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1.
《Ceramics International》2016,42(4):4819-4826
Porous mullite supports are firstly fabricated by casting and reaction sintering based on kyanite with Al(OH)3 as porogenic agent. The effects of composition and sintering temperature on phase evolution, microstructure, apparent porosity, pore size distribution, linear shrinkage, gas permeation flux and mechanical property of supports are systematically investigated. Results show that the mullitization of kyanite generates needle-like mullite crystals, which form skeleton structures and improve the apparent porosity and strength of supports. Al(OH)3 addition not only promotes the formation of needle-like mullite but also enhances the apparent porosity of supports. Temperature promotes the development of mullite, from 1450 to 1500 °C, the amount and size of needle-like mullite crystals increase, ≥1500 °C, they reveal columnar morphology. The support prepared with kyanite+40 wt%Al(OH)3 sintered at 1500–1550 °C exhibits high apparent porosity, good gas permeation flux, excellent mechanical performance and interlocked network structure composed of well development needle-like mullite. 相似文献
2.
《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
3.
《Journal of the European Ceramic Society》2014,34(13):3181-3194
Low-cost porous mullite ceramic membrane supports were fabricated from recycling coal fly ash with addition of natural bauxite. V2O5 and AlF3 were used as additives to cause the growth of mullite crystals with various morphologies via an in situ reaction sintering. Dynamic sintering, microstructure and phase evolution of the membrane supports were characterized in detail and open porosity, pore size, gas permeation and mechanical properties were determined. It showed the membrane support with 3 wt.% V2O5 and 4 wt.% AlF3 addition exhibits an open porosity of ∼50%, mechanical strength of 69.8 ± 7.2 MPa, an interlocking microstructure composed of anisotropically grown mullite whiskers with an aspect ratio of 18.2 ± 3.6 at 1300 °C. Addition of more V2O5 lowered the secondary mullitization temperature, resulting in more mullite formation at lower temperatures. The fabricated membrane supports feature high porosity without mechanical strength degradation, possible strengthening mechanism of the mullite whiskers was further discussed. 相似文献
4.
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
5.
《Ceramics International》2016,42(10):12185-12193
In this work, the effects of mechanical activation on the sintering of mullite produced from kaolin and aluminum metal powder was investigated. Because of the higher content of silica in kaolin it is necessary to add alumina or aluminum oxide in order to obtain the stoichiometric mullite composition. After mechanical treatment for different milling time, the reactions and phase transformations between kaolin and aluminum metal powder were studied using thermal techniques (DTA/TG), X-ray diffraction (XRD) and infrared spectroscopy (FT-IR). The heated samples at different temperatures were studied by XRD, apparent density, open porosity measurements and SEM analysis. The results showed the formation of silicon, quartz and small amount of nacrite after 40 h of milling at room temperature. All mixture powders milled for different time showed the formation of several alumina transitions during heat treatment. The formation of alumina transitions, α-alumina, cristobalite crystallization of and mullite (primary and secondary) formation was affected by ball milling time. The mixture of kaolin and aluminum milled for 40 h show the formation of kyanite (Al2SiO5) at 1300 °C. The mechanical treatment enhances the formation and sintering of mullite. 相似文献
6.
《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
7.
《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
8.
《Journal of the European Ceramic Society》2014,34(1):119-126
A silicate ceramic that is similar to porcelain and exhibits a maximum toughness of 4.6 MPa m1/2 was obtained by tape casting from kaolin and 3 vol% of alumina fibers. Improved toughness and strength are achieved with the organized micro-composite microstructure that results from preferential orientation during the shaping of kaolinite particles and fibers in-plane of layers. During sintering, typical nucleation and growth processes of mullite produce specific microstructural characteristics, such as bulk zones, oriented fibers and large interfacial zones between the fibers and the bulk. Toughening is attributed to the decreased crack energy in the bulk ceramic, in which a dense and organized network of short mullite occurs, and in interfacial zones containing a superimposed network of large mullite. The silicate ceramic that is reinforced by only 3 vol% of the alumina fibers is strong (95 MPa) and tough (4.6 MPa m1/2); although these properties are often mutually exclusive. 相似文献
9.
《Ceramics International》2017,43(18):16430-16435
For recycling waste refractory materials in metallurgical industry, porous alumina ceramics were prepared via pore forming agent method from α-Al2O3 powder and slide plate renewable material. Effects of slide plate renewable material (SPRM) on densification, mechanical strength, thermal conductivity, phase composition and microstructure of the porous alumina ceramics were investigated. The results showed that SPRM effectively affected physical and thermal properties of the porous ceramics. With the increase of SPRM, apparent porosity of the ceramic materials firstly increased and then decreased, which brought an opposite change for the bulk density and thermal conductivity values, whereas the bending strength didn’t decrease obviously. The optimum sample A2 with 50 wt% SPRM introducing sintered at 1500 °C obtained the best properties. The water absorption, apparent porosity, bulk density, bending strength and thermal conductivity of the sample were 31.7%, 62.8%, 1.71 g/cm3, 47.1 ± 3.7 MPa and 1.73 W/m K, respectively. XRD analysis indicated that a small quantity of silicon carbide and graphite in SPRM have been oxidized to SiO2 during the firing process, resulting in rising the porous microstructures. SEM micrographs illustrated that rod-like mullite grains combined with plate-like corundum grains to endow the samples with high bending strength. This study was intended to confirm the preparation of porous alumina ceramics with high porosity, good mechanical properties and low thermal conductivity by using SPRM as pore forming additive. 相似文献
10.
《Ceramics International》2015,41(4):5894-5902
The biodegradable ceramic scaffolds with desirable pore size, porosity and mechanical properties play a crucial role in bone tissue engineering and bone transplantation. A novel porous β-dicalcium silicate (β-Ca2SiO4) ceramic scaffold was prepared by sintering the green body consisting of CaCO3 and SiO2 at 1300 °C, which generated interconnected pore network with proper pore size of about 300 μm and high compressive strength (28.13±5.37–10.36±0.83 MPa) following the porosity from 53.54±5.37% to 71.44±0.83%. Porous β-Ca2SiO4 ceramic scaffolds displayed a good biocompatibility, since human osteoblast-like MG-63 cells and goat bone mesenchymal stem cells (BMSCs) proliferated continuously on the scaffolds after 7 d culture. The porous β-Ca2SiO4 ceramic scaffolds revealed well apatite-forming ability when incubated in the simulated body fluid (SBF). According to the histological test, the degradation of porous β-Ca2SiO4 ceramic scaffolds and the new bone tissue generation in vivo were observed following 9 weeks implantation in nude mice. These results suggested that the porous β-Ca2SiO4 ceramic scaffolds could be potentially applied in bone tissue engineering. 相似文献
11.
《Ceramics International》2017,43(4):3741-3747
Silicon carbide reticulated porous ceramics (SiC RPCs) with three-layered struts were fabricated by polymer replica method, followed by infiltrating alumina slurries containing silicon (slurry-Si) and andalusite (slurry-An), respectively. The effects of composition of infiltration slurries on the strut structure, mechanical properties and thermal shock resistance of SiC RPCs were investigated. The results showed that the SiC RPCs infiltrated with slurry-Si and slurry-An exhibited better mechanical properties and thermal shock resistance in comparison with those of alumina slurry infiltration, even obtained the considerable strength at 1300 °C. In slurry-Si, silicon was oxidized into SiO2 in the temperature range from 1300 °C to 1400 °C and it reacted with Al2O3 into mullite phase at 1450 °C. Meantime, the addition of silicon in slurry-Si could reduce SiC oxidation of SiC RPCs during firing process in contrast with alumina slurry. With regard to slurry-An, andalusite started to transform into mullite phase at 1300 °C and the secondary mullitization occurred at 1450 °C. The enhanced mechanical properties and thermal shock resistance of SiC RPCs infiltrated alumina slurries containing silicon and andalusite were attributed to the optimized microstructure and the triangular zone (inner layer of strut) with mullite bonded corundum via reaction sintering. In addition, the generation of residual compressive stress together with better interlocked needle-like mullite led to the crack-deflection in SiC skeleton, thus improving the thermal shock resistance of obtained SiC RPCs. 相似文献
12.
This work aims at studying the influence of thermal treatment on the microstructure, resistivity and technological properties of porous alumina ceramics prepared via starch consolidation casting (SCC) technique. Colloidal suspensions were prepared with three different contents of alumina solid loading (55, 60 and 65 mass%) and corn starch (3, 8 and 13 mass%). The sintered samples at 1400, 1500, 1600 and 1700 °C, show open porosity between 46 and 64%, depending on the starch content in the precursor suspensions and sintering temperature. The pore structures were analyzed by SEM. The effect of corn starch content on the apparent porosity, pore size distribution, linear shrinkage and electrical resistivity as well as cold crushing strength of the sintered porous alumina ceramics was also measured. These porous alumina ceramics are promising porous ceramic materials for using in a wide range of thermal, electrical and bioceramics applications as well as filters/membranes and gas burners, due to their excellent combination properties. 相似文献
13.
An-Nan Chen Jia-Min Wu Yu-Xuan Liu Rong-Zhen Liu Li-Jin Cheng Wen-Long Huo Yu-Sheng Shi Chen-Hui Li 《Ceramics International》2018,44(5):4845-4852
A novel forming method for preparing porous alumina ceramics using alumina fibers as raw materials by direct coagulation casting (DCC) combined with 3D printing was proposed. Porous fibrous alumina ceramics were fabricated through temperature induced coagulation of aqueous-based DCC process using sodium tripolyphosphate (STPP) as dispersant and adding K2SO4 as removable sintering additives. The sacrificial coated sand molds was fabricated by 3D printing technology, followed by the infiltration of silica sol solution for the subsequent suspension casting. Stable alumina suspension of 40 vol% solid loading was obtained by adding 2.0 wt% STPP and 40 wt% K2SO4. The controlled coagulation of the suspension could be realized after heating at 90 °C for about 35 min. The ceramic sample sintered at 1450 °C for 2 h showed the highest compressive strength of 24.33 MPa with porosity of 57.38%. All samples sintered at 1300–1450 °C had uniform pore size distributions with average pore size of 7.2 µm, which indicated the good structure stability when sintered at high temperature. 相似文献
14.
《Ceramics International》2016,42(13):14894-14902
The emerging porous Y2SiO5 ceramic is regarded as a promising candidate of thermal insulator owing to its very low thermal conductivity. However, recent works on porous Y2SiO5 are confronted with severe problems such as large linear shrinkage (18.51–20.8%), low porosity (47.74–62%) and low strength (24.45–16.51 MPa) at high sintering temperatures (1450–1500 °C). In this work, highly porous Y2SiO5 ceramic with low shrinkage and excellent high-temperature strength was fabricated by in-situ foam-gelcasting method at 1550 °C. The as-prepared sample has unique multiple pore structures, low linear shrinkages of 6.3–4.5%, controllable high porosities of 60.7–88.4%, high compressive strengths of 38.2–0.90 MPa, and low thermal conductivities of 0.126–0.513 W/(m K) (porosity: 87.1–60.2%). The effects of relative density on relative strength, as well as porosity on thermal conductivity were quantitatively discussed. The present results indicate that porous Y2SiO5 is the potential high-temperature thermal insulation material of light weight, low thermal conductivity, and high strength. 相似文献
15.
《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
16.
Kiyoshi Okada Shuhei Uchiyama Toshihiro Isobe Yoshikazu Kameshima Akira Nakajima Taisuke Kurata 《Journal of the European Ceramic Society》2009,29(12):2491-2497
Porous mullite ceramics with unidirectionally oriented pores were prepared by an extrusion method to investigate their capillary rise properties. Rayon fibers 16.5 μm in diameter and 800 μm long were used as the pore formers by kneading with alumina powder, kaolin clay, China earthen clay and binder with varying Fe2O3 contents of 0, 5 and 7 mass%. The resulting pastes were extruded into cylindrical tubes (outer diameter (OD) 30–50 mm and inner diameter (ID) 20–30 mm), dried at room temperature and fired at 1500 °C for 4 h. The bulk densities of the resulting porous ceramics ranged from 1.31 to 1.67 g/cm3, with apparent porosities of 43.2–59.3%. The pore size distributions measured by Hg porosimetry showed a sharp peak at 10.0 μm in the sample without Fe2O3 and at 15.6 μm in the samples containing Fe2O3; these pores, which arose from the burnt-out rayon fibers, corresponded to total pore volumes ranging from 0.24 to 0.34 ml/g. SEM showed a microstructure consisting of unidirectionally oriented pores in a porous mullite matrix. Prismatic mullite crystals were well developed on the surfaces of the pore walls owing to the liquid phase formed by the Fe2O3 component added to color the samples. The bending strengths of the tubular samples ranged from 15.6 to 26.3 MPa. The height of capillary rise, measured under controlled relative humidities (RH) of 50, 65 and 85%, was greater in the ceramics containing Fe2O3 than in those without Fe2O3, especially in the thinner samples. The maximum capillary rise reached about 1300 mm, much higher than previously reported. This excellent capillary rise ability is thought to be due to the controlled pore size, pore distribution and pore orientation in these porous mullite ceramics. 相似文献
17.
《Ceramics International》2017,43(12):8743-8754
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. 相似文献
18.
《Ceramics International》2015,41(4):5857-5862
Microporous corundum aggregates were fabricated based on superplasticity, with α-Al2O3 micropowder as the main raw material, by adding nano-sized alumina sol and MgO micropowder. The relationship between the superplasticity and the in-situ stress during sintering, the corresponding sintering properties, and the microstructures of the fabricated microporous corundum aggregates were investigated by means of X-ray diffraction (XRD), mercury porosimetry, and scanning electron microscopy (SEM). The experimental results show that the relationship between the superplasticity and the in-situ stress is the main factor that influences the sintering behavior of the microporous corundum aggregates. Various amounts of MgO micropowder were added to the α-Al2O3 micropowder for a fixed content of nano-sized alumina sol. With increasing MgO micropowder, which results in a greater in-situ stress, the total and closed porosity increased initially and decreased afterwards whereas the apparent porosity and bulk density decreased first and then increased. Microporous corundum aggregates with high closed porosity, low apparent porosity and small pore size were obtained with the addition of 1 wt% MgO micropowder. Therefore, the relationship between the superplasticity and the in-situ stress should be controlled in order to fabricate microporous refractory aggregates which have high closed porosity and small pore size. 相似文献
19.
Hanna Tiainen David Wiedmer Håvard J. Haugen 《Journal of the European Ceramic Society》2013,33(1):15-24
In the present study, the effect of sintering time and recoating procedures on the pore architectural parameters and compressive strength of highly porous ceramic TiO2 foams were investigated. Long sintering times (>5 h) at 1500 °C led to an inward collapse of one wall of the triangular voids typically found in the strut interior of foams prepared using the replication method. This strut folding led to increased compressive strength, while the pore architectural features were not significantly affected. Furthermore, majority of the internal porosity of the foam struts was partially eliminated and became accessible for infiltration with TiO2 slurry. Recoating procedures were found to markedly reduce the flaw size and number in the TiO2 foam struts, which led to significant strengthening of the ceramic structure (0.7 → 3.4 MPa) by improved structural uniformity and slightly increased strut diameter. 相似文献
20.
《Ceramics International》2015,41(7):9009-9017
Porous mullite ceramics were prepared via foam-gelcasting using industrial grade mullite powder as the main raw materials, Isobam-104 as the dispersing and gelling agent, sodium carboxymethyl cellulose as the foam stabilizing agent, and triethanolamine lauryl sulfate as the foaming agent. The effects of processing parameters such as type and amount of additive, solid loading level and gelling temperature on rheological properties and gelling behaviors of the slurries were investigated. The green samples after drying at 100 °C for 24 h were fired at 1600 °C for 2 h, and the microstructures and properties of the resultant porous ceramic samples were characterized. Based on the results, the effects of foaming agent on the porosity level, pore structure and size and mechanical properties of the as-prepared porous mullite ceramics were examined. Porosity levels and pore sizes of the as-prepared samples increased with increasing the foaming agent content up to 1.0%, above which both porosity levels and pore sizes did not change. The compressive strength and flexural strength of the as-prepared sample with porosity of 76% and average pore size of 313 μm remained as high as 15.3±0.3 MPa and 3.7±0.2 MPa, respectively, and permeability increased exponentially with increasing the porosity. 相似文献