Preparation of Porous TiO2 Sheets by Aqueous Tape Casting and their Photocatalytic Activation

Porous titania (TiO₂) sheets were prepared by aqueous tape casting. In slurry preparation, ammonium polyacrylate, polyvinyl alcohol, and polyethylene glycol were used as dispersant, binder, and plasticizer, respectively. The properties of slurries were characterized by ζ-potential, sedimentation test, and rheological behavior. The influences of sintering temperature on the open porosity, phase composition, and microstructure of the specimens were studied. The open porosity of the specimens ranged from 44% to 58%. The results indicate that the photocatalytic efficiency of specimens is closely related to the phase composition, the open porosity as well as the grain size of TiO₂ sheet. The porous TiO₂ sheets have lower efficiency than TiO₂ powder; however, the porous sheets do not result in the secondary contamination problem.     

Preparation of high strength lamellar porous calcium silicate ceramics by directional freeze casting

In this study, porous calcium silicate (CS) ceramics with oriented arrangement of lamellar macropore structure were prepared by directional freeze casting method. The lamellar macropores were connected by the micropores on the pore wall, which had good pore interconnectivity. The effects of solid loading of the slurry, freezing temperature, sintering additive content, and sintering temperature on the microstructures and compressive strength of the synthesized porous materials were investigated systematically. The results showed that with the increase of solid loading (≤20 vol%) and sintering additive content, the sizes of lamellar pores and pore walls increased gradually, the open porosity decreased and the compressive strength increased. The sintering temperature had little effect on the pore size of the ceramics, but increasing the sintering temperature (≤1050 °C) promoted the densification of the pore wall, reduced the porosity, and improved the strength. The decrease of freezing temperature had little effect on porosity, but it reduced the size of lamellar pore and pore wall, so as to improve the strength. Finally, porous CS ceramics with lamellar macropores of about 300–600 μm and 2–10 μm micropores on the pore wall were obtained. The porous CS ceramics had high pore interconnectivity, an open porosity of 66.25% and a compressive strength of 5.47 MPa, which was expected to be used in bone tissue engineering.     

Characterization of functionalized zirconia membranes manufactured by aqueous tape casting

In this study, porous zirconia membranes were developed by aqueous tape casting. The influence of poly (methyl methacrylate) (PMMA) as a pore former, and sintering temperatures (1300, 1400, and 1500 °C) on open porosity and pore size was investigated. The rheological behaviour of the suspensions was measured. The slurries showed pseudoplastic behavior, which is desirable for tape casting. Functionalization with an amino silane precursor (3-aminopropyl triethoxysilane, APTES) was carried out to increase the hydrophilic properties of the membranes. The functionalized samples were characterized by SEM-EDX to identify the moieties attached to the surface. Membranes with open porosity ranging from 27% to 51% and average pore sizes from 0.2 to 1.4 μm were obtained. Samples sintered at 1400 °C with added pore former yielded the highest water flux, 257 Lm⁻²h⁻¹, which increased to 642 Lm⁻²h⁻¹ after functionalization. Membranes with tailored porosity and pore size obtained in this study are indicated for applications involving separation processes, especially for microfiltration systems.     

Effects of nano-alumina content on the formation of interconnected pores in porous purging plug materials

The physical properties and microstructure of porous purging plug materials added with different nano-alumina contents and firing temperatures were investigated by means of X-ray diffraction, scanning electron microscopy, air permeability, pore size distribution, mean pore size, apparent porosity, bulk density, and cold crushing strength (CCS) tests. The results showed that the addition of nano-alumina had a great effect on the physical properties and microstructure of the porous purging plug materials. With increasing nano-alumina content in the composition, the main phase was α-Al₂O₃ in all compositions and the mean pore size, apparent porosity and air permeability all increased due to the increased number of pores and pore size of the specimens which facilitated the formation of interconnected pores. When the sintering temperature was changed from 1550 °C to 1650 °C, some of the smaller pores vanished due to solid phase sintering, which reduced the apparent porosity, and some open pores connected to form interconnected pores, which promoted increased air permeability. In addition, the strength and porosity were found to follow the relationship σ = σ₀ exp (-b P). When the apparent porosity increased, the CCS decreased, and vice versa.     

Elaboration and characterization of tubular macroporous ceramic support for membranes from kaolin and dolomite

A low cost macroporous support for ceramic membranes was prepared by in situ reaction sintering from local natural mineral kaolin with dolomite as sintering inhibitor. The characterization focused on the phase evolution, microstructure, pore structure, mechanical strength and water permeability at various compositions and sintering temperatures. The sintering of kaolin was improved with 5 wt% dolomite, but clearly inhibited with ≥10 wt% dolomite. For the 20 wt% dolomite samples, the crystalline phases were mainly composed of mullite, cordierite and anorthite after sintering between 1,150 and 1,300 °C. Moreover, both mean pore size and mechanical strength increased with increasing sintering temperature from 1,100 to 1,300 °C, but the water permeability and porosity decreased. The 1,250 °C sintered macroporous support with 20 wt% dolomite exhibited good performances such as porosity 44.6%, mean pore size 4.7 μm, bending strength 47.6 MPa, water permeability 10.76 m³ m⁻² h⁻¹ bar⁻¹, as well as good chemical resistance. This work provides opportunities to develop cost-effective ceramic supports with controllable pore size, porosity, and high strength for high performance membranes.     

Reaction-bonded robust SiC ceramic membranes sintered at low temperature with coal gangue

Herein, we report an in-situ reaction-bonded SiC membrane sintered at low temperature using a solid waste (i.e. coal gangue) as the sintering aid to form strong neck connections. The effects of sintering temperature and coal gangue proportion on their properties regarding pore size, open porosity, bending strength and pure water permeability were investigated. The single-channel tubular SiC membrane sintered at 1300 °C with a coal gangue proportion of 12 wt% was optimal, exhibiting an average pore size of 2.78 μm, a open porosity of 47.08%, a bending strength of 34.01 ± 1.3 MPa and a high water permeability of 83967 L m⁻² h⁻¹ bar⁻¹. The membrane could completely reject D₅₀ = 0.87 μm SiC solids and presented a steady-state water permeability of 458 L m⁻² h⁻¹·bar⁻¹. The SiC membrane could be regenerated through ultrasonication and its steady-state water permeability was almost unchanged for 3 cycles, proving its mechanical robustness. This work may appeal to the practical low-cost production of high-performance SiC membranes.     

Influence of Green Formulation and Pyrolyzable Particulates on the Porous Microstructure and Sintering Characteristics of Tape Cast Ceramics

Porous morphology and total porosity produced in sintered ceramic tapes was controlled by the amount and distribution of pyrolyzable graphite particles added to a colloidal suspension during a tape casting operation. A conceptual model of the green tape microstructure was used to explain the influence of graphite and tape formulation on sintering characteristics. The creation of a connected, open porous network in the sintered body was the result of graphite particle percolation within the green body. Additional voidage introduced by particle bridging was the source of excess porosity and also resulted in a bimodal pore size distribution. Sintering shrinkage was determined by the ceramic packing density, which was primarily determined by the tape formulation.     

Sintering and characterization of in situ formed porous cordierite ceramics with nano boehmite additions

In this study, we investigated the effect of sintering temperature and nano boehmite additions on the phase composition, densification, and mechanical properties of porous cordierite ceramics. Ceramic samples were sintered at temperatures ranging from 1200 to 1400°C. Carbon powder was used as a pore forming agent to improve the porosity of the ceramic structure. Nano boehmite and carbon additions significantly enhanced ceramic porosity and average pore size in sintered samples. The bulk density and apparent porosity of the sintered samples were found to be 0.96–1.53 g/cm³ and 42.3%–65.6%, respectively. Sintered samples had cold crushing strengths of 1.5–14.3 MPa. The microstructure obtained by scanning electron microscopy was used to measure average pore size in sintered samples and was found to be 41.93 µm for stoichiometric composition (SC), 67.72 µm for SC and nano boehmite, and 102.98 µm for SC, nano boehmite, and carbon. The microstructure of the sintered samples revealed that the crystallinity of the in situ formed phases increased with the increase in nano boehmite additions.     

Preparation and characterization of porous alumina ceramics through starch consolidation casting technique

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.     

Highly porous ZrO2 ceramics fabricated by a camphene-based freeze-casting route: Microstructure and properties

A camphene-based freeze-casting method was adopted to create ceramics with aligned, equiaxed pores applied so far exclusively for ceramics—is demonstrated for ZrO₂ porous ceramics. The pore volume fraction, channel size and pore shape were controlled by varying the freezing temperature, solid content and sintering condition. After sublimation of camphene, the samples were sintered for 2 h at elevated temperatures ranging from 1400 to 1550 °C. The initial level of solid loading played a primary role in the resulting porosity of the product. The porosity decreased from 82.5 to 65.5 vol.% when the solid loading was increased from 10 to 20 vol.%. The relationship of the compressive strength versus initial solid loading and sintering temperature was discussed. This technique is considered potentially useful in fabricating novel porous ceramics with special structure, and introduces a new application field of freeze-casting.     

Characterization of porous bi-modal Ni structures

A new nickel-based porous structure, exhibiting a bi-modal pore size distribution, has been developed through the combination of nickel foam (INCOFOAM) with sintered nickel filamentary powder (T255). Sintering was carried out in the 900–980 °C temperature range in a vacuum environment. These bi-modal nickel samples were examined for their microstructure, hydraulic behaviour including capillary head and permeability, specific surface area (SAA), and overall porosity. The incorporation of a layer of sintered nickel filamentary powder (T255) onto the nickel foam was shown to increase both the specific surface area and capillary pumping pressure of the foam, while simultaneously maintaining high porosity and liquid permeability. Both the sintering temperature and the degree of nickel powder coverage were determined to be critical factors contributing to the properties of these bi-modal nickel porous structures.     

Macro-porous ceramic supports for membranes prepared from quartz sand and calcite mixtures

A new type of porous ceramic supports for membranes has been designed. The new supports have been fabricated from polycrystalline quartz sand and calcite raw materials. In this work, two configurations of support (tubular and flat) have been produced using extrusion method. The open porosity, the pore size distribution, the average pore size (APS), the strength and the permeability of sintered supports have been found to depend mainly on the weight ratio of calcite (CaCO₃) additive. The results showed that with the addition of 15–35 wt.% of calcite and sintering temperature of about 1375 °C for 1 h the best characteristics of sintered supports could be obtained. The developed tubular ceramic supports with the APS 6.3–12 μm, open porosity 42–55%, the water permeability (16–68 m³/h m² bar) and flexural strength 8–18 MPa hopefully offer many perspectives for a wide use in membranes technology.     

Alumina/zirconia ceramic membranes fabricated by temperature induced forming technique

It is well known that the fabrication technique of porous ceramic composites has a significant effect on their microstructure and properties. In the present study, alumina/zirconia ceramic composites doped with magnesia were fabricated by temperature induced forming technique using tri-ammonium citrate and polyacrylic acid (PAA) as dispersant and gelling agents, respectively. The zirconia content was up to 20 wt% and added at the expense of alumina while the magnesia content was up to 2 wt% over the total mass. The optimum amount of ammonium citrate tribasic needed for dispersing the ceramic slurry was determined by measuring zeta potential of slurries. The prepared green alumina/zirconia composites were subjected for solid state sintering at 1550 °C for 1 h. The densification parameters, phase composition, average pore diameter, microstructure and cold crushing strength of sintered alumina/zirconia ceramics were investigated by the suitable techniques. The results revealed that the addition of tri-ammonium citrate to ceramic slurries enhanced the zeta potential which reached ?28.3 mV by adding 1 wt.-%. The bulk density was decreased while the apparent porosity was increased with the increase of zirconia content. The apparent porosities of sintered porous composites were in the range of 38.8–48.5%. The average pore diameter for the composite containing 15% zirconia was 1.79 μm and pore volume was 0.11 ml/g. The obtained microstructure exhibited zirconia grains located on the grain boundaries of Al₂O₃ matrix. The existence of zirconia in addition to magnesia hindered the growth and deformation of the matrix. The cold crushing strength of porous composites was decreased from 16.0 to 8.5 to MPa by increasing the zirconia content from 5 to 20 wt.-%.     

Processing of porous yttria-stabilized zirconia tapes: Influence of starch content and sintering temperature

The tape-casting process was used to produce porous yttria-stabilized zirconia (YSZ) substrates with volume fractions of porosity ranging from 28.9 to 53 vol.% by using starch as a fugitive additive. Concentrated aqueous YSZ slips with different amounts of starch and an acrylic latex binder were prepared. The influence of the volume fraction of starch and sintering temperature on the sintering behavior and final microstructure were investigated. The microstructure consisted of large pores created by the starch particles with lengths between 15 and 80 μm and smaller pores in the matrix with lengths between 0.6 and 3.8 μm. The pores in the matrix reduced the sinterability of the YSZ leading to the retention of closed porosity in the sintered tapes. The porosities were above those predicted for each of the starch contents. However, larger deviations from the predicted porosity were found as more starch was added. The open to total porosity ratio in the sintered tapes could be controlled by the volume fraction of added starch as well as by the sintering temperature. As the volume fraction of starch increased from 17.6 to 37.8 vol.% there was a gradual increase in the interconnectivity of the pore structure. The sintering shrinkage of the tapes at a given temperature could be directly related to the YSZ packing density in the matrix.     

Effect of hydroxyapatite and tricalcium phosphate addition on protein foaming-consolidation porous alumina

Porous alumina-hydroxyapatite (HA) and alumina-tricalcium phosphate (TCP) composites have been fabricated to investigate the effect of HA and ??-TCP addition on protein foaming-consolidation derived porous alumina. HA and ??-TCP loadings along with yolk content, starch content, and sintering temperature were varied to modulate performance of the porous composites. The rheological behavior of slurry shifted from pseudoplastic flow to a Newtonian fluid with increasing yolk concentration. The foaming capacity of slurry increased with yolk addition. The addition of starch into slurry resulted in bigger pore size and avoided the porous bodies from cracks. The shrinkage of sintered bodies increased with increasing HA loading, but decreased with increasing ??-TCP loading. The compressive strength of porous alumina-HA body was found 2.9?MPa at 45.8% porosity and 20.4?MPa at 36.8% porosity. The increasing porosity of porous alumina-TCP body from 56.1 to 61.6% improved the compressive strength from 3.1 to 4.2?MPa. Increasing sintering temperature resulted in large grain size among powder particles, thus improving the compressive strength of porous bodies. Preliminary results of DF-1 cells culture on the surface of porous alumina and alumina-TCP samples are also reported.     

烧结制度及造孔剂用量对粉煤灰基多孔陶瓷膜支撑体性能的影响

以粉煤灰为原料,采用挤压成型和固态粒子烧结法制备管状粉煤灰基多孔陶瓷膜支撑体.采用TG-DSC技术对粉煤灰进行了热分析,采用SEM和XRD技术对样品的微观结构及物相组成进行了分析,并测定了样品的开孔率、抗压强度及空气渗透速率等性能指标.研究了烧结温度、保温时间和造孔剂添加量对支撑体性能的影响.结果表明:支撑体晶相组成主要为赤铁矿、红柱石和石英;烧结温度为1000 ℃,保温2 h,仅添加1%的粘结剂,不添加造孔剂的条件下制备出的管状支撑体综合性能最优,此时的支撑体孔隙率为44.95%,抗压强度为8.92 MPa,空气渗透速率为2.57×104 m3·h-1·m-2·MPa-1.     

High gas permeability and directional channels of mullite porous ceramics prepared by pectin-based freeze-drying method

New gel system for preparing mullite porous ceramics by gel-casting freeze-drying was proposed, using pectin as gel source and alumina and silica as raw materials. Directional channels were formed due to sublimation of water during freeze-drying and decomposition of pectin during high temperature sintering to prepare porous mullite ceramic membranes. Effects of solid content on the properties of mullite ceramics in terms of phase composition, microstructure, apparent porosity, bulk density, pore size distribution, compressive strength, thermal conductivity, pressure drop, and gas permeability were investigated. It was found that prepared porous mullite possessed high apparent porosity (56.04%–75.34%), low bulk density (.77–1.37 g/cm³), uniform pore size distribution, relatively high compressive strength (.61–3.03 MPa), low thermal conductivity (.224–.329 W/(m·K)), high gas permeability coefficient (1.11 × 10⁻¹⁰–4.73 × 10⁻¹¹ m²), and gas permeance (2.18 × 10⁻²–9.32 × 10⁻³ mol⋅m⁻²⋅s⁻¹⋅Pa⁻¹). These properties make prepared lightweight mullite ceramic membranes promising for application in high temperature flue gas filtration. Proposed gel system is expected to provide a new route to prepare porous ceramics with high porosity and directional channels.     

Porosity features and gas permeability analysis of bi-modal porous alumina and mullite for filtration applications

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.     

Fabrication and characterization of cordierite-bonded porous SiC ceramics

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%.     

Novel structure of ceramic tape for multilayer devices

To reduce the content of binders surrounding ceramic powders in a ceramic tape and the residual pore after burnout to a minimum, a ceramic tape with double layers was manufactured. One layer was comprised of only organic binder, which imparted sufficient strength and strong adhesive property to the green tape. The other one was a ceramic layer with a very small amount of binder. The binder content of the slurry for ceramic layer was less than 2 wt%, which could lower the viscosity, make the slurry well dispersed and considerably increase solid loading in the slurry. This higher solid loading led to higher green tape density, higher fired density of the product. The two-layer ceramic tape showed much better qualities than a common (or conventional) green tape especially in microstructure, laminatablilty, and tape density. In the multilayer structure made of the two-layer ceramic tape, the binder layer completely disappeared after binder-burnout and no defects from the two-layer structure were observed.