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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]

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]

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]

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]

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]

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

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

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]

• New nonaqueous gel casting were proposed for dense Si 3 N 4 ceramic fabrication. • Multifunctional acrylates in PEI-OA stabilized slurries induced successful solidification. • Effects of OA content and acrylate structures on the gelation properties were clarified. • Gel casting were applicable to Si 3 N 4 –Y 2 O 3 –Al 2 O 3 –TiO 2 –AlN/α-terpineol slurries. • Gel casted green components were successfully densified by liquid phase sintering. A novel gel casting system using nonaqueous, multicomponent, and concentrated slurries was designed for manufacturing Si 3 N 4 dense ceramics with complex structures. The proposed process involves the dispersion of reagent particles in α-terpineol aided by the saturated adsorption of polyethyleneimine partially complexed with oleic acid (PEI-OA) as well as the addition of small amounts of multifunctional acrylates (MAs). The occurrence of the Michael additive reaction between the MAs and the remaining amines of PEI-OA fixed on the reagent particles resulted in a gradual increase in the viscosity of the slurry until its solidification. Using the Si 3 N 4 /α-terpineol slurry as a model system, the effects of processing parameters such as OA complex ratio, particle volume fraction, and MA structures on the solidification behaviors were systematically investigated. A slurry having higher particle concentration which was treated with PEI-OA comprised from lesser OA ratio found to effectively solidify within 2 h when mixed with MA having larger number of acryloyl group per molecule. The proposed gel casting process was then applied to the multicomponent Si 3 N 4 –Y 2 O 3 –Al 2 O 3 –TiO 2 –AlN/α-terpineol system. The gel casted complex structured green compacts were successfully densified up to 98% by liquid phase sintering at 1750 °C under 0.9 MPa N 2 gas pressure. [ABSTRACT FROM AUTHOR]

Ti 3 AlC 2 bulk ceramics were prepared via aqueous gelcasting followed by C-rich and Al-rich pressureless sintering. The optimized pH value, zeta potential, dispersant content, and solid loading content were determined to be 10, 72.6 mV, 1.6 wt%, and 52 vol%, respectively. Impurities at ppm level containing in the flowing argon could cause severe decomposition of gelcasted bulk Ti 3 AlC 2 , forming whiskers of Al 2 OC and Al 4 O 4 C and floccule of AlN. C-rich pressureless sintering resulted in the delamination of a duplex layer of Ti(CO) and Ti 3 (AlO)C x -Ti(O,C). The channels formed after debinding facilitated the outward diffusion of Al and the inward diffusion of O and C, and thereby promoting the decomposition of C-rich sintered Ti 3 AlC 2. The combined effect of the unclosed channels and the porous reaction Ti 3 (AlO)C x -Ti(O,C) layer brought a catastrophic reduction in the density and mechanical properties of the C-rich sintered Ti 3 AlC 2 ceramic. While the Al-rich pressureless sintering system isolated C, CO and N 2 and supplied a closed Al-rich atmosphere, thereby suppressing the decomposition reactions and promoting the sintering densification and ultimately leading to the superior in mechanical properties. The density, hardness, flexural strength and fracture toughness of the Al-rich sintered ceramic reaches 4.13 g/cm3, 4.36 GPa, 345 MPa, 4.79 MPa m1/2, respectively. [ABSTRACT FROM AUTHOR]

Ti 2 AlC bulk ceramic was produced via aqueous gelcasting followed by Al-rich pressureless sintering. The processing parameters were optimized and two pressureless sintering methods of Al-rich and C-rich were compared and analyzed.The results showed that stable Ti 2 AlC slurry and homogeneous green body can be obtained at the pH value, zeta potential, dispersant content and solid content of 10, 65.2 mV, 1.6 wt%, and 48 vol%, respectively. Impurities of 0.6 ppm O 2 and 0.2 ppm N 2 containing in the flowing argon promoted the thermal dissociation of the gelcasted bulk Ti 2 AlC, forming whiskers of Al 2 OC and cloud-like floccule of AlN and simultaneously resulting in the delamination of a duplex layer, an outer ring layer of Ti 3 AlC 2 and a loose and porous cracking layer of Ti 2 AlC–Ti 3 AlC 2. The synergistic effect of the porous reaction layer and the unclosed channels formed after debinding resulted in a severe decrease in the density and mechanical properties of the C-rich pressureless sintered samples. In contrast, the Al-rich pressureless sintering system can provide a strong and effective protection for the sintering of the gelcasted Ti 2 AlC green body. The density, hardness, flexural strength and fracture toughness of AlRC sample reached 3.98 g/cm3, 4.29 GPa, 341 MPa, 4.83 MPa m1/2, respectively. [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]

Highly transparent MgAl 2 O 4 ceramics have been fabricated by aqueous gelcasting combined with cold isostatic pressing (CIP), pressureless sintering and hot isostatic pressing (HIP) from high purity spinel nanopowders. The gelling system used AM and MABM as monomer and gelling agent. The influences of dispersant and PH on the rheological behavior of the MgAl 2 O 4 slurries were investigated. The spinel slurry with low solids loading (25 vol%) and low viscosity (0.15 Pa s) was obtained by using 6 wt% Duramax-3005 (D-3005) as dispersant. After CIP, the green body had a relative density of 48% with a narrow pore size distribution. The influence of sintering temperature on densification and microstructure was studied, choosing 1500 °C as the sintering temperature. After HIP (1650 °C/177 MPa/5 h), transparent MgAl 2 O 4 ceramic with the thickness of 3 mm was obtained, whose in-line transmittance was 86.4% at 1064 nm and 79.8% at 400 nm, respectively. The ceramic exhibited a dense microstructure with the average grain size of 23 μm. The Vickers hardness and flexure strength of the sample reached 13.6 GPa and 214 MPa, respectively. [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]

Abstract In this research, acrylate gel maker monomers Mathacrylamide (MAM) and Methylenebisacrylamide (MBAM) were used through a gel casting process to fabricate SiC bodies. Investigation of rheological behavior of suspensions showed that optimum amount of surfactant (Tetramethylammonium hydroxide) was equaled with 0.7 wt% of ceramic powders and ceramic powders could be added up to 37 vol% of solvent without any problems in casting. The effects of monomers content, monomers ratio and also solid loading on gelation time, bending strength of samples were investigated. Results showed that increasing the monomers content (MAM + MBAM) and ceramic solid loading led to the reduction of gelation time. Also alteration of these parameters resulted in variation of samples bending strength from ~6 MPa to 19 MPa, the best strength was obtained in the sample containing 35 wt% monomers with the MAM/MBAM ratio of 3 and 35 vol% SiC. Finally the samples containing different amounts of SiC were casted according to the pre-determined optimum parameters and after being dried they were sintered at 2150 °C for 1 h. According to the results, the highest density, Young's modulus, hardness and indentation fracture resistance were obtained in sample containing 37 vol% SiC and were equaled with 96.89%, 499.24 GPa, 27.51 GPa and 6.3 MPa·m1/2, Respectively. Microstructural studies showed that cleavage fracture planes, crack deflection and branching were the most important mechanisms on toughness enhancement. Highlights • Acrylate gel maker monomers were utilized to fabricate SiC bodies. • Minimum viscosity was obtained in the suspension containing 0.7 wt% TMAH. • Bending strength of green bodies, depending on the amount of monomers and monomers ratio, varied from ~6 MPa to 19 MPa. • Crack deflection, crack bridging and cleavage fracture are the most dominant toughening mechanisms. • The highest density, hardness and indentation fracture resistance were obtained in sintered sample containing 37 vol% SiC. [ABSTRACT FROM AUTHOR]

Abstract By utilising soaked millet as a shrinkable pore-forming agent, porous silicon carbide-alumina (SiC-Al 2 O 3) ceramics were prepared via gelcasting. The fabrication of SiC-Al 2 O 3 ceramics based on oxidised and unoxidised coarse-grained SiC was also studied. The water swelling, drying shrinkage, and low-temperature carbonisation of the millet were investigated. We found that the shrinkage of the soaked millet was greater than that of gel body during drying, which left large gaps that prevented shrinkage stresses from destroying the gel body. Low-temperature carbonisation of the millet should be performed slowly at 220–240 °C because its expansion rate increases to 45% at 250 °C, resulting in the cracking of samples. At a constant sintering temperature, the flexural strength of the SiC-Al 2 O 3 ceramics prepared with SiC powders oxidised at 1000 °C was the highest, indicating that oxidised powders can successfully decrease the required sintering temperature and improve the flexural strength of composite ceramics. Based on our optimised process, porous SiC-Al 2 O 3 ceramics were sintered at 1500 °C for 2 h. When their skeletons were fully developed, their pore sizes were in the range of 1.5–2 mm. Their porosity and flexural strength were 60.2–65.1% and 8.3–10.5 MPa, respectively. [ABSTRACT FROM AUTHOR]

Abstract Semi-conductive alumina/nano-carbon ceramic composite with high hole mobility is fabricated by gel-casting and reductive sintering. The hole mobility observed in the fabricated composite is 80-fold higher than the previously reported alumina/graphene composite. Such superior semi-conductive performance of the alumina/nano-carbon composite can be attributed to the homogenous electrically conductive path induced by nano-carbon with well-controlled graphite structure formed during fabrication process. In addition, the influence of sintering temperature on the structure of nano-carbon as well as its relation to the semi-conductive properties of composite are systemically investigated. [ABSTRACT FROM AUTHOR]

Abstract Although the near-net-shape forming ability of gelcasting has been well demonstrated, current attention mainly was focused on manufacturing compact ceramics. In this work we demonstrated that the combination of the gelcasting technique and the ceramic sintering process could prepare the near-net-shape through-pore hydroxyapatite (HAP) ceramics, in which the pore diameter at the range of < 2 μm could be adjusted by changing the content of HAP in green bodies and with the aid of alcohol immersion. Experiments demonstrated that the gels in green bodies and alcohol immersion played important roles in improving the strength of green bodies and decreasing the shrinkage and deformation of green bodies, and thus improving the through-pore and near-net-shape forming of HAP ceramics. Such method reported here possibly extends the gelcasting technique to manufacture other through-pore ceramics for precise filtration, protein separation, or high performance liquid chromatography. [ABSTRACT FROM AUTHOR]

This study employed a low-toxicity N, N-dimethylacrylamide/N, N-methylene acrylamide (DMAA /MBAM) gel system to near net shape SiAlON ceramics from aqueous slurries with a solid loading of 40 wt.% Si3N4, Al2O3, Y2O3, AlN, and Ce2O3 powder mixtures. The green bodies were sintered by one- and three-step pressureless sintering. Results showed that green bodies had a homogeneous microstructure with a high density of 1,9 g/cm3 and high flexural strength of 28,6 Mpa. Equiaxed a-SiAlON was prepared by one-step pressureless sintering, whereas ß-Si4Al2O2N6 with an elongated morphology was fabricated by three-step pressureless sintering. Therefore, a lowtemperature heat preservation stage reduces the nucleation rate, which is favorable for the development of elongated ß-SiAlON grains. [ABSTRACT FROM AUTHOR]

Abstract In this work, Si 3 N 4 ceramics were fabricated through an aqueous gelcasting method using a low–toxic monomer called N, N–dimethylacrylamide (DMAA) followed by gas pressure sintering at 1850 °C for 2 h under 6 MPa N 2 atmosphere. The effect of solid loading on performance of slurries, green and sintered bodies was investigated systematically. The results show that the slurries with a solid loading as high as 50 vol% (viscosity 0.17 Pa.s at 100 s–1) were achieved. With the increase of solid loading (30–50 vol%), the green bodies exhibited a monotonically decreased, however high enough in general, flexural strength of 16.50–11.52 MPa, which was comparable to that of widely–used neurovirulent acrylamide (AM) gelling system. In regard to the sintered bodies, increasing solid loading significantly promoted sintering and improved mechanical properties and thermal conductivity as a result of the increased density, bimodal distribution structure, as well as suitable interfacial bonding strength. The best performance parameters of Si 3 N 4 ceramics, bulk density of 3.25 g/cm3, apparent porosity of 0.67%, flexural strength of 898.92 MPa, fracture toughness of 6.42 MPa m1/2, Vickers hardness of 2.81 GPa, and thermal conductivity of 34.69 W m–1 K–1, were obtained at 50 vol% solid loading. This work renders low–toxic DMAA gelling system promising prospect in preparation of high–performance Si 3 N 4 ceramics by gelcasting. [ABSTRACT FROM AUTHOR]

Abstract Dense Ti 3 AlC 2 components with a complex shape were fabricated using gel casting followed by pressure-less sintering. Low viscosity slurry was prepared using an aqueous based acrylamide (AM) monomer with a 50% solid loading. Homogeneous and crack free Ti 3 AlC 2 green bodies were obtained. The sintering temperatures were set at 1500, 1550 and 1600 °C, highest relative density of 93% was achieved at 1550 °C. Surprisingly, samples sintered at 1600 °C resulted in a drop of relative density because of the abnormal grain growth and entrapped porosity. The pressure-less sintered samples had mechanical properties comparable to hot pressed counterparts with Vickers hardness of 3.1 ± 0.2 GPa, fracture toughness of 4.2 ± 0.2 MPa m1/2 and flexural strength of 302.3 ± 25.0 MPa. Final machining was still required to obtain a net shape components free from surface defects. [ABSTRACT FROM AUTHOR]

Textured TiB 2 -(Ti,Zr)B 2 composites were prepared by gel-casting in 6 T and subsequent pressureless sintering without the magnetic field. These results showed that c-axis of TiB 2 and ZrB 2 grains were oriented to parallel to the direction of the magnetic field in textured green bodies. Separately, the higher c-axis orientation was obtained for TiB 2 and the lower c-axis orientation was obtained for ZrB 2 . After sintering, ZrB 2 phases disappeared and new (Ti,Zr)B 2 solid solutions appeared by the reaction of ZrB 2 and TiB 2 . The degree of texture of TiB 2 increased compared with that in green body. (Ti,Zr)B 2 solid solutions also showed high c-axis orientation. With the increase of sintering temperatures from 1800 °C to 1950 °C, the degree of texture of TiB 2 slightly decreased from 0.95 to 0.92 and the degree of texture of (Ti,Zr)B 2 showed the big decreasing from 0.80 to 0.62. [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]

The here described investigation was essentially aimed at exploring the chemical stabilization and reutilization of iron-rich slag from copper metallurgy, by the manufacturing of glass-ceramic foams. The foams were developed according to a new method, recently reported for pure recycled soda-lime glass. Mixtures of soda-lime glass/slag powders (with slag content ranging from 10 to 30 wt%), suspended in alkaline aqueous solution, underwent progressive low temperature (80 °C) hardening, owing to the formation of hydrated calcium silicate compounds (C S H). Before complete setting, an extensive foaming could be achieved by vigorous mechanical stirring, with the help of a surfactant. After foaming, glass/slag mixtures could be sintered at 800–1000 °C; the mutual interaction caused an extensive crystallization, with precipitation of Ca Fe silicates and iron oxides (hematite and magnetite), promoting the mechanical properties (up to 4.4 MPa, with a porosity of about 80%). Leaching test confirmed the stabilization of pollutants, from the slag, in the final ceramics. Owing to the separation of iron oxides, particularly magnetite, the newly obtained foams exhibited a ferrimagnetic behavior, that could be exploited in electromagnetic shielding applications. [ABSTRACT FROM AUTHOR]

Complex shaped boron carbide with carbon (B 4 C/C) at near-full densities were achieved for the first time using negative additive manufacturing techniques via gelcasting. Negative additive manufacturing involves 3D printing of sacrificial molds used for casting negative copies. B 4 C powder distributions and rheology of suspensions were optimized to successfully cast complex shapes. In addition to demonstrating scalability of these complex geometries, hierarchically meso-porous structures were also shown to be possible from this technique. Resorcinol-Formaldehyde (RF) polymer was selected as the gelling agent and can also pyrolyze into a carbon aerogel network to act as the sintering aid for B 4 C. Due to the highly effective distribution of in situ carbon for the B 4 C matrix, near-full sintered density of 97–98% of theoretical maximum density was achieved. [ABSTRACT FROM AUTHOR]

The in situ silicon nitride nanowires reinforced porous silicon nitride (SNNWs/SN) composites were fabricated via gelcasting followed by pressureless sintering. SNNWs were well distributed in the porous silicon nitride matrix. The tip-body appearance suggested a VLS growth mechanism. The flexural strength and elastic modulus of the prepared composites can achieve 84.3 ± 3.9 MPa and 23.3 ± 2.0 GPa respectively (25 °C), while the corresponding porosity was 40.7 vol.%. Remarkably, the strength retention rate of the composites at 1400 °C was up to 66.1%. This is due to the excellent thermal stability of SNNWs and silicon nitride matrix. Also, the fracture toughness of the composites was improved to ∼42% larger than pure porous silicon nitride ceramics because of the bridging effect of the NWs and the interlocking effect of β-Si 3 N 4 crystals. In addition, a good thermal shock resistance and dielectric properties were indicated. The good overall performance made SNNWs/SN composites promising candidate for advanced high-temperature applications. [ABSTRACT FROM AUTHOR]

This work focuses on studying the effect of processing routes, namely; starch consolidation and freeze gelcasting techniques on the properties of porous TiO 2 and TiO 2 /5-wt% hydroxyapatite (HA) materials sintered at 1100 °C. The proposed routes were used to control pore characteristics and microstructure of prepared porous structures to be used for biomedical, membranes and environmental applications. Starch and tertiary butyl alcohol (TBA) were used as pore forming agent in the proposed methods, respectively. Phase composition, physical properties, microstructure, compressive strength, and pore size distribution of fabricated materials were investigated. The results indicated that both methods were suitable for production of porous structures with good properties. The samples fabricated by freeze gelcasting route showed improved properties as compared with those prepared by starch consolidation technique due to their improved pore characteristics (homogenous pore size and pore-size distribution) and microstructure. TiO 2 /HA composites prepared by both methods had lower porosity and mechanical properties than those prepared from pure TiO 2 . [ABSTRACT FROM AUTHOR]

In this paper, a transparent magnesium aluminate spinel ceramic was fabricated through the newest colloidal gel casting method, using a synthetic powder with the average particle size of 90 nm and Isobutylene-Maleic Anhydride (ISOBAM) additive. ISOBAM served as both a dispersant and a gelation agent to achieve a dense body. Also, the suspension rheological behavior was optimized by the solid loading of 85 wt%, the additive content of 0.7 wt%, and the gelation time of 350 s. This led to a green body with a density equal to 65% of theoretical density and the green strength of 14.48 MPa. The results revealed that the reduction of porosity and the uniform distribution of pores in the green body (smaller than half of the initial powder particle size, 35 nm), as accompanied by spark plasma sintering (SPS), resulted in the final body density of 99.97%, as well as the high in-line transmittance of 86.7% at the wavelength of 1100 nm. [ABSTRACT FROM AUTHOR]

Highly porous bioactive glass-ceramic scaffolds were effectively fabricated by an inorganic gel casting technique, based on alkali activation and gelification, followed by viscous flow sintering. Glass powders, already known to yield a bioactive sintered glass-ceramic (CEL2) were dispersed in an alkaline solution, with partial dissolution of glass powders. The obtained glass suspensions underwent progressive hardening, by curing at low temperature (40 °C), owing to the formation of a C--S--H (calcium silicate hydrate) gel. As successful direct foaming was achieved by vigorous mechanical stirring of gelified suspensions, comprising also a surfactant. The developed cellular structures were later heat-treated at 900-1000 °C, to form CEL2 glass-ceramic foams, featuring an abundant total porosity (from 60% to 80%) and well-interconnected macro- and micro-sized cells. The developed foams possessed a compressive strength from 2.5 to 5 MPa, which is in the range of human trabecular bone strength. Therefore, CEL2 glass-ceramics can be proposed for bone substitutions. [ABSTRACT FROM AUTHOR]

Gel-casting of ceramics is a promising technique that can be used to manufacture complex structures in a netshape approach, with the density and mechanical properties of the green and sintered structures being strongly influenced by the composition of the gel formulation and the casting approach. In this study, a parametric study was performed to assess the influence of the gel formulation (solid loading and resin content), the casting approach (centrifugal casting versus gravity casting), and the sintering treatment on the microstructural and mechanical properties development in gel-cast sialon ceramics. Optimum levels of solid loading and resin content were identified for the gel formulation. The study showed that a significant improvement in the high temperature flexural strength (~1.5–2 folds) can be achieved by employing a centrifugal gel-casting approach, due to the reduction of the porosity caused by the entrapped gas that gets entrapped during the standard casting process. [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]

In order to improve the connectivity between pores of gelcasted and solid-state-sintered SiC (S-SiC) foams, we utilized the synergetic poring mechanism of direct foaming and sacrificial solid template through introducing organic micro-beads into aqueous foamed SiC-B 4 C-C suspensions. The addition of micro-beads accelerated the formation of more bubble-derived pores in S-SiC foams, and generated abundant bead-derived pores in the bubble-derived-pore struts and partial-sintering-derived pores between SiC grains as well. This multiple pore microstructures induced excellent connectivity between pores and an ultrahigh porosity of 89.5%. Consequently, an outstanding nitrogen gas permeability of 9.2 × 10 −11 m 2 was acquired under the condition of a superior compressive strength of 2.2 ± 0.4 MPa. [ABSTRACT FROM AUTHOR]

The possibility of obtaining solid-state sintered silicon carbide (SiC) through aqueous gelcasting using commercial SiC powders was demonstrated. Green bodies were prepared from thixotropic SiC slurries in aqueous medium with optimized pH and solid-loading. The monomer system in gelcasting provides strength to the green bodies through formation of a gel network by polymerization and the carbon from polymeric gel enhances the densification of SiC, thereby avoiding addition of carbon externally to the gelcasting batches. Maximum bulk density of 3.16 g/cm 3 (98.4% of relative density) was achieved in gelcast SiC on sintering at 2150 °C in argon atmosphere. The effect of carbon on SiC densification is evinced from the changes in microstructure of sintered SiC with increase in carbon content. The density and microstructure of gelcast and sintered SiC was comparable to that obtained from dry pressing and sintering of additive mixed SiC powders. [ABSTRACT FROM AUTHOR]

Multilayer dense ceramic materials composed of Al 2 O 3 and Al 2 O 3 -Co 3 O 4 layers have been obtained by gelcasting. The key stage in the process was the optimization of the polymerization idle time in order to ensure strong adhesion between layers without cracks and delamination in a green state and after sintering. The significant advantage of this method is occurence of strong connections between consituent layers due to the slight migration of the slurry to the gelled bottom part of the sample, what is not obseved in techniques based on lamination processes. The multilayer samples were composed of two Al 2 O 3 layers and two Al 2 O 3 -Co 3 O 4 layers arranged alternately. The rheological characterization of the slurries was done. The properties of the sintered multilayer bodies were examined in comparison to the single-layer alumina samples. Observations in SEM and ligth miscroscope were performed. The presence of the transition layer in the sintered bodies was observed. [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]

Highly transparent Nd:YAG ceramics were fabricated by non-aqueous gelcasting and vacuum sintering for the first time, using epoxy resin and polyamine curing agent as gelling system. The influences of dispersant, solid loading and the organics of gelling system on the viscosity of suspensions and the stability of suspensions were discussed. The optimized nonaqueous slurry was of 54 vol% solid loading, comprising the commercial α-Al 2 O 3 , Nd 2 O 3 and Y 2 O 3 powders. The slurry with low viscosity and good fluidity was obtained by using 0.45 wt% PEI as dispersant. The homogenous and dense green body was obtained through solidificating the slurry in-situ. The green body after burnout had a relative density of 55.0% with a narrow pore size distribution. The transmittance of the Nd:YAG ceramics sintered at 1775 °C for 30 h with the thickness of 1.5 mm reached 83% at 1064 nm. The average grain size of the sample was about 71 μm. [ABSTRACT FROM AUTHOR]

A new gelling system based on the polymerization of hydantion epoxy resin and 3,3′-Diaminodipropylamine (DPTA) was successfully developed for fabricating silicon nitride (Si 3 N 4 ) ceramics. The effects of pH value, the dispersant content, solid volume fraction and hydantion epoxy resin amount on the rheological properties of the Si 3 N 4 slurries were investigated. The relative density of green body obtained from the solid loading of 52 vol% Si 3 N 4 slurry reached up to 62.7%. As the concentration of hydantion epoxy resin increased from 5 wt% to 20 wt%, the flexural strength of Si 3 N 4 green body enhanced from 5.3 MPa to 31.6 MPa. After pressureless sintering at 1780 °C for 80 min, the sintered samples exhibited the unique interlocking microstructure of elongated β-Si 3 N 4 grains, which was beneficial to improve the mechanical properties of Si 3 N 4 ceramics. The relative density, flexural strength and fracture toughness of Si 3 N 4 ceramics reached 97.8%, 687 MPa and 6.5 MPa m 1/2 , respectively. [ABSTRACT FROM AUTHOR]

A non-aqueous gel casting process based on the mixed solvent (ethanol and polyethylene glycol) and low-toxicity N,N-dimethylacrylamide (DMAA) was developed for an aluminum nitride (AlN) ceramic. In the present work, rheological properties of non-aqueous concentrated AlN suspensions were investigated in the presence of mixed solvent, dispersant, milling time, monomer and solid loading, in order to screen for the most suitable experimental conditions to obtain a good rheological behavior for gel casting. The results showed that the 50 vol% slurry with 0.2 wt% dispersant concentration, 2 h milling time, 6 wt% -monomer content, and a solvent ratio of 3:1, can meet the requirements for the casting process of AlN ceramic slurries. After being dried at 100 °C for 1 h, the optimum bulk density and maximum flexural strength of the AlN green bodies were as high as 1.97 g/cm 3 and 18.68 MPa, respectively. SEM photographs revealed that the green body had a relative uniform microstructure when the solid loading was 50 vol%. The shrinkage and deformation of shaped sintered bodies prepared through gel casting were small after sintering. The sintering shrinkage, apparent porosity, bulk density and flexural strength were 14.8%, 0.22%, 3.21 g/cm 3 and 310 MPa, respectively. [ABSTRACT FROM AUTHOR]

Highly porous alumina particle stabilized foams were prepared by combining the concepts of particle stabilized foams and gelcasting, using sulfonate surfactants and poly vinyl alcohol (PVA) as the gelcasting polymer. The ceramic samples sintered at 1500 °C for 2 h had porosities from 65% to 93%, with pore sizes in two categories: “ big pore ” around 300 μm and “ small pore ”, around 100–150 μm, depending on the type and amount of surfactant added. The mechanical behaviour of the foams (axial and diametral compression) depended on the overall porosity and pore size. On average, tensile and compressive strengths around 5 and 16 MPa respectively were measured for samples with bigger pore sizes and larger porosities. Samples with smaller pore sizes and lower porosities produced average values of 12 and 57 MPa for tensile and compressive strengths, respectively. The elastic modulus reached a maximum around 3GPa for “ small pore ” size samples. The effect of increasing amount of PVA in the samples had a strong effect on the green mechanical strength, but it did not significantly affect the mechanical response of the sintered alumina foams. Large and complex shape sintered components produced using this route showed a remarkable damage tolerance, due to crack tip blunting. [ABSTRACT FROM AUTHOR]

In order to fabricate a radome material with small volume shrinkage and not only good mechanical properties but also excellent dielectric properties, gel-casting and pressureless sintering were adopted to prepare porous silicon nitride (Si 3 N 4 ) ceramics. By adjusting the solid loading and the additives’ (Y 2 O 3 /Al 2 O 3 ) content, the drying and sintering shrinkage of ceramics could be controlled under 5% and 15%, respectively. Through decreasing temperature and prolonging holding time properly, the flexural strength of porous Si 3 N 4 with few sintering aids could get close to that of ceramics with more additives. Both the flexural strength and the logarithmic dielectric constant showed a linear relation with the porosity of ceramics. Typically, the porous Si 3 N 4 sintered at 1650 °C for 3 h with only 3 wt% sintering additives displayed relatively good performance, attaining a porosity of 39.28%, a flexural strength of 146.0 MPa, a fracture toughness of 1.44 MPa m 1/2 and a calculated dielectric constant of 4.03 at a resonant frequency of 14 GHz. [ABSTRACT FROM AUTHOR]

C -axis textured SiC ceramics were prepared by a strong magnetic field of 6 T assisted gel-casting and subsequent pressureless sintering. The optimal suspension parameters for gel-casting were determined by analyzing the influences of pH value and dispersant content on the stability and dispersibility of suspensions. The effect of sintering conditions on the texture development and properties of SiC ceramics was discussed. It was found that the increasing sintering temperature or holding time promoted the densification process of SiC ceramics. The c -axis of SiC grain was aligned parallel to the magnetic field by applying a strong magnetic field of 6 T. The degree of texture of SiC ceramics showed a slightly increasing trend with the increase of sintering temperature or holding time. When the samples were sintered at 1950 °C for 4 h or 6 h, the large elongated grains were formed in the samples, leading to the extremely evident anisotropic microstructure on different planes. Textured SiC ceramics exhibited the anisotropic bending strength. [ABSTRACT FROM AUTHOR]

With starch as pore forming agent, porous silicon carbide (SiC) ceramics were successfully fabricated by gelcasting. A novel and simple gelling system of isobutylene and maleic anhydride (Isobam) can gel in air at room temperature was used. The rheological behaviors of SiC slurries were investigated as a function of starch content. The gelled SiC green bodies were sintered at 2050–2150 °C through solid state sintering with B 4 C and carbon as sintering additives. Porosity of the porous SiC ceramics sintered at 2100 °C was well controlled from 34.20% to 42.68% with the starch content increasing from 0 to 20 wt%. With increasing the sintering temperature from 2050 to 2150 °C, flexural strength and porosity of porous SiC ceramics with 20 wt% starch varied from 61.0 to 128.0 MPa and 48.1% to 34.2%, respectively. The porous SiC ceramics fabricated with 20 wt% starch addition and sintered at 2100 °C were proved to possess excellent thermal shock resistance. The ceramics after water-quenching at 1500 °C showed an average flexural strength of 95.8 MPa, which was higher than the strength of samples without quenching. [ABSTRACT FROM AUTHOR]

A transparent yttrium alumina garnet (YAG) ceramic was successfully prepared by gelcasting a mixture of Al 2 O 3 and Y 2 O 3 powders aided by a reactive sintering process. A water-soluble epoxy resin gelling system was employed to fabricate large, sheet-like ceramic pieces. A stable slurry with 75 wt% solid loading and low viscosity was prepared. After casting, drying, and pre-sintering, vacuum sintering was performed at 1720 °C for 6 h. Homogeneous microstructures of both pre-sintered and sintered bodies were obtained. The resulting YAG ceramic (60 × 50 × 0.5 mm 3 ) with an average grain size of 10 μm had an in-line transmittance of 83.0% and 80.7% at the wavelength of 1064 nm and 400 nm, respectively. [ABSTRACT FROM AUTHOR]

Translucent alumina ceramics with high transparency were successfully prepared via gelcasting and vacuum sintering. Effects of powder properties and copolymer content on solids loading of the slurry and then on the porosity, microstructures of both green bodies and sintered ceramics, as well as optical transmittance of the final ceramics were extensively investigated. Fine and de-agglomerated alumina powder was effective to prepare slurries with higher solids loading. They resulted in lower porosity (higher relative density) and smaller pore size in green bodies. After sintered at 1860 °C for 6 h in vacuum, the resultant ceramics from higher solids loading had less residual pores. In-line transmittance of the ceramic (1 mm thick) from 55 vol% solids loading reached as high as 53.6% at 600 nm, much higher than previously reported data (<30%). [ABSTRACT FROM AUTHOR]

Highly porous γ-Y 2 Si 2 O 7 is fabricated by the in situ foam-gelcasting reaction sintering method using Y 2 O 3 and SiO 2 starting powders. The prepared porous γ-Y 2 Si 2 O 7 has multiple pore structures, including interconnected large pores and small pores in the skeleton. The sample sintered at 1550 °C has low linear shrinkage (6.0%), high porosity (84.9%), high compressive strength (6.22 MPa), and low thermal conductivity (0.230 W/(m K)). This work sheds light on porous γ-Y 2 Si 2 O 7 as a promising high-temperature thermal insulator. [ABSTRACT FROM AUTHOR]

Alumina spherical green bodies (∅≈75 mm) prepared by gelcasting were presintered at 1000 °C. Green bodies׳ temperature difference between the center and surface as a function of solids loading, heating rate, and gel system were extensively investigated. Temperature in the center was lower than that on surface of the alumina spheres cast using PIBM gel system during presintering, and temperature difference (Δ T : T center − T surface ) slightly decreased with increased solids loading but significantly increased with heating rate. Temperature difference (Δ T <0) generated compressive stress near the surface and tensile stress in center, which led to a porosity difference between the center and the surface. Moreover, the porosity exponentially decreased with increased compressive stress. Tensile stress in the center of the green body cast using PIBM gel system was estimated as 0.3 MPa, which was less than the minimal strength. Therefore, the body was successfully presintered without cracking. However, cracking was found on the surface of the body cast by epoxy-amine gel system, which exhibited a more severe temperature difference fluctuation. [ABSTRACT FROM AUTHOR]

Alumina spherical green bodies (∅≈75 mm) prepared by gelcasting were presintered at 1000 °C. Green bodies׳ temperature difference between the center and surface as a function of solids loading, heating rate, and gel system were extensively investigated. Temperature in the center was lower than that on surface of the alumina spheres cast using PIBM gel system during presintering, and temperature difference (Δ T : T center − T surface ) slightly decreased with increased solids loading but significantly increased with heating rate. Temperature difference (Δ T <0) generated compressive stress near the surface and tensile stress in center, which led to a porosity difference between the center and the surface. Moreover, the porosity exponentially decreased with increased compressive stress. Tensile stress in the center of the green body cast using PIBM gel system was estimated as 0.3 MPa, which was less than the minimal strength. Therefore, the body was successfully presintered without cracking. However, cracking was found on the surface of the body cast by epoxy-amine gel system, which exhibited a more severe temperature difference fluctuation. [ABSTRACT FROM AUTHOR]

Dense chromic oxide refractories were prepared by aqueous gelcasting process. Effect of solid loading on rheological property of slurries, properties of green bodies and sintered bodies were investigated. AN-2000 was selected as the dispersant for obtaining slurries with high solid loading and low viscosity. The solid loading of suspension that can meet the requirement for casting was as high as 52 vol%. However, it was found that the highest relative density of the green body and the sintered body separately reached 66·17% and 85·38% when the solid loading came to 50 vol%, while the flexural strength of them were 13·60 MPa and 62·71 Mpa. Once the solid loading increased to 52 vol%, the relative density and mechanical properties of the green body decreased noticeably, which caused by the increase of the slurry viscosity. Besides, SEM images proved that green bodies and sintered bodies had the homogeneous microstructure when the solid loading was 48-50 vol%. As the solid loading was 52 vol%, hard agglomerations and pores formed in the green body, which had a significant influence on the properties of the sintered body. [ABSTRACT FROM AUTHOR]

In this paper, dense silicon carbide ceramics were prepared by aqueous gelcasting and pressureless sintering using dextrin as the carbon source. The influence of carbon content and solid content on the microstructure and mechanical properties of green and as sintered SiC samples was studied. It was shown that the carbon content should be 1 wt% or higher for the fully densification of silicon carbide ceramics. The influence of solid content on the green density and the mechanical properties of SiC ceramics was studied. The optimal solid content with 1 wt% carbon as sintering additives is around 52 vol%. Results showed that dextrin is an effective carbon source for developing SiC ceramics by aqueous gelcasting and pressureless sintering method. [ABSTRACT FROM AUTHOR]