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Many studies have reported that additive manufactured ceramic lattices with microarchitectures often exhibit low‐strain brittle fracture behavior. In this work, the fracture behavior of ceramic triply periodic minimal surface (TPMS) lattices was optimized by introducing a hybrid design strategy that utilizes different microarchitectures. Hybrid ceramic TPMS structures incorporating Gyroid and Primitive unit cells were successfully fabricated using the Lithography‐based ceramics manufacturing (LCM) technique, and their mechanical properties were evaluated under both quasistatic and dynamic compression. The hybrid designs exhibited improved damage tolerance and fracture strength compared to their normal counterparts. Compared to normal Gyroid and Primitive structures, the G2P2 structure exhibits the best energy absorption capacity of 12.5 × 104 J/m3, demonstrating a 13% and 217% increase in energy absorption capacity under quasistatic loading, respectively. Additionally, compared with other normal and hybrid designs, the G2P2 structure exhibits the highest fracture strength of 13.03 MPa under quasistatic loading conditions. Moreover, the P2G hybrid structure displayed a distinct deformation pattern characterized by a smoother stress decrease under quasistatic loading, enhancing damage tolerance. The order of Young's modulus under quasistatic loading was Normal Gyroid ≈ G2P2 > G2P1 > Normal Primitive > P2G. Fracture strength follows the order of G2P2 ≈ Normal Gyroid > Normal Primitive > G2P1 > P2G. The mechanical properties of hybrid TPMS structures suggest that the hybrid design strategy can broaden the achievable range of mechanical properties among ceramic TPMS structures. [ABSTRACT FROM AUTHOR]

Sintering for large‐sized, stoichiometric Bi0.5Na0.5TiO3 (BNT) ceramics is of great challenge due to the loss of volatile Bi/Na at A‐site of perovskite structure. In this work, BNT ceramic tile with the size of ∼10 × 10 cm2 and near‐stoichiometric composition has been successfully fabricated by Isobam‐assisted gelcasting process, followed by sintering with 1150°C calcined power bed. The powder bed used and sintering duration were found to have a great influence on the formation of the Na‐deficient phase (Bi4.5Na0.5Ti4O15) in the ceramics, and the strategies to eliminate it have been explored. The obtained ceramics exhibit a dielectric constant/loss of 673.6/0.039 at 1 kHz, as well as an electrostrictive strain of ∼0.07% which corresponds to a converse piezoelectric constant d33∗$d_{33}^*$ of 105.2 pm/V. Our work thus provides an effective approach to prepare large‐sized and stoichiometric BNT ceramics. [ABSTRACT FROM AUTHOR]

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]

Dense ceramic components of complex shapes are fabricated by combining the techniques of rapid prototyping and gelcasting (RPGC process). Free‐flowing slurries of ceramic powders are set into precision molds fabricated out of expanded polystyrene (EPS) from computer‐aided design files, employing subtractive manufacturing. The removal of the mold from gelled parts is often a serious problem when attempting to produce large and complex‐shaped products. The EPS molds have advantages over the commonly used acrylonitrile butadiene styrene (ABS) molds in this context. Process innovations led to easy demolding and near‐net shaping of components of large and complex geometries that required minimal machining. Fabrication of complex‐shaped products out of alumina with a density of 99%, flexural strength of 389 MPa, and fracture toughness of ∼3 MPa√m is demonstrated. The RPGC process is extended to fabricate composites of alumina and yttria‐stabilized zirconia (YSZ) with α‐alumina platelet inclusions, with enhanced fracture toughness. The components have exhibited uniform density across the body of large and complex‐shaped parts, uniform microstructures, and good mechanical properties. EPS molds are also cost effective for fabricating large parts. The process is generic, allows for easy design modifications to include corrections for shrinkage, and also enables uniform distribution of second phases. [ABSTRACT FROM AUTHOR]

Magnesia porous insulation materials were prepared via foam-gelcasting using industrial grade mid-range magnesia powder as the main raw materials, a copolymer of isobutylene and maleic anhydride (Isobam-104) as the dispersing and gelling agent, sodium carboxymethyl cellulose (CMC) as the foam stabilizing agent, and cetyltrimethylammonium bromide (CTAB) as the foaming agent. The effects of processing parameters such as amount of Isobam-104 (0.1 wt%, 0.15 wt%, 0.2 wt%, 0.25 wt%, and 0.3 wt%) and firing temperature (1300 ℃, 1350 ℃, and 1400 ℃) on magnesia porous insulation materials were investigated. In addition, the universal testing machine (WDW-100E) and the scanning electron microscope (SEM) were employed to characterize the firing samples. The results indicated that the compressive strength of the prepared samples increased with the increase in firing temperature, and the porosity decreased gradually. When the firing temperature was 1350 °C, the internal pores of the samples were uniformly distributed, the average pore size was in the range of 26.2 μm to 35.6 μm, and the compressive strength was in the range of 7.8 MPa to 11.5 MPa when porosity varied from 65.2% to 60.4%. The thermal conductivity of the prepared magnesia porous insulation materials was in the range of 0.481 W/(m·K) to 0.842 W/(m·K). [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 the present work, porous ceramics with open pores were fabricated using the gel casting method, which utilizes carrageenan as a cross-linking agent. Beyond the foaming agents or templates techniques, this approach employed large-sized Al2O3 particles (~ 45 μm) as the underlying framework material, enabling the direct formation of minute open pores within the green bodies and sintered samples. In order to finely adjust the pore structure and bolster flexural strength, micropowders of α-Al2O3 and Kaolin were incorporated as filling materials, alongside the introduction of rare-earth oxides as sintering additives. The study diligently examined the impact of varying the content of sintering additives as well as the sintering temperatures on the characteristics of the porous ceramics. As a result, remarkable achievements were obtained, culminating in the production of Al2O3-based porous ceramics measuring 8 mm in thickness, exhibiting flexural strength exceeding 160 MPa, porosity surpassing 30%, and exceptional gas permeability of over 30 L/min/cm2 under a pressure drop of 100 kPa. [ABSTRACT FROM AUTHOR]

In view of the lack of conformal, load‐bearing, light‐weight, and high temperature‐resistant integrated wave‐absorbing composites suitable for extremely complex conditions, the gel‐casting process was successfully applied to porous Si3N4 wave‐absorbing composites in this work. A universal low‐slurry for gel casting was prepared by using two dispersants acting together (tetramethylammonium hydroxide solution and sodium lauryl sulfate), which ensured the smooth completion of the gel casting process. Combining the thermogravimetric and differential thermal gravity curves of the composite green body, reasonable parameters of the rubber discharge process are given to avoid the problem of the green body swelling and cracking. The porous TiC/Si3N4 composites were successfully prepared by holding them at 1650°C for 3 h. The bending strength, density, minimum reflection loss, absorption bandwidth, and matched thickness in the P‐band of the composites with 30 wt.% TiC addition were 54.08 ± 3.02 MPa, 1.906 g/cm3, ‐37.75 dB, 1.9 GHz, and 4.1 mm, respectively. The electromagnetic wave loss mechanisms of the composites are a combination of conductivity loss, multiple reflections and scattering, interfacial polarization, and defect polarization. [ABSTRACT FROM AUTHOR]

PVC/FeCr2O4/x wt% tetrapropylammonium iodide (TPAI, x = 0, 2.5, 5, 10, 20) polymers were prepared using casting and sol gel methods. Rietveld refinement was used to determine the structural and microstructural properties of FeCr2O4 nanofiller. XRD, FTIR, and SEM techniques were applied to explore the effect of fillers on the structural features of PVC polymer. The effect of FeCr2O4 and/or TPAI on the linear/nonlinear optical properties of PVC was explored. Absorbance was obviously enhanced, and transmittance reduced in the range 200–450 nm upon doping with TPAM. The refractive index and reflectance were increased by loading FeCr2O4. The direct (4.25 eV) and indirect (4.1 eV) bandgap values of the pure PVC were reduced to 4.21 and 3.95 eV upon loading with FeCr2O4; both reduced further, but irregularly, as the amount of TPAI increased attaining lowest values 3.11 and 2.62 eV for TPAI content 2.5 wt%. The optical conductivity and the dielectric constant were greatly enhanced by TPAI doping, while the nonlinear optical parameters were improved by FeCr2O4 loading. Under different excitation wavelengths, the fluorescence intensity was quenched upon loading FeCr2O4, then reduced a little by adding TPAI; the corresponding CIE chromaticity diagrams were obtained. [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]

Ceramic cores are the key intermediate components of hollow blades for aero-engine. Conventional processes, such as hot-press molding and gel film casting, face difficulties in fabricating complex-structured ceramic cores due to the complexity of moulds and long process cycles. Stereolithography 3D printing provides a new idea for the fabrication of complex-structured ceramic cores. The effect of sintering temperature on open porosity, bulk density, weight loss rate, shrinkage rate, flexural strength and microstructure of the Al2O3-based ceramic core doped with 10vol.% polysilazane (PSZ) was studied. The sintering mechanism of PSZ-reinforced ceramic cores was analyzed. Results show that the optimum sintering temperature of PSZ-reinforced ceramic cores is 1,450 °C. At this temperature, the open porosity of the ceramic core is 36.60%, bulk density is 2.33 g·cm-3, weight loss rate is 22.11%, shrinkage rate along the X, Y, Z directions is 5.72%, 5.01%, 9.61%, respectively; the flexural strength is 28.794 MPa at 25 °C and 13.649 MPa at 1,500 °C. Properties of 3D printing PSZ-reinforced ceramic cores can meet the casting requirement of superalloy hollow blades, which is expected to promote the industrial application of 3D printing complex structure ceramic cores. [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]

Excessive sintering shrinkage leads to severe deformation and cracking, affecting the microstructure and properties of porous ceramics. Therefore, reducing sintering shrinkage and achieving near‐net‐size forming is one of the effective ways to prepare high‐performance porous ceramics. Herein, low‐shrinkage porous mullite ceramics were prepared by foam‐gelcasting using kyanite as raw material and aluminum fluoride (AlF3) as additive, through volume expansion from phase transition and gas generated from the reaction. The effects of AlF3 content on the shrinkage, porosity, compressive strength, and thermal conductivity of mullite‐based porous ceramics were investigated. The results showed that with the increase of content, the sintering shrinkage decreased, the porosity increased, and mullite whiskers were produced. Porous mullite ceramics with 30 wt% AlF3 content exhibited a whisker structure with the lowest shrinkage of 3.5%, porosity of 85.2%, compressive strength of 3.06 ± 0.51 MPa, and thermal conductivity of 0.23 W/(m·K) at room temperature. The temperature difference between the front and back sides of the sample reached 710°C under high temperature fire resistance test. The low sintering shrinkage preparation process effectively reduces the subsequent processing cost, which is significant for the preparation of high‐performance porous ceramics. [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]

Gel casting is one of the new and promising methods for producing ceramics. Current research on the production of ceramic materials by gel casting covers a wide range of materials, including dense as well as porous ceramic materials. The advantages of this method, such as ease of processing, use of the process equipment of conventional methods, heightened productivity, and possibility of obtaining products having large shapes and complex geometries, are creating a surge in new R&D. This article reviews publications devoted to research conducted during recent decades on the production of both dense ceramics for the manufacture of structural elements and porous ceramics for the manufacture of thermal insulation, porous filters, and membranes by the gel casting method. [ABSTRACT FROM AUTHOR]

The objective of this study was to investigate the osteogenic and antimicrobial effect of bioactive glass S53P4 incorporated into β-tricalcium phosphate (β-TCP) scaffolds in vitro and the bone neoformation in vivo. β-TCP and β-TCP/S53P4 scaffolds were prepared by the gel casting method. Samples were morphologically and physically characterized through X-ray diffraction (XRD) and scanning electron microscope (SEM). In vitro tests were performed using MG63 cells. American Type Culture Collection reference strains were used to determine the scaffold's antimicrobial potential. Defects were created in the tibia of New Zealand rabbits and filled with experimental scaffolds. The incorporation of S53P4 bioglass promotes significant changes in the crystalline phases formed and in the morphology of the surface of the scaffolds. The β-TCP/S53P4 scaffolds did not demonstrate an in vitro cytotoxic effect, presented similar alkaline phosphatase activity, and induced a significantly higher protein amount when compared to β-TCP. The expression of Itg β1 in the β-TCP scaffold was higher than in the β-TCP/S53P4, and there was higher expression of Col-1 in the β-TCP/S53P4 group. Higher bone formation and antimicrobial activity were observed in the β-TCP/S53P4 group. The results confirm the osteogenic capacity of β-TCP ceramics and suggest that, after bioactive glass S53P4 incorporation, it can prevent microbial infections, demonstrating to be an excellent biomaterial for application in bone tissue engineering. [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]

Polymer networks incorporated with iron and zinc oxide nanoparticles have superparamagnetic and electrical characteristics where it can be employed in a variety of significant applications. To achieve optimal distribution and connection of nanoparticles in various polymeric matrices, it is required to investigate their dispersion performance with varied contents and the impact on their physical characteristics. A controlled sol-gel method is used combined with gel casting to synthesize organic-inorganic nanocomposites of (ZnO)x(1 − x)Fe2O3 loaded within a polystyrene-polyethylene glycol matrix. The structural and morphological assembly of the hydrogen bonds between the inorganic and organic parts is verified using X-ray diffraction (XRD) and scanning/transmission electron microscope (SEM/TEM) for the synthesized nanocomposites. The existence of the Fe aggregates, Zn/Fe pairs, and organic molecules was also confirmed by FTIR spectra. Optical and magnetic properties were evaluated. The band gap, refractive index, optical dielectric constant, and optical electronegativity were extracted. [ABSTRACT FROM AUTHOR]

The objective of this paper is to present an overview of the development of gel casting methods on synthesis techniques and the characteristics of gel casting porous ceramics and its applications. The gel casting method is a colloidal ceramic synthesis method that requires a short period for the ceramic body to develop. This review provides the latest developments in the gel casting process of synthesizing porous ceramics. At the beginning of the gel casting method development, the acrylamide (AM) system was the most commonly utilized system. Over time, the use of the AM system began to be minimized because of its toxicity. Researchers began to develop natural polymers as pore templates and natural minerals as raw materials in the gel casting method. In addition to polymers and raw materials, the gel casting process also requires additives such as gelling agents and dispersants. At the end of this review, a mapping of how to select the additives in the gel casting process, for AM systems and non-AM systems for the fabrication of porous ceramics is presented. The characteristic of porous ceramics produced by AM and non-AM systems are almost similar. Porous ceramic applications have been used as bone tissue supports, energy storage, filters, and catalyst support. This review will be a reference for future research related to the process of fabrication of advanced porous ceramics using the environmentally friendly gel casting method. [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]

Porous Si3N4 ceramics were prepared by gel casting combined with a reaction bonding route using monodispersed PMMA as the pore former, and Isobam was used as a gel agent. With the PMMA addition varying from 0 to 20 wt.%, the bending strength was degraded from 94.0 to 39.1 MPa owing to the increased porosity and decreased bulk density. The β‐Si3N4 prismatic grains and round pores introduced by the monodispersed PMMA micro balls would endow the samples with high strength, and the permeability of the resulting samples was increased obviously with the increase of PMMA addition. Flue gas filtration test exhibited that the filtration efficiency of the porous ceramics filter was not degraded with introducing of the PMMA pore former, even though the permeability was increased obviously. The block type of the sample with 20‐wt.% PMMA additions during filtration was cake filtration, which indicates that the sample has the characteristic of being reusable after back‐blowing in flue gas filtration applications. Porous Si3N4 with high strength and permeability fabricated via the reaction bonding route exhibits great potential for low‐cost high‐performance ceramics filters. [ABSTRACT FROM AUTHOR]

Low‐cost and environment‐friendly MgO was used as a new gelling and consolidating agent to fabricate porous Al2O3‐based ceramics via a gel casting routine. Effects of 800°C calcined additions of MgO (.5, 1.0, 1.5, and 2.0 wt%, respectively) on open porosity (OP), pore size distribution, gas flux, and microstructure of the porous ceramics were investigated deliberately. The experimental results showed that 800°C calcined MgO exhibits excellent gelling and consolidating performance at 80°C, mainly owing to the hydration reaction between MgO and H2O and thus results in high‐quality porous Al2O3‐based ceramics without deformation and cracking. The Al2O3–water suspensions with different MgO additions have good flowability at room temperature. Moreover, water absorption, open porosity, and gas flux of the as‐prepared porous ceramics increase remarkably with rising of MgO addition. Furthermore, MgO addition significantly suppresses the abnormal growth of Al2O3 grains, and thus the microstructure of the porous Al2O3‐based ceramics becomes more uniform. This technique of gel casting using MgO as a new gelling and consolidating agent offers an alternative routine for a large‐scale production of porous ceramics. [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]

The use of ceramic–metal laminated composites is an efficient way to improve the toughness of brittle ceramics. Uniform multilayered Al2O3–Ni laminated composites were prepared through a combined method of gel casting and hot pressing, which is less cumbersome than the traditional sequential lamination method. The wettability, diffusion and chemical reaction between Al2O3 and Ni were controlled through surface oxidation treatment of the Ni sheets. The results show that when the surface-oxidized Ni sheets were used, the microstructure of the Al2O3–Ni interface changed with the hot-pressing temperature. As the hot-pressing temperature was increased from 1150 to 1300 °C, a straight and clean interface formed, the interface became interlocked and, finally, a stable layer of NiAl2O4 formed at the interface. The interlocked microstructure was especially beneficial for interfacial bonding, and the plastic deformation of the Ni layers was restrained, thereby leading to slip steps rather than dimple formation on the fracture surfaces of the Ni layers. In addition, the toughening effects of plastic deformation and crack deflection in the Al2O3–Ni laminated composites were significant, which resulted in ductile fracture rather than brittle fracture. As a result, the Al2O3–Ni laminated composite that was prepared using the oxidized Ni sheets and the combined method of gel casting and hot pressing achieved a higher work of fracture than laminated composites that were prepared via other methods. [ABSTRACT FROM AUTHOR]

Phosphors-in-glass (PiGs) regarded as a promising phosphor-converter for white light emitting diodes (WLEDs) is being researched widely. However, there are few reports on the effect of changing the shape of PiGs on the color rendering index (CRI) and heat dissipation of WLEDs. In this paper, gel casting with Isobam was first attempted in preparing special-shaped PiGs successfully. It exhibited that 76 wt.% was the optimum solid content based on the rheological properties of slurry and the shrinkage of green bodies. The sintering rate should be kept at a low speed and glass transition temperature (Tg) of glass powders must be higher than sublimation temperatures (Ts) of APS and Isobam. The CRI of PiGs was increased by about 27% after changing the shape of PiGs from cylinder to dome. Most importantly, operating temperature also reduced effectively the increase of the surface area of PiGs. Therefore, changing the shape of PiGs by gel casting with Isobam is a creative way for high-power WLEDs lighting. [ABSTRACT FROM AUTHOR]

MgAl2O4 transparent ceramics were shaped by a commonly used polyacrylic acid (PAA), which acted as both dispersant and gelling agent. The spinel slurries were prepared by ball‐milling MgAl2O4 powder, PAA, and water in an attrition mill. The gelling of slurries happened at room temperature in air atmosphere without any other organic additive. The gelling mechanism was the formation of chelates between Mg2+ and carboxyl groups (‐COO−) of PAA. The frequency‐based testing method was applied to investigate the gelling process of the as‐prepared slurry. In addition, a novel in situ characterization method based on a modified indentation testing was invented to better understand the strengthening of the wet green body with time and to guide when demolding could be carried out. After sintering, transparent MgAl2O4 ceramics with high in‐line transmittance were resulted. [ABSTRACT FROM AUTHOR]

Porous alumina, with monodispersed PMMA as pore former and Y2O3 as sintering additive, was prepared via a gel casting route with Isobam as a gelling agent. The effects of PMMA addition on its properties, including apparent porosity, bulk density, strength, permeability, and corrosion resistance to acid/alkali, were investigated. With PMMA addition increased, the apparent porosity and permeability were increased obviously, while strength and corrosion resistance to acid/alkali were deteriorated due to increased porosity. Higher firing temperature resulted in lower porosity, higher strength, lower permeability, and better corrosion resistance to acid/alkali. Coarser raw powders resulted in lower strength and higher permeability due to the coarser structure and larger pores of the fabricated samples. Because Y2O3 was used as a sintering additive, and no silica was introduced, the resulting samples possess better corrosion resistance to acid and alkali, especially much better corrosion resistance to alkali, than those reported with silica introduced. [ABSTRACT FROM AUTHOR]

Mullite‐bonded porous SiC ceramics sintered in air by gelcasting are still challenges due to the high porosity induced severe oxidation of SiC, which results in the formation of large amount of detrimental cristobalite phase. Here in this work, small amounts of Y2O3 and CaF2 were added in SiC and Al(OH)3 raw materials as sintering additives for the in situ growth of mullite reinforcement. This additive system promoted the reaction between oxidation‐derived SiO2 from SiC and Al2O3 decomposed from Al(OH)3 to mullite phase. Almost no cristobalite phase was detected when sintered at 1450℃/2 h with CaF2 addition of more than 2.0 wt%. Mullite whisker reinforcement was in situ formed due to the gas reaction mechanism caused by CaF2 addition. Thus obtained porous SiC ceramics exhibited a flexural strength of 67.6 MPa at porosity of 41.3%, which maintained exceeding 36 MPa after 8 h corrosion in 10 wt% NaOH 80℃ solution, being the best performance up to now. This high performance of porous SiC was attributed to the additive induces proper phase control and in situ formation of whisker‐like mullite reinforcement. [ABSTRACT FROM AUTHOR]

Tetragonal zirconia polycrystals (TZP) represent a favorite material for monolithic ceramic dental restorations. However, all approaches employed so far to improve the translucency of dental zirconia ceramics are accompanied by a significant decline in strength. In this investigation, we developed dental 3Y‐TZP ceramics that can provide excellent strength combined with enhanced translucency. The machinable tetragonal zirconia discs and blocks were prepared from fine mesostructured zirconia particles stabilized with 3 mol% of yttria using the gelcasting method. Zirconia ceramics with an average biaxial strength of 1184 MPa and translucency of 41.1% for a 1 mm thick sample were obtained. Due to its unique microstructure, this tetragonal ceramic provided a favorable combination of high translucency comparable to the high‐translucent, tetragonal/cubic 4Y‐TZP and very high strength achievable only in the pure tetragonal 3Y‐TZP. The applicability and resistance to low‐temperature degradation of the new dental ceramics was demonstrated. [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]