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.     

Sintering behavior and dielectric properties of SiO2–BPO4 glass-fluxed ceramics

(1–x)SiO₂–xBPO₄ (x?=?23–70?wt%) glass-fluxed ceramics have been prepared by a traditional ceramic process. The phase assemblage, sintering, crystallization behavior, microwave dielectric properties and chemical compatibility with Ag/Cu have been studied. The SiO₂-rich compositions (x?=?23–50?wt%) could be well densified at ～975?°C/2?h, while the BPO₄-rich compositions demonstrated poor sinterability and porous microstructure. The SiO₂-rich compositions sintered at 975?°C/2?h contained BPO₄, low temperature cristobalite and glassy phases. Crystallization of BPO₄ occurred at lower temperature than that of SiO₂. Good combined microwave dielectric properties with ?_r?=?～5, Q?×?f?=?25,000?GHz and τ_f value of –7.3?ppm/°C could be obtained when 10?wt% TiO₂ was added after sintering at 975?°C/2?h. The x?=?23?wt% composition chemically reacted with Ag, but exhibited good chemical compatibility with Cu after sintering at 975?°C/2?h.     

Asymmetric porous cordierite ceramic membranes prepared by phase inversion tape casting and their desalination performance

Asymmetric porous cordierite ceramic membranes were fabricated by phase inversion tape casting method. It is shown that the membranes consist of a relatively dense skin layer on the top, a sponge layer at the bottom and a finger-like layer in the middle. The membranes have a hierarchical pore structure, where macrovoids (denoted as dozens-micron-sized (DMS) pores) are present in the finger-like layer and micron-sized (MS) pores are located in the skin layer, sponge layer and the wall of macrovoids. After surface silylation by post-grafting with 1H,1H,2H,2H-perfluorodecyltriethoxysilane (FAS), the sample with a starting powder/polyethersulfone (PESf) weight ratio of 9 (M − 4) becomes hydrophobic, with a water contact angle of 150°. At a NaCl concentration of 3.5 wt%, a feed rate of 18L/h and a feed temperature of 80 °C, the hydrophobic M − 4 membrane exhibits a water permeate flux of 22.33 kg/m²h, which is considerably larger than that of the membranes prepared by dry pressing method previously, and a salt rejection of 99.9%. The higher water permeate flux is attributed to the much lower transport resistance of water vapor in the membranes of the present work.     

Fabrication of low cost,green silica based ceramic hollow fibre membrane prepared from waste rice husk for water filtration application

In order to develop low cost ceramic membranes and effectively utilize abundantly and dumped waste agriculture, fabrication of green silica based ceramic hollow fibre membranes from waste rice husk was evaluated. Rice husk was converted into amorphous and crystalline silica based rice husk ash (ARHA and CRHA) by burning process at 600?°C and 1000?°C, respectively. The properties of silica based rice husk ashes were studied by transmission electron microscopy (TEM), x-ray powder diffraction (XRD), Fourier-transform infrared spectroscopy (FTIR), BET analysis, thermogravimetry and differential thermal analysis (TG/DTA) and x-ray fluorescence (XRF). Effect of silica content and sintering temperature towards membrane fabrication were investigated and characterized in term of morphological properties, mechanical strength, surface roughness, pore size distribution, porosity and pure water flux (PWF). The ceramic hollow fibre membrane (CHFM) prepared at 37.5?wt% CRHA content and sintered at 1200?°C achieved a good mechanical strength (71.2?MPa) and excellent porosity (50.2%). As a result, high PWF with value ~ 300?L/m² h and stable at 20?min was obtained. Due to the excellent pure water flux, the prepared ceramic membrane from waste rice husk hold promise for water treatment application.     

Preparation and corrosion resistance of cordierite–spodumene composite ceramics using zircon as a modifying agent

To prolong the service life of cordierite–spodumene composite ceramics applied to the solar heat transmission pipeline, the zircon modifier was introduced to improve the corrosion resistance of the ceramics. The effects of zircon on the density, bending strength, crystalline phase, microstructure and chemical stability were studied. The results showed that the sintering temperature range of the composite ceramics was broadened to 40–60?°C with the introduction of 5–15?wt% zircon. Moreover, the mechanical strength and corrosion resistance of the ceramic materials were improved with the zircon introduction. In particular, sample C3 containing 15?wt% of zircon and sintered at 1360?°C exhibited the best performance, which had the 0.03% Wa, 0.07% Pa, 2.34?g?cm^?3 Db and 100.17?MPa bending strength. After acid and alkali corrosion, the water absorption was still less than 0.5% and the strength loss rate decreased to less than 5.3%. The XRD and SEM analyses demonstrated that the ZrSiO₄ grains dispersed at the grain boundaries could enhance the mechanical properties. Furthermore, the existence of the Zr⁴⁺ ions not only reduced the cationic solubility of the glassy phases but also led to a reaction with OH^? to form Zr(OH)₄ on the surfaces. This improved the corrosion resistance of the composite ceramics and endowed it with a high residual strength after the acid and alkali corrosion.     

Reuse of mineral wool waste and recycled glass in ceramic foams

Novel ceramic foams have been prepared by high temperature sintering of waste mineral wool and waste glass using SiC as a foaming agent. The aim of the research was to understand the effects of composition and sintering conditions on the properties and microstructure and produce commercially exploitable ceramic foams. Optimum ceramic foams were formed from 40 wt% mineral wool waste and 2 wt% SiC, sintered at 1170 °C using a heating rate of 20 °C/min with a 20 min hold at peak temperature. The ceramic foams produced had a bulk density of 0.71 g/cm³ and a uniform pore size distribution. The research shows that ceramic foams can be formed from waste mineral wool and these can be used for thermal insulation with associated economic and environmental benefits.     

Tuning microstructures and separation behaviors of pure silicon carbide membranes

This study reports the preparation of silicon carbide ceramic membranes with pure silicon carbide particles without sintering aids. The effects of sintering temperature on the microstructure, mechanical and filtration properties were investigated. The porosity of the substrate layer increased from 37% to 41% when the sintering temperature ranged from 2150 to 2300 °C, whereas the flexural strength increased from 14.5 to 18.2 MPa. The separation layer was coated on the substrate layer using a spray process. When sintered at 1850 °C, a smooth and defect-free layer was formed with an average pore size and layer thickness of 1.2 and 60 μm, respectively. With the increase of average pore size, the filtration flux increased from 2650 to 2800 L/(m² h bar). Such ceramic membranes can be used to separate corrosive wastewater and high-temperature wastewaters owing to the exclusion of sintering aids, unlike the conventional ceramic membranes.     

Influence of solid loading on the rheological,porosity distribution,optical and the microstructural properties of YAG transparent ceramic

Stable aqueous dispersed mixture of commercial Al₂O₃ and Y₂O₃ nano powders was prepared by ball mill. Ammonium poly meta acrylate (Dolapix CE64) and tetraethyl orthosilicate (TEOS) were added as dispersant and sintering aid, respectively. The effects of slurry solid loading on the fabrication of transparent polycrystalline YAG ceramics by slip casting method were investigated. The rheological properties of slurries with different solid loading (64, 70 and 76?wt%) were studied by measuring the viscosity and shear stress as a function of shear rate. The effect of solid loadings on the porosity distribution was examined. The specimens were vacuum-sintered at 1715?°C for 10?h. Slips with 64 and 70?wt% solid loading behaved as near-Newtonian and as non-Newtonian with thixotropic behavior at 76?wt% solid loading. The relative densities of the green bodies increased from 58.0?±?0.6% (SD?=?0.424) to 64.0?±?0.3% (SD?=?0.228) by increasing the solid loading from 64?wt% to 70?wt% and then decreased to 63.0?±?0.2% (SD?=?0.141) at 76?wt% solid loading. The results showed that the suitable solid loading for fabricating transparent YAG ceramics is 70?wt%. This sample had the narrowest pore size distribution (4–100?nm), homogenized surface fracture of green body, dense microstructure (99.990?±?0.005% final relative density, SD?=?0.003) and the average grain size of 6?µm. It had the highest in-line transmittance, which was approximately 77% at 1064?nm.     

Preparation of porous cordierite ceramic by gel-casting method

Porous cordierite ceramics were synthesised by gel-casting method, using talcum powder, kaolin and alumina as raw materials. Organic monomers and cross-linker were used as additives. The phase composition and microstructure were investigated by X-ray diffraction and scanning electron microscope. The open porosity, compressive strength and thermal expansion coefficient were tested by the Archimedes method, universal testing machine and thermal expansion instrument, respectively. The results indicate that sintering temperature and holding time have a great influence on the cordierite properties. We obtain the good performance of porous cordierite ceramic sintering at 1350°C for 3?h. The cordierite phase content in the sample is higher and the crystallinity is better. At this point, the porosity is 58.53%, the compressive strength is 22.44?MPa and thermal expansion coefficient reaches 1.69?×?10^?6?°C^?1.     

Investigation on low-temperature sinterable behavior and tunable dielectric properties of BLMT glass-Li2ZnTi3O8 composite ceramics

The novel low-temperature sinterable ceramic composites were fabricated by mixing B₂O₃-La₂O₃-MgO-TiO₂ (BLMT) glass with Li₂ZnTi₃O₈ ceramic. All composites could be well sintered at 900?°C for 2?h through liquid-phase sintering and viscous sintering process. With BLMT glass increasing, the main phase of composites changed from Li₂ZnTi₃O₈ to LaBO₃ phase crystallized from glass. Nevertheless, the rutile phase was observed in composites with ≥10?wt% glass, which could adjust the temperature coefficient of resonant frequency (τ_f) to near-zero owing to the opposite τ_f value to other phases. Simultaneously relative permittivity (ε_r) and quality factor (Q$\times$f) could be controlled by varying the content of Li₂ZnTi₃O₈ ceramic and BLMT glass. The composite with 20?wt% glass exhibited excellent dielectric properties: ε_r?=?22.7, Q?×?f?=?19,900?GHz, and τ_f ?=?0.28?ppm/°C. In addition, the good chemical compatibility between the composite with 5?wt% glass and Ag electrode made it as a potential candidate for LTCC technology.     

Air-sintered silicon (Si)-bonded silicon carbide (SiC) hollow fiber membranes for oil/water separation

In this work we evaluated the effect of adding Si as sintering additive into SiC for producing air-sintered hollow fiber membranes. According to crystallographic analyses, SiC and Si were converted to SiO₂ after sintering at 1350 °C. The addition of 30 wt% of Si into SiC ceramic material promoted the binding of SiC particles and improved the membrane mechanical resistance to 42.25 ± 3.39 MPa after air sintering at 1350 °C. The produced asymmetric ceramic membrane presented a packed pore-network and micro-voids with pore sizes of 1.73 and 5.29 μm, respectively. The filtration of an oil/water emulsion enabled oil retention 98.75 ± 0.95 %. Cake formation was the main fouling occurrence and membrane regeneration with equivalent oil retention and similar steady sate flux was achieved after water cleaning under ultrasound irradiation. Thus, the use of Si as air-sintering aid was favorable for producing Si-bonded SiC hollow fiber membranes with suitable application for oil/water separation.     

Ceramic membrane synthesis based on alkali activated blast furnace slag for separation of water from ethanol

The main purpose of this research is synthesis of zeolite ceramic membranes based on alkali activated blast furnace slag for pervaporation separation of ethanol/water mixture (90 wt%). A new and simple method was applied to fabricate these ceramic membranes. In addition, gross waste of steel industry (blast furnace slag) was firstly used as the main starting material for making the membranes. In this study, for making the zeolite ceramic membranes, some experiments were conducted with water levels of 38, 40, 42 and 44 wt% of the blast furnace slag and NaOH levels of 4, 4.2, 4.4 and 4.6 wt% of the blast furnace slag. At first, for making the membranes, a primary geopolymer gel was prepared. Afterward the membranes were cast at 25 °C for 24 h. In order to form the zeolite layer, the membranes after geopolymerization process were kept at 90 °C for 24 h. The maximum value of selectivity (2579.48) was obtained for separation of water from ethanol using the synthesized membrane with 42 wt% water and 4 wt% NaOH.     

Synthesis and characterization of low CTE value La2O3-B2O3-CaO-P2O5 glass/cordierite composites for LTCC application

Low-softening-point La₂O₃-B₂O₃-CaO-P₂O₅ (LBCP) glass-ceramic/cordierite composite systems have been prepared in this work. Influence of the ratio of La₂O₃ to B₂O₃ and the content of cordierite on the sintering behavior, microstructure, sintering quality, thermal properties and dielectric properties of composites are studied. The results show that high La₂O₃/B₂O₃ ratio improves the crystalline quality of LBCP glass-ceramic, but also narrows its process window. The increase of cordierite content reduces the coefficient of thermal expansion (CTE) value of composites obviously. However, excess cordierite is detrimental to the densification of the composite microstructure, and too low cordierite content causes serious foaming. Sample containing 30?wt% LBCP1 glass-ceramic and 70?wt% cordierite sintered at 850?°C shows excellent properties: relative density of 95.26%, CTE value of 4.12?ppm/°C, dielectric constant of 4.78 (1?MHz)/4.52 (12.8?GHz), dielectric loss of 2.3?×?10^?3 (1?MHz)/2.5?×?10^?3 (12.8?GHz) and the ability to co-fire with silver, which suggests that LBCP glass/cordierite composite system has potential to meet the requirements of LTCC substrate material.     

Spark plasma sintering of TiN ceramics codoped with SiC and CNT

In this research, we investigated the effects of SiC and multi-walled carbon nanotube (MWCNTs) addition on the densification and microstructure of titanium nitride (TiN) ceramics. Four samples including monolithic TiN, TiN-5?wt% MWCNTs, TiN-20?vol% SiC and TiN-20?vol% SiC-5?wt% MWCNTs were prepared by spark plasma sintering at 1900?°C for 7?min under 40?MPa pressure. X-ray powder diffraction patterns and scanning electron microscope (SEM) micrographs of the prepared ceramics showed that no new phase was formed during the sintering process. The highest calculated relative density was related to the TiN ceramic doped with 20?vol% SiC, while the sample doped with 5?wt% MWCNTs presented the lowest density. In addition, the SEM investigations revealed that the addition of sintering aids e.g. SiC and MWCNTs leads to a finer microstructure ceramic. These additives generally remain within the spaces among the TiN particles and prohibit extensive grain growth in the fabricated ceramics.     

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.     

Fabrication and properties of Si3N4 bioscaffolds with orderly–interconnected big pore channels and well–distributed small pores

This paper focuses on investigating the technical potential for fabricating porous ceramic bioscaffolds for the repair of osseous defects from trauma or disease by inverse replication of three–dimensional (3–D) printed polymer template. Si₃N₄ ceramics with pore structure comprising orderly–interconnected big pore channels and well–distributed small pores are successfully fabricated by a technique combining 3–D printing, vacuum suction filtration and oxidation sintering. The Si₃N₄ ceramics fabricated from the Si₃N₄ powder with addition of 10?wt% talcum by sintering at 1250?°C for 2?h have little deformation, uniform microstructure, low linear shrinkage of 4.1%, high open porosity of 58.2%, relatively high compression strength of 6.4?MPa, orderly–interconnected big pore channels and well–distributed small pores, which are promising bioscaffold in the field of bone tissue engineering.     

Porous alumina ceramics with enhanced mechanical and thermal insulation properties based on sol-treated rice husk

To improve the properties of porous alumina ceramics, which were typically prepared by adding pore-forming agents, rice husk (RH) as pore-forming agent was pretreated with zirconia sol. The effects of sol-treatment on the thermal conductivity and compressive strength of the resultant ceramics were characterized. Furthermore, the pore size distribution, pore shape, microstructure, and phase evolution also were studied. The results showed that the RH pretreatment optimizes the microstructure of the ceramic pores. Moreover, complete morph-genetic RH is clearly observed in the pores, which is established as a key factor in improving the properties of the resultant ceramic. The thermal insulation properties are determined to significantly improve, although the thermal conductivity increases slightly with the increment of zirconia sol concentration from 5 to 10?wt%. Meanwhile, after sintering at 1550?°C, the compressive strength is significantly greater for the specimen prepared with 10?wt% zirconia sol-treated RH (65.56?MPa) than that with untreated RH (43.37?MPa). Hence, it was demonstrated that the use of zirconia sol-pretreated RH as a pore-forming agent could enhance the mechanical and thermal insulation properties of porous alumina ceramics.     

Recycling of lime mud and fly ash for fabrication of anorthite ceramic at low sintering temperature

Lime mud is a kind of waste generated during causticization reaction of an alkali recycling process in paper industry. Lime mud and fly ash were reused as raw materials to fabricate anorthite ceramics through solid state reactions. Both sintering temperature and lime mud content influenced the crystalline phases in the prepared ceramics. Anorthite was the major phase in all samples (samples L36, L40, L50 and L60) and it was prominent in sample L36 (containing 36 wt% lime mud). The results also showed that anorthite ceramic can be synthesized at low sintering temperature (1100 °C). Gehlenite and wollastonite were formed in the samples possessing higher calcium (above 40 wt% lime mud) or at lower sintering temperatures. Bulk density, water absorption and compressive strength were measured. These ceramics were of light weight and had high water absorption. Recycling of lime mud and fly ash as raw materials of anorthite ceramic is a feasible approach to solve the solid wastes.     

A new Li-based ceramic of Li4MgSn2O7: Synthesis,phase evolution and microwave dielectric properties

A pure-phase Li₄MgSn₂O₇ (L₄MS) was successfully synthesized through optimizing the calcination condition. Microwave dielectric properties of the L₄MS ceramic with the phase evolution were investigated together with its low-temperature sintering. The sample maintains a single L₄MS phase as sintered below 1200?°C, such that τ_f remains a constant value of ～12.4?ppm/°C. Accompanied by the appearance of impurity phases (Li₂SnO₃)_ss and especially (MgO)_ss at higher sintering temperatures, excellent microwave dielectric properties of ε_r?=?13.1–13.5, Q?×?f?=?106,800–126,810?GHz and τ_f ?=?0–?4.2?ppm/°C are obtained in samples sintered at 1215–1260?°C for 4?h. Reduction of sintering temperature using LiF sintering aid also helps achieve pure-phase dense L₄MS ceramic. The L₄MS?+?x wt.% LiF ceramic exhibits ε_r～13.7, Qxf～97,000?GHz (x?≤?3) and τ_f ～8–13?ppm/°C sintered at 850?°C for potential LTCC applications, and ε_r ～13.9, Qxf～146,000?GHz and τ_f ～1.5–6?ppm/°C (x?≥?4) as sintered 1000?°C, exhibiting large potentials for microwave dielectric candidates.     

Preparation of high–strength closed–pore foamed ceramics from desalted sea sand at temperatures below 1000 °C

Based on high–temperature sintering with SiC as the foaming agent, the technical potential of preparing foamed ceramics (FCs) from desalted sea sand at temperatures below 1000 °C was studied. Rapid melting of the ceramic bodies at elevated temperatures helped to seal more foaming gas, resulting in a large foaming volume for the FCs. If the interior of the ceramic bodies melted quickly during sintering, the foaming gas was trapped in situ, resulting in a homogenous FC pore structure. By coordinating the borax content and sintering temperature of the green bodies, the melting characteristics of the ceramic bodies could be optimised during sintering, usually producing a large foaming volume and a homogeneous FC pore structure. The FCs sintered from the green bodies with 25–35 wt% of borax at 900–1000 °C obtained high total/closed porosities of (68–75)%/(65–72)%, a relatively dense surface, a homogenous pore structure, and a relatively high compressive strength of 8.1–11.2 MPa.