Properties Of Porous Alumina Ceramics Research Articles

Fabrication of porous aluminum ceramics beyond device resolution via stereolithography 3D printing

This paper presents a new method for fabricating high-resolution porous ceramics using the 3D printing technology. Stereolithography 3D printing was used to create porous alumina parts with polyamide 12 (PA12) powder, alumina ceramic particles, and acrylic resin as the sacrificial porogen, aggregate, and mixture, respectively. After subsequent de-binding and sol impregnation treatments, a porous alumina part with a particle size of 15 μm was obtained after sintering. The use of aluminum sol enhanced the mechanical properties of porous alumina ceramics, thus enhancing their strength. A discrete element method model was used to simulate and explain the results, thereby providing insights into the optimization of the method design. Accordingly, this study demonstrated the potential for using the stereolithography 3D printing technology to fabricate high-resolution porous ceramics with tailored properties for various applications.

Porous Alumina-Bentonite Ceramics: Effects of Fillers and Molding Technique

In porous ceramics processing, the green body shaping technique largely determines the control of the final porous structure and material properties. The study is aimed at finding affordable approaches for the shaping of two different narrow-fraction fillers: F240 electro-corundum and hollow alumina microspheres. The results revealed the influence of accessible shaping techniques (semi-dry pressing, direct casting, and slip casting) on the structural and mechanical properties of porous alumina ceramics. The starting materials were characterized by XRD, SEM, EDX, and BET. The manufactured ceramics were studied in terms of microstructure, density, porosity, and flexural strength. Free stacking of the fillers’ particles during the direct and slip casting resulted in a higher porosity of ceramics compared with that of semi-dry pressing, while reducing its mechanical strength. Direct casting appeared preferable for ceramics with hollow microspheres because it maintained the integrity of the filler particles and preserved their inherent porosity in the ceramics. The optimal parameters for porous ceramics processing were determined as follows: pressing at 30 MPa and sintering at 1280–1320 °C with a bentonite content of 15 wt.%. In this case, the average density and open porosity of F240 samples reached 2.22 g cm−3 and 40.4%, while samples containing hollow microspheres reached 2.20 g cm−3 and 36.7%, respectively.

Preparation and properties of porous alumina ceramics for ultra-precision aerostatic bearings

γ-alumina powder was mixed with α-alumina powder to fabricate porous ceramics. With an increase in the γ-alumina content, the porosity of the ceramics first increased and then decreased. The open porosity of the ceramics was the same as their total porosity when the γ-alumina content was equal to or greater than 20 wt%. The permeability and open porosity of the porous alumina had a power-function relationship. The addition of γ-alumina not only realised pore transfixion, but also effectively enhanced the compressive strength of the ceramics. The maximum pore size of the ceramics increased with an increase in the γ-alumina content, which contributed to the increase in the bearing capacity and stiffness. When the γ-alumina content was 50 wt%, the porous alumina exhibited an open porosity of 25% and a permeability of 3.2 × 10−15 m2, while the compressive strength and elastic modulus were 325 MPa and 145 GPa, respectively. The bearing stiffness of the film with a thickness of 7.5 μm reached 13.5 N/μm at the air supply pressure of 0.3 MPa. These ceramics showed potential for application in ultra-precision aerostatic bearings.

Preparation of self-lubricating porous alumina ceramics with PMMA /PAO6 microcapsules and their tribological properties

In this work, we showed that immersing polymethyl methacrylate (PMMA)/poly alpha olefins (PAO6) microcapsules into the porous matrix can improve the lubrication properties of porous alumina ceramics dramatically. PMMA/PAO6 microcapsules were synthesized by microemulsion polymerization, and the microcapsules were immersed in the porous alumina ceramic matrix by vacuum impregnation. The lubrication behaviors of the porous alumina ceramics with PMMA/PAO6 microcapsules have been investigated under different loads. As compared with the unprocessed porous alumina ceramics, the coefficient of friction (COF) of the porous ceramics impregnated with microcapsules could be reduced to 4% of that without microcapsules, and the wear rate could be reduced by two orders of magnitude. No obvious change of the COF was noticed for the matrices with different pore sizes. The good self-lubrication properties were achieved by releasing the PAO6 in the microcapsules during the friction process.

Tailored pore structures and mechanical properties of porous alumina ceramics prepared with corn cob pore‐forming agent

AbstractIn this work, the effects of porosity and different particle sizes of pore‐forming agent on the mechanical properties of porous alumina ceramics have been reported. Different grades of porous alumina ceramics were developed using corn cob (CC) of different weight contents (5, 10, 15, and 20 wt%) and particle sizes (<63 µm, 63‐125 µm and 125‐250 µm) as the pore‐forming agent. Experimental results showed that total porosity and pore cavity size of the porous alumina ceramics increased with rising addition of CC pore former. Total porosity increased with increasing particle size of CC with the Al2O3‐<63CC5 sample exhibiting the lowest total porosity of 41.3 vol% while the highest total porosity of 68.1 vol% was exhibited by the Al2O3‐125‐250CC20. The particle size effect of CC on the mechanical properties revealed that diametral tensile strength and hardness of the porous alumina ceramics deteriorated with increasing particle size of CC pore former. The Al2O3‐<63CC5 sample exhibited the highest diametral tensile strength and hardness of 25.1 MPa and 768.2 HV, respectively, while Al2O3‐125‐250CC20 exhibited the lowest values of 1.1 MPa and 35.9 HV. Overall, porous alumina ceramics with the smallest pore sizes under each particle size category exhibited superior mechanical properties in their respective categories.

Optical Properties of Porous Alumina Ceramics with Micron Open Cells

Porous ceramic material is widely used in a great deal of fields. In this work, porous alumina ceramics with micron open cells are modeled by applying the inverse opal structure. The considered porous alumina ceramics are periodic with different size parameters. The diameters of spherical pores are 200, 400, 600, and 800 nm, while the ratios of height to diameter range from 0.1 to 0.9. The absorptivity, transmissivity, and reflectivity for the wavelength range from 0.2 to 2 μm are calculated using the finite difference time domain (FDTD) method. Then the effects of size parameters and incident angle on the optical properties are discussed. The results show that the absorptivity is usually very small. For the transmissivity, a wide dip in the transmission spectrum appears when the diameter and height exceed the critical values, and a red shift of the transmission spectrum's wide dip with increasing height is observed. When the incident wavelength is longer than the critical wavelength, the spectral transmissivities of porous ceramics with a certain diameter reach a stable domain. Moreover, the red shift of the wide dip, the critical incident wavelength, and the critical ratio of height to diameter are visibly affected by the size parameters and the incident angle.

Investigation of mechanical properties of porous alumina ceramics: experiment and simulation

The paper presents the experimental data on elastic and strength characteristics of specimens made of porous Al2O3 ceramics in three-point bending. Ceramics specimens were prepared by the slurry casting of commercially pure Al2O3 powder and subsequent sintering at the temperatures 1400, 1500, and 1600 °C. The simulation results were reported for the mechanical behaviour of specimens of porous Al2O3-based ceramics at the mesolevel. We studied the mesovolumes with an explicit treatment of pores loaded in uniaxial tension. The pore structure of the mesovolumes was borrowed from experimental SEM images. The mesoscopic fracture was described using the fracture criterion which includes the Lode parameter to make allowance for the stress state type. Despite wide scatter, the experimental and calculated elastic and strength characteristics of the material agree rather well.

Effect of Nano-Copper Additives on the Physical Properties of Porous Alumina Ceramics using Graphite Waste as a Pore-Forming Agent

Solid state and sacrificial techniques were used to prepare the porous alumina ceramics. The target of the present research is to investigate the effect of Cu metal addition of nanoscale particle size on the physical properties of porous alumina ceramics using graphite waste as a pore-forming agent. X-Ray Diffraction (XRD), a Field Emission Scanning Electron Microscope (FESEM) and a Transmission and Electron Microscope (TEM) were used to analyse the microstructure and ceramic phases. Different ratios of Cu metal were added (3, 6, 9 and 12 wt.%) at different ratios of graphite waste. The results of this investigation show that with increasing ratios of Cu metal, the porosity decreased while the shrinkage and densities increased. Increases in the density and decreases in the porosity of porous alumina ceramics and the formation of the tenorite (CuO) phase due to sintering at high temperature (1600°C) may lead to improving the strength of porous alumina ceramics. Some potential applications include gas filtration components and as thermal insulation materials.

Porous alumina ceramics by gel casting: Effect of type of sacrificial template on the properties

AbstractThe effect of type of sacrificial template on the processing and properties of porous alumina ceramics was investigated. Two templates, (a) hollow pre‐expanded polymer spheres (Expancel) and (b) dense glassy carbon, were used to prepare porous alumina ceramics by gel casting. The results showed that the burnout of sacrificial expandable polymer microspheres from alumina ceramics was 10 times faster than glassy carbon without compromising the compressive strength. Moreover, the effect of the size of the porous ceramic component during the burnout showed that the template decomposition and the escape of the formed gases took a longer time for the thicker specimens than the thinner one and it was significant in case of glassy carbon. It was found that the burnout of expandable microspheres could happen at a faster rate, and the time of the burnout cycle could be reduced significantly to save energy while keeping the mechanical strength twice as high than porous alumina ceramics after burnout of glassy carbon. Furthermore, the CO2 emissions during the burnout of sacrificial templates and the microstructure of the prepared porous alumina were compared for these two types of sacrificial templates. The prepared foams with pre‐expanded microspheres showed potential for being used in industrial applications, where the decreasing of the released gases is critical for saving time and energy for the fabrication of large ceramic parts.

Evaluation of mechanical properties of porous alumina ceramics obtained using rice husk as a porogenic agent

Abstract The objective of this work was to evaluate the mechanical properties of porous alumina ceramics, using the rice husk as a porogenic element. The rice husk was milled and graded in two granulometry, <65 μm and 65-150 μm, and added in a high purity calcined alumina in the proportion of 5, 15 and 30 wt%. The samples were pressed by uniaxial pressing and sintered at 1450 oC for 1 h. Sintered density, total porosity, Young’s modulus, modulus of rupture, and compressive strength were evaluated. Samples were also prepared without the addition of rice husk (RH) in order to compare the properties. Porous ceramics with total porosity ranging from 24% to 54% were produced, and with the composition of 5% RH 65-150 μm, a high porosity value was obtained for a lower loss in mechanical properties.

Porous alumina ceramics with enhanced mechanical and thermal insulation properties based on sol-treated rice husk

To improve the properties of porous alumina ceramics, which were typically prepared by adding pore-forming agents, rice husk (RH) as pore-forming agent was pretreated with zirconia sol. The effects of sol-treatment on the thermal conductivity and compressive strength of the resultant ceramics were characterized. Furthermore, the pore size distribution, pore shape, microstructure, and phase evolution also were studied. The results showed that the RH pretreatment optimizes the microstructure of the ceramic pores. Moreover, complete morph-genetic RH is clearly observed in the pores, which is established as a key factor in improving the properties of the resultant ceramic. The thermal insulation properties are determined to significantly improve, although the thermal conductivity increases slightly with the increment of zirconia sol concentration from 5 to 10 wt%. Meanwhile, after sintering at 1550 °C, the compressive strength is significantly greater for the specimen prepared with 10 wt% zirconia sol-treated RH (65.56 MPa) than that with untreated RH (43.37 MPa). Hence, it was demonstrated that the use of zirconia sol-pretreated RH as a pore-forming agent could enhance the mechanical and thermal insulation properties of porous alumina ceramics.

Effects of B4C addition on the microstructure and properties of porous alumina ceramics fabricated by direct selective laser sintering

Direct selective laser sintering (dSLS) is a promising method for the fabrication of complex-shaped ceramic parts. In this paper, boron carbide (B4C) was used as an inorganic additive to improve the laser sintering behavior of alumina. The effects of B4C addition on the microstructure and mechanical properties of porous alumina ceramics were investigated. Mixture of alumina powders and different amount of B4C were directly sintered using different SLS parameters. Results indicated that the process window of alumina could be expanded by the addition of B4C. Furthermore, the amount of B4C played an important role in surface morphologies of alumina ceramics. It could be explained by the increase of mass transfer due to the addition of B4C, which enhanced the densification process. The compressive strength of sintered samples increased with the increase of B4C, which reached its maximum value when the content of B4C was 7 wt% and the density of the samples after post treatment could reach 1.4 g/cm3. In addition, a size expansion phenomenon was observed. The size expansion could reach 5% after SLS, which could be attributed to the pin effects and oxidation behavior of B4C particles.

Enhanced mechanical properties and decreased thermal conductivity of porous alumina ceramics by optimizing pore structure

In order to reduce thermal conductivity but to exhibit better mechanical properties of porous alumina ceramics (PACs), a novel approach, based on the modification of pore structures (i.e. mean pore size, micro-pore proportions and pore shape factor) by impregnation of alumina sol, is reported in the present work. The properties of as-impregnated samples were compared with commercial alumina hollowsphere bricks. Results show that impregnation of alumina sol in PACs has a positive influence on pore structures, leading to a superior strength and a lower thermal conductivity. In particular, when 8 wt% alumina sol solid content is impregnated, the crushing strength (35.3 MPa) and thermal conductivity (0.15 W/m K at 200 °C) of sample are much better than that of the commercial alumina hollowsphere bricks. This novel method for excellent PACs provides promising applications as insulating lining materials in the fields of industrial furnace.

Optimal design on the high-temperature mechanical properties of porous alumina ceramics based on fractal dimension analysis

Fractal theory and regression analysis were employed for the first time to investigate the effect of pore size and pore distribution on high-temperature mechanical properties of porous alumina ceramics (PAC). In the present work, PAC with the comparable porosity, different pore sizes and pore distributions were prepared using carbon black as the pore-forming agent. Particular emphasis in this study was placed on the establishment of correlation between the thermal shock resistance and pore properties. The relationship between fractal dimension (Df) andthermal shock resistance parameter (Rst) in specimens presented the negative power function, indicating that low Df could benefit the improvement of thermal shock resistance in specimens. The results showed that the increase of pore size and pore sphericity leads to a reduced Df, the enhanced hot modulus of rupture (HMOR) and. The decrease of proportion of micro-pores below 2 μm, the increase of mean pore size and pore sphericity could result in the decrease of Df, and then improve Rst and HMOR of specimens. Based on the correlation between Rst and pore characteristics, PAC with improved thermal shock resistance could be achieved when their pore structure meets the above features.

Effect of agro‐waste pore formers on the microstructure, hardness, and tensile properties of porous alumina ceramics

AbstractThis study demonstrates a simple and economically viable approach to fabricate porous alumina ceramics shaped with low‐priced natural organic pore‐forming agents (PFAs) from rice husk (RH) and sugarcane bagasse (SCB) of various weight contents using the powder metallurgy method. Experimental findings revealed that the total porosity (44‐67vol%) and average pore size (70‐178 μm) maintained a linear relationship with rising PFA inclusion. Using the diametral compression test, the mechanical response of porous alumina samples was evaluated as a function of porosity and pore geometry. From the overall mechanical strength characterization, the susceptivity of strength on porosity became well marked as the agro‐waste shaped porous ceramics exhibited hardness, tensile strength, and elastic modulus of 529.1‐26HV, 20.4‐1.5MPa and 1662‐57MPa, respectively. Moreover, the fractography of the RH and SCB graded porous alumina samples was evaluated as a function of the respective microstructural features. With a plausible tradeoff between pore interconnectivity and mechanical strength, recommended areas of application include solid oxide fuel cells (SOFCs) design, filtration, and thermal insulation systems.

Optimal design on the mechanical and thermal properties of porous alumina ceramics based on fractal dimension analysis

AbstractIn order to investigate the relationship between pore structure and thermal conductivity as well as mechanical strength, porous alumina ceramics (PAC) with various pore structures were fabricated, using starch as the pore‐forming agent. Fractal theory was employed to characterize the pore size distribution more accurately than ever used parameters. The results show that the increase in starch content in PAC leads to an enhanced porosity, a higher mean pore size, and reduced fracture dimension, thermal conductivity and strength. The fractal analysis indicated that the fractal dimension decreases gradually and reaches its minimum value with increasing the starch content up to 25 wt%, but the further incorporation results in an opposite trend. It is suggested from micro‐pore fractographic analysis that the optimization of both thermal insulation performance and mechanical strength are positively correlated with the increase in the mean pore size and proportion of 2‐14 μm pores but negatively corrected with the porosity. These results provide a new perspective and a deeper understanding for fabrication of PAC with both excellent thermal insulation and mechanical performance.

Effect of Cu Metal of Nanoscale Particle Size on the Porosity and Mechanical Properties of Porous Alumina Ceramics using Yeast as a Pore Agent

The main goal of this study is to determine the effect of the addition of Cu metal of nanoscale particle on the mechanical properties and porosity of porous alumina ceramics. Porous alumina reinforced ceramics were prepared using nanoscale Cu metal particles as their strengthening phase. Solid state and sacrificial techniques were used to prepare the porous alumina reinforced ceramics. A FESEM was used to analyse the microstructure. Different ratios of Cu metal were added (3 wt%, 6 wt%, 9 wt% and 12 wt% Cu) at different ratios of yeast used as a pore agent. The results indicated that with increasing the ratios of Cu metal, the porosity decreased and the mechanical properties increased. The increase in the mechanical properties could be attributed to the decrease in the porosity and the toughening mechanism of porous alumina ceramics. Some potential applications include, filtration, thermal and purging of gas.

Investigating the effect of porosity level and pore former type on the mechanical and corrosion resistance properties of agro-waste shaped porous alumina ceramics

The strength integrity and chemical stability of porous alumina ceramics operating under extreme service conditions are of major importance in understanding their service behavior if they are to stand the test of time. In the present study, the effect of porosity and different pore former type on the mechanical strength and corrosion resistance properties of porous alumina ceramics have been studied. Given the potential of agricultural wastes as pore-forming agents (PFAs), a series of porous alumina ceramics (Al2O3-xPFA; x=5, 10, 15 and 20 wt%) were successfully prepared from rice husk (RH) and sugarcane bagasse (SCB) through the powder metallurgy technique. Experimental results showed that the porosity (44–67%) and the pore size (70–178 µm) of porous alumina samples maintained a linear relationship with the PFA loading. Comprehensive mechanical strength characterization of the porous alumina samples was conducted not just as a function of porosity but also as a function of the different PFA type used. Overall, the mechanical properties showed an inverse relationship with the porosity as the developed porous alumina samples exhibited tensile and compressive strengths of 20.4–1.5 MPa and 179.5–10.9 MPa respectively. Moreover, higher strengths were observed in the SCB shaped samples up to the 15 wt% PFA mark, while beyond this point, the silica peak observed in the XRD pattern of the RH shaped samples favored their relatively high strength. The corrosion resistance characterization of the porous alumina samples in hot 10 wt% NaOH and 20 wt% H2SO4 solutions was also investigated by considering sample formulations with 5–15 wt% PFA addition. With increasing porosity, the mass loss range in RH and SCB shaped samples after corrosion in NaOH solution for 8 h were 1.25–3.6% and 0.44–2.9% respectively; on the other hand, after corrosion in H2SO4 solution for 8 h, the mass loss range in RH and SCB shaped samples were 0.62–1.5% and 0.68–3.3% respectively.

Properties of porous alumina ceramics

Properties of porous alumina ceramics

Fabrication and properties of porous alumina ceramics with three different pore sizes

Porous alumina ceramics with uniform total porosity (69.6–70.3%), spherical pores, and different pore size (22.9 ± 10.3, 197.7 ± 80.0 and 714.1 ± 207.2 μm) were prepared by using suspension emulsion, direct foaming, and solid template as pore forming mechanism, respectively and gelcasting technology. Different drying methods were selected according to the different pore forming agents. Pore size could significantly affect the mechanical and thermal properties. The compressive strength decreased evidently from 116.25 ± 10.96 to 22.43 ± 1.15 MPa and thermal conductivity of 1000 °C increased from 0.28 ± 0.01 to 0.58 ± 0.01 W/(m K) with the increasing pore size (from 22.9 ± 10.3 to 714.1 ± 207.2 μm).