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1.
Catalin Popa Ken-ichi Katsumata Toshihiro Isobe Nobuhiro Matsushita Akira Nakajima Taisuke Kurata Kiyoshi Okada 《Ceramics International》2013,39(2):1443-1449
Four kinds of porous mullite ceramics, named lotus ceramics because of the similarity of their microstructure with lotus roots, were prepared by an extrusion method using rayon fibers of four different diameters (8.1, 9.6, 16.8 and 37.6 μm) as the pore formers. The physicochemical properties of these samples were characterized to test their applicability for the generation of microbubbles. The lotus ceramic samples contained pores of 9.4, 10, 15.6 and 30 μm size and porosities of 45–48%. SEM micrographs confirmed that the cylindrical pores were oriented unidirectionally along the extrusion direction and the degree of alignment was greater with larger fiber diameter. The permeability for gaseous CO2 increased with increasing pore size from 3×10?13 to 8×10?13 m2. The four lotus ceramic samples, a commercial air stone (72 μm) and two simple tubes (1000 and 3500 μm) were used to generate microbubbles in water under ambient conditions from a gas mixture of CO2 and air. It was found that the bubble size could be decreased with bubblers of smaller pore size. In the bubble size measurements for pure CO2 and air, the air bubbles were larger than the CO2 bubbles due to partial dissolution of CO2 into the water during bubbling. In order to generate smaller size bubbles using porous ceramic bubblers, the liquid must penetrate through the pores of the lotus ceramics before the gas is introduced into the system. 相似文献
2.
Jiahai Bai 《Ceramics International》2010,36(2):673-678
High purity calcined carbonaceous kaolin and α-Al2O3 powders were employed to prepare porous mullite ceramics (Sample A) using graphite as pore former with the reaction sintering method. For the purpose of comparison, porous mullite ceramics (Sample B) was also fabricated from the uncalcined carbonaceous clay incorporated with α-Al2O3 powders. Mullitization in the two samples was both nearly complete at 1500 °C, despite the fact that calcination of the clay remarkably depressed mullitization and promoted the formation of glass phase. The Sample A sintered at 1500 °C fractured mainly in an intergranular way, while the Sample B mainly underwent transgranular fracture. The experimental results revealed that densification behavior/open porosity of the Sample A was far more sensitive to sintering temperature. The pore size of the Sample A as well as the Sample B sintered at 1500 °C was in a narrower range of 0.3–5 μm. 相似文献
3.
Kiyoshi Okada Mai Shimizu Toshihiro Isobe Yoshikazu Kameshima Munetoshi Sakai Akira Nakajima Taisuke Kurata 《Journal of the European Ceramic Society》2010,30(6):1245-1251
Porous mullite ceramics with unidirectionally oriented pores were prepared by an extrusion method using rayon fibers as the pore formers and the characteristics of microbubbles generated by these porous ceramics were investigated. The 1200 mm long ceramics were tubular and of thick or thin types of 20–30 mm inner diameter and 30–50 mm outer diameter, respectively. The thin and thick samples had porosities of 47 and 49% and average pore radii of 7.8 μm. The gas permeabilities of the thick and thin samples were 4.1 × 10?14 and 5.4 × 10?14 m2, respectively. Microbubbles were generated by introducing N2 gas through the ceramic tube by immersing it into water. The minimum pressure (bubble point pressure) for generation of microbubbles was 20 kPa, much lower than for other bubble-forming methods. The average microbubble radii ranged from about 70 to 105 μm at flow rates of 0.15–0.25 L/min in the thin sample and 0.3–0.7 L/min in the thick sample. These bubble sizes are much smaller than calculated for a Fritz-type bubble such as generally formed by bubbling from pores and/or orifices. However, the present bubble sizes agree well with the calculated value based on nanobubbles, indicating that bubble formation occurs by mixing the gas with water in small pores. Since microbubbles enhance the dissolution rate of a gas phase in water, they are potentially useful for improving water environments, especially oxygen-deficient water. The effectiveness of gas dissolution in water was confirmed by determining the dissolution behavior of CO2 gas using these porous ceramics. 相似文献
4.
《Ceramics International》2017,43(7):5478-5483
Porous fibrous mullite ceramics with a narrow range of pore size distribution have been successfully prepared utilizing a near net-shape epoxy resin gel-casting process by using mullite fibers, Al2O3 and SiC as raw materials. The effects of sintering temperatures, different amounts of fibers and Y2O3 additive on the phase compositions, linear shrinkage, apparent porosity, bulk density, microstructure, compressive strength and thermal conductivity were investigated. The results indicated that mullite-bonded among fibers were formed in the porous fibrous mullite ceramics with a bird nest pore structure. After determining the sintering temperatures and the amount of fibers, the tailored porous fibrous mullite ceramics had a low linear shrinkage (1.36–3.08%), a high apparent porosity (61.1–71.7%), a relatively high compressive strength (4.4–7.6 MPa), a low thermal conductivity (0.378–0.467 W/m K) and a narrow range of pore size distribution (around 5 µm). The excellent properties will enable the porous ceramics as a promising candidate for the applications of hot gas filters, thermal insulation materials at high temperatures. 相似文献
5.
《Journal of the European Ceramic Society》2007,27(1):53-59
Porous alumina ceramics having unidirectionally aligned cylindrical pores were prepared by extrusion method and compared with porous ceramics having randomly distributed pores prepared by conventional method, and their gas permeability and mechanical properties were investigated. SEM micrographs of the porous alumina ceramics prepared by the extrusion method using nylon fibers as the pore former showed excellent orientation of cylindrical pores. The bending strength and Weibull modulus of the extruded porous alumina ceramics with 39% porosity were 156 MPa and 17, respectively. These mechanical properties of extruded samples were higher than those of the conventional porous alumina ceramics. The strength decreased from 156 to 106 MPa with increasing pore size from 8.5 to 38 μm. The gas permeability of the extrusion samples is higher than that of the conventional samples and increased with increasing of porosity and pore size. 相似文献
6.
《Ceramics International》2016,42(5):6080-6087
In this work, anorthite–mullite–corundum porous ceramics were prepared from construction waste and Al2O3 powders by adding AlF3 and MoO3 as mineralizer and crystallization catalyst, respectively. The effects of the sintering temperature and time on open porosity, mechanical properties, pore size distribution, microstructure, and phase composition were characterized in detail. The results showed that the formation of the mullite whiskers and the properties of the anorthite–mullite–corundum porous ceramics depended more on the sintering temperature than the holding time. By co-adding 12 wt% AlF3 and 4 wt% MoO3, mullite whiskers were successfully obtained at sintering temperatures upon 1350 °C for 1 h. Furthermore, the resultant specimens exhibited excellent properties, including open porosity of 66.1±0.7%, biaxial flexural strength of 23.8±0.9 MPa, and average pore size of 1.32 µm (the corresponding cumulative volume percent was 37.29%). 相似文献
7.
《Journal of the European Ceramic Society》2014,34(5):1329-1340
This new and economic approach to fabricate resistant porous membrane supports consists of Algerian kaolin and calcite (CaCO3) instead of Al2O3. The porous mullite (3Al2O3·2SiO2) and anorthite (CaO·Al2O3·2SiO2) based ceramics were obtained by solid state reaction. Different calcite amounts (10–28 wt%) have been added into kaolin halloysite type (Al2O3·2SiO2·4H2O) in order to control pores forming with appropriate distribution and sizes. Based on a pore distribution and formed phases, a kaolin + 15 wt% calcite (K15C) mixture was selected for flat and tubular configurations. A porosity of 45–52% was also obtained when K15C compacts were sintered at 1100–1250 °C. For example, porosity, average pore size (APS) and 3 point flexural strength were 49%, 3 μm and 87 MPa (same as Al2O3 value), respectively when K15C compacts were sintered at 1250 °C for 1 h. Finally, a correlation between microstructure and mechanical properties of elaborated supports has been discussed. 相似文献
8.
《Ceramics International》2016,42(15):17179-17184
Mullite-whisker-reinforced anorthite-mullite-corundum porous ceramics were prepared from construction waste and Al2O3 powder by adding AlF3 and MoO3 as the additive and crystallization catalyst, respectively. The effects of AlF3 and MoO3 content on the properties of mullite whiskers, such as open porosity, mechanical properties, pore size distribution, microstructure and phase structure, were investigated in detail. The results showed that the morphology of the mullite whiskers and properties of the porous ceramics were greatly influenced by the AlF3 and MoO3 content. The specimen obtained by co-adding 12 wt% AlF3 and 3 wt% MoO3, and sintering at 1350 °C for 1 h, exhibited excellent properties, including an open porosity of 67.4±0.5% and biaxial flexural strength of 24.0±0.8 MPa. The mullite whiskers were uniformly distributed; the whiskers had a diameter of 0.05–0.5 µm, length of 8–10 µm, and aspect ratios (length to diameter ratio) of 20–30 on average. 相似文献
9.
In-Hyuck Song Il-Min Kwon Hai-Doo Kim Young-Wook Kim 《Journal of the European Ceramic Society》2010,30(12):2671-2676
A novel processing route for producing microcellular SiC ceramics with a duplex pore structure has been developed using a polysiloxane, carbon black, SiC, Al2O3, Y2O3, and two kinds of pore former (expandable microspheres and PMMA spheres). The duplex pore structure consists of large pores derived from the expandable microspheres and small windows in the strut area that were replicated from the PMMA spheres. The presence of these small windows in the strut area improved the permeability of the porous ceramics. The gas permeability coefficients of porous SiC ceramics were 0.13 × 1012 m2 for the porous SiC without PMMA spheres, 0.47 × 1012 m2 for the porous SiC with 10 wt% PMMA spheres, and 0.82 × 1012 m2 for the porous SiC with 20 wt% PMMA. 相似文献
10.
Shaojun Qiu Xiaodong Zheng Chao Gao Xiaoxian Gan Jin Chen Chen Yang Huiqing Fan 《Ceramics International》2009,35(2):733-740
Using non-aqueous Pechini method, Pb(Zr0.95Ti0.05)O3 powders were prepared at low temperature by one-step pyrolysis process. The polymeric gels and powders were characterized using a range of techniques, such as DTG, XRD, SEM, Raman spectroscopy, and laser particle size distribution. The perovskite phase was formed at about 350–400 °C and some oxocarbonate impurities can be detected in all samples after calcining at 400–850 °C by one-step pyrolysis process. Phase pure and porous Pb(Zr0.95Ti0.05)O3 ceramics were obtained without pore formers from the powders by one-step pyrolysis process at 500 °C for 4 h. The relative densities were 87%, 91% and 94% for the ceramics sintered at 1100, 1150 and 1200 °C for 2 h, respectively. The porous ceramics sintered at 1200 °C for 2 h have homogeneously dispersed pores and fine-grain structures with an individual grain size of 0.7–2 μm. 相似文献
11.
《Journal of the European Ceramic Society》2006,26(6):957-960
Porous alumina ceramics with unidirectionally-oriented pores were prepared by extrusion. Carbon fibers of 14 μm diameter and 600 μm length to be used as the pore-forming agent were kneaded with alumina, binder and dispersing agent. The resulting paste was extruded, dried at 110 °C, degreased at 1000 °C and fired at 1600 °C for 2 h. SEM showed a microstructure of dispersed highly oriented pores in a dense alumina matrix. The pore area in the cross section was 25.3% with about 1700 pores/mm2. The pore size distribution of the fired body measured by Hg porosimetry showed a sharp peak corresponding to the diameter of the burnt-out carbon fibers. The resulting porous alumina ceramics with 38% total porosity showed a fracture strength of 171 MPa and a Young's modulus of 132 GPa. This strength is significantly higher than the reported value for other porous alumina ceramics even though the present pore size is much larger. 相似文献
12.
《Journal of the European Ceramic Society》2006,26(9):1637-1646
Four-point bending creep behavior of mullite ceramics with monomodal and bimodal distribution of grain sizes was studied in the temperature range of 1320–1400 °C under the stresses between 40 and 160 MPa. Mullite ceramic with bimodal grain size distribution was prepared using aluminum nitrate nonahydrate as alumina precursor. When γ-Al2O3 or boehmite were used as alumina precursors, mullite grains are equiaxial with mean particle size of 0.6 μm for the former and 1.3 μm for the latter alumina precursor. The highest creep rate exhibited the sample with monomodal morphology and grains in size of 0.6 μm, which is about one order of magnitude greater than that for the monomodal morphology but with grains in size of 1.3 μm. The highest activation energy for creep (Q = 742 ± 33 kJ/mol) exhibits mullite with equiaxial grains of 1.3 μm, whereas for sample with smaller equiaxial grains the activation energy is much smaller and similar to mullite ceramics with bimodal grain morphology. Intergranular fracture is predominant near the tension surface, while transgranular more planar fracture is predominant near the compression surface zone. 相似文献
13.
《Journal of the European Ceramic Society》2006,26(12):2213-2217
Porous alumina ceramics with unidirectionally oriented pores were prepared using an extrusion method. The paste for extrusion was prepared by mixing alumina and nylon 66 fibers with binder and dispersant. The resulting paste was extruded, dried at room temperature, and after removal of the binder at 600 °C, fired at 1500 °C for 2 h. The pore size in the sintered body, determined from SEM micrographs, was 16 μm, corresponding to the size of the burnt-out nylon 66 fibers. The degree of orientation of the cylindrical pores was evaluated from SEM micrographs to be highly aligned to the extrusion direction. The orientation of the pores decreased with increasing fiber loading because of strong interaction between the fibers. The pore size distribution of the extruded samples showed a peak at 16 μm corresponding to the cylindrical pore diameter and also at 4 and 6 μm corresponding to the pores formed by connection of the fibers. 相似文献
14.
《Ceramics International》2016,42(16):18711-18717
Bimodal porous structures were prepared by combining conventional sacrificial template and partial sintering methods. These porous structures were analysed by comparing pore characteristics and gas permeation properties of alumina/mullite specimens sintered at different temperatures. The pore characteristics were investigated by SEM, mercury porosimetry, and capillary flow porosimetry. A bimodal pore structure was observed. One type of pore was induced by starch, which acted as a sacrificial template. The other pore type was due to partial sintering. The pores produced by starch were between 2 and 10 µm whereas those produced by partial sintering exhibited pore size of 0.1–0.5 µm. The effects of sintering temperature on porosity, gas permeability, and mullite phase formation were studied. The formation of the mullite phase was confirmed by XRD. Compressive strengths of 37.9 MPa and 12.4 MPa with porosities of 65.3% and 70% were achieved in alumina and mullite specimens sintered at 1600 °C. 相似文献
15.
《Ceramics International》2017,43(13):9815-9822
Porous acicular mullite (3Al2O3·2SiO2) ceramics containing Cu3Mo2O9 as a soot oxidation catalyst was fabricated by a novel approach using commercial powders of Al2O3 and CuO, and powder obtained by controlled oxidation of ground waste MoSi2. The obtained material consisted of elongated mullite grains which are known to be effective in carbon soot removal from diesel engine exhaust. The presence of in situ created Cu3Mo2O9 was found to catalyze the carbon burnout which is an extremely important feature when it comes to filter regeneration, i.e., the captured soot removal. The carbon burnout temperature in the sample containing 12 wt% CuO was by 90 °C lower than that in the sample without CuO. Effect of sintering temperature as well as the effect of amount of CuO additive on mullite properties were studied. It was found that the increase in amount of CuO in samples sintered at 1300 °C decreased porosity and increased compressive strength of the porous mullite ceramics. The addition of 12 wt% CuO increased the strength of the porous mullite ceramics up to 70 MPa, whereas the porosity was reduced from 62% in the mullite without CuO to 44% in the mullite ceramics containing 12 wt% CuO. Although affected by the amount of CuO, the microstructure still consisted of elongated mullite grains. 相似文献
16.
《Journal of the European Ceramic Society》2017,37(3):1131-1134
Porous SiC/SiCN composite ceramics with heterogeneous pore structure and rod-like SiCN grains were fabricated by foaming and reaction sintering. The mixture slurry containing SiC and silicon as raw materials, cornstarch as binder, Y2O3 as sintering additive and an electrosteric dispersant was stirred with foams derived from pre-foaming using foaming agent. The casted green body was sintered at 1650 °C under nitrogen atmosphere. The results demonstrated that the porous SiC/SiCN ceramics exhibited hierarchical vias ranging from 1 μm to 1 mm and the rod-like crystalline SiCN grains generated in the SiC matrix. 相似文献
17.
A reaction bonding technique was used for the preparation of cordierite-bonded porous SiC ceramics in air from α-SiC, α-Al2O3 and MgO, using graphite as the pore-forming agent. Graphite was burned out to produce pores and the surface of SiC was oxidized to SiO2 at high temperature. With further increasing the temperature, SiO2 reacted with α-Al2O3 and MgO to form cordierite. SiC particles were bonded by the cordierite and oxidation-derived SiO2. The reaction bonding characteristics, phase composition, open porosity, pore size distribution and mechanical strength as well as microstructure of porous SiC ceramics were investigated. The pore size and porosity were strongly dependent, respectively, on graphite particle size and volume fraction. The porous SiC ceramics sintered at 1350 °C for 2 h exhibited excellent combination properties, the flexural strength of 26.0 MPa was achieved at an open porosity of 44.51%. 相似文献
18.
《Journal of the European Ceramic Society》2014,34(10):2401-2412
The present study demonstrates a cost effective way to fabricate porous ceramics with tailored microstructures using rice husk (RH) of various range of particle sizes as a pore former and sucrose as a binder as well as a pore former. Sample microstructures reveal randomly oriented elongated coarse pores and fine pores (avg. size 4 μm) created due to burnout of RH and sucrose, respectively. Porous alumina ceramics with 20–66 vol% porosity and 50–516 μm avg. pore size (length), having isolated and/or interconnected pores, were fabricated using this process. Mechanical properties of the porous samples were determined as a function of porosity and pore microstructure. The obtained porous ceramics exhibited flexural strength of 207.6–22.3 MPa, compressive strength of 180–9.18 MPa, elastic modulus of 250–18 GPa and hardness of 149–18 HRD. Suggested application area includes thermal, filtration, gas purging etc. 相似文献
19.
《Ceramics International》2015,41(7):8599-8604
Using H2O2 aqueous solution as pore-forming agent, hydroxyapatite (HA) porous scaffolds with both lamellar and spherical pores were fabricated by a freeze casting method. The highest porosity was obtained in HA scaffolds prepared using 5 vol% H2O2 aqueous solution. The relationship between the electric field intensity and the properties of HA scaffolds was investigated. Results showed that when the electric field intensity was increased from 0 to 90 kV/m, the average diameters of lamellar and spherical pores of HA scaffold were increased from 460 μm to 810 μm, and from 320 μm to 420 μm, respectively. Vitro cellular assay indicated that HA scaffold with both the lamellar and the spherical pores has a better biocompatibility, compared with that with single pores. 相似文献
20.
《Journal of the European Ceramic Society》2006,26(4-5):475-479
The effects of PMMA as a pore-forming reagent and the powder for Cs-deficient pollucite, Cs9Al0.9Si2.1O6, calcined at 1073 K, on the microstructure of the porous body of Cs0.9Al0.9Si2.1O6 were investigated. The Cs0.9Al0.9Si2.1O6 porous bodies were fabricated by sintering the green compacts of the calcined powder and PMMA adding 35 mass% to the calcined powder. When the green compact was heated at 873 K in air for 20 h, pores <1 μm were observed in the porous body, suggesting that the PMMA previously dissolved in acetone was uniformly distributed in the calcined powder by the ball milling. The pore size of the obtained porous structure increased with increasing the size of the aggregated particles and the pore size distribution was significantly related to the size of Al2O3 balls and the time for the ball milling for mixing the calcined powders and PMMA. 相似文献