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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]

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]

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]

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]

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]

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]

In this research, we studied a roller‐compacted concrete (RCC) arch dam which was reinforced during the construction period to investigate the properties of mechanical parameters of the dam concrete after long‐term operation. Firstly, multiple methods involving core drilling, computerized tomography (CT), spectral analysis of the surface wave (SASW) of elastic waves, and an on‐site inspection were adopted to detect the quality of the dam concrete, which was followed by a forward‐analysis of the measured displacement of the arch dam and the water pressure component of the measured displacement was separated through regression analysis of statistical model of radial horizontal displacement. Subsequently, an optimization inversion of the elastic modulus of the dam body and dam foundation was conducted using a hybrid optimization method. The results showed that the compressive strength of the concrete in the body of the reinforced arch dam was over 30 MPa and the inversion results for the elastic modulus of the dam body were in the range of 30.1 ~ 33.3 GPa. According to the research results of multi‐source inspected and monitoring data during the operation period, the results suggest that the performance of the concrete of the dam body is in accordance with design requirements and the reinforced arch dam is properly operated. [ABSTRACT FROM AUTHOR]

In this work, a fabrication route combined optimized ISOBAM‐104/TAC gel‐casting (where TAC refers to triammonium citrate) and one‐step sintering technology was developed to prepare highly transparent LaxGd2‐xZr2O7 (LGZO) ceramics. The gelling behavior in an alkaline environment was investigated, and the corresponding mechanism was systematically proposed for the advanced spontaneous gel system. The starting materials after ball milling were directly shaped into green bodies without any treatment, and high‐quality LGZO ceramics were obtained by three‐stage debinding and one‐step sintering. The in‐line transmittance of these ceramics reaches 74% at 1100 nm, which is about 95% of the theoretical value. This work not only establishes an efficient method to fabricate LGZO ceramics in large and complex shapes but also elucidates the gelling mechanism in alkaline, which expands the application of gel‐casting technology in transparent ceramics. [ABSTRACT FROM AUTHOR]

Thermal insulators were fabricated by freezing gelatin gels containing calcined kaolinite with alumina nanofibers, followed by sintering. The resultant porosity could be varied from 81.0% to 89.8% by solid loadings in the initial slurry. The relationship among porosity, microstructure, compressive strength, and thermal conductivity was examined. The compressive strength and thermal conductivities of the insulators prepared with initial solid loadings from 3 to 6 vol% ranged from 11.6 to 56.7 MPa and from.25 to.46 W/mK, respectively. Those properties were also estimated by simulation using modeling of overall pore morphology, resulting in good agreement. [ABSTRACT FROM AUTHOR]

The cooling of a melt corresponding to the eutectic between wollastonite (CaSiO3) and diopside (CaMgSi2O6) determines the synthesis of an interesting example of alkali‐free bioactive glass, easily converted into glass‐ceramics featuring two silicate phases, coupled also with åkermanite (Ca2MgSi2O7), by sinter‐crystallization of fine glass powders at 1000°C. The fabrication of scaffolds by digital light processing of glass powders suspended in a photo‐curable, sacrificial binder, is a well‐established technique; the present paper aims at disclosing novel approaches, concerning the topology of scaffolds, offering components with remarkable strength, especially in bending conditions. As an alternative, glass‐ceramic foams were fabricated by the firing of porous precursors derived from the gelation of suspensions of glass powders in alkali‐free basic aqueous solution. [ABSTRACT FROM AUTHOR]

To clarify the densification law of dry pressed MgTiO3 ceramic body during pressureless sintering, SOVS model (Skorohod‐Olevsky Viscous Sintering model) modified with creep characteristics was embedded into finite element software Abaqus. The selected model can effectively express the grain boundary characteristics and densification mechanism. The change law of relative density, shrinkage rate, sintering stress, and grain size of MgTiO3 cylindrical specimens was investigated by the above numerical simulation method. It showed that the average relative density of ceramic body rose from 60% to 97%, and the shrinkage rate respectively reached 17.28% and 11.99% in axial and radial direction. The average grain size increased from 1 to 6 μm. In order to verify the accuracy of the simulation results, corresponding sintering experiments on cylindrical specimens were carried out to obtain actual sintering densities and shrinkage rates. It showed that the errors of relative density and shrinkage were below 5% and 2%. Grain growth trend was also basically consistent with the simulation results. After that, the above numerical simulation method was applied into the prediction of fabricating MgTiO3 filter with complex structure. Therefore, the present work provided a reliable numerical simulation method to predict the densification behavior of MgTiO3 ceramics during the pressureless sintering process, which was helpful to design and fabricate microwave dielectric products. [ABSTRACT FROM AUTHOR]

The Si‐rich pressureless sintering was used to fabricate the Ti3SiC2 bulk ceramic. The results show that the optimized Ti3SiC2 suspension could be prepared at the absolute value of zeta potential, pH level, PAA‐NH4 dosage, and solid loading of 62.1 mV, 11, 2.0 wt%, and 50 vol%, respectively. The channels existing in the Si‐free sintered body facilitated the reactants and products to diffuse to the interior and out of the Ti3SiC2 matrix, thereby forming the porous reaction layer of TiC‐Ti3SiC2. The co‐effects of the channels and the reaction layer of TiC‐Ti3SiC2 severely lowered mechanical properties of the Si‐free sintered Ti3SiC2 ceramic. On the contrary, the Si‐rich sintering method isolated the volatile carbon and established a closed Si‐rich atmosphere to sinter the green Ti3SiC2 cylinder. The porosity, density, fracture toughness, hardness, and flexural strength of the Si‐rich sintered Ti3SiC2 ceramic reached 0.74 vol%, 4.36 g/cm3, 5.49 MPa·m1/2, 4.03 GPa, and 383 MPa, respectively. [ABSTRACT FROM AUTHOR]

The aim of this paper was to establish the general suitability of the centrifugal slip casting technique for fabrication of graded material from the Al2O3–Cu–Ni system. The present investigation is a preliminary one and the obtained results may be regarded as a point for acquiring the new knowledge in the ternary ceramic metal system fabricated using centrifugal slip casting. The rheological study provided the evidence that the suspension used to fabricate composites is a non‐Newtonian slurry. Moreover, the results demonstrated that the prepared slurry is stable over time. The obtained composites has a hollow cylindrical shape with relative density of > 95%. The XRD study results revealed three phases: Al2O3, Ni, and CuNi. The microscopic investigations revealed a nonhomogeneous distribution of the metallic phase in the composite. It has been shown that the content of the metallic phase decreased with the increased distance from the outside to the inner edge of the ceramic‐metal composite. The study results allow to conclude that the interface between the phases is more continuous when sintering was carried out in a solid phase. However, it was found that when sintering was carried out in a liquid phase separated metal particles with spherical phase are formed. [ABSTRACT FROM AUTHOR]

Three‐dimensional (3D) diamond structure photonic crystals (PhCs) with planar defects were fabricated with alumina using 3D printing combining gel casting, sintering process, and vacuum freezing‐dry technique. In this article, the influences of twinned planar defect and the positions of planar defect in a single lattice period on the transmission properties of the electromagnetic wave (EM) in the PhCs is studied. The normalized resonant intensities are 0.5 for twinned planar defected photonic crystals (PhCs). When the planar defect position lies in the nonkey positions (key position is n*(a/4)), the band gap becomes narrow and the resonant peak disappears. When the twinned planar defected with different interval periods is integer, obvious resonant peaks can be found in the EM band gap of the planar defects PhCs with 2 and 3 symmetrical periods. When a PhC with two planar defects is constructed, its band gap width increases and the resonant peaks intensities decrease. [ABSTRACT FROM AUTHOR]

A potentially near‐net‐shape manufacturing procedure for macroporous alumina monoliths with 20%‐75% porosity was presented by gel casting of nano γ‐Al2O3. Although monolith obtained by nano alumina had a high surface area and low sintering temperature, an optimum fraction of micron alumina needed to be added to achieve the proper rheological and mechanical properties of slurries. The preparation parameters including alumina loading, sintering temperature, monomer concentration, and the fraction of nano alumina were investigated. The green densities ranging from 0.66 to 0.86 g cm−3 were obtained by raising alumina loading from 10 to 20 vol%. Depending on the monomer concentration and sintering temperature, the mean pore size ranging from 45 to 412 nm, total porosity (20%–75%), and open porosity varying from 12% to 89% were obtained. The sintered density (from 0.95 to 3.15 g cm−3) and compressive strength (CS) (from 4.2 to 31.46 MPa) were suitable for use in different fields. [ABSTRACT FROM AUTHOR]

Impeller is the key part of centrifugal pump to convey liquid. And combined with the engineering practice, we fabricated two types of open and semi‐open SiC ceramic impellers with diameter of 100 mm and 160 mm via gelcasting and pressureless sintering. B4C and C were used as the sintering additives and sprayed drying granulation method was adopted for the starting SiC powder processing. Given the size and shape complexity of impeller, the optimized pH value, dispersant content, and solid‐loading content for the fabrication of the SiC impellers were determined to be 10‐11, 0.8 wt%, and 40 vol%, respectively. For the open impeller, blade height, cover board thickness, drying shrinkage, and sintering shrinkage are 10.5 mm, 4 mm, 10.3%, and 21.3%, respectively. For the semi‐open ones, the corresponding parameters are 41 mm, 10 mm, 10.3%, and 21.3%, respectively. The average density of the two types of impellers is 3.15 g/cm3, and the mechanical properties of both impellers, including average hardness, flexural strength, compressive strength, and fracture toughness are 2478 HV, 436 MPa, 2093 MPa, and 3.17 MPa·m1/2, respectively. All variation coefficient values are smaller than 5%, which indicates a good uniformity in densities and mechanical properties of both the impellers. [ABSTRACT FROM AUTHOR]

The investigation of a novel gel‐casting system using a water‐soluble co‐polymer of isobutylene and maleic anhydride (trade name ISOBAM) to elucidate its nontraditional gelling mechanism is described. This system enables ceramic slurries to gel at low binder concentrations (0.3‐0.5 wt%), producing a dense, near‐net shaped green body with high solids loading, low organic content, low shrinkage, and moderate strength. The nature of the stabilizing bonds formed during gelation were investigated using Fourier‐transform infrared spectroscopy (FTIR), zeta potential, and rheological measurements which revealed that no covalent network was formed during gelation. It was concluded that the mechanism was based solely on weak interactions. As such, the ISOBAM casting system, and polymeric additive systems that behave similarly, represent a new class of near net‐shaped ceramic processing which could benefit a variety of applications, including ceramic additive manufacturing. [ABSTRACT FROM AUTHOR]

Gel‐casting method was used to fabricate mullite ceramics because this method has not been applied to fabricate dense mullite in literature. Gel‐casting parameters such as monomer types (acrylamide and metyhlenebisacrylamide), effect of initiator (ammonium persulfate), and catalyst (tetramethylenediamine) were studied. All samples reached to relative densities of 97% to 98.2% after sintering at 1540°C for 2 hours. Backscattered SEM images revealed anisotropically grown mullite grains, glassy phase located at triple junctions, hexagonally‐shaped and faceted Al2O3 grains, and white‐color grains consisting of ZrO2 and undissolved TiO2. A Weibull modulus of 12.33 (ie, indicating tough ceramics) and characteristic strength of 186 MPa were calculated, below which no failure was expected. A critical quenching temperature was found as about 400°C (ΔT ~ 380°C) by indentation‐quench method. In addition, a thermal shock resistance parameter (eg, R in °C) of 142.4°C was calculated, which was higher than commonly used Al2O3 ceramics. Lower dielectric constant and loss are desired for wide frequency band application and shorter signal transmission delay time in radomes. The dielectric constant was found as nearly 7.5 up to 10 GHz and loss tangent was 0.0031 at 5 MHz. Dielectric and thermomechanical results suggest that mullite is a suitable candidate ceramic for radome applications. [ABSTRACT FROM AUTHOR]

An approach using AM‐MBAM and Na‐alginate double‐gel was proposed to avoid the cracking of ceramic impingement holes cores (CIHCs) during pyrolysis processing. Finite element analysis (FEA) was used to calculate the thermal stress that caused CIHCs cracking. For ceramic slurry with a double‐gel containing various proportions of alginate, the addition of 15.0 wt.% alginate was the most beneficial for the rheological and mechanical properties of Al2O3‐based ceramic obtained by aqueous gelcasting based on the double‐gel network had a dramatically pyrolyzing strength of 14.1 MPa, which was 72.0 % higher than that of the ceramics based on the single AM‐MBAM system. The double‐gel network was responsible for the improved strength. By comparing the thermal stress with pyrolyzing strength, it was predicted that the available diameter of CIHCs was greater than 0.7 mm. Finally, CIHCs with a minimum diameter of 0.7 mm were successfully fabricated, consistent with the FEA prediction. [ABSTRACT FROM AUTHOR]

In this article, isocyanate was adopted to modify Y2O3 powder for the purpose of preparing transparent Y2O3 ceramics via gel casting. The modification could enhance the hydration resistance of Y2O3 powder through the steric hindrance effect. The coating mechanism can be proved by the infrared spectrum of the surface‐modified Y2O3 powder. Modification could not only prevent Y2O3 particles from reacting with water, but also prevents agglomeration between particles. The viscosity of the slurry with a solid content of 52.7 vol% is only 0.48 Pa·s at the shear rate of 100 s−1, which is suitable for preparing high‐density compacts by gel casting. The transmittance of the sample (1840°C × 8 h, 1 mm thickness) at 1100 nm reaches 75%. The microstructure of the sintered body is dense with the average grain size of 6.5 μm without obvious impurities nor pores. Five mol% ZrO2‐doped Y2O3 transparent ceramic fairing with the diameter of 5 cm without defects was successfully fabricated by gel casting (52.7 vol% solid volume) and vacuum sintering (1840°C × 8 h). [ABSTRACT FROM AUTHOR]

Magnesium aluminum oxynitride (Mg0.27Al2.58O3.73N0.27, termed as MgAlON) ceramics with high transparency and complicated shape was prepared by aqueous gelcasting, pressureless sintering, and followed by hot isostatic pressing. No obvious hydration was found by the characterizations of X‐ray diffraction, pH value, Fourier transform infrared and thermal analysis for the interaction between MgAlON spinel powders and water, leading to the stable MgAlON slurry with high solid loading (52 vol%) and low viscosity. This result may be due to different composition of MgAlON from that of MgAl2O4 and AlON. Besides, transparent MgAlON ceramic (1.95 mm in thickness) with a high in‐line transmittance ~86.3% at 3.7 μm was fabricated. The refractive index ~1.7499 at 589.3 nm and absorption coefficient ~1.2 cm−1 at 5 μm of MgAlON are between those of AlON and MgAl2O4 transparent ceramics, and Abbé number ~73.66 of MgAlON is the highest. [ABSTRACT FROM AUTHOR]

Tm3+‐doped mixed sesquioxide transparent ceramics are attractive candidates for the generation of robust ~2.1 μm lasers. In this paper, laser‐quality Tm:(Lu0.8Sc0.2)2O3 mixed sesquioxide ceramics were shaped for the first time by gelcasting of well‐dispersed nanopowders, which were obtained using a modified coprecipitation method. The dispersibility of starting nanopowders was largely improved using alcohol‐water solvent. The rheological properties of slurries were optimized for gelcasting. We also investigated the densification behavior of the gel‐casted green compacts. In contrast to the dry‐pressing route, it was found that gelcasting could yield more homogeneous and transparent ceramics. The optical in‐line transmittance of the ceramic rod 12 mm in length was as high as 80.3% at 2090 nm. Upon pumping the ceramic rod by 796 nm diode laser, a 1.88 W CW laser at 2090 nm was acquired with a slope efficiency of 24.6% (with respect to the input pump power). [ABSTRACT FROM AUTHOR]

The ethanolaminic salt of citric acid (commercial name Dolapix CE 64) has commonly been used as a dispersant for colloidal based ceramic forming process. In this paper, a surprise was presented that MgAl2O4 spinel slurries consisting of MgAl2O4 spinel nanoparticles and Dolapix CE 64 gelled in air at room temperature spontaneously. The MgAl2O4 spinel slurries with high solid loading (54 vol%) were prepared with Dolapix CE 64 and the green body with up to 57% relative density was obtained. MgAl2O4 transparent ceramics with small grain size (0.92 μm) and high transmittance (81.7% at 600 nm) were fabricated after pre‐sintering at 1500°C and hot‐isostatic sintering at 1550°C. [ABSTRACT FROM AUTHOR]

Porous Al2O3 ceramics with different contents of alumina fibers were prepared by gel‐casting process. The effects of Al2O3 fiber content on pore size distribution, porosity, compressive strength, and load‐displacement behavior of the ceramic materials were investigated. Initial results showed that with the increase of Al2O3 fiber content, the pore size and porosity of the material is increased, and the compressive strength is decreased. However, upon increasing the fiber content from 50 wt% to 67 wt%, the performance of the samples changed greatly. The compressive strength of the material increased, while the porosity remained unchanged, the pore size increased greatly, and the shape of the load displacement curve changed. It showed that when the fiber content increased from 50 wt% to 67 wt%, the loading body in the fiber‐reinforced porous ceramics changed from particles to fibers. [ABSTRACT FROM AUTHOR]

Abstract: In this paper, we report on a study of electronically conductive porous TiN ceramics prepared by aqueous gel‐casting. The effects of solid loading, sintering temperature, and sintering aids on the phase composition, microstructure, and volume fraction of porosity of the prepared porous TiN ceramics are studied. The SEM results show that porosity is uniformly distributed in all of the samples studied. With increasing solid loading and sintering temperature, the volume fraction of porosity decreases slowly. Moreover, the relationship between volume fraction of porosity and mechanical and electrical properties has also been investigated. Our results show that adding Y2O3‐TiO2 as combined sintering aids results in a sharp decrease in the volume fraction of porosity, and the volume fraction range changes from 42%‐60% to 28%‐52%. Moreover, adding sintering aids results in an increase in flexural strength and electrical conductivity with a change in maximum value from 34.6 MPa and 2.3 × 104 S∙m−1 to 101.6 MPa and 5.1 × 104 S∙m−1, respectively. [ABSTRACT FROM AUTHOR]

Abstract: In this study, Ti2AlC foams were fabricated by direct foaming and gel‐casting using agarose as gelling agent. Slurry viscosity, determined by the agarose content (at a fixed solids loading), as well as surfactant concentration and foaming time were the key parameters employed for controlling the foaming yield, and hence the foam porosity after sintering process. Fabricated foams having total porosity in the 62.5‐84.4 vol% range were systematically characterized to determine their pore size and morphology. The effect of the foam porosity on the room‐temperature compression strength and elastic modulus was also determined. Depending on the amount of porosity, the compression strength and Young's modulus were found to be in the range of 9‐91 MPa and 7‐52 GPa, respectively. Permeability to air flow at temperatures up to 700°C was investigated. Darcian (k1) and non‐Darcian (k2) permeability coefficients displayed values in the range 0.30‐93.44 × 10−11 m2 and 0.39‐345.54 × 10−7 m, respectively. The amount of porosity is therefore a very useful microstructural parameter for tuning the mechanical and fluid dynamic properties of Ti2AlC foams. [ABSTRACT FROM AUTHOR]

Abstract: The freeze‐cast ceramics process involves the use of an aqueous slurry in which ice acts as a fugitive template, providing control of the morphology of the resultant green body, which is then sintered. Here, we report a variety of applications of ice‐templated ceramics, showcasing the versatility of the process. Applications include: as a suitable scaffold for silver loading and release at concentrations that could show antibacterial properties; as a component of a robust composite material with negative thermal expansion but reduced material cost; as thin porous structures for dye‐sensitized solar cells. [ABSTRACT FROM AUTHOR]

Abstract: Machinable hydroxyapatite foams for subtractive manufacturing of customized bone scaffolds have been developed. The foams were prepared by direct foaming of water‐based hydroxyapatite suspension with dissolved epoxy resin. The foams were consolidated by gelation of the epoxy‐based suspension in air atmosphere. The effect of processing conditions on the foam structure was investigated. The foams had a cellular‐like structure with interconnected pores. The sintered foam with 78% open porosity, the most frequent pore size 430 μm, and the most frequent interconnecting pore window size 150 μm, has been chosen as the foam with the optimal structure from the viewpoint of an application in bone regeneration. The compressive strength of this sintered foam reached 3.3 MPa. The machinability of the optimal foam was investigated using computer numerical controlled (CNC) milling of a test pattern. The milling tests were carried out with the foam at different processing stages and after impregnation with paraffin wax. The best milling result was obtained for a dried foam impregnated with paraffin. The applicability of the whole processing chain was demonstrated and a customized scaffold was manufactured. [ABSTRACT FROM AUTHOR]

Foam-gelcasting-freeze drying method is developed to fabricate porous Y2SiO5 ceramic with ultrahigh porosity of 92.2%-95.8% and isotropous multiple pore structures. As prepared porous samples have quite low shrinkages of 0.8%-1.9% during demolding and drying processes, lightweights of 0.19-0.35 g/cm3, and extremely low thermal conductivities of 0.054-0.089 W·(m·K)−1. Our approach combines the merits of foam-gelcasting method and freeze drying method. It is a simple and effective method to fabricate porous ceramics with very high porosity and extremely low thermal conductivity through low shrinkage of green body and near net complex shape forming. [ABSTRACT FROM AUTHOR]

Abstract: A novel kind of 3D interconnected porous carbon‐bonded B4C preform with flexural strength of about 20MPa is fabricated by gel‐casting method. As the control, the B4C/C preforms via molding‐produced method are fabricated. The B4C/C preforms own the same carbon content and almost the same porosity with different molding method. Compared with the conventional compression molding‐produced B4C/C preform, the 3D‐interconnected porous carbon‐bonded boron carbide preforms afford three‐fold advantages in the fabrication of reaction‐bonded boron carbide (RBBC) composite via the liquid silicon infiltration (LSI) process, including induced formation of continuous SiC‐bonded boron carbide skeleton structure, a reduction in the size of residual silicon, and prevented the coarsening of ceramic grains as well. As a result, the RBBC composite fabricated by gel‐casting appears as a more refined structure resulting in enhanced mechanical properties: the Vickers hardness, flexural strength, and fracture toughness of I‐GC composites fabricated from 3D‐interconnected porous carbon/B4C preforms are 19.4 ± 1.3 GPa, 389 ± 17 MPa, and 4.37 ± 0.1 MPa·m1/2, respectively, which are statistically higher than those of RBBC fabricated by the conventional compression molding‐produced B4C/C preform. [ABSTRACT FROM AUTHOR]

Pure anorthite porous ceramics have been fabricated using γ-Al2O3, CaCO3, and SiO2 as raw materials through foam-gelcasting method. XRD, thermal analysis, SEM, and TEM were used to study the synthesis and grain growth of anorthite during the in situ process. The results indicated that the initiator (ammonium presulfate) took part in the chemical reaction to form CaSO4, which played an effective role during synthesis of anorthite. Besides, CaO and CaSiO2 were the other intermediate phase during synthesis. Anorthite first occurred at 1050°C, and it was the only phase after it sintered over 1260°C. With sintering temperature increasing from 1300°C to 1450°C, the large sphere pore wall got denser and the anorthite grains obviously showed platelike. It was deduced that the preferential growth of anorthite crystals was parallel to the (004) plane. [ABSTRACT FROM AUTHOR]

This work investigates the influence of eight different vegetable and animal sources of fatty acids as soap foam precursors in the processing of highly porous geopolymers. Four sources rich in saturated chains (coconut and babassu oils, palm stearin and beef tallow), two sources rich in monounsaturated chains (olive and castor oils) and two sources rich in polyunsaturated chains (sunflower oil and soybean biodiesel) were selected. For all soap precursors, bodies treated at 300°C possessed a very high total porosity (84-88 vol%), open porosity (79-85 vol%) and relatively high specific surface area (35.1-63.5 m2/g), but rather low compressive strength (0.2-0.4 MPa). The increase in the thermal treatment temperature caused a slight decrease in porosity but a substantial increase in compressive strength and decrease in specific surface area due to sintering and formation of crystalline phases. The Darcian permeability coefficients of all bodies (0.6-10.6×10−10 m2) were typical of gelcasted foams, aerosol filters and fibrous mats. The morphology of pores could be well-associated to the features of lathers produced by the respective soap precursors. [ABSTRACT FROM AUTHOR]

Fused silica ceramics was prepared by using conventional organic binder, mathacrylamide- N, N′-methylenebisacrylamide ( MAM- MBAM) system by gelcasting process. Mechanical properties of green bodies were studied as a function of solid loading varying from 60 to 72 vol%. After evaluating the green body mechanical properties, the samples were densified at different sintering temperature from 1200 to 1450°C with definite intervals of 50°C and subjected to flexural strength analysis. Variation in flexural strength with sintering temperature was observed and correlated with the quantity of devitrification of fused silica during sintering. Quantification of devitrified cristobalite was carried out by using 20 wt% rutile (TiO2) as an internal standard by X-ray diffraction. It was found that, as the cristobalite content increased, flexural strength decreased. Reliability studies were carried out for the samples having maximum flexural strength with and without crystalline content. Reliability studies have shown that for this organic binder system the sample sintered at 1300°C is crystalline free and most reliable product. The mechanical properties and reliability of this product processed with organic binder are compared with inorganic binder system. Results indicate that the sample fabricated using inorganic binder system is exhibiting high Weibull modulus and thus better reliability. [ABSTRACT FROM AUTHOR]

The study demonstrates the aqueous processing of solid-state-sintered SiC foams by gelcasting technique. Aside from increasing strength of green bodies, gelcasting monomers were the source of carbon additive which helped in sintering of SiC foams. Sintered foams with the relative density ( RD) between 0.44 and 0.11 were processed by direct foaming of SiC slurries followed by gelcasting and sintering. Structural analysis by X-ray tomography showed the presence of spherical pores with bimodal pore size distribution and the proportion of large size cell and their interconnectivity increased in low RD foams. SEM study revealed that decreased RD resulted in gradual changes in the strut microstructure from the grains with faceted interface to smooth interfaced grains. The analysis of changes in Young's modulus and thermal conductivity with RD were in agreement with the Ashby model for open cell foams. [ABSTRACT FROM AUTHOR]

Ethylene glycol diglycidyl ether ( EGDGE), a water-soluble epoxy resin, was used as a complementary gelling agent to improve the strength of alumina green bodies gelcast using PIBM (a copolymer of isobutylene and maleic anhydride acting as both dispersant and gelling agent) gelling system. The effects of EGDGE on the gelling behavior of PIBM- EGDGE aqueous solutions and alumina slurries, mechanical properties of the resultant alumina gels, green bodies, and sintered ceramics were evaluated. Gelation of both the solutions and the slurries was accelerated with the addition of EGDGE. The changes in storage modulus (G′) of the slurries during gelation were quite different from those of the solutions. With the addition of 0.6 wt% EGDGE, G′ of the gel from a slurry with 50 wt% solid loading and 0.3 wt% PIBM increased 63% (100 min of testing), and flexural strength of the resultant green body increased 167%. Such gels and green bodies are strong enough for subsequent processing. They resulted in presintered bodies with low porosity and sintered ceramics with high relative density and flexural strength. [ABSTRACT FROM AUTHOR]

Recently, we developed an efficient method for rapid drying and improving relative density of the gelcast green body. In this work, polymerization and rheological behavior of the thermoresponsive gelcasting system based on N-isopropylacrylamide were investigated. To initiate reaction of the system with 4 mL/L of catalyst, 0.25-0.5 mg/mL of initiator is considered optimal in the optimized temperature range 15-20°C. Suspensions with 40-55 vol.% solid loading still show shear-thinning behavior, which is favorable for mixing, degassing, and casting. The final storage moduli of consolidated suspensions are approximately 104 Pa, which is sufficiently high for gelcast green bodies. [ABSTRACT FROM AUTHOR]

An eco-friendly gelcasting system has been developed for the fabrication of alumina ceramics using alumina sol as a binder. 0.5 wt% of ammonium polymethacrylate dispersant was used based on total alumina solid loading to obtain completely dispersed slurry with high solid loading. Ceramic slurries having different volume percentage of alumina loading from 46 to 52 vol% in alumina sol were made, and the rheological properties were evaluated. 51 vol% of alumina slurry having viscosity 0.73 Pa.s with 2 wt% of alumina sol binder content per weight of alumina was optimized. The gelling behavior of concentrated slurry was evaluated by measuring storage modulus, and the consolidated green sample is homogeneous and exhibiting the bending strength of 4 MPa and 55% theoretical density. On sintering the sample at 1550°C for 2 h, the flexural strength was found to be 317 ± 30 MPa, and the corresponding theoretical density was 98%. [ABSTRACT FROM AUTHOR]

In this study, aluminum nitride ( AlN) ceramics were first prepared by aqueous gelcasting. The effect of various parameters such as concentration of N, N-dimethylacrylamide ( DMAA, as monomers), N, N′-methylenbisacrylamide ( MBAM, as cross-linking agent), ammonium persulfate amount ( APS, as initiator), solid content and polymerization temperature on AlN ceramics was discussed for aqueous gelcasting system. Finally, drying methods of aqueous gelcasting AlN green bodies were investigated. Aqueous gelcasting AlN ceramics, sintered at 1850°C for 4 h, had homogeneous grain size and little grain boundary phase, and the relative density, flexural strength and thermal conductivity of aqueous gelcasting AlN ceramics were 99.9%, 333(±10) MPa, 136(±9) W/(m·K), respectively. [ABSTRACT FROM AUTHOR]

The near-net shaping of gelcast ceramic parts can be achieved using freeze-drying technology. It was discovered that the cracks probably occurred inside the part during freeze drying due to the formation of liquid water. To explain the formation mechanism of cracks, the electrical resistance method was employed to measure the part's eutectic temperature which can be used to determine the freezing and melting state of the part. Affecting factors on cracking were investigated by testing the temperature and water loss of the part during the drying stage, and the cracks inside the part were detected through computed tomography ( CT). It was found that when the temperature of the part was higher than the eutectic temperature, the ice crystals at the sublimation front would melt, resulting in the formation of wet green body. The cracks will occur inside the part because great capillary forces are formed in the wet green body. Cracks could be controlled through reducing heat supply by lowing shelf temperature, decreasing pressure of the drying chamber or lowering the dried layer resistance against water vapor by improving the freezing temperature or reducing the solid loading of the part. [ABSTRACT FROM AUTHOR]

To achieve high-density green bodies, a novel route without needing high solids loading suspensions, that is postcontraction process has been developed. In this process, the wet green body is immersed in heated liquid desiccants (polyethylene glycol [ PEG] aqueous solution), which is prepared by gelcasting with thermoresponsive gel system. The density of green bodies is improved through releasing water quickly and shrinking rapidly. It is attributed to the cooperative action of the interior aggregation forces stemming from the shrinkage of network-structured polymer and the exterior osmotic pressure from PEG aqueous solution. Alumina nanoparticle green bodies with different solids loadings were prepared by gelcasting with PNIPAM Poly(N-isopropylacrylamide) gel system. The postcontraction process was almost completed in 30 min in liquid at 50°C, and meanwhile the bodies were almost dried. The relative densities of all green bodies and sintered parts are in accordance with each other, around 43% and 94%, respectively. [ABSTRACT FROM AUTHOR]

Gelcasting is a colloidal processing method for fabricating high-strength and complex shape ceramic green bodies. However, industry has been reluctant to use the gelcasting technique because the most commonly used gel, acrylamide ( AM), is a neurotoxin. Here, we report an attempt at the gelcasting of fused silica glass using a natural and nontoxic gel, glutinous rice flour ( GRF) as binder. The GRF-based aqueous system was found to behave excellently in the gelcasting process. Flexural strength of fused silica green bodies solidified with only 3 wt% GRF is up to 11.87 MPa. Bulk density and flexural strength of fused silica glass sintered at 1275 °C are 1.75 g/cm3 and 47.02 MPa, respectively. [ABSTRACT FROM AUTHOR]

Dense (97.3%) zirconium diboride (ZrB2) ceramics were obtained via gelcasting and pressureless sintering. Four wt% B4C was used as sintering aid. ZrB2, SiC, and B4C can codisperse well in the alkaline region, using a polyacrylate dispersant. Compared with monolithic ZrB2 (Z), the mechanical properties of ZrB2-SiC ( ZS) were enhanced. The Vickers hardness and fracture toughness of ZS were (13.1 ± 0.6) GPa and (2.5 ± 0.4) MPa m1/2, respectively. [ABSTRACT FROM AUTHOR]

Porous YSZ ceramics reinforced by different fibers were prepared by gel-casting with 15% solid content and pressureless sintering. The four kinds of fibers (mullite, aluminosilicate, Al2O3, and YSZ fibers) were added into the YSZ ceramics with the same 10% vol content. After sintered at 1500°C for 2 h, aluminosilicate and mullite fibers could not be found in the samples of porous YSZ ceramics, which showed they reacted with YSZ ceramics at high temperature, while YSZ and Al2O3 fibers still kept perfect after sintering. Furthermore, the influences of fiber content, sintering temperature, porosity of matrix materials on compressive strength and porosity of the porous YSZ ceramics were studied. The results showed that Al2O3 fiber showed more obvious reinforcing effect than YSZ fiber on porous YSZ ceramics. The fiber-reinforcing effects depend on fiber content, sintering temperature, and porosity of matrix materials. The fiber addition can improve the shrinkage behavior of porous ceramics during sintering and strengthen the skeleton of porous ceramics. [ABSTRACT FROM AUTHOR]

Porous mullite ceramics were fabricated from an industrial grade mullite powder by gelcasting process using fly ash cenospheres ( FAC) as a pore-forming agent. The influence of content of FAC and sintering temperature on the density and strength was evaluated. The microstructure showed that FAC can act as a sintering aid and a pore-forming agent. When the sintering temperature at 1200°C, porous mullite ceramics with a relatively high porosity (48.1-72.2%), low density (0.84-1.64 g/cm3), low thermal conductivity (0.16-0.22 W/m · K), and high compressive strength (6.21-14.70 MPa) have been obtained. [ABSTRACT FROM AUTHOR]

ZrB2-SiC green ceramics were fabricated by aqueous gelcasting based on single AM- MBAM, single Na-alginate, and double gel network system. ZrB2-SiC ceramics obtained by aqueous gelcasting based on AM- MBAM and Na-alginate double gel network had a dramatically highest green strength of 98.6 ± 5.1 MPa, which was 103% and 61% higher than that of ZrB2-SiC ceramics based on single AM- MBAM system and Na-alginate system, respectively. A 'scratch test' was conducted to evaluate the green machinability of as-prepared ZrB2-SiC ceramics. The ZrB2-SiC ceramics based on this double gel network was found to have the best green machinability. [ABSTRACT FROM AUTHOR]