discharge process to enable covalent immobilization of lightly cross-linked polymer colloid particles on all pore surfaces in the monolith. Solvent swelling and chemical derivitization of the covalently immobilized polymer colloid particles produce a pore-surface gel phase of well-defined thickness, organic amine content, and gel-phase porosity. The low degree of cross-linking in the polymer colloid particles prevents dissolution of the immobilized colloid in good solvents and enables the formation of pore-surface gel phases having high gel porosity on swelling in good solvents. The pore-surface amination introduced by the flowing discharge process varies by less than 17% through 5-mm thickness of the macroporous UHMWPE material. The properties of the pore-surface gel phase also vary by less than 17% through the cross section. The pore-surface immobilized polymer colloid particles swell by a factor of 10 in water and tetrahydrofuran after derivitization with polyethylene glycol.

Prediction of thermal conductivity of micro/nano porous dielectric materials: Theoretical model and impact factors

<div class="htmlview paragraph">A two dimensional CFD model has been developed to study the mechanism of soot deposition on the porous wall surface in a Diesel Particulate Filter (DPF). The goal is to improve understanding of the soot deposition and its interaction with the hydrodynamic behaviour of the device. The <i>KIVA3V</i> CFD code and pre-processor were modified to simulate a single channel in a DPF. The code was extended to solve the conservation equations in porous media materials, to account for the sticking of particles on a porous surface and to evaluate the increasing resistance to the flow as the soot inside the trap accumulates. The code is already configured to track Lagrangian particles and these were modified to represent the soot particles in the flow. The code pre-processor was modified to allow definition of a double-symmetric geometry and to specify porous cells. The numerical model can predict the hydrodynamic performance and pressure drop of a clean particulate filter with results compared to experimental data and simple one-dimensional DPF models. The soot cake layer thickness on the porous wall increases in time with a spatial distribution determined by the fully coupled particle-hydrodynamics in the gaseous flow. As the soot cake increases in thickness, it alters the particle laden gaseous flow profiles. A set of unsteady simulations were run to steady state, at different loading conditions and the results have been compared with the experimental data available from literature. An extensive set of simulations has been carried out and an analysis of the spatial distribution of kinetic energy in the system (as a function of Reynolds number and of the geometric features of the trap) has been done, in order to study the correlation between the velocity field inside the channels and the soot deposition profile.</div> <div class="htmlview paragraph">The simulation results have been compared with the results of a CFD commercial code (Fluent) and with the results of a 1D simulation code, based on Bissett's approach and developed by the authors.</div> <div class="htmlview paragraph">The model can be used as a tool to predict the pressure drop across a Diesel Particulate Filter, the velocity profile inside the channels, and to study the deposit of soot along a porous surface as a function of time.</div>

Electrophoretic deposition (EPD) is a good method in the fabrication of the coating materials. Its processing parameters are easy to be operate. It is a nonbeeline process and can be used in the deposition on complex shape and porous surface. It has been widely used in many ways. This paper reviews the principles and fabrication steps of EPD and points out the influencing factors. The developments of EPD in the fabrication of materials, such as solid surface coatings, porous structure materials and gradient materials, are introduced in detail. The future of the application of EPD is also discussed.

A simplified method for the correction of velocity slip and inertia effects in porous aerostatic thrust bearings

A flexible superhydrophobic thermoplastic polyurethane porous surface with good self-cleaning function prepared by supercritical CO2 foaming

Activated carbon (AC) is a multifunctional adsorbent with a high adsorption capacity because of its pore structure comprising a large pore volume and surface area. However, its pore structure properties are largely influenced by the chemical composition and manufacturing conditions of the raw material. This study examined the effect of activation heating rate parameter on pore structure and methylene blue adsorption in teak sawdust AC. The adsorbent was dehydrated, carbonized and activated at 105, 750 and 700 °C for 2 h, 50 min, and 6 to 14 °C/min, with a nitrogen flow rate of 200 mL/min for 50 min. Several characterizations were carried out to identify pore structure, proximate substance, functional groups, surface morphology, and methylene blue-adsorption capacity of AC. The results showed that activation heating rate with the best properties and capacity of MB adsorption were adsorbed at a peak of 10 °C/min. AC obtained has a C-C aromatic rings functional group, an amorphous crystal structure, an interplanar length of 3.03 Å, 75.74 % fixed carbon, pore surface area of 126.279 m2/g, pore volume of 0.235 cc/g, and a multimodal micropore-mesopore size distribution. This is in addition to adsorption capability of 13.48 mg/g for methylene blue.

Characterization of pore structure is one of the key problems for fabrication and application research on porous materials. But, complexity of pore structure makes it difficult to characterize pore structure by Euclidean geometry and traditional experimental methods. Fractal theory has been proved effective to characterize the complex pore structure. The box dimension method based on fractal theory was applied to characterizing the pore structure of fiber porous materials by analyzing the electronic scanning microscope (SEM) images of the porous materials in this paper. The influences of image resolution, threshold value, and image magnification on fractal analysis were investigated. The results indicate that such factors greatly affect fractal analysis process and results. The appropriate magnification threshold and fractal analysis are necessary for fractal analysis.

The traditional technological process for creating highly porous materials from carbonaceous raw materials involves two stages of thermal treatment: carbonization (pyrolysis) and activation (gasification), aimed at forming a porous structure capable of adsorption. Combining both stages into a single process with chemical activation allows for efficient raw material utilization and control of the material's porous structure at different levels, providing the ability to customize its characteristics. The choice of a chemical activator depends on the type of raw material and the required characteristics of porous carbon materials. In this study, it is established that the analysis of surface properties of highly porous carbon materials synthesized from coal tar pitch, obtained by distillation of coal tar resin from JSC "Shubarkolkomir," confirms the outstanding operational characteristics of this material. The application of a combined process of carbonization and activation of coal tar pitch at an optimal temperature in an inert atmosphere leads to the formation of porous carbon materials with a high specific surface area: 561 (traditional method), 789 (chemical activation), and 881 m²/g (templating method), as well as a pore volume of 0.30; 0.40; and 0.48 cm³/g, respectively. This work not only expands the technological methods of obtaining carbon materials from coal tar resin but also underscores their potential for improving soil structure and increasing the efficiency of agricultural production.

Effects of surface pore size on the tribological properties of oil-impregnated porous polyimide material