Research of Microstructure,Phase,and Mechanical Properties of Aluminum-Dross-Based Porous Ceramics

In this study,the effect of sintering temperature and the addition of kaolin,a sintering agent,on the microscopic,phase,and mechanical properties of ceramics were investigated using secondary aluminum dross(SAD)as the main component in the manufacturing of ceramics.The basic phases of the ceramics were Al_(2)O_(3),MgAl_(2)O_(4),NaAl_(11)O_(17),and SiO_(2)without the addition of kaolin.The diffraction peaks of MgAl_(2)O_(4),NaAl_(11)O_(17),and SiO_(2)kept decreasing while those of Al_(2)O_(3)kept increasing with an increase in temperature.In addition,the increase in temperature promoted the growth of the grains.The grains were uniform in size and regular in distribution,with a shrinkage of 2.2%,porosity of 72.5%,bulk density of 1.076 g/cm^(3),and compressive strength of 1.12 MPa.When the sintering temperature was 1450°C,the basic phases of the ceramic after the addition of kaolin were Al_(2)O_(3),MgAl_(2)O_(4),NaAl_(11)O_(17),and SiO_(2).With the increase of kaolin,the diffraction peaks of NaAl_(11)O_(17)and SiO_(2)decreased until they disappeared,while the diffraction peaks of Al_(2)O_(3)increased significantly.When kaolin was added at 30 wt.%,the ceramics obtained had shrinkage of 18%,a porosity of 47.26%,a bulk density of 1.965 g/cm^(3),and compressive strength of 31.9 MPa.Cracks existed inside the ceramics without the addition of kaolin,while the addition of kaolin significantly changed this defect.It is shown that SAD can obtain porous ceramics with good properties at a sintering temperature of 1450°C and a kaolin addition of 30 wt.%.

Carbon Capture from Flue Gas Based on the Combination of Non-Contact Hydrophobic Porous Ceramic Membrane and Bubbling Absorption

A hybrid system combined with a non-contact membrane and bubbling absorption is proposed to capture CO_(2) from flue gas.The non-contact way of membrane and liquid absorbent effectively avoids the reduction of gas diffusion flux through the membrane.High-porosity ceramic membranes in hybrid systems are used for gas-solid separation in fuel gas treatment.Due to the high content of H_(2)O and cement dust in the flue gas of the cement plant,the membrane is hydrophobically modified by polytetrafluoroethylene(PTFE)to improve its anti-water,anti-fouling,and self-cleaning performances.The results show that the diffusion flux of CO_(2) through the membrane is still higher than 7.0×10^(−3) mol/m^(2)s(20%CO_(2) concentration)even under the influence of water and cement dust.In addition,slaked lime selected as the absorbent is cheap and the product after bubbling absorption is nano-scale light calcium carbonate.To sum up,the hybrid system combining non-contact membrane and bubbling absorption is expected to be used to capture carbon dioxide from the flue gas of the cement plant.

Progress in Preparation Technology of Porous Ceramics for High Temperature Dust Filtration

With the rapid industrialization and urbanization,the demand for air quality management is more and more urgent.High temperature dust filtration is one important environmental management technology.Porous ceramics are used as filter materials in the field of high-temperature dust filtration because of their unique advantages such as high filtration efficiency,as well as high temperature stability,particle loss resistance,corrosion resistance and durability.This paper mainly introduced several common preparation techniques of porous ceramics,including the traditional organic foam impregnation method,foaming method,in-situ combustion method,pore-forming method and other new methods such as the template method,gel injection molding method,freeze-drying method,multi-component co-precipitation method and hydrogel method.The principle,advantages and disadvantages of these preparation technologies and their research status were described.The application of these technologies in the field of high temperature dust filtration was briefly reviewed.Finally,the application prospect of the porous ceramics in the field of high temperature dust filtration was prospected.

Design calculation of porous ceramics tube type dew point indirect evaporative cooler

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.

Preparation of nano-TiO_2/diatomite-based porous ceramics and their photocatalytic kinetics for formaldehyde degradation

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.

Preparation and characterization of porous ceramics prepared by kaolinite gangue and Al(OH)_3 with double addition of MgCO_3 and CaCO_3

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）.

A Novel Approach for the Effective Thermal Conductivity of Porous Ceramics

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.

Progress on Porous Ceramic Membrane Reactors for Heterogeneous Catalysis over Ultrafine and Nano-sized Catalysts

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.

Constructing Straight Pores and Improving Mechanical Properties of GangueBased Porous Ceramics

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.

Preparation and properties of porous ceramics from spodumene flotation tailings by low-temperature sintering

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.

Preparation and characterization of the porous ceramics from fly ash

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.

Preparation of SiC Porous Ceramics by Crystalline Silicon Cutting Waste

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.

Preparation and Characterization of Nanotitanium Dioxide Coating Film Doped with Fe^(3+) Ions on Porous Ceramic

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.

Effect of Starch Addition on Properties of Corundum-mullite Porous Ceramics

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.

Preparation and properties of a low-cost porous ceramic support from low-grade palygorskite clay and silicon-carbide with vanadium pentoxide additives

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.

Preparation and characteristics of porous ceramics

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.

Effects of Pore-forming Agents on Properties of Silicon Carbide Porous Ceramics Prepared from Crystalline Silicon Cutting Waste

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.

Preparation of Si3N4 Porous Ceramics via Combined Foam-gelcasting and Catalytic Nitridation with Fe Powder as Catalyst

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.

Research Progress on Porous Ceramics Prepared from Industrial Solid Wastes

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.

Thermal Insulation Materials of Alumina Based Porous Ceramics

Significant energy saving effects can be made through the improvement of furnace refractories,especially the thermal insulation refractories. In this study,the preparation and the application of different alumina based porous ceramics were briefly introduced. Alumina based porous ceramics were prepared combined foaming method with gelcasting,sol- gel process or cement curing process. The influences of different preparation methods on the sintering shrinkage, porosity, phase composition, microstructure, compressive strength and thermal conductivity were discussed. Alumina based porous ceramics with relatively high strength and low thermal conductivity could be obtained through the above mentioned methods. Compared with the traditional lining materials,about 40% energy could be saved when they were used as the furnace wall.