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.     

Preparation of mullite ceramic microfilter membranes using Response surface methodology based on central composite design

In this paper effect of free silica removal from mullite microfilter membranes using different sodium hydroxide (NaOH) concentrations at different temperatures and for different removal times was studied. The prepared membranes were subjected to XRD, SEM, porosity analysis, and mechanical strength measurement. Response surface methodology (RSM) based on central composite design (CCD) was used to design the experiments and analyze three operating parameters including; NaOH solution concentration, NaOH solution temperature and removal time. The optimum porosity of 49.4 was obtained with NaOH solution concentration of 35 wt% at temperature 75 °C and removal time equal to 8 h.Water flux and mechanical strength as important characteristics were measured for all the membranes. For the membrane with the optimum porosity, water flux, mechanical strength, and free silica removal percentage were 61.7 kg/m² h, 21.6 MPa, and 28.2%, respectively. The maximum rejection percentage was 97.2% and emulsion flux for this state was 15.6 kg/m² h at temperature 25 °C and cross flow velocity of 1.5 m/s.     

Preparation and characterization of low-cost ceramic microfiltration membranes for the removal of chromate from aqueous solutions

Low-cost ceramic microfiltration membranes were prepared using clay of IIT Guwahati. Two membranes were prepared by paste casting followed by sintering at different temperatures, the first one from clay only (membrane A) and the second one from clay with small amounts of sodium carbonate, sodium metasilicate and boric acid (membrane B). Both the membranes were characterized by TGA, SEM, XRD, water permeability test and acid–base treatment. With the increase of sintering temperature, pore size as well as permeability and flexural strength were increasing while porosity and pore density were decreasing. The overall performance of membrane B was better than membrane A. The average pore size, porosity, pore density and flexural strength of membrane B sintered at 1000 °C were 4.58 μm, 0.42, 2.06 × 10¹⁰ m^− 2 and 11.55 MPa respectively. This membrane was used for the removal of chromate from aqueous solutions by micellar enhanced microfiltration (MEMF) using cetylpyridinium chloride (CPC). 100% rejection of chromate ions were obtained at a feed ratio (CPC/chromate) of 10. Based on raw material prices, the membrane cost was estimated to be $19/m². The prepared low-cost membrane showed good promise for the treatment of wastewater containing such heavy metals.     

Composite ceramic membranes from natural aluminosilicates for microfiltration applications

This work concerns to the development and characterisation of support, active layer and tubular composite membranes (CM) from natural aluminosilicates as principal components (clay, bentonite, feldspar, quartz, alumina). The selection of these raw materials was primarily based on their low cost and they are locally produced. In the substrates preparation, the effect of materials compositions, additives, particle sizes, paste rheological properties, and drying-sintering temperatures was investigated. The consolidated ceramic substrates were characterised by SEM, DTA–TG, X-Ray diffraction, Hg intrusion, mechanical resistance, and water flux measurements. Extrusion has been used as the forming process of tubular support. The CM was fabricated depositing a thin active layer by slip-casting method on the support. The CM sintered at 1200 °C showed the best structural characteristics, porosities of 50%, active layer pore size between 0.08 and 0.55 μm. The CM hydraulic permeabilities (10–274 L/h m² kPa) were comparable and greater than several inorganic commercial membranes and CM obtained from other researches. The CM microfiltration effectiveness was tested with different substances from food industry, i.e. slaughterhouse wastewater treatment and goat milk pasteurisation. The obtained results, insoluble residue rejections (100%) and high bacterial removal (87–99%), make the ceramic CM suitable for microfiltration processes.     

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.     

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.     

Thermal,mechanical and electrical properties of hard B4C,BCN, ZrBC and ZrBCN ceramics

We study the thermal, mechanical and electrical properties of B₄C, BCN, ZrBC and ZrBCN ceramics prepared in the form of thin films by magnetron sputtering. We focus on the effect of Zr_x(B₄C)_1−x sputter target composition, the N₂+Ar discharge gas mixture composition, the deposition temperature and the annealing temperature after the deposition. The thermal properties of interest include thermal conductivity (observed in the range 1.3–7.3 W m⁻¹ K⁻¹), heat capacity (0.37–1.6×10³ J kg⁻¹ K⁻¹ or 1.9–4.1×10⁶ Jm⁻³ K⁻¹), thermal effusivity (1.6–4.5×10³ J m⁻² s^−1/2 K⁻¹) and thermal diffusivity (0.38–2.6×10⁻⁶ m² s⁻¹). We discuss the relationships between materials composition, preparation conditions, structure, thermal properties, temperature dependence of the thermal properties and other (mechanical and electrical) properties. We find that the materials structure (amorphous×crystalline hexagonal ZrB₂-like×nanocrystalline cubic ZrN-like), more than the composition, is the crucial factor determining the thermal conductivity and other properties. The results are particularly important for the design of future ceramic materials combining tailored thermal properties, mechanical properties, electrical conductivity and oxidation resistance.     

Crystalline phases and physical properties of modified stoneware body with glaze sludge

Ceramic stoneware body has been modified with ceramic and glass industrial wastes by replacing 25–100% as flux in the formula. The effects of solid wastes added to the bodies were studied after firing in the temperature range 950–1280 °C. The physical properties of linear shrinkage, bulk density, apparent porosity, water absorption and 3-point bending strength were determined. A composition which related to the general stoneware properties was found when using soda-lime cullet and glaze sludge. It had a firing range lowered to 1050–1100 °C. SEM results demonstrated the sintered microstructure increased in density with increase in solid waste in the modified body. XRD results after firing showed the crystalline phases comprised of mullite, albite calcian and quartz. Thermal expansion was measured in the range 6.53–6.67 × 10^?6 K^?1 at 30–500 °C. The modified bodies were capable of forming prototype products by slip casting and jiggering.     

Preparation and characterization of a nigerian mesoporous clay-based membrane for uranium removal from underground water

This study reports the removal of uranium in underground wastewater using a Nigerian clay-based membrane. The clay and sintered clay were characterized using XRD, XRF, TGA/DTA, FESEM and PSD. The raw clay was mixed with cassava starch (10, 15, 20 and 25 wt%) and sintered at a temperature of 1300 °C. A multi-point BET analysis of the produced clay-based membranes was conducted to determine the surface area, pore volume and average pore size. Sintering characteristics were determined by apparent porosity, bulk density and flexural strength. The radioactivity of the feed and the permeated water was counted using a gamma spectrometer with an HPGe detector. From the XRD, TGA and FESEM, 1300 °C was found to be optimum for the mullite formation from the clay. The average pore sizes of the produced membranes from the BET results were observed to be in the range from 51 to 70 Å and with a steady state flux range of the tested membranes in the range 1.92×10⁻⁵–2.09×10⁻⁴ m³ m⁻² s⁻¹. The permeation flux produced is of high quality with a rejection in the range of 1.78–2.56 Bq/l of the uranium activity by the tested membranes. This low-cost membrane will have an application for the treatment of uranium-containing wastewater from fracking, oil exploration and phosphate mining industries.     

Processing of alumina-coated clay–diatomite composite membranes for oily wastewater treatment

Crack-free alumina-coated clay–diatomite composite membranes were successfully prepared by a simple pressing and dip-coating route using inexpensive raw materials at a temperature as low as 1000 °C in air. The changes of porosity, flexural strength, pore size, flux, and oil rejection rate of the membranes were investigated while changing the diatomite content. A simple burn-out process subjected to the used membranes in air completely recovered the specific surface area, steady state flux, and oil rejection rate of the virgin membranes. The recycled membranes showed an exceptionally high oil rejection rate (99.9%) with a feed oil concentration of 600 mg/L at an applied pressure of 101 kPa. The typical porosity, pore size, flexural strength, oil rejection rate, and steady state flux of the recycled alumina-coated clay–diatomite composite membrane were 36.5%, 0.12 μm, 32 MPa, 99.9%, and 6.91×10⁻⁶ m³ m⁻² s⁻¹, respectively, at an applied pressure of 101 kPa.     

Fabrication and characterization of anorthite-based ceramic using mineral raw materials

The purpose of this study is to design a novel single crystalline phase ceramic based on anorthite whose properties fulfill the tableware market requirements such as high appearance quality, strength and thermal shock resistance. To obtain the single phase anorthite ceramic, ball clay, quartz, calcite, feldspar and alumina were used as raw materials. The single phase anorthite ceramic was fabricated by slip casting and sintering at 1230 °C for 1 h. It has a high flexural strength of 103 MPa, which is higher than that of the conventional porcelain. The single phase anorthite ceramic had relatively low (4.9 × 10^?6 K^?1) thermal expansion coefficient which can be matched with applicable glaze easily. Furthermore, the single phase anorthite ceramic had high degree of whiteness (L* = 94) and excellent translucency behavior which could achieve a high-quality decorative effect.     

Dynamic removal of n-hexane from water using nanocomposite membranes: Serial coating of para-aminobenzoate alumoxane,boehmite-epoxide and chitosan on Kevlar fabrics

Nanocomposite membranes were fabricated by dip-coating technique. Para-aminobenzoate alumoxane, boehmite–epoxide and chitosan were consecutively coated on the Kevlar fabric surface. The membranes were utilized for removing n-hexane from water using a gravity-driven dead-end filtration setup. UV–vis, FTIR and SEM analyses were performed for characterization. Water affinity analyses revealed highly hydrophilic nature of the modified membranes. Effect of pH was examined with the pH 2 providing the best condition for oil–water separation. Maximum flux and rejection were obtained as 1128 L m⁻² h⁻¹) and 94%, respectively. Deposited oil layer was effectively removed from the membrane surface using hot citric acid solution.     

Effect of sintering temperature on microstructure and mechanical properties of zirconia-toughened alumina machinable dental ceramics

This study investigated the effect of sintering temperature on the microstructure and mechanical properties of dental zirconia-toughened alumina (ZTA) machinable ceramics. Six groups of gelcast ZTA ceramic samples sintered at temperatures between 1100 °C and 1450 °C were prepared. The microstructure was investigated by mercury intrusion porosimetry (MIP), X-ray diffraction (XRD), and scanning electron microscopy (SEM) techniques. The mechanical properties were characterized by flexural strength, fracture toughness, Vickers hardness, and machinability. Overall, with increasing temperature, the relative density, flexural strength, fracture toughness, and Vickers hardness values increased and more tetragonal ZrO₂ transformed into monoclinic ZrO₂; on the other hand, the porosity and pore size decreased. Significantly lower brittleness indexes were observed in groups sintered below 1300 °C, and the lowest values were observed at 1200 °C. The highest flexural strength and fracture toughness of ceramics reached 348.27 MPa and 5.23 MPa m^1/2 when sintered at 1450 °C, respectively. By considering the various properties of gelcast ZTA that varied with the sintering temperature, the optimal temperature for excellent machinability was determined to be approximately 1200–1250 °C, and in this range, a low brittleness index and moderate strength of 0.74–1.19 µm^−1/2 and 46.89–120.15 MPa, respectively, were realized.     

Advanced multifunctional graphene aerogel – Poly (methyl methacrylate) composites: Experiments and modeling

In this work, graphene aerogel (GA)–poly (methyl methacrylate) (PMMA) composites are first developed by backfilling PMMA into the pores of the GAs, providing uniform distribution of multi-layer reduced graphene oxide (m-rGO) sheets in the PMMA matrix. Electrical, mechanical and thermal properties of the as-prepared GA–PMMA composites are investigated by two-probe, microindentation and comparative infrared techniques respectively. As graphene loadings increase from 0.67 to 2.50 vol.%, the composites exhibit significant increases in electrical conductivity (0.160–0.859 S/m), microhardness (303.6–462.5 MPa) and thermal conductivity (0.35–0.70 W/m K) from that of pure PMMA as well as graphene–PMMA composites prepared by traditional dispersion methods. Thermal boundary resistance between graphene and PMMA is estimated to be 1.906 × 10⁻⁸ m² K/W by an off-lattice Monte Carlo algorithm that takes into account the complex morphology, size distribution and dispersion of m-rGO sheets.     

Fabrication and properties of borazine derived boron nitride bonded porous silicon aluminum oxynitride wave-transparent composite

Boron nitride bonded porous silicon aluminum oxynitride composite was fabricated by gel-casting, precursor infiltration and pyrolysis process, and the composition, microstructure, mechanical and dialectical properties of the composite were characterized. The results show that the composite is comprised of β-SiAlON (z = 3) synthesized from mixed ceramic powders, and continuous h-BN pyrolyzed from borazine, with a relatively high porosity of 24.21%. The flexural strength, elastic modulus and fracture toughness of the composite are 178.58 MPa, 75.51 GPa and 4.54 MPa m^1/2, respectively. The sintering shrinkage of SiAlON ceramics can be greatly decreased by the borazine infiltration and pyrolysis process. The existence of h-BN phase and the high porosity reduce the values of dielectric constant and loss tangent of the composite, which are 3.51–3.69 and 0.9–3.1 × 10⁻³ at the frequency from 7 to 18 GHz with the elevating temperature from 25 to 1200 °C.     

Correction of moisture and sucrose effective diffusivities for shrinkage during osmotic dehydration of apple in sucrose solution

Shrinkage, moisture and sucrose effective diffusivities were correlated for infinite slab shape samples of apple during osmotic dehydration in sucrose solution. Experiments were carried out in the sucrose solutions of different concentrations (30%, 40% and 50%) and temperatures (30 °C, 40 °C and 50 °C). The two parameter model, developed by Azuara et al. (1992), was used to predict water loss and solid gain at equilibrium condition. Moisture and sucrose diffusivities were estimated by fitting the experimental moisture loss and solid gain data to the modified form of Fick's second law of diffusion, considering the shrinkage of the apples during osmotic dehydration. Results showed that the volume of the samples decreased linearly with water loss (WL) and weight reduction (WR). For above conditions of osmotic dehydration, effective diffusivities without considering the shrinkage were found to be in the range of 1.36 × 10⁻¹⁰ m²/s–2.00 × 10⁻¹⁰ m²/s, and those with considering the shrinkage were in the range of 0.87 × 10⁻¹⁰ m²/s–1.27 × 10⁻¹⁰ m²/s. The values of the effective diffusivities estimated by considering the shrinkage were smaller than those without considering this phenomenon.     

The ablation behavior and mechanical property of C/C-SiC-ZrB2 composites fabricated by reactive melt infiltration

In order to improve the ablation resistance of carbon/carbon (C/C) composites, SiC-ZrB₂ di-phase ceramic were introduced by reactive melt infiltration. The ablation properties of these composites were evaluated by oxyacetylene torch with a heat flux of 2.38 MW/m² for 60 s. Compared with the pure C/C composites, the C/C-SiC-ZrB₂ composites show a significant improvement in the ablation resistance, and the linear and mass ablation rates decreased from 10.28×10⁻³ mm/s to 6.72×10⁻³ mm/s and from 3.08×10⁻³ g/s to 0.61×10⁻³ g/s, respectively. After ablation test, the flexural strength retentions of the C/C and C/C-SiC-ZrB₂ composites near the ablated center region are 39.7% and 81.6%, respectively. The higher strength retention rate of C/C-SiC-ZrB₂ composites was attributed to the introduction of SiC-ZrB₂ ceramic phases, which have excellent ablation resistant property. During ablation test, an ‘embedding structure’ of Zr-O-Si glass layer was formed, which could act as an effective barrier for oxygen and heat. The oxide ceramic coating could protect the C/C-SiC-ZrB₂ composites from further ablation, and thus contribute to retaining the mechanical property of C/C-SiC-ZrB₂ composites after ablation.     

Application of response surface methodology for modeling and optimization of membrane distillation desalination process

In this work, response surface methodology (RSM) was applied for modeling and optimization of operating parameters for water desalination by direct contact membrane distillation (DCMD) process using polypropylene membrane (PP) with low pore size. Operating parameters including vapor pressure difference, feed flow rate, permeate flow rate and feed ionic strength were selected and the optimum parameters were determined for DCMD permeate flux. The developed model for permeate flux response was statistically validated by analysis of variance (ANOVA) which showed a high value coefficient of determination value (R² = 0.989). The obtained optimum operating parameters were found to be 0.355 × 10⁵ Pa of vapor pressure difference, feed flow rate of 73.6 L/h, and permeate flow rate of 17.1 L/h and feed ionic strength of 309 mM. Under these conditions, the permeate flux was 4.191 L/(m² h). Compared to a predicted value, the deviation was 3.9%, which confirms the validity of the model for the DCMD process desalination optimization. In terms of product water quality, the DCMD process using hydrophobic PP membrane can produce high quality of water with low electrical conductivity for all experimental runs.     

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.     

Enhanced performance of Fe2O3 doped yttria stabilized zirconia hollow fiber membranes for water treatment

Fe₂O₃ powders were introduced as sintering aid to fabricate yttria-stabilized zirconia (YSZ) hollow fiber membranes using a combined wet-spinning and post-sintering method. The obtained Fe₂O₃-YSZ hollow fiber membranes show enhanced performance for water treatment with fine crystal structure in terms of bending strength and pure water permeability. Scanning electron microscopy (SEM), X-ray powder diffraction (XRD), and thermogravimetric analysis (TGA) along with mechanical tests were employed to investigate the structural evolution in the sintering process and the effect of Fe₂O₃. It is suggested that the Fe₂O₃ dopants dissolve into YSZ at elevated temperatures, providing defect sites and vacancies for fast ion migration, favoring for densification and grain growth of the YSZ, which yields dense microstructures of fine crystallites at relatively low sintering temperature. The Fe₂O₃-YSZ hollow fiber membranes sintered at 1150 °C show a 3-fold increase of the permeate flux of pure water (F) (743 L m⁻² h⁻¹) along with comparable bending strength (152 MPa) compared to pure YSZ membranes. This modified method can reduce sintering costs and therefore fabrication costs which should pave the way for scale-up production for ceramic hollow fiber membranes.