Porous ceramic composites with directional microchannels from micrometer to dozens of micrometer levels have attracted more and more attention in various fields including aerospace,biomedicines,and thermal insulation ...Porous ceramic composites with directional microchannels from micrometer to dozens of micrometer levels have attracted more and more attention in various fields including aerospace,biomedicines,and thermal insulation due to their excellent fluid permeability,mechanical properties,etc.In this article,we summarize the recent directional porous ceramics developments including their main processing routes and respective properties.Meanwhile,the properties get from different processing routes have been com-pared and analyzed in terms of microstructures,mechanical properties,and permeability.Emphasis has been given to the deeper understanding which can allow one to control the microstructural features of these porous ceramic composites to obtain the desired characteristics.This work can provide a useful reference for the development and application of porous ceramic composites with directional microchan-nels.展开更多
The quest for lightweight and functional materials poses stringent requirements on mechanical performance of porous materials.However,the contradiction between high strength and elevated porosity of porous materials s...The quest for lightweight and functional materials poses stringent requirements on mechanical performance of porous materials.However,the contradiction between high strength and elevated porosity of porous materials severely limits their application scenarios in emerging fields.Herein,high-strength multifunctional mullite-based porous ceramic monoliths were fabricated utilizing waste fly ash hollow microspheres(FAHMs)by the protein gelling technique.Owing to their unique shell-pore structure inspired by shell-protected biomaterials,the monoliths with porosity of 54.69%–70.02% exhibited a high compressive strength(32.3–42.9 MPa)which was 2–5 times that of mullite-based porous ceramics with similar density reported elsewhere.Moreover,their pore structure and properties could be tuned by regulation of the particle size and content of the FAHMs,and the resultant monoliths demonstrated superior integrated performances for multifunctional applications,such as broadband sound insulation,efficient thermal insulation,and high-temperature fire resistance(>1300℃).On this basis,mullite-based porous ceramic lattices(porosity 68.28%–84.79%)with a hierarchical porous structure were successfully assembled by direct ink writing(DIW),which exhibited significantly higher compressive strength(3.02–10.77 MPa)than most other ceramic lattices with comparable densities.This unique shell-pore structure can be extended to other porous materials,and our strategy paves a new way for cost-effective,scalable and green production of multifunctional materials with well-defined microstructure.展开更多
To improve the wall surface hydrophilicity of a tube type indirect evaporative cooler,a new method adopting porous ceramics is proposed.This method realizes the combination of porous ceramics and the evaporative cooli...To improve the wall surface hydrophilicity of a tube type indirect evaporative cooler,a new method adopting porous ceramics is proposed.This method realizes the combination of porous ceramics and the evaporative cooling technique.The design calculation of the porous ceramics tube type dew point indirect evaporative cooler are carried out from such aspects as the volumes and status parameters of the primary and secondary air,the cooler structure,the heat transfer of the solid porous ceramic tubes and the resistance of the cooler.The calculation results show that the design is reasonable.Finally,based on the design calculation,the porous ceramics tube type dew point indirect evaporative cooler is successfully manufactured.展开更多
Porous ceramics were prepared from kaolinite gangue and Al（OH）3 with double addition of MgCO3 and CaCO3 by the pore-forming in-situ technique.The characterizations of porous ceramics were investigated by X-ray diffr...Porous ceramics were prepared from kaolinite gangue and Al（OH）3 with double addition of MgCO3 and CaCO3 by the pore-forming in-situ technique.The characterizations of porous ceramics were investigated by X-ray diffractometry,scanning electron microscopy,and mercury porosimetry measurements,etc.It is found that although the decomposition of MgCO3 and CaCO3 has little contribution to the porosity,the double addition of MgCO3 and CaCO3 strongly affects the formation of liquid phase,and then changes the phase compositions,pore characterization,and strength.The appropriate mode is the sample containing 1.17wt% MgCO3 and 1.17wt% CaCO3,which has high apparent porosity（41.0%）,high crushing strength（53.5 MPa）,high mullite content（76wt%）,and small average pore size（3.24 μm）.展开更多
Diatomite-based porous ceramics were adopted as carriers to immobilize nano-TiO2 via a hydrolysis-deposition technique. The thermal degradation of as-prepared composites was investigated using thermogravimetric-differ...Diatomite-based porous ceramics were adopted as carriers to immobilize nano-TiO2 via a hydrolysis-deposition technique. The thermal degradation of as-prepared composites was investigated using thermogravimetric-differential thermal analysis, and the phase and microstructure were characterized by X-ray diffraction, Fourier transform infrared spectroscopy, and transmission electron microscopy. The results indicated that the carriers were encapsulated by nano-TiO2 with a thickness of 300-450 nm. The main crystalline phase of TiO2 calcined at 650~C was anatase, and the average grain size was 8.3 nm. The FT-IR absorption bands at 955.38 cm1 suggested that new chemical bonds among Ti, O, and Si had formed in the composites. The photocatalytic （PC） activity of the composites was investigated un- der UV irradiation. Furthermore, the photodegradation kinetics of formaldehyde was investigated using the composites as the cores of an air cleaner. A kinetics study showed that the reaction rate constants of the gas-phase PC reaction of formaldehyde were k = 0.576 mg＇m3·min^-1 and K = 0.048 m3/mg.展开更多
A new approach in combination of the effective medium theory with the equivalent unit in numerical simulation was developed to study the effective thermal conductivity of porous ceramics. The finite element method was...A new approach in combination of the effective medium theory with the equivalent unit in numerical simulation was developed to study the effective thermal conductivity of porous ceramics. The finite element method was used to simulate the heat transfer process which enables to acquire accurate results through highly complicated modeling and intensive computation. An alternative approach to mesh the material into small cells was also presented. The effective medium theory accounts for the effective thermal conductivity of cells while the equivalent unit is subsequently applied in numerical simulation to analyze the effective thermal conductivity of the porous ceramics. A new expression for the effective thermal conductivity, allowing for some structure factors such as volume fraction of pores and thermal conductivity, was put forward, and the results of its application was proved to be close to those of the mathematical simulation.展开更多
Heterogeneous catalysts with ultrafine or nano particle size have currently attracted considerable attentions in the chemical and petrochemical production processes, but their large-scale applications remain challengi...Heterogeneous catalysts with ultrafine or nano particle size have currently attracted considerable attentions in the chemical and petrochemical production processes, but their large-scale applications remain challenging because of difficulties associated with their efficient separation from the reaction slurry. A porous ceramic membrane reactor has emerged as a promising method to solve the problem concerning catalysts separation in situ from the reaction mixture and make the production process continuous in heterogeneous catalysis. This article presents a review of the present progress on porous ceramic membrane reactors for heterogeneous catalysis, which covers classification of configurations of porous ceramic membrane reactor, major considerations and some important industrial applications. A special emphasis is paid to major considerations in term of application-oriented ceramic membrane design, optimization of ceramic membrane reactor performance and membrane fouling mechanism. Finally, brief concluding remarks on porous ceramic membrane reactors are given and possible future research interests are also outlined.展开更多
The large-scale accumulation and pollution of solid mining waste is an urgent issue.Coal gangue is a prominent type of solid waste,and shows promise for use in high value-added products due to its content of many impo...The large-scale accumulation and pollution of solid mining waste is an urgent issue.Coal gangue is a prominent type of solid waste,and shows promise for use in high value-added products due to its content of many important compounds,including SiO_(2) and Al2O3.This study proposed the preparation of highly porous ceramics from coal gangue,coal slime,and coconut palm fibers.The ceramics were produced at a sintering temperature of 950℃ with a fiber content of 6 wt%,which led to the formation of porous ceramics with a porosity of 66.93%,volume density of 1.0329 g/cm^(3),compressive strength of 1.1025 MPa,and thermal conductivity is 0.3919 K(W/mk).A finite element model of the porous ceramics was established using the Abaqus module in ANSYS software,where the stress distribution and compressive strength were simulated.Further,the relationship between porosity and compressive strength was analyzed.The thermal properties of the porous ceramics were analyzed using the Fluent module,where the simulated changes in porosity under various sintering temperatures were consistent with the experimental data.The preparation of this highly porous ceramic from solid waste coal gangue shows promise for the minimizing the impact of waste gas and wastewater pollution in the future.展开更多
Porous ceramics were prepared with spodumene flotation talings(SFT),kaolin and low-melting point glass(LPG)powder,whose pores were formed by the chemical reaction of hydrogen peroxide(H_(2)O_(2)).LPG was used to reduc...Porous ceramics were prepared with spodumene flotation talings(SFT),kaolin and low-melting point glass(LPG)powder,whose pores were formed by the chemical reaction of hydrogen peroxide(H_(2)O_(2)).LPG was used to reduce the sintering temperature of porous ceramics and kaolin was used to realize the adsorption to methylene blue(MB)of porous ceramics.The average flexural strength,compressive strength,apparent porosity,water absorption and maximum MB adsorption capacity were 5.60 MPa,4.66 MPa,52.27%,44.32%and 0.7 mg/g,respectively.Moreover,the results of orthogonal experiments present that the sintering temperature and the dosage of H_(2)O_(2)had great influence on the mechanical properties and apparent porosity of porous ceramics,respectively.The main reason for the improvement of mechanical properties of porous ceramics was that LPG gradually became soft with increasing the sintering temperature,which made the mineral particles adhere to each other closely.Kaolinite was not completely converted into metakaolin at 550℃,which might be the main reason why porous ceramics had adsorption properties.展开更多
Porous ceramics was made from coal fly ash, and the microstructure and other properties were characterized as a function of the amount of the pore-forming agent and firing temperature. The results indicated that the p...Porous ceramics was made from coal fly ash, and the microstructure and other properties were characterized as a function of the amount of the pore-forming agent and firing temperature. The results indicated that the proper sintering temperature for the useful ceramic materials is 1 250℃, and a liquid-phase was involved in the densification process.展开更多
SiC porous ceramics were prepared at 1 400 ℃ for4 h with crystalline silicon cutting waste and activated carbon as main starting materials and NH4HCO3 as the pore-forming agent. Effects of NH4HCO3 additions( 0,20%,30...SiC porous ceramics were prepared at 1 400 ℃ for4 h with crystalline silicon cutting waste and activated carbon as main starting materials and NH4HCO3 as the pore-forming agent. Effects of NH4HCO3 additions( 0,20%,30%,40%,by mass) on the phase composition,microstructure,sintering properties,cold compressive strength and thermal shock resistance of as-prepared Si C porous ceramics were investigated. The results show that:( 1) addition of NH4HCO3 remarkably influences the apparent porosity and cold compressive strength of specimens. The apparent porosity achieves its maximum value( 63. 40%) when 40% NH4HCO3 is added,while the minimum cold compressive strength is 4. 77 MPa;( 2) the specimen with 40% NH4HCO3 has the best thermal shock resistance. The thermal cycling times between1 000 ℃ to room temperature reach 62;( 3) the addition of NH4HCO3 does not remarkably affect the phase composition of the specimens;( 4) the specimens include a large number of SiC particles and a small amount of SiC whiskers.展开更多
The nanotitanium dioxide （TiO2） photocatalytic and porous ceramic filtering technique is one of the advanced methods to effectively treat organic wastewater. The TiO2 sol doped with Fe^3＋ ions was prepared by sol-g...The nanotitanium dioxide （TiO2） photocatalytic and porous ceramic filtering technique is one of the advanced methods to effectively treat organic wastewater. The TiO2 sol doped with Fe^3＋ ions was prepared by sol-gel processing. The influences of the process conditions of coating nanophotocatalytic material- Fe^3＋-TiO2 film on the surface of porous ceramic filter by dipping-lift method on the performance of porous ceramic filter were studied. The porous ceramic filters have two functions at the same time, filtration and photocatalytic degradation. The results of this study showed that the pH and viscosity of the sol, amount of Fe^3＋ ions doped as well as the coating times greatly affect the quality of coating film, the performance parameters and the photocatalytic activity of the porous ceramic filter. When the pH of the sol is 3-4, the viscosity is about 6 mPa.S, the amount of doped Fe^3＋ ions is about 2.0 g/L, the porous ceramic filter has been shown to have the best filtering performance and photocatalytic activity. In this condition, the porosity of porous ceramic is about 42.5%, the pore diameter is 8-10μm. The degradation of methyl-orange is 74.76% under lighting for 120 rain.展开更多
Fibrous porous ceramics are attractive for use as thermal insulation materials.However,the intrinsic brit-tleness of rigid materials has remained challenging and severely restricts their applications.Here,we demonstra...Fibrous porous ceramics are attractive for use as thermal insulation materials.However,the intrinsic brit-tleness of rigid materials has remained challenging and severely restricts their applications.Here,we demonstrated a facile method for fabricating elastic fibrous porous ceramics(EFPCs)with high com-pressive strength and low thermal conductivity through ordinary press filtration and subsequent heat treatment.The quasi-layered structure and the well-bonded bridging fibers between layers are the key points for the elasticity of EFPCs.The advanced EFPCs exhibited low density(∼0.126 g cm^(−3)),high com-pressive stress(∼0.356 MPa),and low thermal conductivity(∼0.026 W m^(−1) K^(−1)).Compared with rigid porous fibrous materials,the EFPCs had deformability and excellent shape recovery.In contrast to flexible materials,the EFPCs possessed high compressive stress,thus endowing them with good resistance to de-formation.The emergence of this fascinating material may provide new insights for candidate materials in thermal insulation and other fields.展开更多
Corundum-mullite porous ceramics(CMPCs)were fabricated using fly ash and aluminum ash as the raw materials,adding different amounts of starch(0,10%,20%,and 30%,by mass)as the pore-forming agent,molding and firing at 1...Corundum-mullite porous ceramics(CMPCs)were fabricated using fly ash and aluminum ash as the raw materials,adding different amounts of starch(0,10%,20%,and 30%,by mass)as the pore-forming agent,molding and firing at 1200℃ for 1 h.The apparent porosity,the bulk density,the cold compressive strength,the thermal shock resistance and the thermal conductivity of the CMPCs were tested.The phase composition and the microstructure of the CMPCs were characterized by XRD and SEM.The effect of the starch addition on the properties of the CMPCs was studied.The results show that:(1)the CMPCs with high porosity can be successfully prepared by adding starch as the pore-forming agent and firing at 1200℃ for 1 h;(2)with the starch addition increasing,the porosity increases;the cold compressive strength and the number of the quenching cycles of the CMPCs decrease,but they remain at high levels;meanwhile,the thermal conductivity decreases;(3)generally,when adding 20 mass%starch,the CMPC has the apparent porosity of 48.6%,the cold compressive strength of 52.1 MPa,the quenching cycles of 5 and the thermal conductivity of 1.63 W·m-1·K-1 and 1.52 W·m-1·K-1,respectively,at 25℃ and 500℃,showing good performance.展开更多
Alow-cost porous ceramic support was prepared from low-grade palygorskite clay(LPGS) and silicon carbide(SiC)with vanadium pentoxide(V_(2) O_(5)) additives by a dry-press forming method and sintering.The effects of Si...Alow-cost porous ceramic support was prepared from low-grade palygorskite clay(LPGS) and silicon carbide(SiC)with vanadium pentoxide(V_(2) O_(5)) additives by a dry-press forming method and sintering.The effects of SiC-LPGS ratio,pressing pressure,carbon powder pore-forming agent and V_(2) O_(5) sintering additives on the microstructure and performance of the supports were investigated.The addition of an appropriate amount of SiC to the LPGS can prevent excessive shrinkage of the support during sintering,and increase the mechanical strength and open porosity of the supports.The presence of SiC(34.4%) led to increases in the open porosity and mechanical strength of 40.43% ± 0.21% and(17.76 ± 0.51) MPa,respectively,after sintering at 700℃ for 3 h.Because of its low melting point,V_(2) O_(5) can melt to liquid during sintering,which increases the mechanical strength of the supports and retains the porosity.Certainly,this can also encourage efficient use of the LPGS and avoid wasting resources.展开更多
Pyrophyllite is always used for making porous ceramics. In order to design the preparation technics of porous ceramics with pyrophyllite reasonably we must know the classifications, characteristics, properties and app...Pyrophyllite is always used for making porous ceramics. In order to design the preparation technics of porous ceramics with pyrophyllite reasonably we must know the classifications, characteristics, properties and applications of porous ceramics. The classification and characteristics of porous ceramics are reviewed in this article; and several common preparations with their advantages and disadvantages are also introduced. The authors discussed the problems existing in researching and developing process for porous ceramics, and forecasted the development prospect of porous ceramics.展开更多
SiC powder was rapidly synthesized in an induction furnace with crystalline silicon cutting waste and active carbon as raw materials,and then SiC porous ceramics were prepared at 1600 t for 4 h with carbon embedded us...SiC powder was rapidly synthesized in an induction furnace with crystalline silicon cutting waste and active carbon as raw materials,and then SiC porous ceramics were prepared at 1600 t for 4 h with carbon embedded using the powder as raw material,the starch and the graphite as pore-forming agents.Effects of additions of different pore-forming agents on the phase composition,microstructures,physical properties,and cold crushing strength of the porous ceramics were investigated.The results show that the main crystalline phases of the synthetic powder areα-S iC(6H-SiC)andβ-SiC(3C-SiC).The phase composition of the porous ceramics includesα-S iC(6H-SiC),β-SiC(3C-SiC),FeSi,quartz and Si2N20.The apparent porosity and closed porosity of the porous ceramics prepared by adding starch are higher,and the cold compressive strength of the porous ceramics added with graphite is higher.As increasing the additions of the starch,the apparent porosity,closed porosity and linear shrinkage ratio of the porous ceramics increase,and the bulk density decreases correspondingly.When 20 mass%starch is added,the apparent porosity,closed porosity,linear shrinkage ratio and cold compressive strength are 57.05%,2.03%,5.10%and 10.20 MPa,respectively.展开更多
In this paper,we reported a novel method for synthesis of non-oxide porous ceramics by using random copolymers as precursors.A silazane oligomer and styrene monomer were used as starting materials,which were copolymer...In this paper,we reported a novel method for synthesis of non-oxide porous ceramics by using random copolymers as precursors.A silazane oligomer and styrene monomer were used as starting materials,which were copolymerized at 120 ℃ to form random polysilazane-polystyrene copolymers.The copolymers were then pyrolyzed at 500 ℃ to obtain porous ceramics by completely decomposing polystyrene（PS） and converting polysilazane（PSZ） into non-oxide Si-C-N ceramics.The obtained material contained a bi-model pore-structure consisting of both micro-sized and nano-sized pores with very high surface area of more than500 m;/g.We also demonstrated that the pore structure and surface area of the materials can be tailored by changing the ratio of the two blocks.Current results suggest a promising simple method for making multiscaled porous non-oxide materials.展开更多
Si3N4 porous ceramics were fabricated by a combined foam-gelcasting and catalytic nitridation method at 1473-1623 K using silicon powder as the starting material,hexadecyl trimethyl ammonium bromide(CTAB)as the foamin...Si3N4 porous ceramics were fabricated by a combined foam-gelcasting and catalytic nitridation method at 1473-1623 K using silicon powder as the starting material,hexadecyl trimethyl ammonium bromide(CTAB)as the foaming agent,and different amounts of micron Fe powder as the catalyst.The effects of the nitridation temperature and the Fe powder addition on the phase composition,the mechanical properties,and the microstructure of the samples were researched.The results show that when nitriding at 1573 K for 5 h and adding 1 mass%Fe powder(with respect to the Si powder),the sample has a high porosity and suitable mechanical properties:the porosity of 76.5%,the compressive strength of 16.2 MPa,and the specific strength of 22.7 MPa•cm3•g^-1.展开更多
The situation of porous ceramics prepared from industrial waste slag(fly ash,red mud,metallurgical slag,tailings,etc.)was summarized.It was pointed out that the preparation of porous ceramics from industrial waste sla...The situation of porous ceramics prepared from industrial waste slag(fly ash,red mud,metallurgical slag,tailings,etc.)was summarized.It was pointed out that the preparation of porous ceramics from industrial waste slag can bring long-term economic and social benefits.The development trend of secondary utilization of industrial waste slag was also prospected.展开更多
基金supported by the National Science and Technol-ogy Major Project(No.J2019-IV-0003-0070)the National Natural Science Foundation of China(Grant No.12202343)the China Postdoctoral Science Foundation(No.2021M702582).
文摘Porous ceramic composites with directional microchannels from micrometer to dozens of micrometer levels have attracted more and more attention in various fields including aerospace,biomedicines,and thermal insulation due to their excellent fluid permeability,mechanical properties,etc.In this article,we summarize the recent directional porous ceramics developments including their main processing routes and respective properties.Meanwhile,the properties get from different processing routes have been com-pared and analyzed in terms of microstructures,mechanical properties,and permeability.Emphasis has been given to the deeper understanding which can allow one to control the microstructural features of these porous ceramic composites to obtain the desired characteristics.This work can provide a useful reference for the development and application of porous ceramic composites with directional microchan-nels.
基金financially supported by the National Natural Science Foundation of China(Grant No.51802347)the Natural Science Foundation of Hubei Province(Grant No.2022CFB939).
文摘The quest for lightweight and functional materials poses stringent requirements on mechanical performance of porous materials.However,the contradiction between high strength and elevated porosity of porous materials severely limits their application scenarios in emerging fields.Herein,high-strength multifunctional mullite-based porous ceramic monoliths were fabricated utilizing waste fly ash hollow microspheres(FAHMs)by the protein gelling technique.Owing to their unique shell-pore structure inspired by shell-protected biomaterials,the monoliths with porosity of 54.69%–70.02% exhibited a high compressive strength(32.3–42.9 MPa)which was 2–5 times that of mullite-based porous ceramics with similar density reported elsewhere.Moreover,their pore structure and properties could be tuned by regulation of the particle size and content of the FAHMs,and the resultant monoliths demonstrated superior integrated performances for multifunctional applications,such as broadband sound insulation,efficient thermal insulation,and high-temperature fire resistance(>1300℃).On this basis,mullite-based porous ceramic lattices(porosity 68.28%–84.79%)with a hierarchical porous structure were successfully assembled by direct ink writing(DIW),which exhibited significantly higher compressive strength(3.02–10.77 MPa)than most other ceramic lattices with comparable densities.This unique shell-pore structure can be extended to other porous materials,and our strategy paves a new way for cost-effective,scalable and green production of multifunctional materials with well-defined microstructure.
基金The National Natural Science Foundation of China(No.50846056)
文摘To improve the wall surface hydrophilicity of a tube type indirect evaporative cooler,a new method adopting porous ceramics is proposed.This method realizes the combination of porous ceramics and the evaporative cooling technique.The design calculation of the porous ceramics tube type dew point indirect evaporative cooler are carried out from such aspects as the volumes and status parameters of the primary and secondary air,the cooler structure,the heat transfer of the solid porous ceramic tubes and the resistance of the cooler.The calculation results show that the design is reasonable.Finally,based on the design calculation,the porous ceramics tube type dew point indirect evaporative cooler is successfully manufactured.
基金Puyang Re-fractories Co. Ltd. for financially supporting
文摘Porous ceramics were prepared from kaolinite gangue and Al（OH）3 with double addition of MgCO3 and CaCO3 by the pore-forming in-situ technique.The characterizations of porous ceramics were investigated by X-ray diffractometry,scanning electron microscopy,and mercury porosimetry measurements,etc.It is found that although the decomposition of MgCO3 and CaCO3 has little contribution to the porosity,the double addition of MgCO3 and CaCO3 strongly affects the formation of liquid phase,and then changes the phase compositions,pore characterization,and strength.The appropriate mode is the sample containing 1.17wt% MgCO3 and 1.17wt% CaCO3,which has high apparent porosity（41.0%）,high crushing strength（53.5 MPa）,high mullite content（76wt%）,and small average pore size（3.24 μm）.
基金financially supported by the National Natural Science Foundation of China (No. 50708037)the National Science Fund for Excellent Young Scholars of China (No. 51522402)+1 种基金the Science and Technology Research Projects in Zhengzhou (No. 141PPTGG388)the National Innovation and Entrepreneurship Training Program of the Undergraduate (No. 201610078034)
文摘Diatomite-based porous ceramics were adopted as carriers to immobilize nano-TiO2 via a hydrolysis-deposition technique. The thermal degradation of as-prepared composites was investigated using thermogravimetric-differential thermal analysis, and the phase and microstructure were characterized by X-ray diffraction, Fourier transform infrared spectroscopy, and transmission electron microscopy. The results indicated that the carriers were encapsulated by nano-TiO2 with a thickness of 300-450 nm. The main crystalline phase of TiO2 calcined at 650~C was anatase, and the average grain size was 8.3 nm. The FT-IR absorption bands at 955.38 cm1 suggested that new chemical bonds among Ti, O, and Si had formed in the composites. The photocatalytic （PC） activity of the composites was investigated un- der UV irradiation. Furthermore, the photodegradation kinetics of formaldehyde was investigated using the composites as the cores of an air cleaner. A kinetics study showed that the reaction rate constants of the gas-phase PC reaction of formaldehyde were k = 0.576 mg＇m3·min^-1 and K = 0.048 m3/mg.
文摘A new approach in combination of the effective medium theory with the equivalent unit in numerical simulation was developed to study the effective thermal conductivity of porous ceramics. The finite element method was used to simulate the heat transfer process which enables to acquire accurate results through highly complicated modeling and intensive computation. An alternative approach to mesh the material into small cells was also presented. The effective medium theory accounts for the effective thermal conductivity of cells while the equivalent unit is subsequently applied in numerical simulation to analyze the effective thermal conductivity of the porous ceramics. A new expression for the effective thermal conductivity, allowing for some structure factors such as volume fraction of pores and thermal conductivity, was put forward, and the results of its application was proved to be close to those of the mathematical simulation.
基金Supported by the National Natural Science Foundation of China （20990222, 21106061）, the National Basic Research Program of China （2009CB623406）, the National Key Science and Technology Program of China （2011BAE07B05） and the Natural Science Foundation of Jiangsu Province, China （BK2010549, BK2009021）.
文摘Heterogeneous catalysts with ultrafine or nano particle size have currently attracted considerable attentions in the chemical and petrochemical production processes, but their large-scale applications remain challenging because of difficulties associated with their efficient separation from the reaction slurry. A porous ceramic membrane reactor has emerged as a promising method to solve the problem concerning catalysts separation in situ from the reaction mixture and make the production process continuous in heterogeneous catalysis. This article presents a review of the present progress on porous ceramic membrane reactors for heterogeneous catalysis, which covers classification of configurations of porous ceramic membrane reactor, major considerations and some important industrial applications. A special emphasis is paid to major considerations in term of application-oriented ceramic membrane design, optimization of ceramic membrane reactor performance and membrane fouling mechanism. Finally, brief concluding remarks on porous ceramic membrane reactors are given and possible future research interests are also outlined.
基金National Natural Science Foundation of China under Grant No.(51372197)Key Innovation Team of Shaanxi Province under Grant No.(2014KCT-04)Provincial Joint Fund of Shaanxi(2021JLM-28).
文摘The large-scale accumulation and pollution of solid mining waste is an urgent issue.Coal gangue is a prominent type of solid waste,and shows promise for use in high value-added products due to its content of many important compounds,including SiO_(2) and Al2O3.This study proposed the preparation of highly porous ceramics from coal gangue,coal slime,and coconut palm fibers.The ceramics were produced at a sintering temperature of 950℃ with a fiber content of 6 wt%,which led to the formation of porous ceramics with a porosity of 66.93%,volume density of 1.0329 g/cm^(3),compressive strength of 1.1025 MPa,and thermal conductivity is 0.3919 K(W/mk).A finite element model of the porous ceramics was established using the Abaqus module in ANSYS software,where the stress distribution and compressive strength were simulated.Further,the relationship between porosity and compressive strength was analyzed.The thermal properties of the porous ceramics were analyzed using the Fluent module,where the simulated changes in porosity under various sintering temperatures were consistent with the experimental data.The preparation of this highly porous ceramic from solid waste coal gangue shows promise for the minimizing the impact of waste gas and wastewater pollution in the future.
基金The authors are grateful for the financial supports from the National Natural Science Foundation of China(Nos.51674207,51922091)the Young Elite Scientists Sponsorship Program by CAST,China(No.2018QNRC001)the Sichuan Science and Technology Program,China(Nos.2019YFS0453,2018JY0148).
文摘Porous ceramics were prepared with spodumene flotation talings(SFT),kaolin and low-melting point glass(LPG)powder,whose pores were formed by the chemical reaction of hydrogen peroxide(H_(2)O_(2)).LPG was used to reduce the sintering temperature of porous ceramics and kaolin was used to realize the adsorption to methylene blue(MB)of porous ceramics.The average flexural strength,compressive strength,apparent porosity,water absorption and maximum MB adsorption capacity were 5.60 MPa,4.66 MPa,52.27%,44.32%and 0.7 mg/g,respectively.Moreover,the results of orthogonal experiments present that the sintering temperature and the dosage of H_(2)O_(2)had great influence on the mechanical properties and apparent porosity of porous ceramics,respectively.The main reason for the improvement of mechanical properties of porous ceramics was that LPG gradually became soft with increasing the sintering temperature,which made the mineral particles adhere to each other closely.Kaolinite was not completely converted into metakaolin at 550℃,which might be the main reason why porous ceramics had adsorption properties.
文摘Porous ceramics was made from coal fly ash, and the microstructure and other properties were characterized as a function of the amount of the pore-forming agent and firing temperature. The results indicated that the proper sintering temperature for the useful ceramic materials is 1 250℃, and a liquid-phase was involved in the densification process.
文摘SiC porous ceramics were prepared at 1 400 ℃ for4 h with crystalline silicon cutting waste and activated carbon as main starting materials and NH4HCO3 as the pore-forming agent. Effects of NH4HCO3 additions( 0,20%,30%,40%,by mass) on the phase composition,microstructure,sintering properties,cold compressive strength and thermal shock resistance of as-prepared Si C porous ceramics were investigated. The results show that:( 1) addition of NH4HCO3 remarkably influences the apparent porosity and cold compressive strength of specimens. The apparent porosity achieves its maximum value( 63. 40%) when 40% NH4HCO3 is added,while the minimum cold compressive strength is 4. 77 MPa;( 2) the specimen with 40% NH4HCO3 has the best thermal shock resistance. The thermal cycling times between1 000 ℃ to room temperature reach 62;( 3) the addition of NH4HCO3 does not remarkably affect the phase composition of the specimens;( 4) the specimens include a large number of SiC particles and a small amount of SiC whiskers.
文摘The nanotitanium dioxide （TiO2） photocatalytic and porous ceramic filtering technique is one of the advanced methods to effectively treat organic wastewater. The TiO2 sol doped with Fe^3＋ ions was prepared by sol-gel processing. The influences of the process conditions of coating nanophotocatalytic material- Fe^3＋-TiO2 film on the surface of porous ceramic filter by dipping-lift method on the performance of porous ceramic filter were studied. The porous ceramic filters have two functions at the same time, filtration and photocatalytic degradation. The results of this study showed that the pH and viscosity of the sol, amount of Fe^3＋ ions doped as well as the coating times greatly affect the quality of coating film, the performance parameters and the photocatalytic activity of the porous ceramic filter. When the pH of the sol is 3-4, the viscosity is about 6 mPa.S, the amount of doped Fe^3＋ ions is about 2.0 g/L, the porous ceramic filter has been shown to have the best filtering performance and photocatalytic activity. In this condition, the porosity of porous ceramic is about 42.5%, the pore diameter is 8-10μm. The degradation of methyl-orange is 74.76% under lighting for 120 rain.
基金financially supported by the National Key Research and Development of China (No.2021YFB3400200)the National Natural Science Foundation of China (Nos.12090031 and 11602125)the Beijing Institute of Technology Research Fund Program for Young Scholars.
文摘Fibrous porous ceramics are attractive for use as thermal insulation materials.However,the intrinsic brit-tleness of rigid materials has remained challenging and severely restricts their applications.Here,we demonstrated a facile method for fabricating elastic fibrous porous ceramics(EFPCs)with high com-pressive strength and low thermal conductivity through ordinary press filtration and subsequent heat treatment.The quasi-layered structure and the well-bonded bridging fibers between layers are the key points for the elasticity of EFPCs.The advanced EFPCs exhibited low density(∼0.126 g cm^(−3)),high com-pressive stress(∼0.356 MPa),and low thermal conductivity(∼0.026 W m^(−1) K^(−1)).Compared with rigid porous fibrous materials,the EFPCs had deformability and excellent shape recovery.In contrast to flexible materials,the EFPCs possessed high compressive stress,thus endowing them with good resistance to de-formation.The emergence of this fascinating material may provide new insights for candidate materials in thermal insulation and other fields.
基金The authors gratefully acknowledged the supports of National Natural Science Foundation of China(Grant No.U1908227)open research fund for State Key Laboratory of Advanced Refractories(Grant No.SKLAR201904).
文摘Corundum-mullite porous ceramics(CMPCs)were fabricated using fly ash and aluminum ash as the raw materials,adding different amounts of starch(0,10%,20%,and 30%,by mass)as the pore-forming agent,molding and firing at 1200℃ for 1 h.The apparent porosity,the bulk density,the cold compressive strength,the thermal shock resistance and the thermal conductivity of the CMPCs were tested.The phase composition and the microstructure of the CMPCs were characterized by XRD and SEM.The effect of the starch addition on the properties of the CMPCs was studied.The results show that:(1)the CMPCs with high porosity can be successfully prepared by adding starch as the pore-forming agent and firing at 1200℃ for 1 h;(2)with the starch addition increasing,the porosity increases;the cold compressive strength and the number of the quenching cycles of the CMPCs decrease,but they remain at high levels;meanwhile,the thermal conductivity decreases;(3)generally,when adding 20 mass%starch,the CMPC has the apparent porosity of 48.6%,the cold compressive strength of 52.1 MPa,the quenching cycles of 5 and the thermal conductivity of 1.63 W·m-1·K-1 and 1.52 W·m-1·K-1,respectively,at 25℃ and 500℃,showing good performance.
基金the financial support of the National Natural Science Foundation of China (No. 21978109, 21878118)Natural Science Foundation of the Jiangsu Higher Education Institutions of China (19KJA430011)+2 种基金Natural Science Foundation of Jiangsu Province (BK20171268)Jiangsu Province industry-university-research cooperation project (BY2019179)Jiangsu Qing Lan Project。
文摘Alow-cost porous ceramic support was prepared from low-grade palygorskite clay(LPGS) and silicon carbide(SiC)with vanadium pentoxide(V_(2) O_(5)) additives by a dry-press forming method and sintering.The effects of SiC-LPGS ratio,pressing pressure,carbon powder pore-forming agent and V_(2) O_(5) sintering additives on the microstructure and performance of the supports were investigated.The addition of an appropriate amount of SiC to the LPGS can prevent excessive shrinkage of the support during sintering,and increase the mechanical strength and open porosity of the supports.The presence of SiC(34.4%) led to increases in the open porosity and mechanical strength of 40.43% ± 0.21% and(17.76 ± 0.51) MPa,respectively,after sintering at 700℃ for 3 h.Because of its low melting point,V_(2) O_(5) can melt to liquid during sintering,which increases the mechanical strength of the supports and retains the porosity.Certainly,this can also encourage efficient use of the LPGS and avoid wasting resources.
文摘Pyrophyllite is always used for making porous ceramics. In order to design the preparation technics of porous ceramics with pyrophyllite reasonably we must know the classifications, characteristics, properties and applications of porous ceramics. The classification and characteristics of porous ceramics are reviewed in this article; and several common preparations with their advantages and disadvantages are also introduced. The authors discussed the problems existing in researching and developing process for porous ceramics, and forecasted the development prospect of porous ceramics.
文摘SiC powder was rapidly synthesized in an induction furnace with crystalline silicon cutting waste and active carbon as raw materials,and then SiC porous ceramics were prepared at 1600 t for 4 h with carbon embedded using the powder as raw material,the starch and the graphite as pore-forming agents.Effects of additions of different pore-forming agents on the phase composition,microstructures,physical properties,and cold crushing strength of the porous ceramics were investigated.The results show that the main crystalline phases of the synthetic powder areα-S iC(6H-SiC)andβ-SiC(3C-SiC).The phase composition of the porous ceramics includesα-S iC(6H-SiC),β-SiC(3C-SiC),FeSi,quartz and Si2N20.The apparent porosity and closed porosity of the porous ceramics prepared by adding starch are higher,and the cold compressive strength of the porous ceramics added with graphite is higher.As increasing the additions of the starch,the apparent porosity,closed porosity and linear shrinkage ratio of the porous ceramics increase,and the bulk density decreases correspondingly.When 20 mass%starch is added,the apparent porosity,closed porosity,linear shrinkage ratio and cold compressive strength are 57.05%,2.03%,5.10%and 10.20 MPa,respectively.
基金financially supported by the National Natural Science Foundation of China(Grant Nos.21174112 and 51242009)the Research Fund of State Key Laboratory of Solidification Processing(Grant No.82-TZ-2013)+1 种基金the project "111"(B08040)the grant of the New Century Excellent Talents of Education Ministry of China(NCET-110817)
文摘In this paper,we reported a novel method for synthesis of non-oxide porous ceramics by using random copolymers as precursors.A silazane oligomer and styrene monomer were used as starting materials,which were copolymerized at 120 ℃ to form random polysilazane-polystyrene copolymers.The copolymers were then pyrolyzed at 500 ℃ to obtain porous ceramics by completely decomposing polystyrene（PS） and converting polysilazane（PSZ） into non-oxide Si-C-N ceramics.The obtained material contained a bi-model pore-structure consisting of both micro-sized and nano-sized pores with very high surface area of more than500 m;/g.We also demonstrated that the pore structure and surface area of the materials can be tailored by changing the ratio of the two blocks.Current results suggest a promising simple method for making multiscaled porous non-oxide materials.
基金National Natural Science Foundation of China(Grant No.51672194 and 51872210)Program for Innovative Teams of Outstanding Young and Middle-aged Researchers in the Higher Education Institutions of Hubei Province(T201602)+1 种基金Key Program of Natural Science Foundation of Hubei Province,China(Contract No.2017CFA004)the China Scholarship Council(CSC)(No.201808420278).
文摘Si3N4 porous ceramics were fabricated by a combined foam-gelcasting and catalytic nitridation method at 1473-1623 K using silicon powder as the starting material,hexadecyl trimethyl ammonium bromide(CTAB)as the foaming agent,and different amounts of micron Fe powder as the catalyst.The effects of the nitridation temperature and the Fe powder addition on the phase composition,the mechanical properties,and the microstructure of the samples were researched.The results show that when nitriding at 1573 K for 5 h and adding 1 mass%Fe powder(with respect to the Si powder),the sample has a high porosity and suitable mechanical properties:the porosity of 76.5%,the compressive strength of 16.2 MPa,and the specific strength of 22.7 MPa•cm3•g^-1.
基金financially supported by the open research fund for the State Key Laboratory of Advanced Refractories (Grant No. SKLAR201904)Fundamental Research Fund for the Central Universities (Grant No. N150204021)National Natural Science Foundation of China (Grant No. 51772277)
文摘The situation of porous ceramics prepared from industrial waste slag(fly ash,red mud,metallurgical slag,tailings,etc.)was summarized.It was pointed out that the preparation of porous ceramics from industrial waste slag can bring long-term economic and social benefits.The development trend of secondary utilization of industrial waste slag was also prospected.
