Properties Of Porous Ceramics Research Articles

Preparation and Properties of High Sound-Absorbing Porous Ceramics Reinforced by In Situ Mullite Whisker from Construction Waste.

Porous sound absorption ceramic is one of the most promising materials for effectively eliminating noise pollution. However, its high production cost and low mechanical strength limit its practical applications. In this work, low-cost and in situ mullite whisker-reinforced porous sound-absorbing ceramics were prepared using recyclable construction waste and Al2O3 powder as the main raw materials, and AlF3 and CeO2 as the additives, respectively. The effects of CeO2 content, AlF3 content, and sintering temperature on the microstructure and properties of the porous ceramics were systematically investigated. The results showed that a small amount of CeO2 significantly promoted the growth of elongated mullite crystals in the resultant porous ceramics, decreased the growth temperature of the mullite whiskers, and significantly increased the biaxial flexural strength. When 2 wt.% CeO2 and 12 wt.% AlF3 were added to the system, mullite whiskers were successfully obtained at a sintering temperature of 1300 °C for 1 h, which exhibited excellent properties, including an open porosity of 56.4 ± 0.6%, an average pore size of 1.32-2.54 μm, a biaxial flexural strength of 23.7 ± 0.9 MPa, and a sound absorption coefficient of >0.8 at 800-4000 Hz.

Effect of holding time on the properties of porous ceramics with high-volume polished slag and its pore structure characteristics

Poor utilization of ceramic polishing slag and uneven foaming at high temperatures are some of the crucial problems associated with the formation of porous ceramics. To overcome this, the present study was designed to prepare closed-ended polishing slag porous ceramics by controlling the holding time. Scanning electron microscope, XRD, and X-CT were used to investigate the effects of holding time on the microstructure, pore structure, and phase composition of porous ceramics. The results showed that the holding time had a great influence on the physical properties of the samples, and it provides uniform porosity without significant change in the composition of the material phase of the porous ceramics. Under a holding time of 30 min, volume density reached up to 0.68 g/cm3, while the water absorption and the apparent porosity were 27.33% and 15.49%, respectively. The compressive strength reached 13.07 MPa, and the pore size distribution is mainly between 25 μm and 100 μm, of which the d30 pore diameter accounted for about 28%, the d50 pore diameter accounted for 25%, the d70 pore diameter accounted for 12%, and the d90 pore diameter accounted for 10% of the pore size distribution. In conclusion, the present study clearly shows that the pore structure and properties of porous ceramics can be effectively controlled by controlling the holding time while using a high volume of polishing slag. The feasibility of X-CT for studying the pore distribution inside porous ceramics was verified.

Low sintering shrinkage porous mullite ceramics with high strength and low thermal conductivity via foam‐gelcasting

AbstractExcessive sintering shrinkage leads to severe deformation and cracking, affecting the microstructure and properties of porous ceramics. Therefore, reducing sintering shrinkage and achieving near‐net‐size forming is one of the effective ways to prepare high‐performance porous ceramics. Herein, low‐shrinkage porous mullite ceramics were prepared by foam‐gelcasting using kyanite as raw material and aluminum fluoride (AlF3) as additive, through volume expansion from phase transition and gas generated from the reaction. The effects of AlF3 content on the shrinkage, porosity, compressive strength, and thermal conductivity of mullite‐based porous ceramics were investigated. The results showed that with the increase of content, the sintering shrinkage decreased, the porosity increased, and mullite whiskers were produced. Porous mullite ceramics with 30 wt% AlF3 content exhibited a whisker structure with the lowest shrinkage of 3.5%, porosity of 85.2%, compressive strength of 3.06 ± 0.51 MPa, and thermal conductivity of 0.23 W/(m·K) at room temperature. The temperature difference between the front and back sides of the sample reached 710°C under high temperature fire resistance test. The low sintering shrinkage preparation process effectively reduces the subsequent processing cost, which is significant for the preparation of high‐performance porous ceramics.

Preparation and properties of porous ceramics from nickel slag by aerogel gelcasting

To further resource industrial solid waste, porous ceramics with high porosity were prepared by a gelcasting method using nickel slag and kaolin as raw materials and hydrophilic nontoxic SiO2 aerogel as a gelling agent. The effects of nickel slag content, dispersant and solid content on the properties and microstructure of porous ceramics were investigated in detail in terms of density, compressive strength, porosity, phase composition and micromorphology. The results confirmed that a certain amount of nickel slag can effectively improve the porosity of porous ceramics, while the addition of dispersant can promote the flow of the slurry, enhanced the denseness of the raw billet and significantly improved the compressive strength. However, its excessive use had a negative effect on the ceramic density and porosity. At the same time, the solid content played a key role in the performance of porous ceramics prepared by gelcasting, and too much solid content was also not conducive to the generation of pores. When the nickel slag content was 55%, the amount of dispersant was 2%, and the solid content was 60 vol%, the porous ceramic had a better overall performance, the density of the porous ceramic was 510 kg/m3, the compressive strength was 1.3 MPa, and the porosity reached 80.1%. The major crystalline phases of porous ceramics prepared by nickel slag were cordierite and anorthite.

Effect of sintering temperature on structure and properties of porous ceramics from tungsten ore tailings

• A novel disposal of tungsten ore tailings with a high reduction of its volume. • Phase composition and microstructure of porous ceramics were comprehensively studied. • Formation mechanism of the porous microstructure was proposed. • The obtained porous ceramics have potential as lightweight permeable building materials.

Preparation of Porous Ceramic Building Decoration Materials by Foaming Method and Research on Nanomechanical Properties.

Because of its excellent properties, mullite porous ceramics are widely used in thermal insulation materials, catalyst carriers, gas-liquid filtration, separation materials, etc. At the same time, zirconia not only has the advantages of high melting point, good chemical stability, and high strength but also can significantly improve the strength of ceramics through phase transformation and particle dispersion in the matrix and is widely used in the reinforcement of ceramics. In this paper, using mullite powder as the raw material, Al2O3 and SiO2/ZrSiO4 as the starting material for the mullite self-bonding phase, and AlF3·3H2O, ZrO2, and Y2O3 as additives, the zirconia-reinforced mullite was prepared by the foaming-injection method. The volume density, linear shrinkage rate, microstructure, room temperature, etc. of nanozirconia-reinforced mullite porous ceramics were studied by the amount of the foaming agent, the amount of mullite self-bonding phase powder, the type and amount of additives, etc. Effects of mechanical properties and thermal conductivity were also analyzed. The research results show that zirconia-reinforced mullite porous ceramics were prepared with mullite powder and 6 wt% AlF3·3H2O as raw materials, and ZrO2 and Y2O3 as additives. Adding an appropriate amount of ZrO2 and Y2O3 can significantly improve the mechanical properties of porous ceramics. When ZrO2 is 6 wt% and Y2O3 is 8 wt%, the porosity is 66.4% and the flexural strength and compressive strength of porous ceramics with a large pore size of 168 μm can reach 14.3 MPa and 36.3 MPa, respectively, which are obviously better than the strength of mullite porous ceramics without adding Y2O3 (flexural strength 11.3 MPa, nanocompressive strength 29.4 MPa).

Tunable Size of Hierarchically Porous Alumina Ceramics Based on DIW 3D Printing Supramolecular Gel.

A new three-dimensional (3D) printing gel is developed to construct hierarchically porous ceramics with adjustable millimeter-, micrometer-, and nanometer-scale size for application in thermal management. Not only does the gel based on supramolecular micelles exhibit excellent DIW 3D printability but also the supramolecular micelles act as templates that can precisely control the structure of micrometer-scale pores. The effect of millimeter- and μmicrometer-scale size on properties of porous ceramics is investigated in detail. The 3D-printed ceramic foam with millimeter-scale pores and smaller micrometer-scale pores shows better thermal insulation and lower compressive strength. For the thermal insulation, the local temperature of a chip exposed to contact heat is only 34.2 °C in the presence of a printed foam cap with a pore size of 41.5 μm, while the local temperature is 54.8 °C in the absence of the printed foam cap. The study provides a new method to construct hierarchically porous alumina ceramics with precisely tunable size, avoiding the issues of subtractive manufacturing and opening up new applications in portable devices or consumer electronics.

The Effects of a Zirconia Addition on the Compressive Strength of Reticulated Porous Zirconia-Toughened Alumina

Porous ceramics have attracted researchers due to their high chemical and thermal stability. Among various types of porous ceramics, reticulated porous ceramics have both high porosity and good permeability. These properties of porous ceramics are difficult to replace with porous metals and polymers. ZTA is used in a variety of applications, and a wealth of experimental data has already been collected. However, research reports on reticulated porous zirconia-toughened alumina (ZTA) are insufficient. Therefore, we prepared reticulated porous ZTA via the replica template method. In this study, various processing conditions (average particle size, zirconia content, solid loading, dispersant, and thickener) were adjusted to improve the compressive strength of the reticulated porous ZTA. As a result, the optimized processing conditions for improving the compressive strength of reticulated porous ZTA could be determined.

Processing study of gel-cast tubular porous NiO/SDC composite materials from gel-combustion synthesized nanopowder

In the present research, NiO–SDC (Samarium doped Ceria) nanopowder was synthesized through sol–gel combustion method using citric acid as a reducing agent (fuel) and metal nitrates as an oxidant. The characteristics of the synthesized powder were thoroughly analyzed by DTA/TG, XRD, BET and FESEM/EDX. Tubular gel-casted porous specimens of NiO–SDC (50:50 wt%) composite materials were produced after stabilizing suspensions of composite powder in an aqueous environment by addition of 3 wt% dispersant and 2.5 wt% agar as the gel builder. The effect of Dolapix CE64 as a dispersant, agar as a gel-builder and the amount of solid loadings on the processing and properties of porous ceramics was investigated. Viscosity measurements, zeta potentials of suspensions with and without dispersant and sedimentation measurement were used to determine the optimum dispersant concentration and solid concentration needed to prepare a stable slurry. The phase composition and microstructure of sintered samples were studied by X-ray diffraction (XRD) and scanning electron microscopy (SEM). Moreover, the distribution and porosity of the samples were determined through mercury porosimetry method. Results confirmed that stable NiO–SDC slurries with high solid loading (60 %) were achieved with Dolapix CE64, which also met the requirements to reach porous tubular samples with up to 60% porosity.

Effect of Different Particle Sizes and Pore-Making Agent Ratio on Properties of SiC Porous Ceramics

In this paper, SiC particles of different particle sizes were used as aggregates to prepare SiC porous ceramics (50-70 mesh, 70-80 mesh and 80-90 mesh), and their flexural strength, filtration pressure drop and porosity were tested. On this basis, SiC with 80-90 mesh size was used as the aggregate, and the properties of porous ceramics were measured by using different proportions of pore-making agent. The results showed that when SiC particles were 80-90 mesh and the ratio of pore-making agent was 2:1, the samples prepared at 1300°C for 1.5h had the best comprehensive performance, the porosity was 33.9%, the flexural strength was up to 38.28MPa, and the filtration pressure drop was relatively low.

Influence of different types of chamot on a structure and properties of porous ceramics

The results of research of porous materials on the basis of products of ceramic production - chamot as a fractionating filler are given.. The features of formation of structure of material at the use of chamot with different chemical and mineralogical compositions in the conditions of speed baking are shown.
 Porous ceramics for filtration and aeration is obtained by a technology based on the regulation of porosity parameters by the use of chamotte of a certain granulometric composition and special binders.
 However, the granulometric composition of chamotte is a necessary but not sufficient factor to optimize the properties of porous filter ceramics. Along with the granulometry of chamotte, its chemical and mineralogical composition and surface energy must be taken into account. It depends in turn on the technological properties and the firing parameters of the original clay raw material.
 This paper presents the results of a study of porous materials based on ceramic products - chamotte as a fractionated filler. The chemical and mineralogical composition of chamotte made of poly-mineral clay at maximum firing temperature of 950°С and of refractory clay at firing at 1320°C was analyzed.
 The energy state of the surface of the chamotte particles was determined with the wetting by polar and non-polar liquids (water and benzene respectively). The differences in the specific effective surface area, lyophilicity and filtration coefficients was determined.
 The peculiarities of the formation of the pore structure of ceramics obtained using the specified samples of chamotte in the conditions of high-speed firing in the roller oven are shown. Significant differences in the formation of open and closed pores were observed, the predominant specific proportion of open pores in the material using polymineral clay.
 The possibility of properties regulation of the pore structure and the energy state of the surface of the filter material when applying a mixture of chamotte varieties was experimentally confirmed.

Preparation of near net size porous alumina‐calcium aluminate ceramics by gelcasting‐pore‐forming agent processs

AbstractIn the processing of porous ceramics, shrinkage from green body to sintered compact during drying and sintering is one of the key concerns which affect microstructure and properties of porous ceramics. Through releasing gases from the burning of the pore forming agents, and volume expansion from the formation of low density resultants during sintering, the sintering shrinkage can be effectively compensated and near net size preparation can be achieved. Herein, near net size porous alumina‐calcium aluminate ceramics with controllable shrinkage have been prepared using a combination of gelcasting and pore‐forming agent process by adjusting the amount of CaCO3 and polymethyl methacrylate (PMMA) microspheres added. Al2O3 and CaCO3 were used as raw materials, PMMA microspheres were used as pore‐forming agent, isobutylene/maleic anhydride copolymer (Isobam104) was used as gelling agent and dispersing agent. The effects of the addition amounts of CaCO3 and PMMA in the slurry on the phase composition, shrinkage, porosity, and strength of porous alumina‐calcium aluminate ceramics were investigated. The results show that as the CaCO3 addition amount increases from 0 to 20 wt%, the shrinkage of the samples gradually decreases from 7.3% to −1.4%, and the consequent porosity increases from 58% to 66%, while the compressive strength increases from 5.9 to 15.5 MPa. When PMMA content increases from 10 to 50 wt%, the shrinkage of the samples decreases first and then increases, the porosity increases from 51% to 74%, and the compressive strength decreases from 12.5 to 5.3 MPa. The mechanisms for controlling shrinkages during preparation of porous alumina‐calcium aluminate ceramics can be attributed to the following aspects: on one hand, gas release from burning of PMMA and decomposition of CaCO3 during sintering; on the other hand, volume expansion due to the formation of lower density calcium aluminates which come from the reactions between CaO and Al2O3. The near net size preparation technique is of great significance for the manufacture of porous ceramics since the subsequent machining cost can be effectively reduced.

Computation of effective thermo-piezoelectric properties of porous ceramics via asymptotic homogenization and finite element methods for energy-harvesting applications

We consider the linear thermo-piezoelectric properties of a ceramic matrix with cylindrical empty pores distributed periodically. The asymptotic homogenization method is applied to an elliptical tensor-weighted boundary value problem in the Stress-Charge-Entropy formulation of the constitutive relations with rapidly oscillating coefficients and free boundary conditions on the surfaces of the pores. For different shapes of the pore cross section, we solve the local problems via finite element method to compute the effective coefficients as functions of the physical properties of the matrix, the shape of the pore cross section and their volume fraction. The numerical results show excellent agreement with analytical formulae. When the effective coefficients are transformed to the Strain-Charge-Entropy formulation of the constitutive relations, they become independent of the shape of the cross section, which further validates the importance of the analytical formulae. We compute the piezoelectric and pyroelectric figures of merit for energy-harvesting applications, which depend on the effective coefficients and are compared with recent experimental results. This contribution could be useful for fine-tuning the properties of this class of materials for energy-harvesting applications.

Effect of alumina fiber content on pore structure and properties of porous ceramics

AbstractPorous Al2O3 ceramics with different contents of alumina fibers were prepared by gel‐casting process. The effects of Al2O3 fiber content on pore size distribution, porosity, compressive strength, and load‐displacement behavior of the ceramic materials were investigated. Initial results showed that with the increase of Al2O3 fiber content, the pore size and porosity of the material is increased, and the compressive strength is decreased. However, upon increasing the fiber content from 50 wt% to 67 wt%, the performance of the samples changed greatly. The compressive strength of the material increased, while the porosity remained unchanged, the pore size increased greatly, and the shape of the load displacement curve changed. It showed that when the fiber content increased from 50 wt% to 67 wt%, the loading body in the fiber‐reinforced porous ceramics changed from particles to fibers.

Effect of waste ceramic adsorbent on wastewater treatment

The preparation of porous ceramic with waste porcelain powder as aggregate research. The influence of the amount of Sesbania powder and the calcination temperature on the adsorption performance of porous ceramics was investigated. The effect of the amount of porous ceramic and the adsorption time on the removal rate of Cu in wastewater containing Cu was investigated.The results showed that the adsorption properties of porous ceramics were related to the calcination temperature and the amount of Sesbania powder. The suitable calcination temperature and the amount of Sesbania powder were 600 °Cand 4 wt%, respectively.The removal rate of Cu in water samples increases with the increase of the amount of porous ceramics and the increase of adsorption time. The suitable amount of porous ceramics is 10 g/L and the adsorption time is 35 min. XRD characterization showed that the crystal particles were grown by calcination, and the properties of porous ceramics were stable before and after adsorption.

Evaluation of static strength properties of porous ceramics with various pore morphology

Evaluation of static strength properties of porous ceramics with various pore morphology

Effects of Al2O3 crystal types on morphologies, formation mechanisms of mullite and properties of porous mullite ceramics based on kyanite

Porous mullite ceramics with different crystal shapes of mullite are fabricated by in-situ reaction with middle-grade kyanite as raw material, Al(OH)3, γ-Al2O3, ρ-Al2O3 and α-Al2O3 as alumina sources. Effects of Al2O3 crystal types on morphology evolution and formation mechanisms of mullite, and properties of porous ceramics are investigated. Results show that mullite in the sample with Al(OH)3 mainly shows acicular morphology, because its (001) plane has the minimum interplanar crystal spacing and maximal attachment energy, it grows fast along [001] direction by screw dislocation mechanism. With a successive slowdown in reactivities of Al(OH)3, γ-Al2O3, ρ-Al2O3 and α-Al2O3, the amount and aspect ratio of mullite reduce, its growth mechanism gradually transforms into two-dimensional nucleation. Acicular mullite not only reinforces samples, but makes effective pore sizes smaller, which enable the sample with Al(OH)3 to present low bulk density, high apparent porosity and linear changes, small average pore size and good mechanical strength.

Utilization of Electrolytic Manganese Residues in Production of Porous Ceramics

Electrolytic manganese residues (EMR) are one of industrial by‐products generated during the production of electrolytic manganese metal. To reduce the EMR hazard to environment and invent value‐added materials, porous ceramics were prepared by the pore‐forming method with EMR and various additives. The influences of the incorporation of different additives, sintering temperature, and molding pressure on properties of porous ceramics were investigated. Properties such as apparent porosity, water absorption, bulk density, and compression strength have been measured. The EMR‐based porous ceramics were also characterized by XRD, SEM, BET‐specific surface area, and BJH pore size distribution measurement. It revealed that the appropriate mode was the sample containing 20 wt% carbon powder, 7.5 wt% dolomite, and 5 wt% kaoline, under which the ceramics with the properties of high apparent porosity (69.70%), high compressive strength (6.97 MPa), and good acidity–alkali stability were obtained successfully. The comprehensive performance of EMR‐based porous ceramics makes them advantageous to use as nonhazardous and valuable materials showing promising potential applications, which not only is a promising new approach to improve the resource utilization of EMR but also can promote the manganese industry's sustainable and healthy development and protect and improve ecological environment.

Reparation and properties of porous ceramics via re-coating technique

Reparation and properties of porous ceramics via re-coating technique

Research Progress in Preparation of Porous Ceramics

Porous ceramics have been extensively studied during the last two decades because of their potential application in the fields of thermal insulators, gas filters, catalytic supports, separation membranes, kiln furniture, and biomedical substitutes for bone and teeth. The properties of porous ceramics are highly dependent on their method of preparation. This mini-review summarizes recent developments in innovative fabrication of porous ceramics such as three-dimensional printing, molten salt synthesis, and the sacrificial template and replica methods. Finally, we conclude with our personal perspectives and recommendations for future research in porous ceramics.