Porous Structure Design Research Articles

Novel Class of Additive Manufactured NiTi-Based Hierarchically Graded Chiral Structure with Low-force Compressive Actuation for Elastocaloric Heat Pumps

Elastocaloric refrigeration is the most promising green solid-state refrigeration technology to replace conventional vapor compression refrigeration. The development direction of the elastocaloric component that acts as a key part of the elastocaloric refrigeration system contains a large elastocaloric effect, low stress hysteresis, high heat exchange performance, and small driving loads. The first two indices can be realized by material modification; however, the last two are more dependent on a novel porous structure design. However, the conventional porous structure is confronted with some critical challenges, including inhomogeneous stress, a significant hysteresis area, and deformation instability under the alternating cyclic loading. In this study, a NiTi-based elastocaloric structure model with chirality feature and gradient design as innovative elements was presented, bio-inspired by the structure of the plant tendrils. A quantitative optimization for the NiTi-based elastocaloric structure was performed using the finite element analysis (FEA) method. Strain and martensite volume fraction (MVF) fields during the loading and unloading processes were predicted and evaluated. The simulated results indicated that increasing the thickness gradient g1 of the strip or decreasing the diameter gradient g2 of the structure was beneficial to achieving more homogeneous strain and martensite distribution, simultaneously with higher energy storage efficiency and specific surface area. In addition, these NiTi-based chiral structures with different structural parameters were fabricated by laser powder bed fusion (LPBF). At the optimized structure parameters of g1 = 2 and g2 = 1.11, the LPBF-fabricated NiTi-based chiral structure could achieve an adiabatic temperature change ΔTad of 2.3 K, driving force of as low as 149.11 N, and |ΔTad/F| of as high as 15.42 K/kN at a recoverable compressive strain of 10%.

Design and 3D printing of porous cavity insulation structure for ultra‐high electrical withstanding capability

AbstractVacuum‐dielectric interface is the most vulnerable part of vacuum insulation systems where surface electrical breakdown is prone to happen, hence severely restricts the development of advanced electro‐vacuum devices with large capacity and its miniaturisation. Generally, a direct and effective way to improve vacuum surface insulation is to alleviate the initiation and development of multipactor phenomena. Inspired by this approach, the authors report a 3D‐printed insulation structure designed with a millimetre‐scale surface cavity covered by periodic through‐pore array via stereolithography, exhibiting remarkable multipactor suppression and flashover threshold improvement, well outperforming the conventional flashover mitigation strategies. Experiments and simulations demonstrate that electrons in the multipactor region pass through‐pores and are unlikely to escape from the cavity, hence no longer participate in the above‐surface multipactor process, and eventually improve flashover threshold. The proposed approach provides new inspiration for the design of advanced insulators featuring ultra‐high electrical withstanding capability and brings up new insight into pertinent industrial applications.

Finite element analysis of irregular porous scaffold for bone tissue engineering

The structure of natural bone, particularly the trabecular structure, is irregular in the microscopic structure. Some related research had demonstrated that irregular porous structures like cancellous were better for cell growth. The correlations between irregular porous structure design parameters and porosity, average pore size, and associated mechanical properties are also complicated. This research uses finite element analysis to analyze irregular porous scaffold models of PLA/HA composite mechanical characteristics. The factors for the design parameters investigated in this study are strut diameters (SD), composite materials (M), and loading orientation (D). A full factorial design of experiments (FFD) was used to determine the optimal mechanical parameters of structure scaffold design. The results of our study illustrated that composite materials and strut diameter are essential factors for compressive strength and elastic modulus. Still, the strut diameter was the most critical variable in this simulation study. This study found that variation of loading direction at all irregular porous scaffolds in this research does little to affect compressive strength and elastic modulus. The optimization method showed that the desired results are obtained with the Z loading direction, 30% hydroxyapatite composition, and 0.65 mm strut diameter. Maximum compressive strength and elastic modulus were calculated to be 25.93 MPa and 1295.24 MPa, respectively. These results suggest that the bone scaffold elastic modulus and compressive strength are comparable to the trabecular bone but less than cortical bone.

Porous structure design and properties of dental implants

At present, selective laser melting (SLM) 3D printing technology can accurately control the internal pore structure and complex cell shape. Three types of reticulated meshes with cubic, G7 and composite structure cell shapes were fabricated by the SLM 3D printing technology using Ti–6Al–4V alloy powders. The bone stresses around the implant and the stresses in the implant were analyzed by ANSYS finite element software, which comprehensively evaluated the effect of porous dental implants with different spatial porosity characteristics on osseointegration. The results show that porous dental implants with composite structure of pore characteristics have improved mechanical and biological properties and can better promote the growth and integration of bone tissue.

One-dimensional nanostructured electrode materials based on electrospinning technology for supercapacitors

Supercapacitors are outstanding electrochemical energy storage devices with high power density, quick charge and discharge and long cycle life. A well-designed structure can significantly increase its electrochemical performance as electrode materials. Carbon nanofibers (CNFs) made by electrospinning technique feature a one-dimensional nanostructure, which can provide directional electron transfer pathways and reduce the internal resistance of materials. This article reviewed the design approaches for one-dimensional nanostructured electrode materials produced from CNFs for supercapacitors, focusing on porous structure design, hollow structure design, surface functional group structure design and core-shell structure design. The porous and hollow structural designs could improve the contact area between electrode and electrolyte, allowing for faster electron/ion transport. Surface functional group structure design had the potential to improve the surface chemical properties of electrode materials, therefore enhancing their capacitance characteristics. The core-shell structure design might result in layered channels, and the diverse components of the core and shell could work together to increase the conductivity and structural stability of electrode materials. The preparation methods and structural properties of these CNF electrode materials with different structural designs were highlighted, as well as their future development.

Design of bio-inspired irregular porous structure applied to intelligent mobility products

Material structure is a crucial part of the design of any product where the intention is to dissipate loads and lighten material. Because some structures today are increasingly complex in geometry and internal structure, it becomes impossible to opt for traditional methods to manufacture them. In this sense, additive manufacturing enables the creation of complex structures with intricate geometries. As manufacturers seek to optimize material properties and performance in a variety of stress conditions, bio-inspired engineering looks at nature for solving the most complex human challenges. By imitating nature’s patterns and shapes, we can optimize fracture resistance, energy absorption, and toughness in materials. In this work, we employ voronoi tessellation patterns and computer-aided design software to design an algorithm for the creation of irregular porous structures, similar to those found in nature (e.g., trabecular bone). This algorithm is scalable and applicable to any product that needs to comply with lightweight requirements and outstanding mechanical properties. Herein, the authors perform static compression tests to determine mechanical properties. The results indicated that the mechanical properties depend directly on the microstructural characteristics of the porous structure itself. Besides, surface area and porosity are the principal parameters to be controlled. Finally, the algorithm has a wide range of engineering applications in the automotive and aerospace industries.

Design, microstructure, and mechanical property of negative Poisson's ratio porous structure fabricated by LPBF of AlCoCrFeNi2.1 eutectic high-entropy-alloy

Negative Poisson's ratio (NPR) materials are a type of structural materials that show an atypical deformation response. In general, metal-based porous materials with NPR do not have good mechanical properties due to the substrate's limited yield strength and plasticity, as the NPR behavior is unlikely to play a continuous role in the deformation. AlCoCrFeNi2.1, a eutectic high-entropy alloy (EHEA) with high yield strength and high ductility was used to fabricate the NPR structures by laser powder bed fusion (LPBF) to enhance the structures mechanical properties and NPR behavior. Structures with four different sets of structural parameters were designed for this study. The microstructure and mechanical properties of AlCoCrFeNi2.1 EHEA, synthesized by LPBF were studied, and the strength and energy absorption effect of NPR porous structure materials were investigated by static and dynamic compression experiments. Research showed the large number of inter-phase interfaces provided by the nano-scale cellular eutectic microstructure effectively restrict dislocation movement, thereby enhancing the strength and toughness of this EHEA alloy, endowing it with superior impact resistance, fracture resistance, and mechanical energy absorption. The compressive performance and the mechanical energy absorption capacity of the 3D EHEA-based NPR porous structure strongly depend on the inclination angle Ф between the thick rod and the horizontal direction in the 2D single-body model design. The strength and energy absorption of the structure with a high inclination angle of 75° material are both higher than those of the structure with a low inclination angle of 45° by almost a factor of two.

Confined Bismuth-Organic Framework Anode for High-Energy Potassium-Ion Batteries.

Metal-organic frameworks (MOFs) with inherent porosity, controllable structures, and designable components are recognized as attractive platforms for designing advanced electrodes of high-performance potassium-ion batteries (PIBs). However, the poor electrical conductivity and low theoretical capacity of many MOFs lead to inferior electrochemical performance. Herein, for the first time, a confined bismuth-organic framework with 3D porous matrix structure (Bi-MOF) as anode for PIBs via a facile wet-chemical approach is reported. Such a porous structure design with double active centers can simultaneously ensure the structure integrity and efficient charge transport to enable high-capacity electrode with super cycling life. As a result, the Bi-MOF for PIBs exhibits high reversible capacity (419 mAh g-1 at 0.1 A g-1 ), outstanding cycling stability (315 mAh g-1 at 0.5 A g-1 after 1200 cycles), and excellent full battery performance (a high energy density of 183Wh kg-1 is achieved, outperforming all reported metal-based anodes for PIBs). Moreover, the K+ storage mechanisms of the Bi-MOF are further unveiled by in situ Raman, ex situ high-resolution transmission electron microscopy, and ex situ Fourier-transform infrared spectroscopy. This ingenious electrode design may provide further guidance for the application of MOF in energy storage systems.

MOFs-derived hierarchical porous carbon supported Co@NC nanocapsules for pH universal oxygen reduction reaction and Zn-air batteries

The rational design and construction of the hierarchical porous structure of carbon framework to support transition metal-based catalysts is critical to increase their active sites density and facilitate mass/electron transport. Herein, we report a novel nanocapsules with cobalt core and nitrogen-doped carbon shells (Co@NC) supported on MOFs-derived hierarchical porous carbon framework. The rational hierarchical porous carbon framework with controllable size and micropore/mesoporous ratio was achieved by one-step pyrolysis of Zn(acac)2·phen ligand and ZIF-67 precursor, which is beneficial for the mass transport in the oxygen reduction reaction (ORR). The 0.4Co@NC-900 electrocatalyst display a distinguished ORR activity in the pH-universal range, with a half-wave potential of 0.91 V in alkaline and 0.76 V in acid electrolytes. The excellent ORR performance of our electrocatalyst can be attributed to its optimized micropore/mesoporous ratio of carbon framework with efficient mass transport, together with the graphitized carbon shell on Co nanoparticles which not only enhances the electron/proton transport, but also suppresses the chemical corrosion of the Co nanoparticles. Impressively, the Zinc-air battery as air electrode offers peak power density of 203 mW cm−2 and long-term stability of 130 h, showing an excellent battery performance. This study offers a fresh method of constructing ORR catalysts with increased activity and durability over a universal pH range.

A Direct Toolpath Constructive Design Method for Controllable Porous Structure Configuration with a TSP-based Sequence Planning Determination

The inherent capabilities of additive manufacturing (AM) to fabricate porous lattice structures with controllable structural and functional properties have raised interest in the design methods for the production of extremely intricate internal geometries. Current popular methods of porous lattice structure design still follow the traditional flow, which mainly consists of computer-aided design (CAD) model construction, STereoLithography (STL) model conversion, slicing model acquisition, and toolpath configuration, which causes a loss of accuracy and manufacturability uncertainty in AM preparation stages. Moreover, toolpath configuration relies on a knowledge-based approach summarized by expert systems. In this process, geometrical construction information is always ignored when a CAD model is created or constructed. To fully use this geometrical information, avoid accuracy loss and ensure qualified manufacturability of porous lattice structures, this paper proposes a novel toolpath-based constructive design method to directly generate toolpath printing file of parametric and controllable porous lattice structures to facilitate model data exchange during the AM preparation stages. To optimize the laser jumping route between lattice cells, we use a hybrid travelling salesman problem (TSP) solver to determine the laser jumping points on contour scans. Four kinds of laser jumping orders are calculated and compared to select a minimal laser jumping route for sequence planning inside lattice cells. Hence, the proposed method can achieve high-precision lattice printing and avoid computational consumption in model conversion stages from a geometrical view. The optical metallographic images show that the shape accuracy of lattice patterns can be guaranteed. The existence of “grain boundaries” brought about by the multi-contour scanning strategy may lead to different mechanical properties.

Ultrathin bimodal porous membranes with uniform small pores separated by laminated large pores for efficient water separation

Bimodal pore structure design of separation membranes is a promising way to simultaneously improve permeability and selectivity. However, the thickness limitation of bimodal porous membranes is an obstacle to further improving the separation efficiency. In this study, a novel bimodal porous structure with uniform small pores on the surface and a unique laminated large pore structure in the thickness direction was successfully constructed through biaxial stretching of gel films in ultra-high molecular weight polyethylene membranes. With an increase in the draw ratio to 12 × 12, the uniformly refined small pores increased the rejection rate of the carbon nanoparticle solution (particle size distribution of 60–400 nm) to 99.4%, and the unique laminated large pore structure enabled the permeance to reach 1141.8 L m-2h−1 bar−1. By further increasing the draw ratio to 16 × 16, the membrane thickness decreased to 0.91 μm and the permeance was further increased to 2008.2 L m-2h−1 bar−1 while the selectivity slightly decreased to 98.9%. Furthermore, a bimodal porous membrane with sufficient strength (237 MPa of 16 × 16) was efficient for long-term water separation. This study proposes a new design idea for ultrathin porous membranes, which can be further expanded to prepare various antifouling, self-cleaning, and multifunctional separation membranes.

Pore structure engineering in carbon microsphere for fast potassium/lithium storage

Porous structure design is generally considered to be an effective strategy to enhance ions diffusion kinetics for carbon anode materials. In particular, mesoporous structures can enrich the active sites and enhance the structure stability during potassium storage. Herein, porous carbon nanosheet microspheres (PCNMs) is reported via the chemical deposition of pitch-derived carbon on the basic zinc carbonate (Zn5(CO3)2(OH)6) microspheres composited of nanosheets. The mesopores is further enriched by the in-situ pulverization of from Zn5(CO3)2(OH)6 nanosheets to ZnO nanoparticles. Compared to carbon monoliths (CMs), PCNMs possess both more abundant mesoporous and carbon defects. Benefiting from rich defect sites and fast ion diffusion kinetics, PCNMs-700 exhibits a superior reversible capacity (323 mAh g−1at 0.05 A g−1 after 50 cycles) with 92% capacity retention and a high rate (157 mAh g−1at 1 A g−1) in potassium-ion half cells. Similarly, when being applied to potassium ion hybrid capacitors, PCNMs-700 electrode performs a fast potassium storage capacity (81.2 mAh g−1 after 1500 cycles at 1 A g−1) with 92% capacity retention. This work provides a rational guide of pore engineering in carbon for fast ion storage.

A novel process to high‐strength and controlled‐shrinkage Al2O3 foams with open‐cell by Al powder hollowing technology

AbstractCeramic foams with open‐cell structures have attracted extensive attention due to their unique structure and superior properties. But these materials often exhibit the weakness of high sintered shrinkage and low strength at high porosity levels. In this work, novel ceramic foams with open‐cell structures have been obtained using Al powder by combining direct foaming and gelation freezing (DF–GF). The foams are assembled by hollow Al2O3 particles resulting from the Kirkendall effect, in which expanded particles overcome the shrinkage of sintering. The influence of sintering temperature on the microstructure and properties of foams are investigated. The Al2O3 foams show near‐zero‐shrinkage at 1773 K after undergoing the process of first expansion and then shrinkage. Compared to other conventional open‐cell foam, this foam displays relatively high compressive strength of 0.35–2.19 MPa at high porosity levels of 89.45%–94.45%, attributed to hierarchical pore structure and reaction bonding between Al and O2. This method from pore structure design provides a novel route for the preparation of controlled shrinkage and high‐compressive strength alumina foam with open‐cell toward potential application.

Evaluation of Compressive and Permeability Behaviors of Trabecular-Like Porous Structure with Mixed Porosity Based on Mechanical Topology

The mechanical properties and permeability properties of artificial bone implants have high-level requirements. A method for the design of trabecular-like porous structure (TLPS) with mixed porosity is proposed based on the study of the mechanical and permeability characteristics of natural bone. With this technique, the morphology and density of internal porous structures can be adjusted, depending on the implantation requirements, to meet the mechanical and permeability requirements of natural bone. The design parameters mainly include the seed points, topology optimization coefficient, load value, irregularity, and scaling factor. Characteristic parameters primarily include porosity and pore size distribution. Statistical methods are used to analyze the relationship between design parameters and characteristic parameters for precise TLPS design and thereby provide a theoretical basis and guidance. TLPS scaffolds were prepared by selective laser melting technology. First, TLPS under different design parameters were analyzed using the finite element method and permeability simulation. The results were then verified by quasistatic compression and cell experiments. The scaling factor and topology optimization coefficient were found to largely affect the mechanical and permeability properties of the TLPS. The corresponding compressive strength reached 270-580 MPa; the elastic modulus ranged between 6.43 and 9.716 GPa, and permeability was 0.6 × 10-9-21 × 10-9; these results were better than the mechanical properties and permeability of natural bone. Thus, TLPS can effectively improve the success rate of bone implantation, which provides an effective theory and application basis for bone implantation.

D-Calcium pantothenate-derived porous carbon: carbonization mechanism and application in aqueous Zn-ion hybrid capacitors

Explored the carbonization mechanism of d-calcium pantothenate, including finding the optimal carbon skeleton reconstruction, pore structure design, and defect fabrication, and constructing stable structure cathodes with high density and long service life.

Unique 3D ternary porous core-shell Ni@MoS2/RGO composites for broadband electromagnetic wave absorption

The core-shell structure can improve the impedance matching characteristics and dispersibility of microwave absorbers, and has become one of the research hotspots of high-performance absorbers. Herein, a 3D ternary porous core-shell Ni@MoS2/RGO composite is synthesized by hydrothermal-precipitation, two-step hydrothermal and modified hummers method. Results show that the synthesized ternary composite with 3D porous core-shell structure exhibits remarkable enhancement of microwave absorption. When the matching thickness is 1.83 mm, the minimum reflection loss (RLmin) of the composite is − 64.05 dB at 6.24 GHz, and its effective absorption bandwidth is up to 7.34 GHz (from 10.66 to 18 GHz) at 2.5 mm. It is believed that its good absorbing performance originates from the specific 3D porous core-shell structure design and abundant interface structure. This work provides an efficient and promising strategy for the structural design and interface construction of novel magnetic/electrical composites with efficient microwave absorption.

Russian-Doll-Like Porous Carbon as Anode Materials for High-Performance Potassium-Ion Hybrid Capacitors.

Pore-structure design with the sophisticated and pragmatic nanostructures still remains a great challenge. In this work, porous carbon with Russian-doll-like pores rather than traditional single modal is fabricated via a boiling carbonization approach, accompanied by K+ -pre-intercalation. The most important internal factor is that alkali can penetrate into the stereoscopic space of layered Malonic acid dihydrazide and the confinement effect leads to the in-depth development of different dimensional pore structures. The oxygenated and nitrogenated surface guarantees the K+ intercalation behavior. Benefiting from their open framework and enlarged interlayer spacing, K+ -pre-intercalated porous carbon with Russian-doll-like pores (denoted as KPCRPs) as anode material exhibits promising potassium storage performance. The assembled KPCRP//activated carbon potassium-ion hybrid supercapacitor in 30m CH3 COOK displays a high energy density of 157.29Whkg-1 , an ultrahigh power output of 14kWkg-1 , and a long cycling life (99.58% capacity retention after 10000 cycles), highlighting the superiority of Russian-doll-like pore structure. This work sheds light on the designing of 3D pores structure, especially for multimodal pore architectures.

Isoporous catalytic ceramic membranes for ultrafast contaminants elimination through boosting confined radicals

Catalytic membrane based oxidation-filtration processes (AOP-CM), a derivative concept of membrane process that combines physical separation and chemical oxidation, offers a high-efficient water purification strategy. However, the application of AOP-CM was still hampered by the low heterogeneous AOPs efficiency of catalytic membranes. In order to improve the heterogeneous AOP efficiency, an isoporous AlOx/La2CoMnO6-δ ceramic membrane (IAPCM) with nano-confinement characteristics was prepared via sol–gel based block copolymer self-assembly route. Benefiting from the well-designed pore structure, IAPCM exhibited excellent pure water permeance (313 L·m−2·h−1·bar−1) and size-exclusion performance (complete rejection of MS2 phages with a diameter of ∼ 20 nm). With the addition of peroxymonosulfate (PMS), IAPCM achieved ultrafast degradation of organic micropollutants (e.g. atrazine, carbamazepine and sulfamethazine) at 0.5 bar (equivalent to a retention time of 4.3 × 10−4 s). Finite-Element analysis confirmed that high-concentration radical fields were generated in the confined nanoscale-pores within the isoporous La2CoMnO6-δ layer. The boosted mass transfer rates and high-concentration radical fields induced ultrafast degradation of micropollutants in IAPCM based oxidation-filtration system. This work highlights the significance of pore structure design for high-performance AOP-CM processes.

Gyroid minimal surface-based composite porous structure with superior mechanical property via triangular grid design and stress distribution optimization

Triply periodic minimal surface structures (TPMS) possess excellent printability during additive manufacturing processing and mechanical properties. However, for TPMS shell structure due to the single connected regions, the porosity and connectivity become limited on the premise of mechanical property. In this study, triangular grid-based design of Gyroid composite porous structure (CPS) and optimized CPS through assigning diameter based on stress distribution were proposed for obtaining higher porosity and improved mechanical properties, following the analysis of curvature distribution characteristics. Afterwards, finite element simulation and quasi-static compression tests were performed for studying the stress distribution and mechanical responses. The results showed that the designed Gyroid CPS with high porosity did not obviously destroy the original curvature characteristic, while strength, modulus and specific energy absorption were enhanced simultaneously. It is expected to provide beneficial inspiration for the design and application of TPMS-based porous structures with the integration of high porosity and mechanical property.

Tuning Co‐Catalytic Sites in Hierarchical Porous N‐Doped Carbon for High‐Performance Rechargeable and Flexible Zn‐Air Battery

AbstractThe strategy of heteroatom doping and metal active sites can synergistically promote oxygen electrocatalysis. Especially, the combination of theoretical simulations with experimental results provides new opportunities to understand the electrocatalytic mechanism. Herein, the 3D carbon nanosheets aggregate with highly branched carbon nanotubes and cobalt active sites (CoCNTs/PNAs) is prepared via the facile self‐assembly‐pyrolysis strategy. The CoCNTs/PNAs electrocatalysts exhibit superior bifunctional activities to oxygen reduction (E1/2 = 0.925 V) and evolution (Ej = 10 = 1.54 V) reactions, surpassing those of Pt/C‐RuO2 catalysts. The theoretical calculations reveal that the electronic interaction of cobalt sites and nitrogen‐doped carbon matrix plays a critical role in boosting the bifunctional electrocatalytic performance. Additionally, the rechargeable Zn‐Air battery (ZAB) assembled with aqueous electrolyte exhibits the largest power density of 371.6 mW cm−2 and outstanding cycling durability (over 2000 h). Furthermore, all‐solid‐state cable‐type ZAB delivers high flexibility with good cycling stability and high energy efficiency (76.5%). This work will open a new avenue to adjust the metal‐carbon support interaction for functional electrocatalysis via hierarchical porous structure design.