Zirconia ultrafiltration membranes on silicon carbide substrate: microstructure and water flux

This study reported the preparation of ZrO₂/SiC ceramic membrane with silicon carbide as the substrate and intermediate layers and zirconia as the selective layer. The substrate and intermediate layers were sintered by evaporation-condensation process at 2200 and 1900 ℃, respectively. After sintering, the intermediate layer presented layer thickness of 50 μm, pore size of 0.87 μm and pure water permeability of 2140 L/(m²·h). The selective lay was deposited on the silicon carbide substrate by dip-coating method and then sintered in the temperature range from 800 to 1000 ℃. For the membrane coated by one dip-coating cycle and sintered at 800 ℃, it presented average pores of 82 nm and water flux of 850 L/(m²·h). Due to the exclusion of low-melting oxides during sintering, the ZrO₂/SiC ceramic membrane can satisfy the separation and purification of chemical corrosion and high temperature wastewater.     

Sol-gel derived zirconia membrane on silicon carbide substrate

To enhance the high temperature and chemical corrosion resistances of ceramics membrane, a ZrO₂/SiC ceramic membrane was prepared through sol-gel route followed by the dip-coating technique. The substrate layer was made of pure silicon carbide phase by evaporation-condensation process, and the separation layer was made of zirconia phase by solid-phase sintering process. The substrate layer was sintered at 2200 ℃ in the vacuum, and the pores were distributed in a narrow size range from 4.5–6.0 μm. When the membrane was sintered at 700 ℃, a defect-free separation layer formed on the substrate. With the increase of sintering temperature, the average pore size of the separation layer declined from 63 to 48 nm, and the water permeability declined from 355 to 273 L/(m²·h·bar). Our results indicate the ZrO₂/SiC ceramic membrane has potential applications in the separation of high temperature or chemically corrosive wastewaters.     

Evaporation-condensation derived silicon carbide membrane from silicon carbide particles with different sizes

Silicon carbide ceramic is a promising membrane material because of the high corrosive and high temperature resistance, and the excellent hydrophility. Here, a silicon carbide ceramic membrane with both substrate layer and separate layer composed of pure silicon carbide phase was successfully prepared. The effect of particle size on the microstructure and properties was investigated. The substrates were prepared from three silicon carbide particles at 2200 ℃. With the content increase of fine particle, the average pore size increased from 5.6 μm to 14.1 μm; meanwhile, the flexural strength of the substrate increased from 14.1 MPa to 24.6 MPa. The separation layers were made from particles of 3.0 μm and 0.5 μm. When sintered at 1900 ℃, the separation layer formed pore network with homogeneous structure. Such silicon ceramic membrane can be used in harsh conditions, including high temperature wastewater and strongly corrosive wastewater.     

Porous cenosphere ceramic microfiltration membrane: Preparation,characterization, permeability evaluation,and cost estimation

Ceramic membranes are now receiving greater attention and are regarded as the best alternative option for reducing energy use. There are currently a number of limitations on the use of ceramic membranes, including high raw material costs and high sintering temperatures during synthesis. Cost-effective raw materials were employed in the synthesis of ceramic membranes to get around these restrictions. Utilizing a straightforward pressing technique, circular disc-type membranes were prepared. To assess the membrane properties, the impact of sintering temperatures between 700 and 900°C was examined. By varying the sintering temperature, the average membrane pore diameter was observed. The membrane, which was sintered at 800°C, had pores that were on average 110 nm in size. Furthermore, the porosity of these synthesized membranes ranged from 22% to 35% with an average pore diameter of 74–121 nm. These manufactured membranes showed very good chemical stability when both acidic and basic solutions were used. Various characterization methods, including thermogravimetric analysis (TGA), x-ray diffraction analysis (XRD), and scanning electron microscopy (SEM), were used. Thermo-gravimetric investigation revealed that the synthesized cenosphere membrane required a minimum sintering temperature of about 700°C. The flux measured with deionized water and the applied transmembrane pressure showed an upward trend. The impact of sintering temperature on permeate flux was investigated. The results showed that as the sintering temperature increased from 700°C to 900°C, the flux reduced. It was determined that the synthesized membrane cost ₹1618.80/m².     

Low-temperature sintering of silicon carbide membrane supports from disks to single- and 19-channel tubes

As the configuration of asymmetric ceramic membranes is determined by the membrane supports, a low temperature sintering process was developed to prepare ceramic membrane supports from disks to single- and 19-channel tubes. The residual of NaA zeolite was introduced into the silicon carbide (SiC) matrix, and porous SiC membrane supports were successfully prepared at 1100 °C. Compared with the disk-like support, the open porosity, average pore size and pure water permeance of the single-channel supports obviously increased, and their bending strength decreased accordingly. These differences were mainly attributed to the incorporation of organic plasticizer and the change in molding process. Notably, the pure water permeance of disks, single- and 19-channel tubes was 70 ± 3, 74 ± 4 and 22 ± 1 m³·m^?2·h^?1·bar^?1, respectively, which was much higher than the previously reported values. Therefore, this work provides important guides to develop of new generation ceramic membranes for practical application.     

Effect of sintering temperature on functional properties of alumina membranes

Supported membranes were prepared from different submicron alumina powders. The evolution of pore size, hardness and permeability were monitored after sintering the films at temperatures ranging from 1000 to 1400 °C. These functional properties and the microstructure of the films were compared with the free-standing membranes. Sintering at temperature range from 1000 to 1200 °C maintained the narrow, monomodal pore size distribution of the supported membranes. The effect of sintering temperature on the hardness of the membranes was weak. The permeability was also independent on the sintering temperature. When sintering temperature was raised up to 1300 and 1400 °C, the pore size increased significantly and distribution was changed to bimodal containing fraction of large pores. The hardness of the membranes increased while significant densification was not observed. Permeability increased due to the large pore size and the high porosity. In sintering of the free-standing membranes pore size remained almost unchanged, density increased when sintering temperature was raised, hardness was dependent on the density and permeability decreased continuously. The substrate did not have effect on the grain growth, which was dependent on the sintering temperature. Evolution of the properties of the free-standing membranes suggests local densification. The rigid substrate restricts the sintering shrinkage leading to densification of small areas. This local densification opens large flow channels between agglomerates. This increases the pore size, broadens the pore size distribution and increases the permeability. The macroscopic densification of the film is small.     

Effects of SDBS and ZrO2 additives on the microstructure and properties of silicon-bonded SiC porous ceramics

Porous silicon-bonded silicon carbide (SBSC) ceramics were prepared under argon atmosphere, with silicon as pore former and bonding material, simultaneously, sodium dodecyl benzene sulfonate (SDBS) and ZrO₂ as sintering additives, the effects of SDBS and ZrO₂ on the porosity, pore size, mechanical, physical and thermal properties and microstructures were investigated. The results suggested that suitable content of SDBS and ZrO₂ could not only effectively lower the sintering temperature to 1450 °C due to the sticky flow of molten silicon, but also increase the pore structure and improve the bending strength. The reason for this is that SDBS decomposed into Na₂O which reacted with ZrO₂ and impurity SiO₂, which was the native oxide film on the surface of SiC particles, to form a bonding phase between SiC particles to improve the bending strength; meanwhile, the disappearances of impurity SiO₂ would benefit the bond of molten silicon and silicon carbide particles, and silicon melt leaving pores in its original position to increase the pore structure. The optimal apparent porosity, bending strength, average pore size, gas permeance and residual bending strength after thermal shock cycles of SBSC porous ceramic sintered at 1450 °C with 5 wt% SDBS and 6 wt% ZrO₂ were 38.33%, 55.4 MPa, 11.3 μm, 106.4 m³/m²·h·kPa and 28.2 MPa, respectively.     

One-step dip-coating method for preparation of ceramic nanofiber membrane with high permeability and low cost

Ceramic nanofiber membrane (CNM) based on attapulgite (APT) without any intermediate layer neither any cracks was fabricated by a one-step dip-coating method. The effects of sintering temperature and dip-coating time on the physicochemical properties and performances of prepared CNMs were investigated. The increase of the sintering temperature up to 700 °C reduced the bending strength, porosity and chemical stability of APT-based CNMs. Meanwhile, with the dip-coating time increased, the membrane thickness increased thereafter reduced. The APT-based CNM fabricated at a sintering temperature of 600 °C and with a dip-coating time of 15 s had an average pore size of 20.4 nm, high porosity (above 60 %), good permeability of 118 L/m² h bar and a rejection of 96.6 % polymers with a molecule weight of 600 kDa. All these properties clearly suggest the practicability of the one-step dip-coating method to prepare ceramic nanofiber membranes.     

Fabrication of high performance macroporous tubular silicon carbide gas filters by extrusion method

Hot gas filtration requires high performance tubular filters, but low permeability, low strength, and high sintering temperature of silicon carbide (SiC) filters limit their use. In this work, a high permeability tubular SiC support was fabricated with high strength at a sintering temperature of 1200?°C, when 100?µm SiC particles were used as aggregate, sodium dodecyl benzene sulfonate (SDBS) was used as sintering aid and organic additives were used as binders. Plasticity of the mixed particles was optimized by adjusting the ratios of methylcellulose, paraffin, and glycerol. The porosity, pore diameter, gas permeation coefficient, and bending strength of the SiC ceramic support reached 45.0%, 34.2?µm, 4.6?×?10^–12 m², and 22.8?MPa, respectively. Furthermore, compared to the cold isostatic pressure (CIP) technique, the extrusion method led to sharper peak of the pore diameter distribution, achieved higher bending strength, and had a more homogeneous microstructure.     

高温除尘碳化硅膜的制备及其抗腐蚀特性

采用喷涂法在碳化硅（SiC）支撑体上覆膜,根据碳化硅材料的氧化特性,设计了有氧烧结和氩气烧结随温度转换的组合烧结制度,并通过优化保温时间降低碳化硅陶瓷膜烧结成本。研究结果表明,新的烧结制度能有效地控制有氧烧结阶段产生的二氧化硅（SiO₂）量,并促进其与烧结助剂氧化锆（ZrO₂）等在气氛烧结阶段的反应,反应生成的锆英石相和添加莫来石相共同形成SiC颗粒连接颈部。制备的碳化硅陶瓷膜平均孔径为3.03 μm,气体通量为175 m³?m^-2?h^-1?kPa^-1。且在100℃的0.25 mol?L^-1的H₂SO₄溶液和0.25 mol?L^-1的NaOH溶液中腐蚀6 h后,膜层表面形貌无明显变化,具有较强的抗腐蚀性能。     

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.     

Recent progress in the pore size control of silicon carbide ceramic membranes

The demand for separation and purification applications under harsh conditions has grown strongly in recent years. Silicon carbide (SiC) ceramic membranes have broad prospects in this aspect due to their unique characteristics, but its pore size control is a crucial problem. Therefore, it is of great significance to develop simple and feasible methods for precise control of the pore size of SiC membranes to improve membrane selectivity and expand their application range. This review describes the pore formation process in the preparation of SiC membranes, focusing on the selection of SiC particles, sintering temperature, sacrificial template, sintering aids, oxidation process and other factors affecting the pore size and analysis. Finally, the control of SiC membrane pore size is summarized and the outlook is proposed.     

Sinterability,microstructure and compressive strength of porous glass-ceramics from metallurgical silicon slag and waste glass

Porous glass-ceramics have been prepared by the direct sintering of powder mixtures of metallurgical silicon slag and waste glass. The thermal behavior of silicon slag was examined by differential thermal analysis and thermogravimetry to clarify the foaming mechanism of porous glass-ceramics. The mass loss of silicon slag below 700 °C was attributed to the oxidation of amorphous carbon from residual metallurgical coke in the silicon slag, and the mass gain above 800 °C to the passive oxidation of silicon carbide. The porosity of sintered glass-ceramics was characterized in terms of the apparent density and pore size. By simply adjusting the content of waste glass and sintering parameters (i.e. temperature, time and heating rate), the apparent density changed from 0.4 g/cm³ to 0.5 g/cm³, and the pore size from 0.7 mm to 1.4 mm. In addition to the existing crystalline phases in the silicon slag, the gehlenite phase appeared in the sintered glass-ceramics. The compressive strength of porous glass-ceramics firstly increased and then decreased with the sintering temperature, reaching a maximal value of 1.8 MPa at 750 °C. The mechanical strength was primarily influenced by the crystallinity of glass-ceramics and the interfaces between the crystalline phases and the glassy matrix. These sintered porous glass-ceramics exhibit superior properties such as light-weight, heat-insulation and sound-absorption, and could found their potential applications in the construction decoration.     

致密超细球形氧化铝制备性能良好的陶瓷超滤膜

热等离子体制备的超细球形氧化铝具有表面致密光滑、分散性好等特点，本工作以超细球形氧化铝为原料，通过浸渍提拉烧结法，制备了孔径分布窄、渗透通量高的陶瓷超滤膜，研究了烧结温度对陶瓷膜微孔结构的演化、孔径分布和渗透通量的影响。随后对1250℃下烧结的陶瓷膜进行了纳米硅水分散液过滤处理，采用不同堵塞模型分析了陶瓷膜过滤纳米硅水分散液的膜污染过程。结果表明，通过调节烧结温度调控陶瓷膜的微孔结构，当烧结温度为1250℃时，陶瓷膜的孔径分布较窄，孔径大小为25?65 nm，渗透通量为986.4 L/(m2?h)。超细球形氧化铝粒径分布较窄及表面致密光滑有助于1250℃下烧结形成均匀的烧结颈，提供了陶瓷膜较窄的孔径分布。对1250℃下烧结的陶瓷膜进行了纳米硅水分散液过滤处理后其浊度下降为0.231 NTU，浊度去除率达99.96%。采用不同堵塞模型分析了陶瓷膜过滤纳米硅水分散液的膜污染过程，结果表明，纳米硅水分散液的堵塞模型是滤饼过滤，属于可逆污染。     

Design and fabrication of whisker hybrid ceramic membranes with narrow pore size distribution and high permeability via co-sintering process

Ceramic microfiltration membranes (MF) with narrow pore size distribution and high permeability are widely used for the preparation of ceramic ultrafiltration membranes (UF) and in wastewater treatment. In this work, a whisker hybrid ceramic membrane (WHCM) consisting of a whisker layer and an alumina layer was designed to achieve high permeability and narrow pore size distribution based on the relative resistance obtained using the Hagen-Poiseuille and Darcy equations. The whisker layer was designed to prevent the penetration of alumina particles into the support and ensure a high porosity of the membrane, while the alumina layer provided a smooth surface and narrow pore size distribution. Mass transfer resistance is critical to reduce the effect of the membrane layers. It was found that the resistance of the WHCM depended largely on the alumina layer. The effect of the support and whisker layer on the resistance of the WHCM was negligible. This was consistent with theoretical calculations. The WHCM was co-sintered at 1000?°C, which resulted in a high permeability of ~?645?L?m^?1 h^?1 ;bar^?1 and a narrow pore size distribution of ~?100?nm. Co-sintering was carried out on a macroporous ceramic support (just needed one sintering process), which greatly reduced the preparation cost and time. The WHCM (as the sub-layer) also showed a great potential to be used for the fabrication of ceramic UF membranes with high repeatability. Hence, this study provides an efficient approach for the fabrication of advanced ceramic MF membranes on macroporous supports, allowing for rapid prototyping with scale-up capability.     

Fabrication of super flux and high thermal shock resistance ceramic membrane support

Ceramic membranes play an important role in high temperature gas-solid filtration. However, the thermal stability of the ceramic support at high temperatures has always been a problem. In this study, porous fused silica ceramic supports were fabricated with hexagonal boron nitride as a sintering aid. The results shown that hexagonal boron nitride could inhibit the crystallization of fused silica ceramic particles at high temperature and act as a sintering addictive to reduce firing temperature. The obtained supports have an average pore size of 72?µm, an open porosity of 42%, a bending strength of 16.5?MPa, a Weibull modulus of 8.67 and a gas permeability of 4.23?×?10⁵ m³/(m² h bar). The bending strength of the support remained 16?MPa after 30 cold-hot cycles, exhibiting high thermal shock resistance. After corrosion in 20?vol% H₂SO₄ solution for 8?h, the weight and the bending strength of the support were diminished by 0.6% and 24.32%, respectively. So, the ceramic support showed good acid corrosion resistance.     

Preparation processes and characterizations of alumina-coated alumina support layers and alumina-coated natural material-based support layers for microfiltration

Recently, porous ceramic membranes have become a subject of significant interest due to their outstanding thermal and chemical stability. To reduce the high manufacturing costs of these porous ceramic membranes, recent research has focused on the utilization of inexpensive natural materials. However, there have not been any well-established direct comparisons of the membrane properties between typical alumina-based membranes and novel natural material-based membranes. Therefore, we compared alumina-coated alumina support layers (with average pore sizes ranging from 0.10 µm ~0.18 µm), alumina-coated diatomite-kaolin composite support layers (with an average pore size of 0.12 µm), and alumina-coated pyrophyllite-diatomite composite support layers (with an average pore size of 0.11 µm) via the dip-coating method and subsequent heat treatment ranging from 1200 °C–1400 °C for 1 h. The pure water permeability of the alumina-coated diatomite-kaolin composite support layer and the alumina-coated pyrophyllite-diatomite composite support layer was found to be approximately 2.0×10² L m⁻² h⁻¹ bar⁻¹, which is similar to that of an alumina-coated alumina support layer. Therefore, we suggest that the average pore size of an alumina-coated natural material-based support layer can be effectively controlled while exhibiting acceptable water permeability.     

Ceramic Coatings and Glass Additives for Improved SiC‐Based Filters for Molten Iron Filtration

Reticulated silicon carbide (SiC) ceramic filters are prepared with modified coatings in an attempt to improve mechanical properties of the sintered filter. Two classes of coatings are used: mixtures of non‐SiC ceramic and sintering aid and mixtures of SiC and glass. Various candidate ceramics, sintering aids, and glasses are screened. The most promising coatings are determined to be silica with 5 wt% bismuth oxide and SiC with ≤10 wt% Spruce Pine Batch glass. Filters with these coatings are prepared and subjected to mechanical abuse. Both coatings improve the ruggedness of the filter relative to the standard uncoated SiC type. Filters with <10 wt% glass additive were subjected to molten metal impingement and filtration of liquid gray iron at 1510°C. Those with 5 wt% glass or more softened during filtration. Those with 2.5 wt% glass or less survived without failure.     

碳化硅质高温陶瓷膜的低温烧成

本文以碳化硅骨料、章村土系结合剂和核桃壳粉为原料，通过等静压成型工艺和 低温烧结制备了碳化硅质高温陶瓷膜材料。研究了成型压力对坯体强度以及成型压力和烧成温 度对膜材料强度、孔径、气孔率和透气阻力的影响。结果发现，当成型压力为 70 MPa、烧成温 度为 1250~1270?C 时，制品综合性能较优。     

Preparation and characterization of novel ceramic membranes for micro-filtration applications

Porous microfiltration range ceramic membranes were prepared using kaolin and other suitable materials like feldspar, quartz, boric acid, activated carbon, sodium metasilicate and titanium dioxide following standard paste casting route. The membranes were casted as circular disks of 40 mm ID and 5 mm thickness. They were characterized using thermo gravimetric analysis (TGA), particle size distribution (PSD), X-ray diffraction (XRD) and scanning electron microscope (SEM) to evaluate the effect of maximum sintering temperature on the structure, porosity and mechanical integrity. The prepared membranes were initially dried at 120 °C and 250 °C for 24 h each and finally sintered at 850 °C, 900 °C and 950 °C for 6 h. Morphological parameters viz. pore size distribution, porosity, average pore size of the prepared membranes were determined and the membrane performance were evaluated by carrying out the permeation experiment with pure water. Results show that the average pore size of the membranes increases from 1.59 µm to 2.56 µm and porosity of the membrane supports decreases from 18.88% to 5.59% with increase in sintering temperature from 850 °C to 950 °C. The membrane corrosion resistance was also tested using acid and base and it is observed that there is no significant weight loss in the process. Based on market price of the inorganic precursors, the membrane cost was estimated to be $92/m² which can be considered low cost in the microfiltration range for industrial applications.