High Packing Density Research Articles

Thicker or Shorter Bark Fragments of Eucalypt Tree Species Make More Densely Packed Fuel Beds, Which Slow Down Fire Spread

Many eucalypt trees shed their bark annually. This bark becomes a component of the litter layer, which acts as fuel, especially during surface fires. The amount and quality of shed bark vary greatly among species, which might have important effects on forest surface fire behavior. In this study, we aimed to compare the bark fuel bed flammability of eight eucalypt tree species and tried to link their bark litter traits via the surface fuel bed structure to bark flammability. In controlled laboratory burns, three flammability parameters, the fire spread rate, total burning time, and maximum temperature, were measured. The bark litter traits included length, curliness, thickness, dry matter content, tissue density, carbon content, nitrogen content, and terpene content, while the litter bed packing ratio and packing density were also measured. We found significant differences in bark traits and flammability among species. Thicker bark fragments of the eucalypt tree species had higher packing densities in fuel beds, a slower fire spread, and a longer burning time. This relationship was strongly driven by the thick bark fragments of Eucalyptus punctata DC. Still, also within the other seven species, bark thickness was the strongest predictor of bark fuel bed flammability, with some additional explanatory power for bark length. For the first time, our study demonstrates that bark traits, particularly litter fragment thickness and length, drive bark litter flammability of eucalypt tree species through their effects on bark fuel bed structure. These findings contribute to our understanding and predictive power of wildfire behavior in forest stands dominated by different eucalypt species.

Hydrangea-like MnO2@sulfur-doped porous carbon spheres with high packing density for high-performance supercapacitor

The high packing density of electrode materials is crucial for the miniaturization and lightweighting of energy storage devices. Nevertheless, a structural contradiction among high packing densities, sufficient ion, and electron transport channels is a challenge. In this research, a unique hydrangea-like compose (MnO2@S-PCS-5) is synthetized by a convenient and environmentally friendly method. The composite comprises a spherical carbon material matrix and MnO2 nanosheets, resulting in a high packing density of 1.79 g cm−3. Furthermore, the hydrangea-like structure exhibits a high number of active sites, facilitating ion transport and exhibiting excellent specific capacitance (Cv: 328.7 F cm−3). The asymmetric supercapacitors (MnO2@S-PCS-5//YP-50) exhibit a maximum energy density of 38.4 Wh kg−1 at a power density of 500 W kg−1, with a wide voltage window of 2.0 V. The results demonstrate densification is important for miniaturization of energy storage devices.

Technology of production of aluminosilicate refractories for units processing fluorinated waste

The aluminium production process through the electrolysis of cryolite-alumina melts involves a series of interconnected, sequential, and parallel technological operations, each defined by a specific level of engineering and technological advancement. The development of the modern aluminum industry is closely tied to the adoption of resource-efficient and environmentally friendly technologies, which focus on recycling secondary materials and industrial waste. Fluorinated carbon-based materials release fluorine into the gas phase at relatively low temperatures when heated, and in thermal units processing fluorinated waste, this fluorine, along with alkali metals, will remain in the gas phase. To enhance the durability of furnace linings against the corrosive atmosphere, refractories with the highest possible density (low porosity) and a high concentration of mullite in the matrix (the finely ground component of the batch) are required. These properties can only be achieved in refractory products produced by the semi-dry pressing method, which ensures high grain packing density and leads to the formation of a ceramic mullite bond after firing.

Optical and stress properties of ZrO2/SiO2 and TiO2/SiO2 anti-reflective coatings deposited by ion-beam-assisted deposition on a flexible substrate

Dielectric films of ZrO2,TiO2, and SiO2 were deposited on flexible polycarbonate (PC) and polyethylene terephthalate (PET) substrates by using ion-beam-assisted deposition (IBAD). Each layer had a thickness ranging from 30 to 210 nm. The optical and anisotropic stress properties were investigated. Two anti-reflective coatings (ARCs), ZrO2/SiO2 and TiO2/SiO2, were selected and deposited on the PET flexible substrate. The anisotropic stresses of the single layer and ARCs were measured using a phase-shifting moiré interferometer. Experimental results showed that the optimal oxygen flow rates for the ZrO2,TiO2, and SiO2 films deposited with IBAD were 10, 10, and 15 sccm, respectively. The refractive index (n) was TiO2(2.37)>ZrO2(2.05)>SiO2(1.46), and the extinction coefficient (k) for all samples was below 10−3. The thermal expansion coefficient of the PC substrate was three times that of the PET substrate, and the high-refraction ZrO2 and TiO2 single-layer films presented cracks and distortions on the PC substrate. Only the low-refractive-index SiO2 sample did not present cracks. The three dielectric films did not crack or distort when deposited on the PET substrate. The anisotropic stress analysis provided the maximum principal and shear stresses for the three dielectric films on the PET substrate. Therefore, the maximum principal stress of the 210 nm single-layer film on a PET substrate is TiO2>ZrO2>SiO2. It was also discovered that the principal stress of the AR multilayer film is significantly decreased due to the damping stacking effect (DSE) of the high- and low-refractive-index materials, ZrO2/SiO2 ARC (−297.3MPa)>TiO2/SiO2ARC(−132.6MPa). Thus, the high packing density of TiO2 gives a better DSE than ZrO2.

Design of a Novel SiP Integrated RF Front-End Module Based on SOI Switch and SAW Filter.

This paper proposes a novel System-in-Package (SiP) integrated architecture that incorporates Silicon-On-Insulator (SOI) switches and Surface Acoustic Wave (SAW) filters within the chip, aiming to fulfill the demands for miniaturization and multi-functionality for application in emerging wireless technologies. The proposed architecture not only reduces the integration complexity but also considers the architectural design of the integrated module, impedance matching techniques, and signal integrity for carrier aggregation (CA) technology realization. The feasibility of employing SOI switches and SAW filters based on SiP design has been validated through the trial production of a Sub-3GHz radio frequency (RF) front-end diversity receiver module. The resulting RF front-end module demonstrates exceptionally high packaging density and enhanced communication reliability, rendering it suitable for diverse applications in miniaturized RF systems.

Enhanced reliability of Cu-Sn bonding through the microstructure evolution of nanotwinned copper

Kirkendall voids are detrimental to the Cu-Sn bonding interface, causing the failure of the high-density package. Herein, the perpendicularly aligned nanotwinned Cu (p-ntCu) and the horizontally aligned nanotwinned Cu (h-ntCu) are prepared by controlling the electrodeposition procedure. The p-ntCu shows advantages both in fast-bonding process and in void suppression through the in-situ microstructure evolution. Compared with h-ntCu, the abundant perpendicularly aligned twin boundaries in p-ntCu provide fast interdiffusion paths to build a bonding interface. In the bonding process, p-ntCu grows to ultra-large-grained Cu with an average grain size of 6.68 μm. The reduced density of normal grain boundaries in p-ntCu lowers the Cu diffusion rate and contributes to more balanced interdiffusion at the bonding interface, which is confirmed by molecular dynamics simulation and kinetic calculations of intermetallic compound (IMC) growth. In addition, the low impurity content in p-ntCu further reduces the diffusion flux imbalance and limits the nucleation of Kirkendall vacancies. Consequently, the p-ntCu/Sn interface keeps void-free during 150 °C long-term thermal aging due to the synergistic effect of reduced grain-boundary diffusion and lower impurity content, which will be beneficial for achieving high-reliability Cu-Sn bonding.

Toward an Enhanced Hydrophilic TiO2 Nanoparticles Adsorption at Air-Liquid Interface Through Ion Regulation.

This study investigates the dynamic properties of air-liquid interfacial tension for hydrophilic TiO2 P25 utilizing the pendant drop method. Additionally, it examines the interfacial adsorption mechanism of hydrophilic TiO2 particles, considering the characteristics of particle surface charge distribution in relation to ion regulation to enhance particle interface adsorption. Experimental results reveal that in the absence of ion addition, the TiO2 P25 suspension system exhibits limited interfacial adsorption due to its superhydrophilicity, regardless of particle concentration. The addition of NaCl increases the surface charge density of the particles, strengthens the electrostatic attraction between particles and the interface, and enhances particle adsorption. Specifically, at a low NaCl concentration (0.01 wt %), the increased surface charge density and contact angle of the particles elevate particle activity and high interfacial packing density. At a higher NaCl concentration (0.1 wt %), while NaCl further increases the particle contact angle, the increased effective cross-sectional area of the air-liquid interface occupied by individual particles leads to a reduction in surface free energy. Despite the enhanced electrostatic attraction, this results in a lower packing density.

Complex topological close-packed phase of rapidly cooled chromium

The topological close-packed phases have attracted extensive attention due to their high packing density and excellent properties. However, it is difficult to identify topological close-packed phases by using numerical methods. In this work, the cooling of pure chromium at a rate of 1010 K/s was studied by molecular dynamics simulation, and the structure evolution was analyzed by the largest standard cluster analysis and visualization technique. It was found that the rapid cooling resulted in a complex topological close-packed solid, which contains A15 phase, Z phase, σ phase, and H phase. The atomic connection characteristics in the A15 and Z units are also detailed. And a method for quick and preliminary identification of σ phase and H phase based on Z15-Z15 bonds is proposed. This work enriched the understanding of topological close-packed phases, and demonstrated the advantage of the largest standard cluster analysis in identifying complex phases.

Dramatic droplet deformation through interfacial particles jamming

Droplets of one fluid in a second, immiscible fluid are typically spherical in shape due to the interfacial tension between the two fluids. Shear forces can lead to droplet deformation when they are subjected to flow, and these effects can be further modified when the droplet is stabilized by a surfactant due to a flow-induced gradients in the surfactant concentration. An alternative method of stabilizing droplets is through the use of colloidal particles, whose stabilization behavior is intrinsically different from molecular surfactants. Under the same flow condition, a gradient of particle concentration can result in the jamming of particles in regions with a high packing density, making the interface solid-like, albeit only under compression and not tension. However, how this asymmetry in the surfactant properties alters the droplet shape under shear is unknown. Here, we show that shear of particle-stabilized droplets can lead to a remarkable array of shape deformations as the droplets flow through a constrained microchannel. The shear-induced migration of particles on the surface results in the formation of an elastic shell at the back of the droplet, which can wrinkle and invaginate, ultimately leading to a unique core-shell structure. The shapes depend on the Peclet number of the flow, reflecting the balance of shear forces that drive the particles and diffusion that randomizes them. These findings highlight the consequences of the asymmetry in the forces between the particles and provide a unique method to controllably create droplets with a vast array of different shapes.

Ammonia Storage in Metal-Organic Framework Materials: Recent Developments in Design and Characterization.

Since the advent of the Haber-Bosch process in 1910, the global demand for ammonia (NH3) has surged, driven by its applications in agriculture, pharmaceuticals, and energy. Current methods of NH3 storage, including high-pressure storage and transportation, present significant challenges due to their corrosive and toxic nature. Consequently, research has turned towards metal-organic framework (MOF) materials as potential candidates for NH3 storage due to their potential high adsorption capacities and structural tunability. MOFs are coordination networks composed of metal nodes and organic linkers, offering unprecedented porosity and surface area, and allowing incorporation of various functional groups and metal sites that can enhance NH3 adsorption. However, the stability of MOFs in the presence of NH3 is a significant concern since many degrade upon exposure to NH3, primarily due to ligand displacement and framework collapse. To address this, recent studies have focused on the synthesis and postsynthetic modification of MOFs to enhance both NH3 uptake and stability. In this Account, we summarize recent developments in the design and characterization of MOFs for NH3 storage. The choice of metal centers in MOFs is crucial for stability and performance. High-valence metals such as AlIII and TiIV form strong metal-linker bonds, enhancing the stability of the framework to NH3. The MFM-300 series of materials composed of high-valence 3+ and 4+ metal ions and carboxylic linkers demonstrates high stability and high NH3 uptake capacities. Ligand functionalization is another effective strategy for improving the NH3 adsorption. Polar functional groups such as -NH2, -OH, and -COOH enhance the interaction between the framework and NH3, particularly at low partial pressures, while postsynthetic modification allows fine-tuning of these functionalities to optimize the framework for higher adsorption capacities and stability. For example, MFM-303(Al), incorporating free carboxylic acid groups, exhibits a high NH3 packing density comparable to that of solid NH3. Creating defect sites by removing linkers or adding metal ions increases the number of active sites available for NH3 adsorption and shows promise for enhancing uptake. UiO-66, a stable MOF framework, can be modified to include defect sites, significantly enhancing the level of NH3 uptake. The full characterization of MOFs and especially their interactions with NH3 are vital for understanding and improving their performance. Techniques such as neutron powder diffraction (NPD), inelastic neutron scattering (INS), diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS), electron paramagnetic resonance (EPR) spectroscopy, and solid-state nuclear magnetic resonance (ssNMR) spectroscopy can elucidate host-guest interactions and binding dynamics between NH3 and the framework structure and afford crucial information for the future design and rational development of new sorbents. This Account highlights our current strategies for the synthesis and characterization of MOFs for NH3 capture, providing an overview of this rapidly evolving field.

Optimizing the microstructure, mechanical, and optical properties of recycled zirconia for dental applications

Efficient recycling of dental zirconia residues from computer-aided design/manufacturing processes is crucial for sustainable development in dentistry. This study employed ball milling to modify recycled zirconia powder (RZP). Initial RZP and ball-milled RZP (RZP-BM) were pre-sintered at 1000–1150 °C and then final sintered at 1500 °C. Initial RZP had irregular shapes, while RZP-BM showed finer and more uniform morphology, higher packing density, and improved de-agglomeration after 6 h of ball milling. For pre-sintered zirconia, RZP-BM samples achieved properties comparable with commercial zirconia at 1100 °C, whereas initial RZP required 1150 °C. For final sintered zirconia, initial RZP samples exhibited lower Vickers microhardness, density, strength, and transmittance, with numerous defects in its microstructure. RZP-BM samples showed significant improvement in mechanical and optical properties, comparable with commercial zirconia. This study establishes a viable approach for recycling dental zirconia residues, enhancing its properties for potential reuse as dental materials.

Efficient C3H6/C3H8 separation within a bifunctional ultramicroporous metal-organic framework with high purity and record packing density

Efficient C3H6/C3H8 separation within a bifunctional ultramicroporous metal-organic framework with high purity and record packing density

From single tube to multi-channel configuration: Constructing nanofiltration membranes with superior adhesion strength on the ceramic support by interfacial polymerization

Ceramic membranes with multi-channel configurations exhibit superior mechanical strength, high packing density, and high separation efficiency, making them more suitable for industrial applications than single tube and hollow fiber membranes. However, the preparation of thin-film composite (TFC) membranes on multi-channel ceramic supports remains a challenge because of the poor compatibility between organic and inorganic materials and their special configuration. In this study, nanofiltration membranes with a stabilized structure supported by 19-channel ceramic membranes were successfully prepared with improved adhesion strength and dynamic interfacial polymerization. TFC membranes with different channels exhibited uniform microstructure and stable performance. Specifically, polyethyleneimine, which served as a polymerization reactant, can be tightly wound on the surface of ceramic membranes via hydrogen bonding and van der Waals forces during interfacial polymerization. Owing to the enhanced cross-linked network interactions between the support and separation layers, the adhesion strength was significantly improved. Consequently, the optimized membranes maintained excellent rejection to MgCl2 of ∼94 % after the back-flush test under the pressure of 4 bar. Additionally, the multi-channel TFC membranes exhibited stable performance, with a pure water permeance of ∼14.9 LMH/bar and a molecular weight cut-off of 450 Da. When filtering sunset yellow for 10 h, the prepared membranes exhibited stable permeance and excellent rejection performance.

Optimized Dropping and Rolling and Virtual Surface Method for High Packing Fraction of Dispersed Fuel Particles in Annular Container

Because of their favorable thermal conductivity and commendable fuel performance, dispersed fuel elements have been widely adopted in research reactors. However, the geometric complexity resulting from the high packing density of dispersed fuel poses challenges to current geometric modeling methods. Various implicit and explicit modeling techniques have been implemented in Monte Carlo codes. Implicit methods struggle to achieve the correct packing fraction and, therefore, lack accuracy. In this paper, we introduce the Optimized Dropping and Rolling and Virtual Surface method for precise and efficient geometric modeling of such structures. Simultaneously, we apply this novel method to the packing process of an annular container. Test results across various packing fraction cases demonstrate that our modified Optimized Dropping and Rolling method significantly enhances packing efficiency, surpassing the Distinct Element Method hundreds of times.

Impact of the feed particle size distribution and its packing characteristics on compression comminution

Due to its lower energy consumption than a conventional grinding circuit, there is an increased interest in the mining industry in the High-Pressure Grinding Rolls (HPGR) technology. Despite the benefits, the high quantity of material required to size the HPGR makes it difficult for new mines to consider this technology. The piston press test has been used at The University of British Columbia to predict the behavior of the HPGR. It is possible to predict energy requirements, size reduction, and throughput by utilizing a small amount of material to size the HPGR. The bulk material’s particle size distribution (PSD) plays an important role in how the particle bed will pack. This study investigates the differences in compressing three different sample PSDs obtained from the same copper ore crushed to −12.5 mm. The first PSD corresponds to the natural distribution resulting from the crusher. The second is created artificially to match the Fuller curve PSD, which theoretically should have the highest packing density. The third corresponds to a truncated feed produced by removing the fines (−300μm) from the natural feed. Tests were performed using a piston-and-die press test apparatus to compress the samples at different force levels. Entirely different behaviors are obtained while compressing the same material with different PSDs. Particularly, the Fuller curve PSD achieves a 31%–40% higher grinding rate than the natural feed, while the truncated feed achieves a 9%–30% higher grinding rate than the natural feed. Differences in the specific energy consumption, grinding efficiency, and final compacted densities highlight the critical influence of feed particle size distribution on the energy usage and generation of fine particles, underscoring the importance of optimizing these parameters for energy-efficient mineral processing. The overall findings indicate that an HPGR feed particle size distribution that matches the Fuller curve and, therefore, has a maximum packing density, results in the most energy-efficient comminution.

Influence of flexible multibeam intensity distributions on selective laser-induced etching process regimes.

The precision and versatility of selective laser-induced etching in fused silica render it indispensable for many applications in medical engineering, the semiconductor industry, and quantum technology. However, its process-limited productivity renders it unsuitable for a wider set of applications, particularly those that require cost-effective solutions. As the process is largely concerned with microprocessing applications, a promising method to enhance process efficiency is through parallelization using multiple beams with high packing density. This study examines the dynamics of flexible multibeam intensity distributions relative to the number of beamlets and spacing. The study identifies stable process regimes, examines the increased absorption from interactions among parallel modified tracks, and develops a strategy for optimized processing using flexible multibeams. The final demonstration illustrates the generation of multibeam fabricated through glass vias with varying degrees of complexity.

Polypropylene membrane with gradient-distributed covalent organic framework for highly efficient blood oxygenation

Hollow fiber membrane (HFM) is widely used for extracorporeal membrane oxygenator (ECMO) because of large membrane area, high packing density, self-supporting structure and good flexibility. However, polymeric HFMs often suffer from a trade-off between gas permeability and anti-plasma leakage performance. In this study, HFMs with gradient structure were prepared by introducing COF-42 as fillers into the polypropylene (PP) matrix through surface segregation. The enriched COF-42 near the upper surface endowed the membrane a gradient structure to reduce the plasma leakage and improve gas permeability. Compared with PP membranes, PP/COF-42 oxygenation membranes retained good blood compatibility and higher mechanical properties. The PP/COF-42–0.5 HFMs exhibited O2 exchange rate of ∼ 342.6 ml min−1 m−2 and CO2 exchange rate of ∼ 989.6 ml min−1 m−2, which was about 218.7 % and 15.4 % larger than that of the PP HFMs, respectively. Moreover, the simulated plasma leakage time could reach 124 h, which was about 21 times longer than that of PP HFMs. The membranes exhibited excellent blood oxygenation performance and anti-plasma leakage performance, which had great potential in ECMO.

Coherent random fiber laser emission from CdSe/ZnS quantum dots.

We experimentally demonstrate the coherent random laser emission by combining CdSe/ZnS colloidal quantum dots (CQDs) with hollow optical fiber. Through the localized surface plasmon resonance (LSPR) induced by Ag nanoparticles (NPs), well-distinguished discrete spikes are observed from the Ag modified hollow fiber loaded with CdSe/ZnS QDs solution. In addition, coherent random laser action with low threshold is also realized in the hollow optical fiber filled with high packing-density CdSe/ZnS QDs even if the Ag NPs is not introduced. The self-assembled clusters of CdSe/ZnS QDs serve as the optical gain media as well as the strong scattering centers. The angle measurement experiments show that the directional emission of random laser can be adjusted by using different pumping manners. This facile, inexpensive, low pump threshold random laser could be widely used in photonic devices and display imaging.&#xD.

Recent Applications and Future Trends of Nanostructured Thin Films-Based Gas Sensors Produced by Magnetron Sputtering

The field of gas sensors has been developing for the last year due to the necessity of characterizing compounds and, in particular, volatile organic compounds whose detection can be of special interest in a vast range of applications that extend from clinical evaluation to environmental monitoring. Among all the potential techniques to develop sensors, magnetron sputtering has emerged as one of the most suitable methodologies for the production of large-scale uniform coatings, with high packing density and strong adhesion to the substrate at relatively low substrate temperatures. Furthermore, it presents elevated deposition rates, allows the growth of thin films with high purity, permits a precise control of film thickness, enables the simple manufacturing of sensors with low power consumption and, consequently, low costs involved in the production. This work reviewed all the current applications of gas sensors developed through magnetron sputtering in the field of VOCs assessment by gathering the most relevant scientific works published. A total of 10 compounds were considered for this work. Additionally, 13 other compounds were identified as promising targets and classified as future trends in this field. Overall, this work summarizes the state-of-the-art in the field of gas sensors developed by magnetron sputtering technology, allowing the scientific community to take a step forward in this field and explore new research areas.

Microporous tungsten oxide spheres coupled with Ti3C2Txnanosheets for high-volumetric capacitance supercapacitors.

In the contemporary landscape of technological advancements, the burgeoning demand for portable electronics and flexible wearable devices has necessitated the development of energy storage systems with superior volumetric performance. Tungsten oxide (WO3), known for its high density and theoretical capacitance, is a promising electrode material for supercapacitors. However, low conductivity and poor cycling stability are still the key bottlenecks for its application. Herein, a novel composite comprising hollow porous WO3 spheres (HPWS) derived by template method was electrostatic self-assembled on the surface of the Ti3C2Tx nanosheets. The resulting electrodes exhibited ultra-high volumetric capacitance of 1930 F cm-3 at 1 A g-1 and rate capability of 46% at 50 A g-1, attributed to enhanced ion accessibility from microporous structure and electron transport from conductive network of Ti3C2Tx even at a high packing density of 3.86 g cm-3. Utilizing HPWS/Ti3C2Tx as the negative electrode and porous carbon as the positive electrode, the assembled asymmetric supercapacitor achieved an energy density of 31 Wh kg-1 at a power density of 650 W kg-1 with over 107% capacitance retention after 5000 cycles. This work provides a promising approach for developing next-generation supercapacitors with ultra-high volumetric capacitance.