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.     

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.     

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。     

Densification and enhancement of SiC particulate-reinforced fine-grain SiC ceramic

Dense sintering of SiC nanopowder under low temperature and pressure remains a big challenge, because of the great resistance caused by the severe agglomeration of nanopowder. A novel sintering strategy is proposed to prepare SiC composite ceramics by sintering the mixture of SiC nanopowder and SiC micron powder at low temperature and pressure. The SiC micron powder was in the size of 100 µm with little sintering activity, which was designed as a pressure conductor to promote the densification of SiC nanopowder. Experimental results showed that the SiC micron powder had a significant effect on increasing of the sintering density of nanopowder and improving the mechanical properties of SiC ceramics. An SiC composite ceramic with a relative density of 98%, a Vickers hardness of 22.6 GPa, and a fracture toughness of 5.43 MPa m^1/2 could be sintered by spark plasma sintering under 1700°C and 30 MPa by adding 30 wt.% 100 µm SiC micron powder as reinforcements.     

硅线石含量对轻质莫来石-刚玉耐火材料的显微结构与性能的影响

以多孔球形莫来石为骨料,板状刚玉细粉、硅线石和粘土为基质,经1400 ℃、1500 ℃和1600 ℃保温3 h烧成,制备了四组轻质莫来石-刚玉耐火材料.采用X-射线衍射仪(XRD)和扫描电子显微镜(SEM)对试样的物相组成和显微结构进行表征,研究了烧成温度及硅线石含量(4%、6%、8%和10%)对试样常温物理性能和显微结构的影响.结果表明:(1)当硅线石含量不变时,随着烧成温度的升高,试样的显气孔率逐渐减小,体积密度逐渐增大,线收缩率逐渐增加,常温耐压强度先降低后升高;(2)当硅线石的含量从4%增加到8%时,经1400 ℃烧后,试样的显气孔率和体积密度变化不大,当硅线石含量超过8%时耐压强度显著下降;经1600 ℃烧后,随硅线石含量的增加,试样的体积密度减小,强度降低,线收缩率也由2.5%减小到1.5%;(3)当硅线石含量为6%、烧成温度为1400 ℃时,试样的线收缩率为0.86%,耐压强度为36.1 MPa,热导率为0.249 W/(m·K)(300 ℃),试样基质中气孔的d50为46.7 μm.     

Electrically conductive SiC ceramics processed by pressureless sintering

Polycrystalline SiC ceramics with 10 vol% Y₂O₃-AlN additives were sintered without any applied pressure at temperatures of 1900-2050°C in nitrogen. The electrical resistivity of the resulting SiC ceramics decreased from 6.5 × 10¹ to 1.9 × 10⁻² Ω·cm as the sintering temperature increased from 1900 to 2050°C. The average grain size increased from 0.68 to 2.34 μm with increase in sintering temperature. A decrease in the electrical resistivity with increasing sintering temperature was attributed to the grain-growth-induced N-doping in the SiC grains, which is supported by the enhanced carrier density. The electrical conductivity of the SiC ceramic sintered at 2050°C was ~53 Ω⁻¹·cm⁻¹ at room temperature. This ceramic achieved the highest electrical conductivity among pressureless liquid-phase sintered SiC ceramics.     

Corrosion resistant ZrO2/SiC ultrafiltration membranes for wastewater treatment and operation in harsh environments

This work focused on the fabrication of a ZrO₂/SiC ultrafiltration membrane by dip coating a high porous SiC support with a ZrO₂ slurry prepared by ceramic processing. The membranes were sintered in different temperatures (1000−1300 °C). With the optimal temperature, it was obtained a mechanically strong, homogenous, and defect free separation layer with 45 μm of thickness and average pore size of 60 nm. A pure water permeability of 360 L.m⁻² h⁻¹ bar^-1 and high retentions of humic acid, indigo dye, and hemoglobin were observed. In a pilot test with an olive oil/water emulsion, 99.91 % of oil was removed without fouling. Long-term corrosion tests at basic and acid baths did not cause change in pore size and morphology. In conclusion, the ZrO₂/SiC membrane has potential to operate in harsh conditions (e.g. heavily contaminated industrial effluents or urban wastewaters) and when severe membrane cleaning and disinfection are required, such as food and pharmaceutical industries.     

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.     

Photonic Sintering of Aerosol Jet Printed Lead Zirconate Titanate (PZT) Thick Films

Lead Zirconate Titanate (PZT) is a commonly used piezoelectric material due to its high piezoelectric response. We demonstrate a new method of printing and sintering micro‐scale PZT films with low substrate temperature increase. Self‐prepared PZT ink was Aerosol‐Jet printed on stainless steel substrates. After drying for 2 h in vacuum at 200°C, the printed PZT films were divided into two groups. The first group was traditionally sintered, using a thermal process at 1000°C for 1 h in an Argon environment. The second group was photonically sintered using repetitive sub‐msec pulses of high intensity broad spectrum light in an atmospheric environment. The highest measured substrate temperature during photonic sintering was 170.7°C, enabling processing on low melting point substrates. Ferroelectric measurements were performed with a low‐frequency sinusoidal signal. The remanent polarization (P_r) and coercive field (E_c) for thermally sintered PZT film were 17.1 μC/cm² and 6.3 kV/cm, respectively. The photonically sintered film had 32.4 μC/cm² P_r and 6.7 kV/cm E_c. After poling the samples with 20 kV/cm electric field for 2 h at 150°C, the piezoelectric voltage constant (g₃₃) was measured for the two film groups yielding ?16.9 × 10^?3 (V·m)·N^?1 (thermally sintered) and ?17.9 × 10^?3 (V·m)·N^?1 (photonically sintered). Both factors indicate the PZT films were successfully sintered using both methods, with the photonically sintered material exhibiting superior electrical properties. To further validate photonic sintering of PZT on low melting point substrates, the process and measurements were repeated using a polyethylene terephthalate (PET) substrate. The measured P_r and E_c were 23.1 μC/cm² and 5.1 kV/cm, respectively. The g₃₃ was ?17.3 × 10^?3 (V·m)·N^?1. Photonic sintering of thick film PZT directly on low melting point substrates eliminates the need for complex layer transfer processes often associated with flexible PZT transducers.     

Sintering temperature dependency on sodium-ion conductivity for Na2Zn2TeO6 solid electrolyte

We investigated the sintering temperature dependency on the properties of Na₂Zn₂TeO₆ (NZTO) solid electrolyte synthesized via a conventional solid-state reaction method. Sintering temperature of calcined NZTO powder, which was obtained by the calcination of precursor at 850℃, was changed in the range from 650 to 850℃. X-ray diffraction analysis showed that P2-type layered NZTO phase was formed in all sintered samples without forming any secondary phases. The relative densities of sintered NZTO samples were approximately 83%−85% for the samples sintered at 700℃ or higher. The all sintered samples showed sodium-ion conductivity above 10⁻⁴ S cm⁻¹ at room temperature and the highest conductivity of 4.0 × 10⁻⁴ S cm⁻¹ in the sample sintered at 750℃. The sintering temperature to obtain the highest room temperature conductivity is 100℃ lower than that used in previous works. Such low sintering temperature compared to other Na-based oxide solid electrolytes could be useful for co-sintering with electrode active materials for fabrication of all-solid-state sodium-ion battery.     

Mechanical and Thermal Properties of Pressureless Sintered Silicon Carbide Ceramics with Alumina–Yttria–Calcia

The effect of sintering temperature on the mechanical and thermal properties of SiC ceramics sintered with Al₂O₃–Y₂O₃–CaO without applied pressure was investigated. SiC ceramics containing A₂O₃–Y₂O₃–CaO as sintering additives can be sintered to >97% theoretical density at temperatures between 1750°C and 1900°C without applied pressure. A toughened microstructure, consisting of relatively large elongated grains and relatively small equiaxed grains, has been obtained when sintered at temperatures as low as 1800°C for 2 h in an argon atmosphere without applied pressure. The achievement of toughened microstructures under such mild conditions is the result of the additive composition. The thermal conductivity of the SiC ceramics increased with increasing sintering temperature because of the decrease in the lattice oxygen content of the SiC grains. Typical sintered density, flexural strength, fracture toughness, hardness, and thermal conductivity of the 1850°C‐sintered SiC, which consisted of 62.2% 4H, 35.7% 6H, and 2.1% 3C, were 99.0%, 628 MPa, 5.3 MPa·m^1/2, 29.1 GPa, and 80 W·(m·K)^?1, respectively.     

Microstructures and properties of solid-state-sintered silicon carbide membrane supports

Porous solid-state-sintered SiC (S–SiC) membrane supports were successfully fabricated by pressureless sintering at 2150 °C in argon, using fine and coarse graded SiC powders as the main starting material. There were uniformly distributed and fully interconnected pores in as-acquired S–SiC membrane supports, accompanied with similar apparent porosities for all of them. When increasing the size of coarse SiC powder, their average pore sizes were distinctly enlarged from ∼1.6 μm to ∼2.3 μm, which significantly enhanced their nitrogen permeability from 0.9 × 10⁻¹³ m² to 2.6 × 10⁻¹³ m². Moreover, S–SiC membrane supports possessed outstanding flexure strengths of 134.1 ± 21.3 MPa at room temperature and 88.7 ± 8.4 MPa at 1000 °C owing to strong interface bonding between SiC grains. Compared with the traditional SiO₂ -bonded and mullite-bonded SiC supports, S–SiC membrane supports presented their great superiority in high-temperature flexure strength as well as acid and alkali corrosion resistance, which permitted them to be potentially applied in high-temperature and strongly corrosive environments.     

纯B4C和掺碳B4C的烧结机制

研究了中位粒径为0．42μm的纯B4C和掺碳B4C的烧结致密化过程。根据烧结温度和保温时间对线收缩率的影响。得出了它们的烧结动力学方程;由特征指数n值对比研究了它们的烧结致密机制。纯B4C的烧结致密机制为体扩散和晶界扩散,而掺碳B4C的烧结机制主要为晶界扩散,因此,掺碳对B4C起到了活化烧结的作用,在2160℃烧结45min,掺碳B4C烧结后相对密度大于90％,掺入的碳除了固溶于B4C晶格中之外,其它均以游离石墨形式存在,不形成新相。掺碳还导致B4C晶粒尺寸大大减小。     

Low temperature sintered MnZn ferrites for power applications at the frequency of 1 MHz

The low power loss Mn-Zn ferrites with fine grains were developed by the low-temperature-sintering ceramic process for power applications at a high frequency of 1 MHz. The LiBO₂ sintering aid was added to promote the low temperature sintering and densification. The effects of LiBO₂ on micromorphology and magnetic properties of the sintered Mn-Zn ferrites were investigated. With the aid of LiBO₂, sintering temperature could be reduced as low as 990 °C. The optimum sample was obtained by the addition of 500 ppm LiBO₂ sintered at 1020 °C. The average grain size of this sample is 2.78 μm, the density reaches 4.82 g/cm³, and the minimum power loss is 310 kW/m³ at 1 MHz/30 m T and 25 °C. This sample shows good wide-temperature stability of power loss. The mechanism of power loss affected by the LiBO₂ addition was also discussed. The ceramic sintering process combining the low temperature sintering and the sintering aid offers a new way to develop high-frequency Mn-Zn ferrites.     

Influence of additive contents on the properties of SiC ceramic membranes and their performance in oil-water separation

The high processing cost is the key challenge for the economic industrial use of SiC membrane The aim of this research was to fabricate mullite bonded porous SiC ceramic membrane at low temperature from novel combinations of fly ash and alumina (FA) in weight ratio 44.5:55.5 as sintering additives. The influences of FA and pore former content on the porosity, morphology, crystalline phase composition, mechanical performance, permeability properties were investigated. The membrane prepared at 1300°C using 20 wt% FA showed pure water permeability 3690 Lm⁻²h⁻¹bar⁻¹ and exhibited high oil removal efficiency of ∼ 98% from the synthetic oil-water emulsion having oil concentration of 1000 mg/L. The corrosion behaviour of silicon carbide membrane in the strong acid and alkali solution and its mechanism were investigated. The utilization of fly ash successfully reduced the raw material cost and sintering temperature and the use of alumina reduced the amount of oxidation of SiC as well as increased the amount of mullite bond phase which resulted excellent mechanical strength to the final ceramics.     

(Ti0.25Zr0.25Nb0.25Ta0.25)C高熵陶瓷的制备、力学性能及氧化行为研究

本文通过对碳化物粉末进行放电等离子烧结(SPS),成功制备了(Ti_0.25Zr_0.25Nb_0.25Ta_0.25)C高熵陶瓷(HECs),系统研究了HECs的微观结构演变、力学性能和氧化行为。结果表明,单相HECs的形成温度为1 800 ℃,低于已报道的HECs烧结温度。1 900 ℃烧结的陶瓷晶粒细小,平均晶粒尺寸约7.5 μm,元素分布均匀,相对密度高达99.2%。1 800 ℃和1 900 ℃烧结的HECs的室温显微硬度值分别为30.9 GPa和33.2 GPa,断裂韧性值分别为(4.6±0.24) MPa·m^1/2和(4.5±0.31) MPa·m^1/2,高于大多数已报道的HECs。原位高温纳米压痕试验结果表明,HECs的硬度随温度的升高而降低,当温度达到500 ℃时,1 800 ℃和1 900 ℃烧结的陶瓷硬度分别下降到21.9 GPa和22.2 GPa,具有突出的高温稳定性。此外,HECs在温度低于500 ℃时无明显氧化,当温度超过650 ℃时会发生明显氧化,氧化速率随温度升高而增加。     

Effect of silicon carbide additive on microstructure and properties of porcelain ceramics

Porcelain green bodies with various silicon carbide contents (0-3 wt.%) were prepared from a porcelain tile powder as a major raw material and SiC particle as an additive, and were sintered at 1000-1240 °C. The samples were systematically characterized by the X-ray diffraction (XRD), scanning electron microscope (SEM) and metallurgical microscope. Effects of the SiC content and sintering temperature on the pore size, SiC particle size and sintered density were investigated in detail, and the correlative mechanism was also discussed. The SiC particle size decreased and the pore size augmented with increasing the sintering temperature. The sintered density decreased and the pore size enlarged with increasing the SiC content. The experimental results indicate that a small amount of SiC can cause porcelain ceramics to foam during sintering, and a foaming origin of the polishing porcelain waste during sintering could be attributed to the oxidation reaction of SiC particles under high temperature and alkaline molten salt conditions.     

Densification of Y2O3 by flash sintering under an AC electric field

Frequency dependence of the densification behavior of undoped Y₂O₃ sintered by the AC-flash sintering was systematically investigated at 500 V·cm^?1 over a frequency range from 0.05 Hz to 1 kHz. The Y₂O₃ bodies sintered under an AC field showed a uniform microstructure, without an asymmetric grain size distribution between the electrodes. Almost fully-densified Y₂O₃ body was consolidated at 1 kHz exhibited a relative density greater than 99 % and an average grain size of 1.6 μm. The almost full densification probably resulted from the high input power at the relatively high onset temperature of 1300 °C at this frequency. The temperature dependence of the power dissipation during the AC-flash sintering experiments can be ascribed to the periodic fluctuations of the specimen temperature at low frequencies and to the phase shift between the applied field and the specimen current at high frequencies.     

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.