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A Numerical Study of Densification Behavior of Silicon Carbide Matrix Composites in Isothermal Chemical Vapor Infiltration
摘要： We studied the characteristics of two-scale pore structure of preform in the deposition process and the mass transfer of reactant gas in dual-scale pores, and observed the physiochemical phenomenon associated with the reaction. Thereby, we established mathematical models on two scales, respectively, preform and reactor. These models were used for the numerical simulation of the process of ceramic matrix composites densified by isothermal chemical vapor infiltration (ICVI). The models were used to carry out a systematic study on the influence of process conditions and the preform structure on the densification behaviors. The most important findings of our study are that the processing time could be reduced by about 50% without compromising the quality of the material, if the processing temperature is 950-1 000 ℃ for the first 70 hours and then raised to 1 100 ℃.
关键词： isothermal chemical vapor infiltration,fiber preform structure,densification behavior,ceramic matrix composites,process parameters
更新于2025-09-23 15:23:52
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Flash sintering of barium titanate
摘要： A novel technique of low temperature and fast sintering is expected to meet the productive requirements of reducing energy consumption and improving efficiency. In this work, a dense Nb-doped BaTiO3 ceramic is obtained by a sintering method applying a direct current electrical field of 140 V cm-1 for 30 s at 1055 °C. In particular, the rapid densification mechanism of flash sintering Nb-doped BaTiO3 ceramic is explained by a model about liquid film which is formed by wetting at particle contacts, due to the Joule heating runaway. It is believed that the capillary forces generated from liquid film play a dominant role during flash sintering, which ensure the compaction of local particles and achieve the densified specimen in a relatively short time.
关键词： Liquid film,Rapid densification,Joule heating runaway,Flash sintering
更新于2025-09-23 15:23:52
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Surface roughness and densification correlation for direct metal laser sintering
摘要： The increasing use of metal additive manufacturing (AM) technologies, such as direct metal laser sintering (DMLS), requires an in-depth understanding of how the optimum DMLS process parameters can be determined to achieve the target properties, such as reduced defect densities and/or desired surface characteristics. To this end, it is important to develop simple strategies that assess part quality and are fast and cost-effective. In this study, the in-plane surface roughness of components fabricated with AM is correlated with the DMLS process parameters and fractional density, enabling rapid and accurate indirect determination of the fractional density of AM components through surface roughness measurements. To this end, two sets of DMLS process parameters and a geometrical parameter are utilized to fabricate more than 150 rectangular cubic samples with varying parameters. All the samples are fabricated using Ti-6Al-4 V powder, which is a frequently used metal alloy for DMLS. Second, two line roughness parameters are defined and measured for all the samples, and their correlations with the DMLS and geometrical parameters are reported. Third, the fractional densities of all the samples are measured and their correlations with the DMLS process parameters are demonstrated. Lastly, a thorough analysis of the observed correlations between the line roughness parameters and fractional density are discussed.
关键词： Ti-6Al-4 V,Surface roughness,Densification,Process parameters,Metal additive manufacturing
更新于2025-09-23 15:21:01
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INFLUENCE OF FLIGHT CONFIGURATION USED FOR LiDAR DATA COLLECTION ON INDIVIDUAL TREES DATA EXTRACTION IN FOREST PLANTATIONS
摘要： In the last decades, several studies have been conducted aiming to the extraction of forest variables from LiDAR data. Although such studies have indicated great potential, the high cost associated with LiDAR data acquisition process inhibits the technology to become an operational technique for forestry applications. The cost of a LiDAR survey, as for any other data collection techniques, is composed of fixed and variable costs. The variable portion, which can be optimized, is dependent, among other factors, on the number of flight hours. The flight time is mainly dependent on the flight configuration used for the survey. The objective of this paper is to investigate the impact of using different operational parameters on different species of forest plantations, to provide inputs for an adequate cost-benefit analysis. The different configurations are evaluated in terms of the number of individual trees automatically detected, individual height and volume, using the forest inventory as the reference data. The experiments have shown that compatible results are obtained using different configurations with flight time varying by a factor of 3.5 to 10 times. Also, for a given point density, preference should be given to the configuration based on a lower flying height.
关键词： volume,remote sensing,forest mensuration,Airborne LiDAR,tree height,progressive densification,operational parameters
更新于2025-09-23 15:21:01
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Variable densification of reduced graphene oxide foam into multifunctional high-performance graphene paper
摘要： Super-flexible, electrically and thermally conductive graphene-based papers are in great demand in the fields of electronics and supercapacitors. However, the applications of graphene-based papers are limited either by their brittleness, small scale, or by their unsatisfactory thermal conductivity. Conventionally, such papers are fabricated by vacuum-assisted filtration, direct evaporation, electrospray coating, or wet spinning. Here we propose a novel strategy, namely, direct densification of reduced graphene oxide foam, to fabricate large-scale multifunctional graphene papers. The graphene paper density could be adjusted by applying different loads. The densities of the graphene papers varied from 0.32 g cm?3 to 1.85 g cm?3. The thermal conductivity, tensile stress, electrical conductivity and electromagnetic interface shielding effectiveness increased with an increase in the density of the graphene paper. When the density of the graphene paper reached 1.85 g cm?3, the tensile stress was up to 50.4 MPa with strain of 4%, the thermal conductivity was 1103 W m?1 K?1 at room temperature and there was high electrical conductivity of 1.1 × 10? S m?1, as well as an electromagnetic interference (EMI) shielding effectiveness of 77.2 dB. Our new strategy is very promising in terms of controlling the thickness, density, and size of graphene paper.
关键词： graphene paper,densification,EMI shielding,electrical conductivity,thermal conductivity
更新于2025-09-19 17:15:36
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Laser energy density dependence of performance in additive/subtractive hybrid manufacturing of 316L stainless steel
摘要： An enormous amount of research effort goes into the manufacturing process for additive manufacturing (AM) or subtractive manufacturing (SM) process for property microstructure. Moreover, additive/subtractive hybrid manufacturing (ASHM), which combines additive and subtractive processes in a single machine, has provided an important opportunity to increase the high percentage of stock utilization and produce complex functional components. However, the system comprehensive investigation and the study of ASHM-manufactured parts by various process parameters have rarely been reported. The present paper depicted the effect of laser energy density (ψ) on the phase change, density, microstructure, Vickers hardness, and tensile testing within the ASHM specimens. It was observed that the highest Vickers microhardness, the largest tensile strength, and the attendant ductility were gained at ψ =222 J/mm3, the most excellent value, which was put down to the high density and relatively fine grains. The results of this study have a better knowledge of the ASHM method to produce a high surface state and mechanical behavior 316L SS component by governing laser energy density (ψ).
关键词： Additive/subtractive hybrid manufacturing,Laser energy density,Microstructure,Densification,Vickers microhardness,Tensile properties
更新于2025-09-16 10:30:52
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Simultaneous densification and nitrogen doping of laser-induced graphene by duplicated pyrolysis for supercapacitor applications
摘要： Laser pyrolysis of polyimide is a facile and cost-effective method to fabricate high performance supercapacitor electrodes. This study proposes a duplicated laser pyrolysis method to densify pyrolyzed carbon electrodes and hence improve electrochemical performance. The initial laser pyrolysis of polyimide generates a graphene-like carbon, called laser-induced graphene (LIG). This LIG is then coated with an additional polyimide layer, and the second laser pyrolysis is applied, producing densified LIG. Laser power effects on densified LIG morphology and electrochemical characteristics are investigated, confirming remarkable density increase. Increased nitrogen content is also observed, signifying significant nitrogen doping. The densified electrode achieves 49.0 mF cm?2 specific capacitance at 0.2 mA cm?2 current density in a standard three-electrode system, approximately 6-fold that for singly pyrolyzed LIG electrodes. A solid-state flexible supercapacitor with densified LIG electrodes is fabricated using a gel electrolyte (PVA-H2SO4), achieving 19.8 mF cm?2 capacitance at 0.05 mA cm?2 current density, with outstanding cyclic charge-discharge stability and mechanical flexibility.
关键词： Nitrogen-doped carbon,Laser pyrolysis,Densification,Laser-induced graphene,Flexible supercapacitors
更新于2025-09-11 14:15:04
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Glass above Megabar Pressures up to 160?GPa Revealed by X-Ray Raman Scattering
摘要： As oxygen may occupy a major volume of oxides, a densification of amorphous oxides under extreme compression is dominated by reorganization of oxygen during compression. X-ray Raman scattering (XRS) spectra for SiO2 glass up to 1.6 Mbar reveal the evolution of heavily contracted oxygen environments characterized by a decrease in average O-O distance and the potential emergence of quadruply coordinated oxygen (oxygen quadcluster). Our results also reveal that the edge energies at the centers of gravity of the XRS features increase linearly with bulk density, yielding the first predictive relationship between the density and partial density of state of oxides above megabar pressures. The extreme densification paths with densified oxygen in amorphous oxides shed light upon the possible existence of stable melts in the planetary interiors.
关键词： oxygen quadclusters,megabar pressures,X-ray Raman scattering,SiO2 glass,densification
更新于2025-09-11 14:15:04
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Effect of High Pressure in the Luminescence of Pr <sup>3+</sup> Doped Ge <sub/>2</sub> O- PbO Glass Containing Au Nanoparticles
摘要： In this paper it was investigated the combined effect of gold nanoparticles and high-pressure densification on the luminescence of Pr3+ doped heavy metal GeO2-PbO photonic glass. Localized states related to ion-trapped exciton defects, S1 and S2, were observed at 342 and 412 nm before densification. After densification under 7.7 GPa the structure of the glass host changed irreversibly, as indicated by the infrared spectrum, refractive index and density measurements. TEM analyses indicated that the high-pressure densification induced the formation of clusters of gold nanoparticles. The modifications observed in the absorption and luminescence spectra of Pr3+ ions in the VIS-NIR range were associated to the changes in the local field surrounding the Pr3+ ions in the host glass induced by high-pressure. For excitation at 445 nm (luminescence from 3P2) and 593 nm (luminescence from 1D2), the combined effect of densification and gold nanoparticles induced an increase in the emission band at 1050 cm-1. For excitation at 488 nm (luminescence from 3P0), the combined effect resulted in a strong decrease in the emission intensities in the VIS, revealing the emergence of non-radiative processes in resonance with 3P0 state. The observed behavior was probably due to energy transfer, ion trapped exciton defects and cross-relaxation processes among the Pr3+ ions and gold nanoparticles.
关键词： cross-relaxation processes,gold nanoparticles,Pr3+ doped,high-pressure densification,energy transfer,GeO2-PbO glass,luminescence
更新于2025-09-11 14:15:04
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[IEEE 2018 19th International Conference on Electronic Packaging Technology (ICEPT) - Shanghai (2018.8.8-2018.8.11)] 2018 19th International Conference on Electronic Packaging Technology (ICEPT) - Study on Interfacial Diffusion Mechanism of The Nonstoichiometric ratio TiN0.3 and AlN composite in the process of sintering
摘要： Covalent compounds have strong covalent bond, thus showing high melting point, high hardness, high temperature resistance, corrosion resistance, wear resistance and other excellent performance, is widely applied to the field of refractory materials and wear-resistant materials.But at the same time this kind of material also has the problem of poor toughness and difficulty in sintering.In this article, by adding the nonstoichiometric ratio to the AlN titanium nitride, a new method were studied to improve the sintering property and reduce the sintering temperature through vacancy diffusion and to study the sintering of micro forming mechanism. The experimental results show that after sintering at the interface between TiN0.3 and AlN two-phase, the TiN0.3 / AlN layer have apparent diffusion zone, AlN in N, Al atom diffusion in TiN0.3 via the vacancy diffusion mechanism. As a result of the existence of a large amount of N of TiN0.3 space, when the diffusion of N atomic migration is absorbed by vacancy,and approaches stoichiometric ratio TiN layer AlN substrate;Al atoms crystallized out of the TiN layer in the hexagonal AlN structure in TiN0.3 matrix.
关键词： Covalent compounds,AlN,Interface densification,non-stoichiometric TiNx
更新于2025-09-10 09:29:36