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•NAOS forms a thin layer (2.36 nm) of SiO2 with high density (3.855 g/cm3).•NAOS-SiO2 (0.0581 A/cm2) is more effective in reducing leakage current density.•The phtotcurrent density of ...NAOS-SiO2/Si photoelectrode increased to −16.26 mA/cm2.•The photocurrent density improvement due to NAOS is equally reproducible.
This study presents the fabrication and comparative evaluation of SiO2/Si photoelectrodes employing two distinct SiO2 oxidation methods. Each SiO2/Si photoelectrodes was successfully generated based on uniform SiO2 layers a top nanoporous Si that have thicknesses of 2.7 nm via hydrogen peroxide oxidation (H2O2 oxidation) and 1.8 nm via nitric acid oxidation of Si (NAOS). Notably, the thin NAOS-formed SiO2 layer resulted in a measured suboxide density approximately 4.8 times lower (0.5192 × 1014 atoms/cm2) than that of the H2O2 oxidation (2.4969 × 1014 atoms/cm2). The presence of this SiO2 layer not only passivates defects but also improves electrical properties. As a result, the photocurrent density of the NAOS-formed SiO2/Si photoelectrode notably outperformed that of the H2O2-formed counterpart (about 1.7 times). This enhancement is attributed to the consistent passivation effects and improved electrical properties achieved due to NAOS-formed SiO2. This study contributes to a deeper understanding of how the SiO2 passivation layer can be utilized to improved photocurrent density.
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•Excess adsorption underestimates actual adsorption of shale gas in reservoirs.•Absolute adsorption is higher than excess adsorption, especially at higher pressures.•SLD theory is a ...more efficient method in determining absolute adsorption.
Absolute adsorption has been found being more accurate than directly measured excess adsorption value for estimating the in-situ shale gas-in-place storage. To obtain accurate absolute adsorption, traditional methods determined the adsorbed gas density using complicated molecular simulation methods, which is employed to correct the measured excess value. In this work, excess adsorption, which is deemed to be inaccurate in previous work, of CH4 and C3H8 is first measured on three typical shale rocks. The adsorbed-layer density is then reasonably calculated using the simplified local density theory (SLD) to obtain corresponding absolute adsorption of CH4 and C3H8. It is found that the adsorbed layer density calculated from SLD theory is comparable to that obtained from molecular simulation methods, while it is more efficient for the density computation. Compared to CH4, C3H8 presents stronger adsorption capacity on shale rocks, suggesting that C3H8 is more affinity to organic shale. The CH4′s absolute adsorption is stronger than its excess value and their deviation enlarges as pressure increases, while absolute adsorption for C3H8 is found to be more or less the same with the measured excess value. The importance of this work lies in that we propose a new method for efficiently obtaining the adsorbed-layer density, which is crucial for accurately determining gas and oil storage in shale reservoirs.
•First experimental validation is presented for a new microwave density diagnostic.•The diagnostic, intensity refractometry, is applicable to tokamak edge and beyond.•The first diagnostic ...implementation called MILS is operated at ASDEX upgrade.•Good agreement with other diagnostics is shown in front of the limiter.•In the example shots, the density coverage is from 2 × 1017 m−3 to 2 × 1019 m−3.
Experimental validation is presented for a new type of microwave diagnostic, first introduced in the theoretical study in M. Usoltceva et al., Rev. Sci. Instrum. 93, 013,502 (2022). A new term is adopted for this technique to highlight its difference from interferometry: intensity refractometry. The diagnostic allows measuring electron density, and in this work, it is applied at the edge of a tokamak. The implementation of this technique at ASDEX Upgrade, called Microwave Intensity refractometer in the Limiter Shadow (MILS), provides the first experimental proof of the diagnostic concept. Densities predicted by MILS are compared to several other diagnostics. The agreement and discrepancy in various radial regions of the density profile are analyzed and possible reasons are discussed. A wide density coverage is shown in the example discharges with densities from 2 × 1017 m−3 to 2 × 1019 m−3 at the limiter position. In these experiments, the radial location of the measurements varied from 5 cm in front of the limiter (up to 1 cm inside the separatrix was measured) to 3 cm in the limiter shadow. Experimental challenges of MILS operation and data processing are presented.
The particle shape influences the part properties in laser powder bed fusion, and powder flowability and powder layer density (PLD) are considered the link between the powder and part properties. ...Therefore, this study investigates the relationship between these properties and their influence on final part density for six 1.4404 (316L) powders and eight AlSi10Mg powders. The results show a correlation of the powder properties with a Pearson correlation coefficient (PCC) of −0.89 for the PLD and the Hausner ratio, a PCC of −0.67 for the Hausner ratio and circularity, and a PCC of 0.72 for circularity and PLD. Furthermore, the results show that beyond a threshold, improvement of circularity, PLD, or Hausner ratio have no positive influence on the final part density. While the water-atomized, least-spherical powder yielded parts with high porosity, no improvement of part density was achieved by feedstock with higher circularities than gas-atomized powder.
We investigated the dependence of electrical properties on vacuum-deposition rate for films of N,N՛-diphenyl-N,N՛-bis(1-naphthyl)-1,1՛-biphenyl-4,4՛-diamine (α-NPD) and ...tris-(8-hydroxyquinoline)aluminium (Alq3), hole- and electron-transport materials widely used in organic light-emitting diodes (OLEDs), respectively. Hole-only devices (HODs) of α-NPD showed an increase of hole current when α-NPD layers were fabricated at high deposition rates, while the tendency was opposite for electron-only devices (EODs) of Alq3. We found that the increased hole current at high deposition rates for HODs was caused by a horizontal orientation of α-NPD molecules relative to a substrate plane which facilitates hole transport through the films. On the other hand, the decreased electron current at high deposition rates for EODs could be ascribed to the increased surface roughness of Alq3 films which decreases electron injection. Additionally, we demonstrated that long-term operational stability was enhanced for HODs fabricated at high deposition rates and operated at a constant current. Use of a high deposition rate means a reduction of deposition time which is helpful in OLED manufacturing. The improved device performance when high deposition rates were used and the detailed understanding of its origins as we demonstrated here would lead to fabrication of high-performance OLEDs at a low cost in the future.
•The current density increased for HODs and decreased for EODs by deposition rate.•The change in current densities was not related to charge trap characteristics.•The average surface roughness of neat films increased by deposition rate.•α-NPD molecules oriented more horizontally at higher vacuum-deposition rates.•HODs and EODs with the best electrical properties had the best stability.
•New equations calculating optimal layer density for variable density multilayer insulation (OVDMLI) are established.•Accounting for the influences of spacers, compressive pressure, gas pressure, ...makes the model accurate and predictable.•The performance of the computed OVDMLI demonstrates a 21.1% improvement compared to that of the standard VDMLI.•The optimal number of spacers for OVDMLI is three times the number of radiative layers.•The gas heat transfer is more affected by pressure on the low temperature side than on the high temperature side.
The extremely high energy density and carbon-free characteristics of liquid hydrogen (LH2) make it suitable for replacing liquefied natural gas (LNG) as a future energy commodity. However, the extremely low evaporation temperature of LH2 results in high heat leakage. Multilayer insulation (MLI), which is the most thermally efficient insulation system known, is widely used in the fields of hydrogen energy, aerospace, and other cryogenic fields. Variable density multilayer insulation (VDMLI), which has emerged in the last two decades, has improved the performance of MLI by adding spacers to change the density of MLI. However, there has been no significant progress in the optimization theory for VDMLI. In this paper, based on the layer by layer model and the Lockheed equation, a generalized optimal layer density calculation model for VDMLI is established by considering the influences of spacers, compressive pressure, gas pressure, etc. The results indicate that compared to general VDMLI and MLI on liquid hydrogen tanks, the optimal layer density VDMLI (OVDMLI) can reduce heat leakage by 21.1% and 25.3%, respectively. After comparison and analysis, the characteristics and reasons for temperature and heat transfer conductivity profiles of MLI, VDMLI, and OVDMLI are pointed out. The effect of the spacer number on heat flux and spacer profile is analyzed. Additionally, gas pressure profile and heat transfer are investigated with consideration given to the vacuum degree at both boundaries.
In this paper, a red-eared slider turtle is used as a prototype for the bionic design of the foamed silicone rubber sandwich structure, and the effect of core layer parameters on the low-velocity ...impact resistance of the foamed silicone rubber sandwich structure is studied by the finite element method. A numerical model with porosity of the foamed silicone rubber intrinsic model and a three-dimensional Hashin fiber plate damage model were used to verify the validity of the model in comparison with the test. On this basis, finite element simulations were performed by varying the core layer density and thickness. The results show that from the perspective of energy absorption, the sandwich structure has better impact resistance with core density of 750 kg/m3∼850 kg/m3 and core thickness of 20 mm–25 mm; from the perspective of structural lightweight requirements, the sandwich structure is more in line with the structural lightweight requirements with core density of 550 kg/m3∼650 kg/m3 and core thickness of 5 mm–10 mm. Therefore, the adoption of suitable core density and thickness is of great significance to the engineering practice.
Figure. Bionic red-eared slider turtle sandwich structure design: (a) A macroscopic morphology of a turtle shell. (b) A cross-sectional view of the turtle shell carapace showing composite layers. (c) Schematic diagram of stacking sequence of bionic sandwich structure and impact region. Display omitted
•In this paper, a red-eared slider turtle is used as a prototype for the bionic design of the foamed silicone rubber sandwich structure, and the effect of core layer parameters on the low-velocity impact resistance of the foamed silicone rubber sandwich structure is studied by the finite element method.•From the perspective of energy absorption, the sandwich structure has better impact resistance with core density of 750 kg/m3∼850 kg/m3 and core thickness of 20mm∼25mm.•From the perspective of structural lightweight requirements, the sandwich structure is more in line with the structural lightweight requirements with core density of 550 kg/m3∼650 kg/m3 and core thickness of 5mm∼10mm.
Flame-retardant multilayer insulation materials act as effective thermal insulation blankets of cryogenic containers that store flammable and explosive cryogenic liquids. This study used standard ...static liquid nitrogen boil-off calorimetry to test the insulation performance of eight groups of flame-retardant multilayer insulation materials with different wrapping parameters. The effects of four factors, namely the layer density, seaming process, number of reflector layer, and variable-density multilayer insulation arrangement, on the insulation performance were analysed. Three layer densities were considered: 4.47, 3.08, and 2.50 layers/mm. Two types of seaming processes were discussed: the overlapped and fold-over seaming processes. Three numbers of reflector layers were considered: 60, 70, and 80. Two variable-density multilayer insulation arrangements with similar thicknesses were discussed: 10-10-40 and 20-20-20 layers of reflectors allocated for low-, medium- and high-density segments. The conclusions are as follows: Decreasing the layer density enhances the performance of multilayer insulation; Using the fold-over seaming process results in less heat flux and lower apparent thermal conductivity; An increase in the number of reflector layers weakens radiative heat transfer, resulting in better thermal insulation; Furthermore, for a given wrapping thickness, reducing the number of reflectors appropriately in low- and medium-density segments improves the insulation performance; Optimizing and controlling the layer density of each density segment are also essential for variable-density multilayer insulation effects. This study provides supporting theories and reference data for practical engineering applications.
Powder bed fusion of polymers is becoming increasingly adopted by a variety of industries to tailor the strength, weight and functionality of end-use products. To meet the high standards of the ...modern manufacturing industry, parts built with powder bed fusion require consistent properties and to be free of defects, which is intrinsically connected to the quality of the powder bed prior to melting. The hypothesis of this work is that the roughness of the top surface of an unmelted powder bed can serve as a proxy for the powder bed density, which is known to correlate with final part density. In this study, a laser line scan profilometer is integrated onto the recoater arm of a custom powder test bench, which is able to automatically create layers of powder. A diverse group of polymers was investigated including polyamide 12 (PA12), polyamide 11 (PA11), polypropylene (PP), and a thermoplastic elastomer (TPU) under different recoating speed in order to increase the variance of the dataset. Data analytics were employed to compare roughness to measured powder bed density and a statically significant correlation was established between them.
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