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Yttrium oxide is an ideal choice for titanium aluminum alloy melting and casting, its wider use is hindered by sintering challenges and low thermal shock resistance. To address this, we propose a gel casting method for calcium oxide-doped yttrium oxide production. We pretreated yttrium oxide with phosphoric acid to prevented hydrolysis and adjusted the isoelectric point of yttrium oxide to match calcium carbonate's. Anions from calcium carbonate increased slurry solid content (up to 58 vol%) while maintaining low viscosity (57.78 mPa·s at 40 s−1 shear rate). After sintering at 1650 °C for 2 h, the material showed a flexural strength of 78 MPa, with a 90% retention rate after thermal shock test. The introduction of calcium oxide induced lattice distortion, improving mechanical properties by aiding sintering and grain boundary diffusion. XPS and STEM analysis confirmed random replacement of Y3+ by Ca2+ at the C 2 position with 1 wt% doping. [ABSTRACT FROM AUTHOR]

Low-yttria doped zirconia polycrystals (Y-TZP) have recently emerged as new fine-grained zirconia ceramics exhibiting a promising combination of high fracture toughness and strength. In this investigation, we optimized the strength and fracture toughness of 2Y-TZP ceramics prepared by gelcasting and pressureless sintering. The 2Y-TZP ceramics with optimized processing reached a mean biaxial strength of 1070 MPa, similar to the strength obtained for the standard 3Y-TZP ceramics. However, a higher transformability of tetragonal grains in 2Y-TZP ceramics resulted in a stronger transformation toughening effect compared with 3Y-TZP ceramics. The fracture toughness obtained for 2Y-TZP exceeded that of 3Y-TZP (7.7 vs. 5.2 MPa m0.5). The differences in the microstructure and toughening mechanism between 2Y-TZP and 3Y-TZP were described, and the potential benefits of the 2Y-TZP were discussed. [ABSTRACT FROM AUTHOR]

In this study, Si powder was used as raw material, Si 3 N 4 powder as a diluent, Al 2 O 3 , MgO, Y 2 O 3, and La 2 O 3 as sintering additives to prepare Si 3 N 4 ceramic with excellent properties using gelcasting and reaction re-sintering method. When the solid content of the slurry is 57.3 %, the viscosity is less than 1 Pa · s during the gelcasting process. After the reaction re-sintering, the sintered body of Si 3 N 4 exhibited a bulk density of 3.15 ± 0.05 g/cm3, a relative density of 96 ± 1 %, open porosity of 5.7 %, bending strength of 610 ± 20 MPa, elastic modulus of 235 ± 10 GPa, thermal conductivity of 48 ± 5 W/(m·K), and a linear shrinkage rate of 12–13 %. These parameters indicate that Si 3 N 4 ceramic possesses outstanding mechanical properties and thermal conductivity. [ABSTRACT FROM AUTHOR]

Porous mullite ceramics exhibit exceptional mechanical and thermal properties in high-temperature environments, making them suitable for applications in thermal insulation. However, a notable challenge associated with high porosity is the tendency for increased sintering shrinkage during the sintering process. The sintering shrinkage can lead to unpredictable cracking and deformation, negatively impacting the final properties of the porous ceramics. In this study, porous mullite ceramics were fabricated using aluminium powder, alumina powder, and silica sol through foam-gelcasting and freeze-drying methods. The oxidative expansion of the aluminium powder was employed to offset the sintering shrinkage. The influence of alumina powder content on the microstructure and properties of porous mullite ceramics was investigated. Particularly, at the alumina content of 50 wt%, the porous mullite ceramics exhibited near-zero sintering shrinkage (0.3%). These ceramics demonstrated high porosity ranging from 78.9% to 83.3%, accompanied with low thermal conductivity (0.24-0.29 W/(m·K)) and great mechanical properties (0.51-1.02 MPa). The temperature difference over 750 °C revealed porous ceramics get excellent thermal stability as ideal lightweight high-temperature thermal insulation materials. This innovative approach presents a novel idea for fabricating complex net-shape porous mullite ceramic components with enhancing yield and low cost. • Near-zero sintering shrinkage porous mullite ceramics were prepared by foam-gelcasting combined with freeze-drying. • The microstructure and properties of porous mullite ceramics was tailored by the ratio of alumina and aluminium. • High porosity, low thermal conductivity and excellent thermal insulation performance were achieved. [ABSTRACT FROM AUTHOR]

This study proposes porous block structures as a viable alternative to conventional pebble bed structures, aiming to overcome the structural drawbacks including low packing fractions, extensive stress concentrations, and low thermal conductivity. To validate the feasibility of the porous block structures, Gyroid Li 2 TiO 3 block breeders were prepared by the hybrid process of stereolithography and gelcasting. The resulting Gyroid Li 2 TiO 3 block breeders, measuring ∼18.8 × 18.8 × 18.8 mm3, achieved a high packing fraction of ∼78.8% through optimized slurry and sintering at 1100 °C for 3 h. These Gyroid Li 2 TiO 3 block breeders exhibited clear contours, integrated channels, a compressive strength of 8.78 MPa, and a low isotropic sintering shrinkage of ∼6%. The hybrid process demonstrated enormous advantages over the reported 3D printing for the preparation of porous block breeders with low shrinkage and large-sized dimensions. This study offers an effective avenue for the manufacture of porous block breeders with tunable tritium-releasing channels and large-sized configurations. [ABSTRACT FROM AUTHOR]

The microstructure and properties of porous ceramics are severely affected by volume shrinkage during the sintering process. Therefore, reducing sintering shrinkage while maintaining the properties of porous ceramics is a serious challenge. Herein, near-net-size porous mullite ceramics with tuneable sintering shrinkage were prepared by the foam-gelcasting method using kyanite as raw material and aluminum fluoride and aluminum powders as additives through the volume expansion generated by the sintering reaction. The effects of Al powder content on the sintering shrinkage, porosity, compressive strength and thermal conductivity of porous mullite ceramics were investigated. The results show that the sintering shrinkage gradually decreases with increasing Al powder content, and expansion is even produced. When the Al powder content was 5 wt%, the sintering shrinkage of porous mullite ceramics was −0.21 %, with porosity of 84.2 %, compressive strength of 2.45 ± 0.15 MPa, and thermal conductivity of 0.19 W/(m·K) at room temperature. The results of the high-temperature fire resistance test showed that the temperature difference between the front and back sides of the sample under the flame gun reached 800 °C, indicating good thermal insulation performance. The near-net-size sintering process of porous ceramics can effectively reduce the subsequent processing cost, open new paths for their production, and broaden the application fields of porous mullite ceramics. [ABSTRACT FROM AUTHOR]

In this study, the fused silica slurries with an ultra-high solid loading of 85 vol%, low viscosity of 0.34 Pa s at 99.4 s−1, and good suspension stability were successfully prepared using two-gradation fused silica raw powders by optimizing the preparation processes. Owing to the inherent characteristics of gelcasting and good dispersion stability of resulting fused silica slurries, all the fused silica ceramics prepared with various solid loadings exhibited a homogeneous bimodal size distribution microstructure after pressureless sintering at 1250 °C for 4 h. Furthermore, a small amount of nanoscale cristobalite was precipitated from fused silica, and solid loading had no significant effect on the crystallization kinetics of cristobalite. A significant increase in solid loading effectively facilitated the densification of fused silica ceramics, enhanced bulk density, decreased sintering shrinkage, and strengthened mechanical properties. However, the increase in solid loading deteriorated dielectric properties within the range of 2–18 GHz. When the solid loading was 85 vol%, the bulk density, linear shrinkage, flexural strength, dielectric constant, and dielectric loss tangent were 2.12 g/cm3, 1.1 %, 72.3 MPa, 3.91–4.36, 0.0081–0.0171, respectively. These properties were favorable making the materials potential applications in the field of microwave transmission. [ABSTRACT FROM AUTHOR]

In fabrication of metal-reinforced ceramics, metallic powders are used as one of the raw materials, however, they hinder obtaining nanometallic particles in the matrix. The use of metallic nanopowders is inefficient, because they are highly flammable and require special storage and handling conditions (cool, dry inert gas, tightly sealed). Replacing metallic powders with coordination complexes allows to obtain nanocomposites in harmless manufacturing processes. The use of coordination complex of molybdenum (molybdenyl acetylacetonate) allowed to fabricate ZrO 2 /Mo composites by slip casting and gelcasting. The increase in fracture toughness (ca. 25%) was observed with the little concentration of the metallic phase (up to 1.5 wt%) in a composite. It results from gaining fine metallic particles (ca. 62 nm) in the ceramic matrix. SEM analysis revealed that crack propagation is inhibited by nano-sized metallic particles according to three mechanisms: crack deflection, crack blocking by plastic deformation and interface debonding. [Display omitted] • Coordination complexes are good substitutes for metal powders in CMCs fabrication. • Molybdenyl acetylacetonate is the beneficial precursor of Mo phase in ZrO 2 matrix. • ZrO 2 -Mo composites showed increased fracture toughness (27%) at low Mo content (1.5%). • Precursors decompose to fine metallic grains (ca. 62 nm) visible in composite microstructure. [ABSTRACT FROM AUTHOR]

In this study, according to the Dinger model, aqueous Si 3 N 4 slurries with a solid loading of 63 vol% and a viscosity lower than 1.0 Pa s were successfully prepared using two-grade Si 3 N 4 powders with D 50 = 7.2 μm and 9.4 μm as starting materials. These resulting slurries exhibited good rheological properties and suspension stability. Notably, the presence of β-Si 3 N 4 seeds existed in the starting materials effectively reduced the nucleation barrier by transforming homogeneous nucleation into heterogeneous nucleation. Consequently, it facilitated the reconstructive phase transformation of α-Si 3 N 4 to β-Si 3 N 4 , promoted the anisotropic growth of β-Si 3 N 4 nucleation, and resulted in the final formation of the bimodal microstructure. This unique microstructure significantly enhanced the mechanical properties of Si 3 N 4 ceramics, resulting in a high flexural strength of 1011.4 MPa and a fracture toughness of 14.8 MPa m1/2. These excellent properties were achieved through the combination of gelcasting and gas pressure sintering. Simultaneously, the Si 3 N 4 ceramics exhibited a low thermal conductivity of 47.7 W m−1 K−1, mainly owing to the low density of 95.3 %, the presence of low-thermal-conductivity silicate-based noncrystalline substances, and the possible existence of lattice oxygen in Si 3 N 4 crystals. [ABSTRACT FROM AUTHOR]

In view of the lack of a conformal, load-bearing, lightweight, and high-temperature resistant integrated microwave-absorbing composites for applications under extremely complex conditions, this study successfully applies gel casting craft to porous Si 3 N 4 microwave-absorbing composites. The high-temperature decomposition reaction of Ti 3 SiC 2 powder was utilized to generate uniform Ti-C x -N 1−x grains in situ and to enhance the mechanical and microwave-absorption properties of porous Ti-C x -N 1−x /Si 3 N 4 composites. The bending strength, fracture toughness, density, maximum reflection loss value, absorption bandwidth and matched thickness in P-band of the composite with 30 wt% Ti 3 SiC 2 addition were 164.87 ± 7.56 MPa, 2.61 ± 0.13 MPa·m1/2, 2.077 g/cm3, 32.42 dB, 1.74 GHz and 4.2 mm, respectively. The fracture toughness and bending strength of the composite were increased by 71.71% and 58.13%, respectively, compared with monolithic porous Si 3 N 4. The electromagnetic wave loss mechanisms of the composites are proposed as a combination of conductivity loss, multiple reflections and scattering, interfacial polarization and defect polarization. [ABSTRACT FROM AUTHOR]

YAG ceramic fiber is the preferred material for the gain medium of the new generation fiber laser. However, the fabrication of hundred-micron and defect-free YAG ceramic fibers is still the primary challenge. In this paper, YAG ceramic fibers with the diameter of 147 µm and length of 113 mm were successfully batch fabricated by the combination of gelcasting and mold design, and the diameter fluctuation rate was only 1.4%. The solid loading of the slurries (46–54 vol%) were systematically investigated to achieve high density and net-shape forming of green fibers. It was found that the YAG ceramic fiber was highly transparent with the optimized solid loading of 52 vol%, and the transmittance of the YAG ceramic (2 mm thick) at 800 nm was 82.6%. Its bending strength was as high as 1124 ± 86 MPa. The ideas and methods of this study will promote the development of gelcasting in the field of hundred-micron ceramic fibers. [ABSTRACT FROM AUTHOR]

Aluminum nitride ceramics were prepared by aqueous gelcasting method and pressureless sintering technique in N 2 atmosphere using Y 2 O 3 as sintering additives with nontoxic curdlan as gel system. The solidification mechanism of curdlan was studied. The effects of curdlan content and solid content on the microstructure, relative density and flexural strength of green bodies were investigated. The influences of Y 2 O 3 content and sintering soaking time on the microstructure and properties of sintered bodies were also studied. The results show that, as the temperature increases to 80 °C, the ceramic powders solidify through three-dimensional gel networks of curdlan during gelling process. The green bodies can be successfully fabricated through aqueous gelcasting method with modified powder as original materials. Suitable curdlan content and solid content contribute to fabricating green body with uniform microstructures and high flexural strength. The relative density and flexural strength of sintered bodies enhance as the Y 2 O 3 content and soaking time increase. The flexural strength and thermal conductivity are about 107.5∼172.3 MPa and 75.2∼112.5 W/(m·K), respectively. The sintered body with 4 wt% Y 2 O 3 soaking for 3 h exhibits the highest thermal conductivity because of appropriate relative density, uniform microstructure and reasonable intergranular phase distribution. The mechanical property and thermal conductivity of sintered bodies can be improved by optimizing the gelcasting process parameter, Y 2 O 3 content, and soaking time. The nontoxic gelling system will have wide application for aqueous gelcasting ceramic with complex shape. Aluminum nitride (AlN) ceramics were prepared by aqueous gelcasting and pressureless sintering technique using Y 2 O 3 as sintering additives with curdlan as gel system. 1.5 wt% curdlan and 50 vol% solid content are conductive to fabricating AlN green body with uniform microstructures. The relative density, grain size and microstructures relate to the properties of AlN ceramics. [Display omitted] • AlN ceramics can be prepared by aqueous gelcasting and pressureless sintering method with curdlan as gel system. • 50 vol% solid content and 1.5 wt% curdlan content are benefit to prepare AlN green body. • Y 2 O 3 sintering additive not only realizes liquid sintering but also effectively promotes properties of AlN ceramic. [ABSTRACT FROM AUTHOR]

There is an increasing interest in understanding the performance and properties of ultra-high temperature ceramics due to their high melting points (<3000 °C) that make them promising for extreme environment applications. In-situ high temperature X-ray diffraction experiments were performed on TiB 2 beads up to ∼3050 °C. For these experiments, TiB 2 powders were fabricated into spherical beads via gel casting methods and densified in a high temperature graphite furnace. These sample beads were then levitated in a conical nozzle levitator with reducing atmosphere (3% H 2 -Ar) while being heated using a 400 W CO 2 laser. During levitation a collimated synchrotron X-ray source was used to perform in-situ, temperature-dependent structural characterizations. The anisotropic coefficients of thermal expansion of TiB 2 were characterized as a function of temperature up to ∼3050 °C. Elucidation of these properties are critical for the advancement of TiB 2 ceramics and other transition metal di-borides for use in high temperature applications such as hypersonic platforms, nuclear reactors, and atmospheric re-entry. [ABSTRACT FROM AUTHOR]

Gelcasting is a kind of colloidal processing with many attractive advantages for fabricating ceramics. In this study, a new and simple gelcasting system with only two additives was investigated using Isobam (a copolymer of isobutylene and maleic anhydride) both as dispersant and monomer, and Tetraethylenepentamine (TEPA) as crosslinker. The gelation studies in solutions showed the reaction between Isobam and TEPA was an acylation reaction which was controlled by temperature and concentration. The rheological behavior and samples' properties of 50 vol% Al 2 O 3 slurries with different Isobam contents were studied. With 8 wt% of Isobam by water, the dried green bodies had relatively density of 56.3% and flexural strength of 25.7 ± 2.2 MPa. After sintering at 1530 °C for 3 h, the relatively density and flexural strength of sintered ceramics were 98.7% and 416 ± 19 MPa respectively. The SEM and macroscopic results showed that dried green bodies and sintered ceramics with homogeneous and defect–free morphology were obtained by using Isobam–TEPA system. [ABSTRACT FROM AUTHOR]

Porous wollastonite ceramic was successfully prepared via a wet milling method using calcium oxide (CaO) and silicon dioxide (SiO 2) as the raw materials, and a gel casting method using potato starch as the pore-forming agent. X-ray diffraction results demonstrated that a single phase of β-wollastonite was obtained at 1050 and 1150 °C. Meanwhile, a single phase of pseudo-wollastonite was obtained at 1250 °C. The increasing sintering temperature has significantly affected the phase, microstructure, linear shrinkage, density, porosity, and compressive strength of the porous wollastonite ceramics. When the sintering temperature was increased, the density and compressive strength of wollastonite ceramics were increased. However, its pore size was decreased with increasing sintering temperature, i.e., the pore size of the sample sintered at 850 °C was 400–500 μm, which was reduced to 300–400 μm after the sample was sintered at 1250 °C. The surface of all porous ceramic samples exhibited apatite formation within a day. Thus, single-phase porous wollastonite ceramics, with good porosity and strength, were successfully fabricated using the gel casting method. [ABSTRACT FROM AUTHOR]

White light diodes (WLEDs) composed of blue chip and phosphor-converter are widely used in liquid crystal display (LCD) projectors as backlights. And it often needs a condenser lens to irradiate white light onto the LCD screen. In this paper, a large size lenticular shaped phosphors-in-glass (PiG) was prepared by Isobam-APS gel casting for the first time. The PiG could act for converting and condensing in LCD projector. Then a rectangular light spot similar to the shape of LCD screen was obtained to reduce the loss of light. The maximum temperatures of the chip and PiG were 62.1 °C and 57.3 °C respectively after working for 600 s and gradually stabilized by simulation. It was proved that simulation result was reliable through comparing with the actual measured value and the lenticular shaped PiG had good heat dissipation capacity for its large area. In conclusion, this is a successful application of PiG in LCD projector, which has guidance and promoting effect. [ABSTRACT FROM AUTHOR]

In this work, drying of bodies prepared by gelcasting fine submicrometre-sized zirconia particles was studied and a drying process for defect-free bodies with large cross-sections was proposed. It was found that the cracking of large bodies could be prevented by reducing the monomer content and using appropriate non-volatile cosolvents. Glycerol and polyethylene glycols with different molecular weights were used as non-volatile cosolvents in aqueous ceramic suspensions. The complex effects of the individual cosolvents on the gelcasting process and, in particular, on the drying step were investigated and explained. The applicability of individual cosolvents for the gelcasting process were discussed and their optimal use was indicated. [ABSTRACT FROM AUTHOR]

In this work, nanosubmicron blue-green pigment powder based on the composition of Mg x Co 1-x Cr 2-y Al y O 4 （0 = x ≤ 1, 0 = y ≤ 2）was prepared by a gel casting method. X-ray diffraction (XRD), scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS), Rietveld refinement with GSAS (General Structure Analysis System), and UV–Vis absorption spectroscopy were used to study the phase composition, grain size, morphology, cation distribution in the crystal structure and spectral absorption of the samples. Colour parameters were also studied by using a colour measurement spectrophotometer. The studies demonstrate that the distribution of cations in the crystal structure is disordered and that divalent and trivalent cations are mixed to occupy tetrahedral and octahedral sites. Furthermore, the substitution of ions at the A/B site leads to a change in the cation distribution ratio at the tetrahedral and octahedral sites. With increasing Mg2+ doping concentration, the inversion parameter of the spinel increases, while with increasing Al3+ doping concentration, the inversion parameter of the spinel decreases. In addition, changes in the calcining atmosphere lead to a change in the oxygen vacancy content in the structure. Under the condition of a reductive atmosphere, the oxygen vacancy content significantly increases, and the inversion parameter also increases. The colour difference for the synthesized Mg x Co 1-x Cr 2-y Al y O 4 spinel powder is related to the proportion of chromophore ions occupying tetrahedral and octahedral sites and the number of oxygen vacancies. [ABSTRACT FROM AUTHOR]

To further resource industrial solid waste, porous ceramics with high porosity were prepared by a gelcasting method using nickel slag and kaolin as raw materials and hydrophilic nontoxic SiO 2 aerogel as a gelling agent. The effects of nickel slag content, dispersant and solid content on the properties and microstructure of porous ceramics were investigated in detail in terms of density, compressive strength, porosity, phase composition and micromorphology. The results confirmed that a certain amount of nickel slag can effectively improve the porosity of porous ceramics, while the addition of dispersant can promote the flow of the slurry, enhanced the denseness of the raw billet and significantly improved the compressive strength. However, its excessive use had a negative effect on the ceramic density and porosity. At the same time, the solid content played a key role in the performance of porous ceramics prepared by gelcasting, and too much solid content was also not conducive to the generation of pores. When the nickel slag content was 55%, the amount of dispersant was 2%, and the solid content was 60 vol%, the porous ceramic had a better overall performance, the density of the porous ceramic was 510 kg/m3, the compressive strength was 1.3 MPa, and the porosity reached 80.1%. The major crystalline phases of porous ceramics prepared by nickel slag were cordierite and anorthite. [ABSTRACT FROM AUTHOR]

A novel approach to fabricate porous mullite ceramics with homogeneous pore size and high-strength using green non-toxic and cost-effective poly- γ -glutamic acid (γ -PGA) gelling system was reported for the first time. Effect of γ -PGA addition, additive amount and solid loading on rheological behavior of the slurries, and microstructure and properties of samples were investigated systematically. By optimizing the solid loading of mullite samples, we are able to get the sample with small pores (< 200 µm) dominating (93.3% of the total pores), and compressive strength of the sample reaches up to 26.62 MPa. In addition, the mullite ceramics exhibited high porosity of 75.7% with low thermal conductivity of 0.279 W/(m·K) at room temperature. This study not only provides a green and non-toxic gelling system but also offers porous mullite ceramics with low thermal conductivity and excellent mechanical strength as an energy-saving thermal insulation material. [ABSTRACT FROM AUTHOR]

Microultrasound (μUS) linear arrays operating at frequencies over 25 MHz have applications in high resolution biomedical imaging. 1–3 connectively piezoceramic – polymer composite ("piezocomposite") material is attractive for fabrication of these devices due to its high effective electromechanical coupling coefficient and low acoustic impedance for better acoustic matching between transducer and tissue. However, a major concern with this type of material comes from interference between the fundamental thickness-mode resonance and spurious modes, which is usually generated by wave propagation and reflection within the repetitive and symmetrical structure of classical piezocomposite. In general, a fine spatial scale is required of the material structure to suppress the spurious modes; however, the fabrication process is challenging using standard dice-and-fill methods at the fine scales required for high frequencies. A promising way to overcome this challenge is to manipulate the lateral geometry and spacing of the piezoceramic pillars with a random distribution. In this work, gel casting in association with a micromoulding technique has been developed for manufacturing 1–3 randomised piezocomposite active material for μUS linear arrays. 48 vol% solid loading of piezoceramic powder with 30 wt% Hydantoin resin content was employed to prepare a low viscosity aqueous suspension. Through varying powder size, it was found that the suspension with 1.22 µm powder had the highest viscosity, ~ 0.47 Pa.s, and a short gelation time, ~ 10 mins. However, all suspensions had viscosities less than 1 Pa.s at a shear rate of 100 s−1, indicating that they had good flowability. The green body samples showed mean flexural strength 49.7 ± 2.49 MPa. After piezocomposite fabrication with randomised pillars, surface planarisation was used to obtain reliable edge definition of photolithographically-defined electrodes. 20-element arrays with 50-μm element pitch were configured using a bilayer lift-off process. The 1–3 randomised piezocomposite demonstrated its capability to minimise the effects of spurious modes in the thickness mode frequency range, while the thickness resonances provided k 33 = 0.67. Without a matching layer, the array produced a − 6 dB bandwidth of 38.4%- and − 20-dB pulse length of 0.26 μs. These results show that 1–3 randomised piezocomposite fabricated from gel-casting associated with a micromoulding technique is feasible for fabrication of μUS linear arrays and may offer a route to small wafer-scale production. • Particle size distribution influences rheological behaviour and gelation time. • Gel casting solves the difficulties in complex shape and micro-scale fabrication and provides homogenous microstructure. • 1–3 randomised piezocomposite demonstrates its capability to minimise spurious modes. • Randomised piezocomposite fabricated from gel-casting offers feasibility of wafer-scale fabrication for μUS linear arrays. [ABSTRACT FROM AUTHOR]

Nitride based ceramics are considered as a kind of promising material for structural and functional integration due to their robust structure, extreme environmental resistance and electromagnetically transparency. It is still challenging to prepare nitride based ceramics with homogeneous and controllable microstructure because of their low self-diffusion coefficient and difficulty in sintering. Here, we developed a gelcasting-SHS process by combining gelcasting forming and self-propagating high temperature synthesis (SHS) for the preparation of porous BN-Si 3 N 4 composite ceramics. First, carbon residue problem in the gelcasting -SHS process was studied. Based on the result, porous BN-Si 3 N 4 composite ceramics with high porosity (69.42 ~ 86.48%), high strength (21.7 ~ 81.0 MPa) and low dielectric constants (1.42 ~ 2.87) were synthesized. In addition, the thermal shock resistance of porous BN-Si 3 N 4 composite ceramics until 1000 ℃ was evaluated. [ABSTRACT FROM AUTHOR]

This study aimed to fabricate and characterise β-wollastonite/cordierite scaffolds synthesised via gel casting method, with different β-wollastonite and cordierite powder (wt.%) ratios of 100:0 (W), 70:30 (W7C3), 50:50 (W5C5), 30:70 (W3C7), and 0:100 (C). β-Wollastonite was synthesised by wet-milling silica and calcium oxide, and then, sintered at 950 °C for 3 h. Cordierite was synthesised using silica, magnesia, and alumina as the raw materials through the quenching method after the ingredients have been melted at 1400 °C and sintered at 980 °C for 2 h. Next, the effect of cordierite composition on the phase composite, and microstructure, as well as the physicomechanical and in vitro bioactivity properties of β-wollastonite/cordierite scaffolds were thoroughly investigated. The sintering linear shrinkage for all scaffolds was observed at 5.35%–15.25%, while bulk density was increased from 1.30 to 1.62 g/cm3. The X-ray diffraction analysis showed that all scaffolds, except the 100% cordierite (C), contained hydroxyapatite phase after being immersed in simulated body fluid (SBF). An apatite layer can be seen on the surface of the W, W3C7, W5C5, and W7C3 scaffolds. Scaffolds with porosities ranging from 70.3% to 53.3% showed compressive strengths ranging from 4.34 to 11.59 MPa. After one week of immersion in SBF, the compressive strength of the scaffolds has decreased dramatically (up to 75%). It was concluded that the W3C7 scaffolds have the best composition for fabricating porous scaffolds. [ABSTRACT FROM AUTHOR]

With the rapid development of hypersonic vehicles and broadband wave-transparent radome, Si 3 N 4 porous ceramics (Si 3 N 4 -PC) have attracted attention due to their excellent intrinsic properties of Si 3 N 4 and high porosity. However, its high porosity results in low strength and toughness, which are fundamental properties for radome. Reaction bonded (RB) Si 3 N 4 -PC has advantages of dielectric properties and cost over general phase transformation sintering (PTS) and sintered reaction bonded (SRB) Si 3 N 4 -PC while it has been neglected in recent years. In this study, RB and SRB Si 3 N 4 -PC prepared by non-aqueous gelcasting and the influence of Si powders ingredient on their properties are discussed in order to illuminate the potential of RB Si 3 N 4 -PC in wave-transparent materials. The results show that RB Si 3 N 4 -PC with dual-granularity ingredients of 5 μm & 45 μm produces a two-tier tissue of framework of coarse whiskers enhanced by a network of tiny whiskers. SRB Si 3 N 4 -PC evolves into a two-tier tissue of framework of columnar and rod-like grains joining together to brace each other. The two-tier microscopic tissue strongly reinforces and toughens the structure and results in higher σ F and γ wof. As a result, the RB and SRB Si 3 N 4 -PC of dual-granularity of 5 μm & 45 μm obtain the maximum σ F of 109.94 MPa and 119.56 MPa as well as maximum γ wof of 990.74 J m-2 and 1167.88 J m-2, respectively. Furthermore, the ε′ and tanδ of RB and SRB Si 3 N 4 -PC of dual-granularity of 5 μm & 45 μm are about 4.20 and 4.52 as well as 7.01 × 10-3 and 22.90 × 10-3, respectively. It is concluded that RB Si 3 N 4 -PC of dual-granularity has good mechanical and dielectric properties, which are favorable for radome. [ABSTRACT FROM AUTHOR]

Herein, hierarchical porous SiC nw -Si 3 N 4 composite ceramics with good electromagnetic absorption properties were prepared. A porous Si 3 N 4 matrix with different pore structures was first prepared by gelcasting-pressureless sintering (G-PLS) and gelcasting combined with particle stabilized foam-pressureless sintering (G-PSF-PLS). SiC nw was then introduced by catalytic chemical vapor deposition (CCVD). An increase in solid loading (25–40 vol%) decreased apparent porosity (47.7–41.3%) and improved flexural strength (142.19–240.36 MPa) and fracture toughness (2.25–3.68 MPa·m1/2). The addition of foam stabilizer propyl gallate (PG, 0.5–1.0 wt%) significantly increased apparent porosity (73.2–86.4%) and realized large-sized spherical pores, reducing flexural strength (58.23–38.56 MPa) and fracture toughness (0.75–0.41 MPa·m1/2). High apparent porosity and large-sized pores facilitated the introduction of SiC nw. The 25 vol% sample exhibited a reflection loss of − 14.67 dB with an effective absorption bandwidth of 3.47 GHz, suggesting a development potential in the electromagnetic wave absorption field. [ABSTRACT FROM AUTHOR]

The current study focuses on the fabrication of hybrid flexible polymers composed of MnFe 2 O 4 /ZnMn 2 O 4 nanocomposites doped polyvinyl chloride (PVC). The doped polymers show great potential for utilization in a wide range of optoelectronics applications. PVC/(1- x)MnFe 2 O 4 / x ZnMn 2 O 4 were made using the casting and sol gel processes. The effect of (1- x)MnFe 2 O 4 / x ZnMn 2 O 4 nanocomposite samples on the optical parameters of PVC polymer has been explored using ultraviolet–visible diffused reflectance measurements. Doped polymers might be useful as protective barriers against ultraviolet radiation of various wavelengths (UVA, UVB, UVC) and as excellent absorber materials for solar cells. The direct and indirect bandgaps (E g) of PVC are 4.26 and 4.08 eV. The direct/indirect optical band gap lowered to their lowest 3.97/3.45 eV as the PVC doped with nanofillers contained 50 %/80 % ZnMn 2 O 4 , respectively. Different models were used to extracted the refractive index (n) of different polymers based on the obtained optical band gaps (direct/indirect). Doped polymers containing 50 and 80 % ZnMn 2 O 4 had the highest n values using direct and indirect E g values, respectively. The n value (obtained from the direct optical bandgap energy) of PVC increased from 2.209 to the maximum value (2.262) as x = 0.5. The n value (obtained from the indirect optical bandgap energy) of PVC increased from 2.349 to the maximum value (2.367) as x = 0.8. All linear and nonlinear optical parameters of PVC polymer were improved as it doped with the nanocomposite fillers. The fluorescence (FL) intensity of PVC was reduced as it was doped with (1- x)MnFe 2 O 4 / x ZnMn 2 O 4 and this intensity reduced as the content of ZnMn 2 O 4. The standard (CIE) color space chromaticity diagram was used to analysis the FL spectra for different samples. The effect of nanocomposite samples on the AC conductivity, dielectric constants and electric modulus of the PVC was studied. At 1 kHz, the dielectric constant of PVC was increased from 11.745 to 12.906 and 12.096 for polymers with x = 0 and x = 0.2, respectively. The enhanced optical and dielectric properties of the PVC/(1- x)MnFe 2 O 4 / x ZnMn 2 O 4 polymers nanocomposites suggest that these materials are suitable for smart electronic devices. • Adding (1-x) MnFe 2 O 4 /x ZnMn 2 O 4 to PVC led to an irregular changes in absorbance and transmittance spectra. • Doped PVC nanocomposite with 80 % ZnMn 2 O 4 has the greatest optical conductivity value. • The decline in FL emission intensity nominated the doped polymer as a prime candidate for photocatalytic uses. • Increases in dielectric constant and AC conductivity were seen for PVC doped with MnFe 2 O 4 alone. • The amount of ZnMn 2 O 4 in the nanocomposite fillers slightly affected the relaxation time of the PVC. [ABSTRACT FROM AUTHOR]

Recently, high-performance ceramic aerogels (CAs) have become a research hotspot because of their multi-functional properties. Compared to their oxide counterparts, non-oxide CAs show better thermal shock resistance and other high-temperature properties, making them suitable for applications in harsh environments. In this work, Si 3 N 4 -BC x N-TiN ceramic aerogels (SBCNT CAs) with molar ratios of B/C/Si/Ti = 2:1:5:5 were synthesized at 1623 K for 3 h via foam-gelcasting, from Si, Ti, melamine and boron acid raw materials. The prepared SBCNT CAs containing 91.0% porosity exhibited the highest compressive strength up to 1.0 MPa, and thermal conductivity of 0.144 W/(m·K) at 298 K. They also exhibited excellent service performance at 1473 K in Ar, demonstrating their great potential for high-temperature applications. [Display omitted] [ABSTRACT FROM AUTHOR]

A new and non-toxic aqueous alumina gelcasting system using natural rubber (NR) latex as a gel former has been studied. A gel of reasonable strength is achieved by freezing concentrated alumina-NR latex co-dispersions in a mould followed by mould removal and aging in acetone. Gelation is achieved by coagulation of latex particles due to the breakdown of the protein layer on their surface during ice crystal growth. The minimum concentration of rubber required to percolate and form a soft and stable gel is 8 wt % of alumina. Aging of the frozen body in acetone for solvent exchange results in strengthening of the alumina-rubber gel network by further coagulation leading to reasonably high strength (∼60 kPa). The frozen body passes through a semi-fluid state during aging in acetone which enables the gel to reorganize and fill the space created by melting of ice crystals and thereby preventing the occurrence of pores in the green ceramics. The exchange of water in the gelled body with acetone enables easy and faster gel drying at room temperature. The diametrical compressive strength of the green body increases from 0.35 to 2.14 MPa during annealing at 200 °C due to the cross-linking of rubber. The cross-linked rubber in the green body undergoes near-steady state burnout without creating any crack. Debinding followed by sintering of the gelcast bodies at 1550 °C produce ceramics of ∼96% density. The sintered ceramics show a dense microstructure with an average grain size of 1.3 μm. The gelcasting using the NR latex is capable of producing complex near-net-shapes. [ABSTRACT FROM AUTHOR]

Silicon nitride (Si 3 N 4) slurries with high solid loading, low viscosity and good stability is difficulty prepared, due to low intrinsic surface charge and a large refractive index (RI) difference between Si 3 N 4 powder and resin. In this paper, the curing behavior of Si 3 N 4 slurry with different functional group and RI of resin monomer were systematically researched, and then the kind and optimum content of dispersant were investigated. Subsequently, a high solid loading Si 3 N 4 slurry (44 vol%) with good curing behavior, low viscosity and favorable stability was successfully prepared. Lastly, the dense Si 3 N 4 ceramic parts were fabricated by the suitable Si 3 N 4 slurry (44 vol%) via stereolithography. After debinding and sintering process, the relative density and flexural strength of Si 3 N 4 ceramic were 98.28% and 800 ± 27.28 Mpa, respectively. [ABSTRACT FROM AUTHOR]

In this work, X-band microwave absorbing properties of gelcasted SiC-Si 3 N 4 ceramics with different hierarchical pore structures at both room temperature and high temperature were reported for the first time. Effects of pore structures, sample thickness and temperature on complex permittivity and microwave absorption performance of SiC-Si 3 N 4 ceramics were investigated systemically. The results suggested that the introduction of appropriate hierarchical pore structure was beneficial to improve the absorbing performance of the material. The minimum reflection loss value can reach -59.2 dB for the 3.8 mm thick sample at 8.35 GHz and room temperature. By elevating the temperature, the effective absorption bandwidth of porous SiC-Si 3 N 4 with a thickness of 3.0 mm covers the entire X-band. The excellent microwave absorbing property of porous SiC-Si 3 N 4 ceramics was attributed to the multiple reflections brought about by the existence of hierarchical pores, interfacial polarization between SiC and Si 3 N 4 grains, and defect dipole polarization in grains and grain boundaries. The good absorbing property and the clarification of absorbing mechanism of porous gelcasted SiC-Si 3 N 4 ceramics will provide a solid foundation for the development of porous SiC-based absorbing parts. [ABSTRACT FROM AUTHOR]

Highly transparent Li 0.07 Al 2.76 O 3.64 N 0.36 discs (φ 22 × 2.0 mm) and blocks (45 × 40 × 12 mm) were successfully prepared by aqueous gelcasting and two-step preparation. After introducing a small amount of lithium, the lower N1s binding energy and higher intensity of Al–N bonds on the surface of Li 0.07 Al 2.76 O 3.64 N 0.36 powder cause Al–N breakage to be effectively avoided, which inhibits the hydrolysis of powder. Using MAM and MABM as monomers and gelling agents, a stable aqueous suspension with solid loading up to 55 vol% and low viscosity of 83 mPa s was prepared, and the rheological properties and gelating behaviour of the slurries were evaluated. Due to its composition and novel crystalline structure, the Li 0.07 Al 2.76 O 3.64 N 0.36 component presented significantly different performances from γ-AlON. The Vickers hardness reached 15.44 ± 0.34 GPa at a load of 9.8 N, and the in-line transmittance reached ∼84.7% at 3.7 μm. [ABSTRACT FROM AUTHOR]

In view of technical difficulties in preparing ceramics with complex shapes, gel casting combined with 3D printing was here adopted to prepare silicon carbide ceramic green body, and gaseous silicon infiltration sintering was used to prepare 3D lattice-structured ceramics. The preparation of the slurry, gel curing, and ceramic molding was investigated. Results demonstrate that the ratio of components affects the fluidity and stability of slurry. However, when volume fraction of the solid phase of the slurry reaches 56%, the viscosity of slurry is only 300 mPa s, and drying shrinkage rate of green body is 6.6%; these characteristics make slurry suitable for 3D complex model injection molding. Furthermore, both the temperature and the initiator affect gel curing speed. As the temperature and initiator content increase, the induction and gel time are rapidly shortened. When demolding at 300 °C and when gaseous silicon infiltration sintering is carried out at 1550 °C, a 3D lattice-structured ceramic with relative density of 87% and average compressive strength of 433 MPa can be obtained. [ABSTRACT FROM AUTHOR]

Porous Si 3 N 4 ceramics were fabricated by combining gelcasting and pressureless sintering. The roles of sintering temperatures and sintering additives (Y 2 O 3 , Al 2 O 3 , and Y 2 O 3 -Al 2 O 3) in regulating phase composition, microstructure, sintering, mechanical, and dielectric properties of porous Si 3 N 4 ceramics were systematically studied. Compared with Y 2 O 3 and Al 2 O 3 , owing to the lower eutectic temperature, Y 2 O 3 -Al 2 O 3 was more effectively in promoting the particle rearrangement and dissolution-diffusion-reprecipitation processes during high-temperature sintering, leading to higher phase transformation degree of α→β-Si 3 N 4 , larger aspect ratio of columnar β-Si 3 N 4 grains, and higher densification of porous Si 3 N 4 ceramics. Furthermore, the increasing sintering temperature and the present β-Si 3 N 4 seeds within the raw powders were also conducive to phase transformation of α→β-Si 3 N 4 , β-Si 3 N 4 growth, and developing highly interlocking microstructure contributing to strengthening mechanical properties. At 10 wt% Y 2 O 3 and 5 wt% Al 2 O 3 , the complete phase transformation of α→β-Si 3 N 4 and sufficient β-Si 3 N 4 growth were achieved by pressureless sintering at 1750 ℃ for 1 h. The apparent porosity, bulk density, flexural strength, and fracture toughness of porous Si 3 N 4 ceramics reached 2.7%, 2.98 g/cm3, 450.9 MPa, and 4.35 MPa·m1/2, respectively, exhibiting superior mechanical properties. At 2 wt% Y 2 O 3 and 1 wt% Al 2 O 3, the resulting porous Si 3 N 4 ceramics had dielectric constant of 4.28–4.38 and dielectric loss tangent of 2.1 × 10−3-3.2 × 10−4 throughout X-band, showing good microwave transmission properties. This study indicates that the gelcasting combined with pressureless sintering was proved to be a feasible method to prepare high-strength and low-dielectric porous Si 3 N 4 ceramics using Y 2 O 3 -Al 2 O 3 as sintering additives. • Porous Si 3 N 4 ceramics were fabricated by gelcasting and pressureless sintering. • A low-toxic DMAA gelling system was applied in gelcasting of porous Si 3 N 4 ceramics. • α→β transformation and β-Si 3 N 4 growth relied on sintering temperature and additives. • Y 2 O 3 -Al 2 O 3 effectively promoted dissolution, diffusion and reprecipitation processes. • Superior mechanical and dielectric properties at X-band were achieved. [ABSTRACT FROM AUTHOR]

The application of insulation materials in buildings and energy storage facilities is gaining global attention to reduce energy consumption, heat loss, and CO 2 emissions. Given the high insulation performance, glass foam is gaining popularity replacing combustible, high energy-consuming, and costly conventional insulation materials. The industrial process of glass foam manufacturing is an energy-consuming and non-ecofriendly process which requires the annealing of glass around its melting temperature. Therefore, researchers have developed powder sintering and gel casting methods to sinter glass foam mix at a temperature slightly above its glass transition point. However, research findings on these two methods are scattered because of the different parameters being used by researchers. The properties and performances of glass foam depend on the processing parameters, especially on the materials design and sintering conditions. Therefore, this study aimed to provide a comprehensive review on the key parameters for material selection and sintering of glass foams and provide necessary guidelines for the best practice and a direction for future research. Moreover, this review covers the current strategies and challenges associated with the powder sintering and gel casting methods including their sustainability and environmental performance. [ABSTRACT FROM AUTHOR]

In this study, porous halloysite nanotube ceramics were prepared by the foam-gelcasting method using sodium carboxymethyl cellulose (CMC) as a foam stabilising agent, Isobam 104 as a dispersant and triethanolamine lauryl sulphate (TLS) as a foaming agent, respectively. Then, the effects of firing temperature on the phase composition, microstructure, and pore size distribution of porous halloysite nanotube ceramics were analyzed using X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), Brunner-Emmet-Teller (BET), thermogravimetry (TG) and differential scanning calorimetry (DSC). The results showed that the prepared porous ceramics contained both mesopores (10–50 nm) and macropores (100–300 μm). As the firing temperature rose, the linear shrinkage and compressive strength of samples increased, while the porosity decreased. When the porosity was as high as 75.7%, the samples still remained the compressive strength of 1.1 MPa, and had the lowest thermal conductivity, reaching 0.194 W/(m·K) (at a testing temperature of 100 °C). [ABSTRACT FROM AUTHOR]

High strength SiC reinforced Si 3 N 4 ceramics aerogels (SCSNCAs) were fabricated via foam-gelcasting and subsequent catalytic reaction, utilizing industrial Si and melamine as raw materials, a small amount of incidental Fe impurities in Si powder as the catalyst and cetyltrimethylammonium bromide (CTAB, the amount of 0.075 wt%) as foaming agent. The effects of solid loading level and reaction temperature on phase composition, microstructure and mechanical properties of the as-prepared SCSNCAs were examined. The aerogels prepared at 1423 K using a slurry of solid loading level of 30 wt% (Si:melamine = 3:1, mass ratio) had porosity of 91.9%, having compressive and specific strength of 0.8 MPa and 3.8 MPa·cm3·g−1 exhibited the lowest thermal conductivity of 0.066 W/(m·K) at 473 K. Compared with the control sample (without melamine, i.e., Si 3 N 4 aerogels without the formation of SiC), the specific strength of the SCSNCAs increased by about 10%, which was attributed to the additional reinforcement from SiC whiskers formed in the Si 3 N 4 matrix of the aerogels. [ABSTRACT FROM AUTHOR]

Oxygen and carbon impurity residues and low density are the main issues for Ti gelcasting. To overcome these difficulties, this study develops a low-oxygen isoprene (Ip)/polyvinyl butyral (PVB) gel system to achieve Ti gelcasting using hydride-dihydride (HDH) Ti6Al4V powder. Slurries with 48 vol% solid loading content are employed to achieve moulding followed by cold isostatic pressing. During gelcasting, powder particles are held in place by the cross-linking of Ip monomer with PVB as adhesive to maintain shape. After sintering, nearly fully dense (4.38 g/cm3) Ti6Al4V alloys with low interstitial contamination (O: 0.356 wt%, C: 0.14 wt%) are successfully fabricated. The samples exhibit acceptable mechanical performance, with ultimate tensile strength of 1062 MPa, yield strength of 987 MPa, and elongation of 8.75%. Typical plastic fracture with river patterns is observed, which is distinctly different from that of HEMA based sample. [Display omitted] • Gelcasting Ti6Al4V parts with density of 4.38 g/cm3 are prepared using HDH powders. • A potential gelcasting method is proposed based on Ip/PVB system combined with CIP. • The tensile strength and elongation are 1062 MPa and 8.75%, respectively. • Oxygen content is significantly reduced from 0.88 wt% to 0.36 wt%. • Carbon content decreases from 0.26 wt% to 0.14%, decreasing by 46%. [ABSTRACT FROM AUTHOR]

[Display omitted] • A novel method for testing paste slurry thixotropy was proposed. • The influence of temperature on the paste slurry thixotropy was investigated. • A quantitative indicator of the stress overshoot phenomenon was proposed. • In continuous shear cycles, the variation law of the DYS is generally the same as that of A thix. Paste slurry exhibits significant thixotropy, which has a significant influence on the slurry pipeline transportation resistance. This paper proposes a novel test method for the thixotropy of paste slurry, which can ensure that the slurry reaches flow equilibrium during the test. Accordingly, the influences of the solid mass concentration, cement-to-tailings ratio, and temperature on thixotropy were studied by employing a control variable method, and the influences of the above three factors on the stress overshoot and rheological parameters were evaluated. The results revealed that the solid mass concentration and temperature have significant influence on the thixotropy. Moreover, with an increase in the solid mass concentration, the time required for the slurry to reach flow equilibrium decreases. The cement content and temperature are proportional to the significance of the stress overshoot, and the change in dynamic yield stress can be considered an indicator for the effective quantification of thixotropy. In the continuous shearing cycles, the maximum apparent viscosity at the start of shearing significantly decreases on the time axis. The solid mass concentration has a significant influence on the minimum apparent viscosity in the slurry flow process, whereas the cement-to-tailings ratio and temperature have no significant influences. [ABSTRACT FROM AUTHOR]

The goal of this research is to fabricate pure transparent yttria ceramics through gel casting and vacuum sintering. A specific processing method has been used and optimized for this purpose. A pure yttria nanopowder was synthesized as the starting material to produce pure transparent ceramics through a low-temperature sintering process. It was attempted to minimize the undesirable nanopowder hydration by using the as-synthesized yttria nanopowder and a rapid deagglomeration and slurry preparation process. The synthesized nanopowders were deagglomerated to enhance the efficiency of both powder shaping and sintering stages. Carrageenan was used as the gelling agent because it is a low-cost and abundant material, and because the temperature is the only catalyst needed for its gelation; therefore, it is possible to control its gelation to obtain high-density and pure optical ceramics. The effect of the deagglomeration method and the processing parameters, including the amounts of dispersant, gelling agent, solid loading, pH, and deagglomeration time, on the rheology of slurry, density, and microstructure of the obtained green yttria ceramics was examined and optimized in order to obtain high solid loading nanoyttria suspensions of 38 vol%, which is more than those obtained in many of the previous investigations. The precise gelling temperature and time were measured, and green gel cast ceramics with a density of 63 % of the theoretical density were produced. A rapid deagglomeration and slurry preparation method was used instead of using a conventional planetary ball-milling approach to minimize the risk of the hydrolysis of yttria nanopowder. No sintering aid was necessary, and transparent yttria ceramics with 99 % of the theoretical density were produced after vacuum-furnace sintering at 10-2 mbar and 1715 °C. [ABSTRACT FROM AUTHOR]

The sintering behaviour and microstructural evolution of two batches of a commercial calcium-deficient hydroxyapatite powder were investigated. First, the sintered density as a function of the starting particle size distribution was studied, and the minimum particle size to get the desired target density was determined. Then, as the two batches were characterized by a slight difference in Ca/P ratio, the role of such ratio on phase and microstructural evolutions during sintering, as well as on mechanical and biological properties was investigated. It was observed that the powder with lower Ca/P ratio underwent significant hydroxyapatite (HA) to β-tricalcium phosphate (β-TCP) decomposition, with a simultaneous formation of tetracalcium phosphate (TTCP). The microstructure of sintered gelcast samples evolved during isothermal sintering at 1300 °C, moving from a starting homogeneous and narrow grain size distribution to a bimodal distribution after 3 h sintering. In fact, over time, large grains decomposed into smaller ones, finally providing a microstructure composed of coarse grains surrounded by plenty of ultra-fine grains. On the contrary, the powder with the higher Ca/P ratio provided a limited HA to β-TCP transformation, and normal grain growth by increasing the sintering time. Such differences lead to different mechanical properties for gelcast samples produced by the two powder batches, as the material with the lower Ca/P ratio affected by lower mechanical strength. Finally, sintered samples from both powders showed in-vitro bioactivity, with a larger surface coverage observed for the lower Ca/P ratio material. The morphology of the apatite layer seemed to be affected by the material composition, too, showing flake-like and needle-like morphologies depending on the Ca/P ratio of the starting powder. [ABSTRACT FROM AUTHOR]

The porous SiC–Si 3 N 4 composite ceramics with good EMW absorption properties were prepared by combination of gelcasting and carbothermal reduction. The pre-oxidation of Si 3 N 4 powders significantly improved the rheological properties of slurries (0.06 Pa s at 103.92 s−1) and also suppressed the generation of NH 3 and N 2 from Si 3 N 4 hydrolysis and reaction between Si 3 N 4 and initiator APS, thereby reducing the pore defects in green bodies and enhancing mechanical properties with a maximum value of 42.88 MPa. With the extension of oxidation time from 0 h to 10 h, the porosity and pore size of porous SiC–Si 3 N 4 composite ceramics increased from approximately 41.86% and 1.0–1.5 μm to 46.33% and ~200 μm due to the production of CO, N 2 and gaseous SiO, while the sintering shrinkage decreased from 16.24% to 10.50%. With oxidation time of 2 h, the Si 2 N 2 O fibers formed in situ by the reaction of Si 3 N 4 and amorphous SiO 2 effectively enhanced the mechanical properties, achieving the highest flexural strength of 129.37 MPa and fracture toughness of 4.25 MPa m1/2. Compared with monolithic Si 3 N 4 ceramics, the electrical conductivity, relative permittivity and dielectric loss were significantly improved by the in-situ introduced PyC from the pyrolysis of three-dimensional network DMAA-MBAM gel in green bodies and the SiC from the carbothermal reduction reaction between PyC and SiO 2 and Si 3 N 4. The porous SiC–Si 3 N 4 composite ceramics prepared by the unoxidized Si 3 N 4 powders demonstrated the optimal EMW absorption properties with reflection loss of −22.35 dB at 8.37 GHz and 2 mm thickness, corresponding to the effective bandwidth of 8.20–9.29 GHz, displaying great application potential in EMW absorption fields. [ABSTRACT FROM AUTHOR]

• Reticulated skeleton ceramic (RSC) was fabricated by freezing casting and enhanced in situ using a gel network. • RSC calcined at 1400 °C has satisfactory mechanical strength and pure water flux. • RSC can remove nearly 80 % of TOC and more than 85 % of calcium ions in feed solutions. • RSC cleaned by NaOH and EDTA has a high flux recovery rate of 72.71 %∼92.64 %. It is of great practical significance to manufacture ceramic membranes with good reusability. We used a macromolecular gel network for in situ enhancement of a reticulated skeleton ceramic (RSC) membrane. The prepared RSC membranes were firstly characterized to determine their physical and chemical properties. The sample calcined at 1400 °C has a porosity of 41.66 %, a pore size of 0.34 μm, a mechanical strength of 4.53 MPa, and a permeability of 63.92 L m−1 h−1 bar−1. This membrane can effectively reduce the content of total organic carbon (TOC) (80 %) and calcium ion (>85 %). In addition, the flux of RSC fouled by alginate, calcium ions, or their mixture is effectively recovered by simple chemical rinsing using sodium hydroxide and ethylenediaminetetraacetic acid. [ABSTRACT FROM AUTHOR]

The potentially useful role of lanthanum zirconate (La 2 Zr 2 O 7 , LZO) porous bulk ceramics has been rarely explored thus far, much less the optimisation of its pore structure. In this study, LZO porous ceramics were successfully fabricated using a tert-butyl alcohol (TBA)-based gelcasting method, and the pore structures were tailored by varying the initial solid loading of the slurry. The as-prepared ceramics exhibited an interconnected pore structure with high porosity (67.9 %–84.2 %), low thermal conductivity (0.083–0.207 W/(m·K)), and relatively high compressive strength (1.56–7.89 MPa). The LZO porous ceramics with porosity of 84.2 % showed thermal conductivity as low as 0.083 W/(m·K) at room temperature and 0.141 W/(m·K) at 1200 °C, which is much lower than the counterparts fabricated from particle-stabilized foams owing to its unique pore structure with a smaller size, exhibiting better thermal insulating performance. [ABSTRACT FROM AUTHOR]

Aluminum borate porous ceramics are excellent candidates for high-temperature insulation applications. Current research on aluminum borate-based porous ceramics mainly focuses on porous ceramics made up of aluminum borate whiskers, whose low aspect ratio leads to a relatively dense porous structure; this results in porous ceramics with low porosity and relatively high thermal conductivity. In this study, we report the manufacturing of aluminum borate nanofibrous porous ceramics by an agar-based gel casting method using electrospun nanofibers with a high aspect ratio as the three-dimensional skeleton structure. We explored the effect of the alumina/boron oxide molar ratio on the microscopic morphology and crystal phase composition of the aluminum borate nanofibers and that of the sintering temperature on the micro and macro properties of porous ceramics based on the nanofibers. The results showed that aluminum borate nanofibers with an alumina/boron oxide molar ratio of 7:2 had the densest microscopic morphology, and the corresponding porous ceramics exhibited a higher porosity (91%) and lower thermal conductivity (0.11 W m−1 K−1) after sintering at 1200 °C than aluminum borate porous ceramics with aluminum borate whiskers as the skeleton. The successful synthesis of aluminum borate nanofibrous porous ceramics provides new insights into the development of high-temperature insulators. [ABSTRACT FROM AUTHOR]

A novel and simple gelling system based on a water-soluble copolymer of isobutylene and maleic anhydride (commercial name, Isobam) was adopted to manufacture various ceramics via spontaneous gelation. The gelation mechanism of AlN slurry was investigated using infrared spectroscopy. Results show that Isobam was hydrolyzed to produce the –COOH group, and the hydrogen bonding was formed between the –COOH and –CONH 2 groups of Isobam during spontaneous gelation. Meanwhile, the gelling process of the Isobam system could be accelerated via enhancing hydrogen bonding through APS addition. With 1 wt% addition of APS, the gelation time reduced to 23 h, the viscosity of 50 vol% AlN slurry decreased to 0.21 Pa·s, and the flexural strength of green body improved by 48%. Therefore, the presence of hydrogen bonding in the Isobam gelation mechanism was confirmed, and it could be enhanced by introducing APS to accelerate gelation. [ABSTRACT FROM AUTHOR]

• A novel aqueous gelcasting route to prepare Yb:YAG transparent ceramic fiber. • A high solid loading and low viscosity into the capillary glass tube. • A green fiber without cracks and deformation. • A diameter of 1.0 mm and a length of 43.0 mm for 15.0 at.% Yb:YAG ceramic fiber. Transparent laser ceramics are the attractive gain medium for solid-state lasers. However, they have not been applied to the fiber lasers due to the difficulty of forming green fibers by traditional methods. In this study, a novel route combined aqueous gelcasting with capillary glass tube was designed to prepare Yb:YAG transparent ceramic fiber with a diameter of 1.0 mm and 43.0 mm in length for the first time. The slurry with high solid loading and low viscosity was smartly inhaled into the capillary glass tube to conquer the difficulty of casting. The green fibers without cracks and deformation had highly dense microstructure. The in-line transmittance of highly doped 15.0 at.% Yb:YAG transparent ceramic disc prepared from the same preparation conditions of Yb:YAG ceramic fiber was 80.0 % at 1064 nm. This study provides a novel route to prepare transparent ceramic fiber differing from extrusion processing, promoting the development of fiber laser. [ABSTRACT FROM AUTHOR]

The preparation process and the properties of Al 2 O 3 -W nanocomposites obtained by gelcasting are reported. The novelty of the synthesis path is the formation of nano-tungsten particles in an in situ reduction of water-soluble precursor during pressureless sintering. The use of water-soluble salt as a tungsten precursor ensured highly homogenous distribution of reinforcing particles and good adhesion between ceramic and metal phases. The maximum content of tungsten in the composites was approximately 0.5 wt%. The size of the reinforcing particles was less than 100 nm. Presence of metallic tungsten and tungsten carbide (W 2 C) in the composites lead to the improvement of mechanical parameters: an increase of hardness by about 10 % and of fracture toughness by about 20 %, compared to the reference sample of pure aluminum oxide. [ABSTRACT FROM AUTHOR]

Gd 2 Zr 2 O 7 ceramic is considered as one of the most promising host minerals for the immobilization of high-level radioactive wastes. Here, the effects of grain size on the aqueous durability of Gd 2 Zr 2 O 7 ceramics were studied. Two kinds of leaching experiments were used to research Gd 2 Zr 2 O 7 ceramic powders and bulks with different grain sizes (5 nm, 78 nm, 1 μm and 18 μm). The results demonstrate that the normalized leaching rates decrease with the increase of grain size. Through characterization and analysis, it is concluded that the hydrolysis reactions of Gd 2 Zr 2 O 7 occur in the leaching experiment and the hydrolysates are Gd(OH) 3 and Zr(OH) 4. Besides, all the samples after leaching exhibit slight lattice contraction, which decreases with the increase of crystal grain size. The influence of leaching on the elemental distribution is most significant for the sample with grain size of 5 nm. This study has theoretical guiding significance for the application of Gd 2 Zr 2 O 7 immobilization. [ABSTRACT FROM AUTHOR]

Spearhead columnar mullite was synthesized by in-situ reaction with V 2 O 5 as additive. When the content of V 2 O 5 was 7 wt%, the length of the spearhead columnar mullite was the longest with an aspect ratio of about 3.5. Furthermore, columnar self-reinforced mullite porous ceramics were prepared by a foam-gelcasting method, and the effects of V 2 O 5 content on the rheological and gelling properties of mullite slurries as well as the microstructure, physical property and thermal insulation property of the prepared mullite porous ceramics were studied. The results showed that the flexural strength and compressive strength of the porous ceramics with 63% porosity prepared by using 2 wt% V 2 O 5 additive were respectively as high as 13.9 and 41.3 MPa, and the thermal conductivity was about 1.04 W m−1 K−1. [ABSTRACT FROM AUTHOR]

Electrokinetic and gel behavior of Si 3 N 4 aqueous suspension for gel casting were investigated in this study. The zeta potential of dilute and concentrated suspension with organic binder was evaluated innovatively. The influence of the binder composition and solid loading on the gel time and viscosity of the slurry was studied. The result showed that absolute value of zeta potential would be lower in the concentrated suspension or suspension with organic binder. The release of NH 3 during ball milling would increase the pH value, while the dissociation of the soluble SiO 2 would increase it during setting. The gel time of the suspension was significantly affected by the organic binder addition. Higher pH value and lower solid loading was conductive to obtain slurry with lower viscosity. [ABSTRACT FROM AUTHOR]