Ceramic cores are the key intermediate components of hollow blades for aero-engine. Conventional processes, such as hot-press molding and gel film casting, face difficulties in fabricating ...complex-structured ceramic cores due to the complexity of moulds and long process cycles. Stereolithography 3D printing provides a new idea for the fabrication of complex-structured ceramic cores. The effect of sintering temperature on open porosity, bulk density, weight loss rate, shrinkage rate, flexural strength and microstructure of the AI.sub.2O.sub.3-based ceramic core doped with 10vol.% polysilazane (PSZ) was studied. The sintering mechanism of PSZ-reinforced ceramic cores was analyzed. Results show that the optimum sintering temperature of PSZ-reinforced ceramic cores is 1,450 degreesC. At this temperature, the open porosity of the ceramic core is 36.60%, bulk density is 2.33 g*cm.sub.-3, weight loss rate is 22.11%, shrinkage rate along the X, Y, Z directions is 5.72%, 5.01%, 9.61%, respectively; the flexural strength is 28.794 MPa at 25 degreesC and 13.649 MPa at 1,500 degreesC. Properties of 3D printing PSZ-reinforced ceramic cores can meet the casting requirement of superalloy hollow blades, which is expected to promote the industrial application of 3D printing complex structure ceramic cores. Keywords: investment casting; ceramic core; 3D printing; sintering temperature; flexural strength CLC numbers: TG221 (+).1 Document code: A Article ID: 1672-6421(2023)05-387-08
As one of the effective methods for solving the greenhouse problem, methane reforming has received increasing attention. The performance of a reactor is strongly influenced by the foam structure with ...different parameters. In this study, the idea of non-uniform partition design of porosity (an expansion kind of hierarchical porous structure) in a porous media reactor was put forward and investigated. The heat and mass transfer phenomena and thermochemical properties of methane reforming under high convergence solar radiation were numerically studied. Finite volume method coupled with thermochemical kinetics is considered to solve this problem. Based on a constant pore size, the porosity of the porous medium is divided into two layers and combined in different forms in an axial direction. The effects of non-uniform porosity on thermochemical performance of solar driven methane reforming are analyzed and an optimization method for non-uniform porosity is proposed. The results show that methane conversion in a reactor with uniform porous media increases with growth up of the porosity. In addition, a reactor with non-uniform porous media exhibits better thermochemical performance and reforming performance compared to one with uniform porous media. Finally, different non-uniform partitions have an impact on methane conversion. When the porosity is constant, methane conversion decreases with an increase of the length of the first layer of porous media, and the maximum methane conversion (82.42%) was achieved at L1 = 0.01 m with φ1 = 0.75, φ2 = 0.9.
•Finite volume method with reaction kinetics is developed to analyze the methane reforming process.•Methane reforming in solar foam reactor with non-uniform porosity is studied.•Methane conversion in reactor with uniform porous media increases with porosity.•Different non-uniform partitions have a certain impact on the methane conversion.
Developing a composite electrode containing both carbon and transition metal/metal oxide as the supercapacitor electrode can combine the merits and mitigate the shortcomings of both the components. ...Herein, we report a simple strategy to prepare the hybrid nanostructure of Co@Carbon and Co3O4@Carbon by pyrolysis a single MOFs precursor. Co-based MOFs (Co-BDC) nanosheets with morphology of regular parallelogram slice have been prepared by a bottom-up synthesis strategy. One-step pyrolysis of Co-BDC, produces a porous carbon layer incorporating well-dispersed Co and Co3O4 nanoparticles. The as-prepared cobalt-carbon composites exhibit the thin layer morphology and large specific surface area with hierarchical porosity. These features significantly improve the ion-accessible surface area for charge storage and shorten the ion transport length in thin dimension, thus contributing to a high specific capacitance. Improved capacitance performance was successfully realized for the asymmetric supercapacitors (ASCs) (Co@Carbon//Co3O4@Carbon), better than those of the symmetric supercapacitors (SSCs) based on Co@Carbon and Co3O4@Carbon materials (i.e., Co@Carbon//Co@Carbon and Co3O4@Carbon//Co3O4@Carbon). The working voltage of the ASCs can be extended to 1.5 V and show a remarkable high power capability in aqueous electrolyte. This work provides a controllable strategy for nanostructured carbon-metal and carbon-metal oxide composite electrodes from a single precursor.
Reinforcing structural members and construction materials using recycled fibers has become popular in the past decades due to sustainable development concerns. The recycled fibers as soil ...reinforcement elements contribute to the increase in shear strength by distributing stresses exerted in the soil along the length of the recycled fibers. Loess, widely spread over the Chinese Loess Plateau, is featured with metastable structure, large porosity, and high water sensitivity. This study presents the results of applying the large-scale stress-controlled direct shear tests on the recycled straw fiber-reinforced loess. The formation mechanism of shearing behaviour enhancement of the loess by straw fiber inclusion is revealed. The associated strain-hardening behaviour can be manifested using the dilation angle or the difference in friction angle between the large-displacement friction angle and the peak friction angle. Further, the shear strength using the displacement-controlled direct shear tests presents good correspondence with that using the stress-controlled direct shear tests. The test results explore the potential of using the recycled straw fiber-reinforced loess to protect the fragile loess environment in the northwest of China.
Zeolites are important heterogeneous catalysts in industrial applications, but always suffer from deactivation caused by carbon deposition. In this work, a simple strategy was developed to engineer ...Ferrierite (FER) zeolites with different pore structure and distribution of Brønsted acid sites by using different organic amine structure directing agents, i.e., pyrrolidine (PY), ethylenediamine (EDA), cyclohexylamine (CyHA). The obtained PY-FER not only exhibited optimal hierarchical porosity, but also showed the highest density of Brønsted acid sites inside micropores and lowest Lewis/Brønsted acid ratio (L/B). Based on the corresponding performance in n-butene skeletal isomerization, it can be concluded that high L/B is prone to coke formation, while a balance between micropores and mesopores is beneficial to the reduction of carbon deposition. Besides, a model y=y0−Aexp(−Kt) was established to describe the behavior of the carbon deposition, which matches well with the properties of the zeolites. These findings are significant for the design of zeolites.
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•The pore structure and distribution of Brønsted acid sites FER can be engineered using different organic amine structure directing agents.•The pyrrolidine-FER exhibits optimal hierarchical porosity, highest density of Brønsted acid sites and lowest Lewis/Brønsted acid ratio.•The hierarchical porosity and low L/B ratio decreases the carbon deposition and enable PY-FER exhibiting high isobutene yield and stability.•A kinetic model is proposed to describe the behavior of carbon deposition.
Natural convection of a fluid inside a closed square porous enclosure with inhomogeneous porosity distribution was studied numerically. The right and left walls of the cavity were cold and hot, ...respectively, provided the upper and lower walls were well insulated. The fluid and solid portions are in thermal equilibrium within the porous medium. Boundary conditions were considered based on the assumptions and were nondimensionalized using suitable dimensionless parameters. The non-uniform distribution of porosity was assumed as linear and quadratic functions with positive and negative gradients along the horizontal (x) and vertical (y) axes. To ensure the accuracy of results, several simulations in the literature performed by the same solution method were replicated, and the results were compared with those reported in these studies. Porosity could be an increasing or a decreasing function of x or y. A total of eight porosity distribution functions were used in this study. The results showed drastic changes in the flow and temperature fields with linear porosity distribution at ϵavg = 0.3 compare to uniform porosity distribution. Furthermore, inhomogeneous porosity caused a decrease in the Nusselt number. The observed reduction in the Nusselt number was maximum for linear porosity distribution along the x-axis and minimum for the Quadratic Porosity distribution along the y-axis.
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•Natural Heat exchange in Inhomogeneous Porous Medium has been analyzed.•Linear and Quadratic Porosity Distribution have been applied.•Inhomogeneous porosity results in a decrease in the Nusselt number.•Reduction in the Nu was maximum for linear porosity distribution.•The lowest reduction of Nu corresponds to Quadratic Porosity distribution.
Converting mineral raw materials into porous materials represents an effective and high-value approach. Among these materials, porous geopolymers made from metakaolin (whether natural or synthetic) ...have garnered significant attention. This review comprehensively explores the methods for introducing pore structures, porous properties, and applications of metakaolin-based porous geopolymers (MPGs). Additionally, it discusses the future development prospects of this field. By summarizing and analyzing research progress, this review aims to provide a comprehensive understanding of the current status of metakaolin-based porous geopolymers research. It highlights innovative foaming routes to achieve desired porous structures, enhance specific properties, and expand or tailor applications. Ultimately, this study aims to stimulate further research and application of bulk-type or shaped porous geopolymers using metakaolin as a raw material, particularly in the field of water purification and pollutant removal.
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Polyoxometalates. In their Research Article (e202218897), De‐Liang Long, Yu‐Fei Song, Haralampos N. Miras, and co‐workers investigate the engineering of porosity of new Keplerate‐type molecular ...nanocontainers.
Concerns with environmental sustainability have promoted adoption of conservationist practices in agricultural production, mainly focused on soil quality preservation or recovery. The aim of this ...study was evaluating short-term soil physical quality improvements under agroforestry system management in Southern Brazil. The agroforestry system was implemented in 2013 in an Ultisol with Sandy Loam texture. Rows of agroforestry system (AFS-R) were composed by biomass producer trees intercalated with wood and fruit producer trees while in the inter-rows (AFS-IR) perennial sub-shrub, perennial grass, and summer and winter green manure annual species were implanted. Soil under native forest was used as control. Soil samples in the 0.0–0.1; 0.1–0.2 and 0.2–0.4 m depths were collected for the determination of physical attributes and the total organic carbon content in 2015, 2016 and 2017. Bulk density decreased about 9% (AFS-R) and 6% (AFS-IR) in 0.0–0.1 m between 2015 and 2017. Total porosity increased over time only in AFS-R, at a rate of 0.025 m
3
m
−3
year
−1
. The total organic carbon content of AFS increased over time only in the 0.0–0.1 m layer, although remained up to 35% less in relation to the native forest. The agroforestry system resulted in consistent improvements of several soil physical attributes over short time, particularly in rows with arboreal plants, highlighting the role of diversified tree root systems and plant residues accumulation, which implied a rapid improvement in soil quality. In this context, long-term studies with agroforestry systems are crucial to understand the benefits on soil quality.
Covalent organic frameworks (COFs) are promising materials for advanced molecular-separation membranes, but their wide nanometer-sized pores prevent selective gas separation through molecular ...sieving. Herein, we propose a MOF-in-COF concept for the confined growth of metal-organic framework (MOFs) inside a supported COF layer to prepare MOF-in-COF membranes. These membranes feature a unique MOF-in-COF micro/nanopore network, presumably due to the formation of MOFs as a pearl string-like chain of unit cells in the 1D channel of 2D COFs. The MOF-in-COF membranes exhibit an excellent hydrogen permeance (>3000 GPU) together with a significant enhancement of separation selectivity of hydrogen over other gases. The superior separation performance for H
/CO
and H
/CH
surpasses the Robeson upper bounds, benefiting from the synergy combining precise size sieving and fast molecular transport through the MOF-in-COF channels. The synthesis of different combinations of MOFs and COFs in robust MOF-in-COF membranes demonstrates the versatility of our design strategy.
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