Additional Porosity Research Articles

Ultrasonic vibration assisted directed energy deposition of titanium alloy: Microstructure control, strengthening mechanisms and fatigue crack behavior

Large-scale titanium alloy structural components fabricated using direct energy deposition (DED) technology have broad application prospects. However, the columnar grain structures and inhomogeneous microstructure due to the inherent characteristics of additive manufacturing seriously affects the mechanical properties of components. In this study, high-intensity ultrasound vibration was introduced into the wire-arc DED deposition of TC4-DT titanium alloy. The results showed that ultrasonic vibration assistance (UVA) significantly improves the grain structure (refine prior-β grain size and weaken α texture) of the as-deposited component, without introducing additional porosity. Compared to conventional wire-arc DED deposited components, the yield strength and tensile strength of UVA alloys increased by 22.23 % and 15.06 %, respectively. Furthermore, the difference in α grain structure caused by UVA results in different fatigue crack growth behaviors. The disorder orientation of the α laths enhanced the fatigue crack initiation resistance of the wire-arc DED component with UVA. This study shows the excellent mechanical properties of UVA DED fabricated TC4-DT alloy, paving the way for the design, fabrication, and application of large structural components of titanium alloys.

High performance CaCO3-based composites using sodium tripolyphosphate as phase controlling additive: Bamboo fiber driven high strength development

Due to the limited carbonation degree caused by the surface densification of carbonated products, the development of high-strength carbonated composites remains challenging. In this work, bamboo fiber (BFs) is utilized as a reaction reinforcing agent along with sodium tripolyphosphate (STPP) as a CaCO3 phase controlling additive to prepare high-strength bamboo fiber reinforced carbonated wollastonite composites (BFRCWs). The phase composition and microstructure are systematically investigated by multiscale physicochemical analysis, followed by the determination of macro properties and volume deformation. Results indicate that BF and STPP have a synergistic effect on the microstructural formation and macro performance of BFRCWs. STPP-treated BF (ST-BF) can serve as an internal curing agent and the porous structure of BF provides more channels for ion and CO2 transport, whereas CaCO3 phase composition and cementitious behavior is modified by STPP. The addition of ST-BF, particularly for long fibers, accelerates the carbonation reaction, resulting in an increased ratio of poorly crystalline CaCO3 and a refined pore structure. With increasing ST-BF dosage (0–3 vol%), the cementitious reaction is enhanced, but excessive fibers (3 vol%) incorporation introduces additional porosity, consequently reducing compressive strength. The desired pore structure with the optimal 2 vol% ST-BF (3–6 mm) shows the highest strength of 103.5 MPa at 28 days.

Dielectric percolation in ceramic matrix composites

This paper presents the results of an experimental study of the percolation behavior of the complex dielectric constant of ceramic matrix composites (CMC). Samples of piezoactive CMC were obtained by joint sintering of synthesized PZT piezoceramic powder (matrix) and crushed particles of sintered PZT piezoceramics (filler) of different compositions. The experimental dependencies of real and imaginary parts of the complex dielectric constant of CMC on the porosity of piezoceramic matrix and volume content of ceramic filler particles were measured and analyzed. It was shown that the additional porosity of the ceramic matrix resulting from sintering of the CMC masks the dielectric percolation transition, that actually occurs at the volume concentration of ceramic filler close to percolation threshold (V ∼ 1/3).

Developing Green Sorbents Derived from Natural Materials for Microextraction and Determination of Emerging Contaminants

Developing Green Sorbents Derived from Natural Materials for Microextraction and Determination of Emerging Contaminants

Investigation of the inner microstructure of composite materials during their densification by scanning electron microscopy – LSM:YSZ electrode case study

An understanding of the high-temperature processes, such as sintering, remains a challenge despite its paramount importance, and has yet to be achieved by the scientific community. Scanning electron microscopy is a valuable technique for investigating morphological changes, including elemental composition, by means of an energy-dispersive X-ray detector associated with these processes, with high resolution in-situ. Historically, this technique has been limited to experiments conducted at ambient temperature. However, by integrating scanning electron microscopy with a MEMS® heating chip, this limitation can be overcome, enabling the study of solid-state processes at temperatures of up to 1 200 °C. This study demonstrates one potential application of in-situ scanning electron microscopy – the densification of La1-xSrxMnO3-δ : (ZrO2:Y2O3) composite. This material, employed as an oxygen electrode in solid oxide cells, exhibits a complex microstructure. Achieving a balance between effective particle interconnection, ensuring high electric conductivity, and efficient mass transport through its porous structure is crucial. A comprehensive understanding of microstructure and surface composition evolution during the sintering process is vital to addressing trade off when optimizing densification conditions. It was shown that the densification of La1-xSrxMnO3-δ : (ZrO2:Y2O3) composite occurs in two steps. At 900 °C a significant additional porosity emerged due to the La1-xSrxMnO3-δ phase shrinkage (densification). The main densification process at 1 150 °C then acts as a self-healing mechanism, leading to the formation of a well-interconnected microstructure. Interparticle ligament formation is exclusively induced by the La1-xSrxMnO3-δ phase. Notably, no common degradation processes, such as La2Zr2O7 formation, were observed under the experimental conditions employed. This study underscores the promise of scanning electron microscopy with a heating chip extension for in-situ investigations pertinent to various high-temperature technologies.

Numerical evaluation of the infill pattern upon mechanical proprieties of 3D printed materials

The effect of the structure that is printed inside an object, known as infill pattern, on mechanical proprieties of ABS specimens was investigated in this paper. Numerous studies demonstrated that parts created with fused deposition molding (FDM) technology present inferior mechanical properties due to additional porosity and anisotropy caused by the nature of the manufacturing process. In this regard the influence of printing parameters may be analyzed for correct evaluation of mechanical behavior and material constants. The methodology proposed in this paper consists of a numerical simulation of the fused deposition moulding 3D printed specimen, identification of the real cross-sectional area and evaluation of the strain-stress curves of the materials. There are several infill pattern geometries, each with benefits and compromises between material usage, printing time or mechanical strength of the obtained part. The current paper analysed specimens with 100% density (infill rate) but having different infill patterns: grid 0°-90° and ±45°, triangular 60°, fast honeycomb, full honeycomb and wiggle. The results are showing the dependence of the specimen's E modulus with the infill pattern and comparison of the strain-stress curves drawn with full cross-section and numerically calculated ones.

Ultrafast Laser Patterning of Silicon/Graphite Composite Electrodes to Boost Battery Performance

The ever-increasing share of electric vehicles in the mobility sector urgently calls for an increase in the production capacity of high-power and high-energy lithium-ion batteries with low production costs. A gravimetric energy density of about 350 Wh/kg flanked by a volumetric energy densities of at least 750 Wh/L were defined as ambitious goals from the European Union to be achieved by 2025. For this purpose, novel, high-capacity anode materials containing significant silicon content should be utilized in next generation batteries. At room temperature, silicon has a theoretical specific capacity of 3579 mAh/g which is one order of magnitude higher compared to the state-of-the-art graphite anode material (372 mAh/g). The volume change which silicon undergoes during lithiation and delithiation and the thereby caused mechanical stresses inside the composite electrode, which lead to loss of electrical contact and delamination, are an obstacle for its implementation in industrial battery production. While many researchers focus on other promising approaches to facilitate the usage of silicon in electrodes, for example pre-lithiation, the usage of graphite-silicon composites, or carbon coating on the silicon particles, here, the implementation of additional porosity via laser patterning is pursued. A water-based silicon/graphite slurry concept for the large-scale electrode production is used. There, the silicon nanoparticles’ agglomerates are destroyed and the silicon is finely dispersed using a ball mill, while the slurry homogenization is finalized using a disk stirrer. This facilitates the production of electrode sheets on a roll-to-roll coater, delivering enough material for the high power, high repetition rate roll-to-roll laser patterning process, both of which exhibit a technology readiness level of 5 to 6. The slurry and electrode characterizations are performed using laser induced breakdown spectroscopy (LIBS) for both the binder and lithium spatial distribution, the cyclability and lifetime of the electrodes is assessed in pouch cells with NMC 622 as counter electrode, and the lithiation of the composite material is determined with cyclic voltammetry. Scanning electron, digital and light microscopy are used for the characterization of the laser patterning, while chemical analysis is used to assess the composition of the electrode and the silicon oxidation during water-based manufacturing.

Mechanical Properties of Microporous Copper Powder Compacts Produced by Oxide Reduction

Powder metallurgy (PM) processes for porous copper and alloys have seen some commercial successes, but PM methods have the disadvantage of relatively low porosity or strength that is compromised by stress-concentrating interparticle bonds. To increase porosity without compromising scalability, a Cu-CuO metal matrix composite powder was utilized to produce additional microscale porosity within the particles by oxide reduction. These Cu-CuO powders were pressed at 1, 2, or 3 GPa, and made porous at 600, 800, or 1000 °C to investigate the effects of pressing and sintering parameters on the overall strength and density. It was found that the formation of porosity is weakly dependent on compaction pressure (maximum 6% difference from 1 GPa to 3 GPa), while the final porosity varied by ~16% overall (~40% for 1 GPa and 600 °C to 24% for 3 GPa and 1000 °C). The strength of the porous Cu was highest after being reduced at 600 °C but also exhibited some flaking at the edges at high strain. The 1 GPa, 600 °C samples have a higher specific strength than wrought Cu annealed at the same temperature, as was demonstrated under uniaxial quasi-static compression as well as split Hopkinson pressure bar impact.

High repetition ultrafast laser ablation of graphite and silicon/graphite composite electrodes for lithium-ion batteries

Laser structuring can be applied to composite electrodes of lithium-ion cells to enhance wetting and to facilitate the usage of thick-film electrodes by reducing the lithium-ion diffusion overpotential and the tortuosity of the electrodes or the usage of electrodes containing silicon, where additional porosity is required to compensate the volume expansion during lithium de-/insertion. To integrate the additional laser processing step in the well-established electrode manufacturing route, the laser processing speed must be significantly increased to match with the belt speed, which is dependent on the electrode thickness and the type of manufacturing route. Upscaling can be realized by increasing the average laser power, laser intensity, and/or laser repetition rate. Here, an ultrashort pulsed laser source with an average power of 300 W and a pulse duration of 600 fs was applied. For the first time, the presented research provides detailed laser ablation processing data for thick-film composite anodes associated with high repetition rates ranging from 4.9 to 48.8 MHz. The patterning results are compared depending on the widths, depths, aspect ratios, the total appearance regarding debris and cracks, and the volume ablation rate. In high repetition rate laser patterning, the subsequent laser pulses interact with the material vapor plasma generated by the previous laser pulses, resulting in lower ablation depths and higher ablation widths. The increase in laser peak intensity leads to higher achievable ablation depths. Processing strategies are identified for two different ablation scenarios focusing on the pouch cells of a Volkswagen ID.3 and the Tesla 4680 cell.

Increased Microporosity in Ceramic and Metal Foams: A Novel Processing Combination

Copper, aluminum, and alumina foams are prepared by a combination of reticulated foaming and freezing processing. This results in all of these foams in an additional strut porosity consisting of lamellar pores and material lamellae; the lamellar pores enable designed access to the inner volume of the struts. To increase the functionality in terms of enlarging the total surface area and increasing the adsorption activity, the foams are loaded with microporous materials by direct crystallization: the copper foams are combined with the metal organic framework HKUST‐1, the aluminum foams are combined with the zeolite SAPO‐34, and the alumina foams are combined with the zeolite silicalite‐1. All microporous materials are shown to access the inner strut pore surface area. Because of different crystal sizes of the different microporous materials, the load of the inner strut surface area varies significantly.

Synthetic Control of the Defect Structure and Hierarchical Extra-Large-/Small-Pore Microporosity in Aluminosilicate Zeolite SWY.

The SWY-type aluminosilicate zeolite, STA-30, has been synthesized via different routes to understand its defect chemistry and solid acidity. The synthetic parameters varied were the gel aging, the Al source, and the organic structure directing agent. All syntheses give crystalline materials with similar Si/Al ratios (6-7) that are stable in the activated K,H-form and closely similar by powder X-ray diffraction. However, they exhibit major differences in the crystal morphology and in their intracrystalline porosity and silanol concentrations. The diDABCO-C82+ (1,1'-(octane-1,8-diyl)bis(1,4-diazabicyclo[2.2.2]octan)-1-ium)-templated STA-30 samples (but not those templated by bisquinuclidinium octane, diQuin-C82+) possess hierarchical microporosity, consisting of noncrystallographic extra-large micropores (13 Å) that connect with the characteristic swy and gme cages of the SWY structure. This results in pore volumes up to 30% greater than those measured in activated diQuin-C8_STA-30 as well as higher concentrations of silanols and fewer Brønsted acid sites (BASs). The hierarchical porosity is demonstrated by isopentane adsorption and the FTIR of adsorbed pyridine, which shows that up to 77% of the BASs are accessible (remarkable for a zeolite that has a small-pore crystal structure). A structural model of single can/d6r column vacancies is proposed for the extra-large micropores, which is revealed unambiguously by high-resolution scanning transmission electron microscopy. STA-30 can therefore be prepared as a hierarchically porous zeolite via direct synthesis. The additional noncrystallographic porosity and, subsequently, the amount of SiOHs in the zeolites can be enhanced or strongly reduced by the choice of crystallization conditions.

Lava – substrate interaction: Constraints on flow emplacement and basal sintering, Lebuj rhyolitic flow, Tokaj Mountains, Carpathian-Pannonian region

The surface extrusion of rhyolite lava is linked with a complex edifice morphology and texturally diverse internal structure. The rarely exposed basal flow/dome zones provide a textural record of the mechanical and thermal stress between the overlying lava and existing topography. The Lebuj flow (Tokaj Mountains, Hungary) developed in a Miocene caldera setting, where the erosion exposed its basal zone, including various textures due to the lava substrate interaction. The flow margin is contacted with underlying volcaniclastics along a steeply inclined (50–75°) plane. The lithology describes a complex ductile-brittle transition in the flow and lithification process in the substrate. The relict obsidian grains (marekanite, 0.1% H2O) in the perlite (2–3% H2O) are proof of an incomplete hydration process below the glass transition temperature. The dynamic loading of the lava caused irregular fragmentation developing a brittle basal shear zone with lens-like glass deformation. The substrate has suffered syn-emplacement lithification and the primary glass structure is completely re-crystallized. FTIR and Raman measurements identified low-temperature phyllosilicate minerals and SiO2 polymorphs, which caused additional porosity loss and densification. Using cooling time-temperature-porosity information given by this reconstruction, we suggest parallel-acting processes at elevated (groundmass crystallization-devitrification) and lower temperature (hydration-secondary mineralization) range. These define a relative timescale for the textural development in the lithologically heterogeneous contact zone.

A Large-Area Patterned Hydrogen-Bonded Organic Framework Electrochromic Film and Device.

Fabrication of a patterned hydrogen-bonded organic framework (HOF) films on a large scale is an extreme challenge. In this work, a large area HOF film (30 × 30 cm2 ) is prepared via an efficient and low-cost electrostatic spray deposition (ESD) approach on the un-modified conductive substrates directly. Combining the ESD with a template method, variously patterned HOF films can be easily produced, including deer- and horse-shaped films. The obtained films exhibit excellent electrochromic performance with multicolor change from yellow to green and violet, and two-band regulation at 550 and 830nm. Benefiting from the inherently present channels of HOF materials and the additional film porosity created by ESD, the PFC-1 film could quickly change color (within 10 s). Furthermore, the large-area patterned EC device is constructed based on the above film to prove practical potential application. The presented ESD method can be extended to other HOF materials; thus, this work paves a feasible path for constructing large-area patterned HOF films for practical optoelectronic applications.

Synthesis and Characterization of Hierarchical Zeolites Modified with Polysaccharides and Its Potential Role as a Platform for Drug Delivery.

Hierarchical zeolites are aluminosilicates with a crystal structure, which next to the micropores possess secondary porosity in the range of mesopores and/or small macropores. Due to their ordered structure and additional secondary porosity, they have aroused great interest among scientists in recent years. Therefore, the present work concerns the synthesis and characterization of hierarchical zeolites with secondary mesoporosity, based on commercial zeolites such as MFI (ZSM-5), BEA (β) and FAU (Y), and modified with polysaccharides such as inulin, hyaluronic acid, and heparin. All materials were characterized by various analytical techniques and applied as a platform for delivery of selected drug molecules. On the basis of X-ray diffraction (presence of reflections in the 2θ angle range of 1.5-2.5°) and low-temperature nitrogen sorption isotherms (mixture of isotherms of I and IV type) additional secondary porosity was found in the mesopore range. Additional tests were also conducted to determine the possibility of loading selected molecules with biological activity into the aforementioned materials and then releasing them in the therapeutic process. Molecules with different therapeutic options were selected for testing, namely ibuprofen, curcumin, and ferulic acid with anti-inflammatory, potentially anticancer, antioxidant, and skin discoloration activities, respectively. Preliminary studies have confirmed the possibility of using hierarchical zeolites as potential carriers for bioactive molecules, as the loading percentage of active substances ranged from 39-79% and cumulative release for ibuprofen reached almost 100% after 8 h of testing.

Manufacturing of scaffolds with interconnected internal open porosity and surface roughness.

Manufacturing of three-dimensional scaffolds with multiple levels of porosity are an advantage in tissue regeneration approaches to influence cell behavior. Three-dimensional scaffolds with surface roughness and intra-filament open porosity were successfully fabricated by additive manufacturing combined with chemical foaming and porogen leaching without the need of toxic solvents. The decomposition of sodium citrate, a chemical blowing agent, generated pores within the scaffold filaments, which were interconnected and opened to the external environment by leaching of a water-soluble sacrificial phase, as confirmed by micro-CT and buoyancy measurements. The additional porosity did not result in lower elastic modulus, but in higher strain at maximum load, i.e. scaffold ductility. Human mesenchymal stromal cells cultured for 24 h adhered in greater numbers on these scaffolds when compared to plain additive-manufactured ones, irrespectively of the scaffold pre-treatment method. Additionally, they showed a more spread and random morphology, which is known to influence cell fate. Cells cultured for a longer period exhibited enhanced metabolic activity while secreting higher osteogenic markers after 7 days in culture. STATEMENT OF SIGNIFICANCE: Inspired by the function of hierarchical cellular structures in natural materials, this work elucidates the development of scaffolds with multiscale porosity by combining in-situ foaming and additive manufacturing, and successive porogen leaching. The resulting scaffolds displayed enhanced mechanical toughness and multiscale pore network interconnectivity, combined with early differentiation of adult mesenchymal stromal cells into the osteogenic lineage.

Synthesis of Hierarchical Micro-mesoporous ZSM-5 Zeolite and its Catalytic Activity in Benzylation of Mesitylene

Hierarchical micro-mesoporous ZSM-5 (MFI type) zeolite was synthesized by using corn plant stem pith powder from agricultural waste as hard template under simple hydrothermal method. The additional porosity generated using this pith powder into the zeolites precursor gel yielded hierarchical micro-mesoporous ZSM-5 zeolite (C-ZSM-5). Conventional micro porous ZSM-5 (ConvZSM-5) was also prepared by same procedure without adding the corn stem pith powder to compare the catalytic performances. The prepared C-ZSM-5 zeolite exhibited 89% conversion, much greater than ConvZSM-5 (33%). Selectivity in the formation of 2-Benzyl-1, 3, 5-trimethylbenzene, by benzylation with C-ZSM-5 (70%) is more than two times than ConvZSM-5 (32%). This benzylation can be used as a test reaction to evidence the formation of hierarchical micro-mesoporous nature of the material. C-ZSM-5 exhibited better selectivity and benzyl alcohol conversion due to the presence of hierarchical pores and strong acidy in C-ZSM-5.The product formed in the above reaction was separated and further confirmed by 1HNMR and 13CNMR. Even after consecutive recycles every month for three months, the conversion and desired products selectivity had not been affected. The hierarchical pores present in the catalyst further improved the stability of the zeolites. Hence this catalyst could be very useful for industrially important reactions.

Challenges in material recycling for postwar reconstruction

Besides the fact that concrete recycling allows to avoid landfills disposal and contributes to a closed-cycle economy, such option may be very much in demand in war struck regions such as Ukraine, which after the end of the war, are faced with the problem of rebuilding and reconstructing. Beyond this emergency, even in peacetime extensive parts of the building stock will sooner or later need to be replaced and concrete recycling is called to play an increasing role there. However, depending on the technology and degree to which aggregates are recycled, concrete may be characterized by poor workability, reduced mechanical properties, increased shrinkage and reduced durability. This deterioration in the properties of recycled concrete is usually attributed to the characteristics of the old cement mortar remaining on the surface of the recycled aggregates, which is best considered as an additional volume of hardened cement paste with fine aggregate and additional porosity. This article attempts to underline how such key concepts help frame the current state of knowledge about concrete recycling, understand the implications of existing regulations, in order to define pragmatic and efficient routes for broadening the use of concrete recycling in war struck regions, with specific examples regarding Ukraine.

Microwave Pyrolysis of Biomass: The Influence of Surface Area and Structure of a Layer

The paper presents the results of experimental research into lab-scale microwave pyrolysis of wood biomass. The influence of the surface area and the structure of the biomass layer on the characteristics of pyrolysis during microwave heating are discussed. We have established that the biomass layer structure and surface area have a significant effect on the yield of pyrolysis gas. The approach of creating artificial deformation of the biomass layer was tested. The elements of artificial porosity made it possible to increase the CO yield by 18% and 32% compared to the pyrolysis of a biomass layer with artificial channels and a uniform layer, respectively. The concentration of H2 was 33% higher compared to the layer without artificial pores and 3% lower compared to artificial channels. The yield of CO2 increased by 25%, and the yield of CH4 doubled. The experiments showed that the distribution of biomass on a half of the bottom of the crucible and the additional porosity of the biomass layer surface effectively increase the yield of the pyrolysis gas components. Recommendations for increasing the efficiency of microwave pyrolysis of biomass were formulated.

MgO-containing porous carbon spheres derived from magnesium lignosulfonate as sustainable basic catalysts

The presence of alkalis in lignosulfonate allows an easy preparation of sustainable MgO-containing carbon catalysts with surface basicity by carbonization of magnesium lignosulfonate and/or further partial gasification of the produced char with CO2. Carbon spheres with different chemical and physical properties were obtained from lignosulfonate treated at temperatures ranging from 500 to 900 ºC. Carbonization at 900 °C generates hollow porous carbon spheres (pore volume of 0.20 cm3/g and apparent surface area of 465 m2/g) with magnesium content of 12%. A kinetic study of CO2 gasification of the carbon spheres obtained at 900 °C at temperatures in the range of 700 – 800 °C revealed that the gasification rate can be accurately described by the random pore model up to conversion values of 0.5. Based on this study, in order to develop additional porosity on the carbon spheres obtained at 900 °C, a partial gasification with CO2 at 750 °C for 30 min was carried out, reaching surface areas higher than 700 m2/g and 15.3% of Mg loading, with an overall preparation yield of 30%. All the obtained carbon materials were tested as catalyst for 2-propanol decomposition, showing a high selectivity to acetone, evidencing the basic character of these carbon catalysts. The highest activity and selectivity were shown by the CO2-activated carbon spheres (conversion and acetone selectivity higher than 90% at 420 °C), indicating that magnesium lignosulfonate is an attractive raw material for the preparation of sustainable carbon catalysts for biorefinery applications.

Hierarchical chabazites synthesized by combining primary and secondary structure-directing agents

Modifying the physical and chemical properties of zeolites by altering the synthesis parameters or using post-synthesis treatments may offer additional properties other than those that make them widely used materials. Remarkably, the chabazite SSZ-13 zeolite possesses a small pore opening that provides access to a large cavity, making the structure suitable for converting methanol to products. Herein, we altered the porosity of SSZ-13 by adding various amounts (2, 4, and 8% in relation to the molar silica content) of dimethyloctadecyl[3-(trimethoxysilyl)propyl] ammonium (DMOAP) into the reaction mixture. The introduction of DMOAP enabled the formation of the pure chabazite structure without affecting the incorporation of aluminum atoms into the zeolite framework. At the same time, its incorporation led to changes in porosity, increasing the external surface area and creating mesopores without affecting the formation of micropores. Concerning the catalytic conversion of methanol into products at low temperatures (210 °C), the additional porosity decreased the methanol to dimethyl ether conversion, indicating that the confinement effect plays an essential role in stabilizing the reaction intermediates. However, at higher temperatures (400 °C), the mesopores played an essential role in the methanol to olefins reaction by increasing the catalyst lifetime and the conversion over time due to improved accessibility of methanol to reaction intermediates confined in the micropores.