•Vertical line-based approach to calculate angular, radial and regional porosities.•Methodology validated against analytical and published results.•Determine angular variation in porosity for ...cylindrical planes and wedges.•Determine radial variation in porosity for radial planes and wedges.•3D variation in porosity of angularly, radially and axially defined regions.
This paper proposes a vertical line-based methodology for the calculation of the porosity of packed beds of spheres. The results for the overall porosity, angular variation in porosity and tangentially averaged radial variation in porosity obtained through the use of this methodology are compared with the results of pre-existing methodologies and found to be in very good agreement, validating the vertical line-based methodology. Building upon this; the angular wedge porosities and angular plane porosities; the radial variation in porosity at different angular planes and the tangentially averaged porosities; and the regional porosities and grid porosities were evaluated for seven packed beds with different sized diameter aspect ratios. From the evaluation of the porosity results for specific points throughout these packed beds, it was found that the vertical line-based methodology has the capability to provide a detailed analysis of the porosity of a packed bed. It is shown that dividing a packed bed into sections, based on axial height, radial range and angular range, can be employed in the calculation of the 3D variation in porosity throughout a packed bed.
•Evaluation of the porosity of the HTTU annular packed bed.•Angular and radial variation in porosity for bottom near-wall region characterized.•Standard deviation and skewness of angular at each ...radial position calculated.•Variation of tangentially averaged porosity in axi-symmetric r-z plane shown.•Average porosity and standard deviation for 20 selected regions presented.
In this paper a comprehensive analysis of the porosity of the annular packed bed of the High Temperature Test Unit (HTTU) is presented. The annular packed bed is generated using a Discrete Element Method (DEM) approach. Semi-analytical methods are then used to analyse the porosity. The quality and representativity of the packed bed are established by evaluating the overlaps between spheres and spheres and walls and comparing the axial and radial variations in porosity with available experimental and numerical data. The angular and radial variation of selected sphere layers in the bottom near-wall region was studied revealing how the spheres in the axial layers and radial rings are staggered with respect to each other. The analysis of the radial variation in porosity also included the standard deviation and the skewness of the angular porosity at each radial position. An analysis of the radial porosity of the layers revealed that only first layer next to the bottom is markedly affected by the bottom wall. The interference between the oscillatory porosity variations perpendicular to the inner, outer, and bottom walls of the annular packed bed is demonstrated by the plot of the variation in porosity on an axi-symmetric r-z plane. The annular packed bed is also divided into 20 regions and the average porosity and the standard deviation of the porosity for each region in provided.
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Metal 3D printing (3DP), a state-of-the-art manufacturing technology that brings the potential to fabricate complex structures at low cost and reduced energy consumption, has been ...extensively adopted in various industries. However, the porosity defects inherited from the printing process can significantly impede the mechanical properties and weaken the performance of as-printed components, potentially challenging this approach's reliability and reproducibility. The advancement of detection techniques currently opens up a more intuitive and deeper study of porosity defects. Given that, this review systematically states the 'restriction role' of porosity defects in metal 3DP by generalizing the detailed information on porosity defects, including their characterizations, formation and migration mechanisms, and their impacts on the performance of printed parts. Furthermore, feasible porosity mitigation measures are discussed to inspire more advanced methodologies for the next generation of metal 3DP.
A series of ionic covalent triazine frameworks (CTFs) bearing charged groups were designed and prepared through ZnCl.sub.2-catalyzed cyclotrimerization of 1,3-bis(4-cyanophenyl)imidazolium chloride ...and tricyanobenzene as an auxiliary monomer. Pore properties of the ionic CTFs could be controlled by varying the proportion of monomer. The resulting ionic CTFs had high BET specific surface areas up to 1105 m.sup.2/g, high pore volumes up to 0.65 cm.sup.3/g, and high physicochemical stability. Among the four ionic CTFs, tCTF-Cl-3 exhibited the highest CO.sub.2 adsorption of 72.7 cm.sup.3/g and highest I.sub.2 capture capacity of 370 wt%. The incorporation of ionic functional groups, the existence of homogenous charge distribution, and the permanent porosity improved the capturing ability and affinity of the ionic CTFs for CO.sub.2 and I.sub.2. This methodology, based on the fine tuning of monomer ratio, can be utilized to obtain new insights into the preparation of functional ionic porous materials.
Catalytic hydrogenation reduction based on sodium borohydride (NaBH
) has gained attention as an appealing "one-stone-two-birds" approach for the simultaneous elimination of nitroaromatic pollutants ...and the production of high-value aminoaromatics under mild conditions. However, the slow kinetics of NaBH
dissociation on the surface of catalysts restrict the catalytic hydrogenation reduction efficiency. Herein, we report an intelligent localized sulfidation strategy for an in situ implantation of Bi
S
nanorods within quasi-Bi-MOF architectures (Bi
S
@quasi-Bi-MOF) by fine-tuning the pyrolysis temperature. In this novel Bi
S
@quasi-Bi-MOF, the porous quasi-Bi-MOF enables efficient adsorption of BH
and 4-nitrophenol (4-NP), while Bi
S
facilitates the BH
dissociation to form H
* species adsorbed on the catalyst surface. Benefiting from the synergistic structure, Bi
S
@quasi-Bi-MOF exhibits excellent performance for the catalytic reduction of 4-NP, delivering a high turnover frequency (TOF) of 1.67 × 10
mmol mg
min
and an extremely high normalized rate constant (
) of 435298 s
g
. The kinetic analysis and electrochemical tests indicate that this catalytic hydrogenation reduction follows the Langmuir-Hinshelwood mechanism. This study enriches the synthetic strategy of MOF-based derivatives and offers a new catalytic platform for hydrogenation reduction reactions.
To further investigate the porosity evolution during selective laser melting (SLM) Inconel 718 alloy, a transient mesoscale model with a randomly packed powder-bed has been proposed by finite volume ...method (FVM), taking consideration of the phase transition, variation of thermo-physical properties and interfacial force. The thermodynamics within molten pool and resulting porosity evolution behavior of a set of laser scanned tracks with various laser scanning speeds were studied using numerical approach. The results evidently revealed that the operating peak temperature was reduced obviously as increasing the scanning speeds. Accordingly, the high cooling rate, short lifespan and limiting depth of pool and small velocity of molten liquid flow were obtained under a high scanning speed. Scanning speed played a crucial role in determining the type of porosity in the terminally SLM-processed Inconel 718 components. At a high scanning speed of 500mm/s, the top surface was primarily dominated by open porosity, accompanying with large-sized inter-layer porosity on the cross section, due to a limiting energy input penetrated into the powder-bed and incomplete melting of powder. By contrast, as a relatively low scanning speed of 200mm/s was employed, the top surface appeared to be smooth free of less metallurgical porosity and no apparent inter-layer porosity on the cross section surface attributing to the escaping of porosity, indicating an well metallurgical bonding of the neighboring layer towards the building direction. Simultaneously, the physical mechanism was thoroughly discussed. The simulated distribution of porosity was found to be consistent with the experimental measurements.
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•A randomly packed powder-bed model was established to investigate the porosity evolution during selective laser melting of Inconel 718 alloy.•The thermodynamic behavior within molten pool was studied.•The porosity distribution on top surface and cross-section was simulated and experimentally validated.•The thermodynamic mechanism of porosity evolution under variable scanning speed was concluded.
Novel NaAGeO4 (A = Sm, Y) ceramics with olivine structures were prepared and characterized. The phase composition, microstructural evolution, and densification behavior of the ceramics were ...investigated. The NaAGeO4 (A = Sm, Y) ceramics possessed a single orthorhombic crystal system with Pbn21 and Pnma space groups. The NaSmGeO4 ceramics had dense grains, clear boundaries, and low sintering temperatures, whereas a relatively wide range of sintering temperatures were feasible for the NaYGeO4 ceramics. The NaSmGeO4 ceramic material sintered at 1025 °C possessed excellent performance-related parameters, i.e., Q × f = 31,281 GHz, εr = 6.29, and τƒ = −48.3 ppm/°C, whereas those for the NaYGeO4 ceramic material were Q × f = 32,646 GHz, εr = 6.74, and τƒ = −39 ppm/°C at 1200 °C. Furthermore, doping the NaYGeO4 ceramic material with CaTiO3 to obtain 0.12CaTiO3-0.88NaYGeO4 yielded a τƒ value close to zero (−3 ppm/°C). The results demonstrate that NaAGeO4 (A = Sm, Y) ceramics have substantial potential for application in microwave devices.
Sandy soils can benefit greatly from the addition of biochar, but the benefits depend on the properties of both the soil and the biochar. This study investigated the role of biochar particle size in ...controlling pore size distribution, hydraulic conductivity and water retention after careful mixing with coarse sandy subsoil. Intact commercial pellets of straw biochar (SB; approx. 8 × 5 mm) and ground pellets separated into 6 size fractions (median diameter 15, 33, 44, 81, 135 and 205 μm) were investigated at two concentrations (1.50 and 3.00 wt%). The results were compared with effects obtained with another feedstock (wood; WB) and another soil. Light microscopy and water retention measurements showed that smaller biochar particles settled into large existing soil pores, creating smaller interstitial pores to a much greater extent than larger particles. Accordingly, small particles (≤44 μm) had large enhancing effects on water retention and hydraulic conductivity in the medium suction range (pF1.7‐pF3.0), which were not found to a similar extent after the addition of larger particles (>81 μm). It was not possible to systematically distinguish the effects obtained with the three smallest particle fractions (SB15, WB18 and SB33). All effects measured were greatest at the highest biochar concentration level. In one soil, amendment with 3.00 wt% of SB15 decreased the fractional volume of drainable pores with an equivalent diameter of ≥60 μm from 31.3 vol% in the control to 19.1 vol%, while increasing the volume of pores in the 0.2–60 μm range that could potentially retain plant‐available water from 8.7 vol% to 20.1 vol%. Hydraulic conductivity at pF1.7 was increased by a factor of 10 (from 2.3 to 22.5 cm/day) and at pF3.0 by a factor of 14 (from 0.1*10−3 to 1.4*10−3 cm/day). Similar effects were observed in the other soil but at slightly different levels. The PDI version of the bimodal van Genuchten model was successfully fitted to measured water retention and log‐transformed hydraulic conductivity data (RMSE values in the interval 0.0011–0.0029 and 0.024–0.215, respectively). Dynamic simulation under variable field conditions including the hydraulic properties of biochar‐amended soil layers could be a useful method to investigate the effects on crop water supply, water and fertilizer utilization and yields.
In this work, the preparation of titanium sponge by magnesium thermal method is regarded as the liquid-phase sintering process of titanium, and powder-metallurgy sintering technology is utilized to ...simulate the aggregation–growth and densification behavior of titanium particles in a high-temperature liquid medium (the molten Mg-MgClsub.2 system). It was found that compared with MgClsub.2, Mg has better high-temperature wettability and reduction effect, which promotes titanium particles to form a sponge titanium skeleton at lower temperature. The aggregation degree of titanium particles and the densification degree of a sponge titanium skeleton can be improved by increasing the temperature and the relative content of Mg in the melting medium. The kinetics study shows that with the increase in temperature, the porosity of the titanium particle aggregates and the sponge titanium skeleton decreases, and their density growth rate increases. With the extension of time, the aggregation degree of titanium particles and the densification degree of sponge titanium gradually increase. This work provides a theoretical reference for controlling the density of titanium sponge in industry.
