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

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

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

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

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

The paper presents the possibility of fabricating ceramic-metal composites by an innovative method of centrifugal slip casting in the magnetic field. It was examined whether the use of this method would allow obtaining a gradient concentration of metal particles in the ceramic matrix. In the applied technique, the horizontal rotation axis was used. The study investigated the effect of solid phase content on the properties and microstructure of the products. Water-based suspensions with 35, 40, 45 and 50 vol.% of solid-phase content were prepared with 10 vol.% additional of nickel powder. The viscosity of prepared slurries was considered. The gradient distribution of nickel particles in the zirconia matrix was observed on SEM. Vickers hardness of ZrO2-Ni composites has been measured. The research revealed that the physical properties depend on the volume fraction of solid content and increase as the volume of solid content increases. [ABSTRACT FROM AUTHOR]

Porous Si 3 N 4 ceramics fabricated by gelcasting with DMAA demonstrated excellent mechanical and dielectric properties after introducing β–Si 3 N 4 seeds into ceramic matrix. The microstructure and properties of slurries, green and sintered bodies were highly correlated with β–Si 3 N 4 seed size, content and morphology. The slurry viscosity reached the maximum of 0.87 Pa s when introducing 10 wt% elongated seeds, but overall, exhibiting good fluidity. The green body strength dropped remarkably after adding small equiaxial seeds, but improved within 6 wt% elongated seeds and afterwards declined to the minimum of 25.99 MPa, which was quite ideal for processing. The elongated seeds impeded liquid phase flow and particle rearrangement more pronouncedly than equiaxial ones during sintering, thereby causing the highest porosity of 41.77% and the largest pore size of 1.04 μm when employing 10 wt% elongated seeds. The elongated seeds were more helpful in developing the strong self–reinforced bimodal microstructure due to the original hexagonal prism morphology and achieved the highest bending strength of 378.50 MPa and fracture toughness of 8.54 MPa m1/2 at 2 wt% and 6 wt% elongated seeds, respectively. The dielectric constant and loss tangent depended strongly on the porosity and separately varied in 4.70–4.82 and 0.041–0.047 ranges in 8.2–12.4 GHz when using 6 wt% elongated seeds, demonstrating superior microwave–penetrating properties. [ABSTRACT FROM AUTHOR]

Aqueous gelcasting has been applied to form multiple advanced ceramics with large size or complex shape. However, the optical performance of transparent ceramics fabricated by gelcasting is not satisfactory due to the microstructure defects and residual organics. YAG ceramics with excellent optical transmittance were prepared through improving solid content of suspension, obtaining fine microstructure of fully dense ceramics without residual organics in this paper. The effects of ammonium citrate tribasic (TAC) and solid content on the rheological performance of suspension as well as the effect of solid content on the microstructure of green body were systematically investigated. The viscosity of suspension with 43 vol% solid content and 0.25 wt% TAC was as low as 0.03 Pa s at 100 s−1. The YAG ceramics (thickness 2.5 mm) with high optical transmittance (T = 83.2% at 1064 nm) were prepared from 43 vol% after vacuum sintering at 1780 °C for 8 h. The green body cast from 45 vol% solid content had an excellent bending strength about 29 MPa, and the residual pores were eliminated after vacuum sintering, while the residual organics was detected by optical microscopy and elemental analyzer inside YAG ceramics. The residual organics results in the decrease of in-line transmittance of YAG ceramic cast from 45 vol% solid content than that of ceramic cast from 43 vol%. This study suggests a promising prospect for AM gelling system in the cost-efficient manufacturing of highly transparent ceramics with high bending strength of green bodies. [ABSTRACT FROM AUTHOR]

Herein, a low–toxic N, N–dimethylacrylamide (DMAA) system was used in preparation of porous Si 3 N 4 ceramics by aqueous gelcasting, and variations in microstructure and properties with solid loading and calcination temperature were systematically investigated. In the considered solid loading range of 28–44 vol%, all the slurries exhibited superior rheological properties (≤145 mPa⋅s at 95.40 s−1 for 44 vol% solid loading) perfectly suitable for casting. With increasing solid loading, a decreased bulk density (1.71–1.69 g/cm3), volume shrinkage (37.73–13.77%) and flexural strength (46.56–26.75 MPa) of green bodies were obtained, exhibiting better mechanical properties than those derived from the conventional acrylamide (AM) system. Regarding Si 3 N 4 ceramics with various solid loadings, the increase in calcination temperature favored the phase transformation α→β–Si 3 N 4 and β–Si 3 N 4 growth, however, the increased solid loading exhibited an inhibiting effect on those since mass transport in gas phase was blocked due to the disruption of pore connectivity. The resulting microstructure changes imparted Si 3 N 4 ceramics increasing flexural strength (110.36–367.88 MPa), fracture toughness (2.54–5.03 MPa⋅m1/2), as well as decreasing porosity (54.21–41.05%) and pore size (0.38–0.33 μm). This work demonstrates the potential research value of DMAA system in preparing high–performance porous Si 3 N 4 ceramics through gelcasting technique. [ABSTRACT FROM AUTHOR]

Porous Si 3 N 4 ceramics with bimodal hierarchical pore structures were fabricated through combining aqueous gelcasting and adding pore–forming agent method wherein a low–toxic monomer N, N–dimethylacrylamide (DMAA) and spherical pore–forming agent polystyrene sphere (PS) were respectively applied. The results demonstrated that PS size and content played an important function in regulating microstructure and properties of slurries, green and sintered bodies. The slurry viscosity increased sharply with the introduction of fine PS and reached a maximum of 1.78 Pa⋅s when adopting 7 wt% PS with d 50 = 2.51 μm. Fine PS addition caused higher porosity in green bodies than coarse one, resulting in a significant reduction in bending strength from 28.50 MPa to 11.50 MPa, however, overall, demonstrating high enough strength for mechanical processing. The formed spherical pores from PS in ceramic matrix facilitated high porosity and highly crosslinked microstructure, thus contributing to lowering dielectric constant and loss. With PS size increasing, the dominant role in mechanical properties was transferred from porosity to microstructure, whilst dielectric properties were merely controlled by porosity and spherical pores. The porosity, bending strength, fracture toughness, dielectric constant and loss at 15 GHz varied in ranges of 36.34–52.91%, 258.42–101.21 MPa, 6.02–3.38 MPa⋅m1/2, 4.29–2.98 and 1.48–1.18 × 10−3, respectively, displaying an excellent comprehensive properties. • Porous Si 3 N 4 ceramics with bimodal hierarchical pore structures were achieved. • Perfect spherical pores depending on PS were evenly distributed in ceramic matrix. • Decisive factors in mechanical properties changed with addition of different PS. • Introduction of spherical pores effectively reduced ε of porous Si 3 N 4 ceramics. • Porous Si 3 N 4 ceramics demonstrated excellent mechanical and dielectric properties. [ABSTRACT FROM AUTHOR]

This work concerns the study of ceramic-metal composite materials processed by gel casting method. Due to limited possibilities of fabrication complex-shape elements obtained by classical methods of powder metallurgy (such as isostatic or uniaxial pressing) the colloidal processes are recently willingly applied in manufacturing of ceramic matrix composites. In the present work Al2O3–10 vol.% Mo composites were formed by aqueous gel casting process and sintered in argon atmosphere. Selected physical properties and phase composition have been described. The microstructure of the green and sintered samples was examined with a scanning electron microscope. Molybdenum particles were homogeneously distributed in the ceramic matrix. Moreover, Mo2C was formed during sintering process that had a positive contribution to enhancing the hardness of the composite. The composite after sintering was characterized by a density higher than 95% of theoretical density and high hardness. The performed studies have confirmed the possibility of application of gel casting method to produce Al2O3–Mo composite system. [ABSTRACT FROM AUTHOR]

Abstract In this study, the low–toxicity monomer N, N–dimethylacrylamide (DMAA), serving as both gelling agent and pore–forming agent, was adopted to fabricate porous Si 3 N 4 ceramics with a regulatable microstructure and property by aqueous gelcasting. Results indicate that monomer content played an important role in regulating and optimizing the properties of sintered bodies. With increasing monomer content (5.94–30.69 wt%), both slurry viscosity (maximum 0.14 Pa s at 95.40 s−1) and green body strength (11.35–49.23 MPa) exhibited monotonic increasing trends, demonstrating superior mechanical properties to those obtained using the neurovirulent acrylamide (AM) gelling system. The increased monomer content not only improved porosity, but also promoted α→β–Si 3 N 4 transformation as well as β–Si 3 N 4 grain growth through enhancing the connectivity of interlocking pores and accelerating the vapor phase transport during liquid–phase sintering. These variations in phase composition and microstructure derived from the varied monomer content further resulted in monotonic changes in porosity (40.32–51.50%), mean pore size (0.27–0.38 μm), flexural strength (202.77–132.15 MPa), fracture toughness (2.93–2.32 MPa m1/2), dielectric constant (3.48–2.78) and loss (3.52–3.09 × 10−3) at 10 GHz for sintered bodies, displaying an excellent comprehensive properties. This study suggests a promising prospect for DMAA in preparation of high–performance porous Si 3 N 4 ceramics by aqueous gelcasting. [ABSTRACT FROM AUTHOR]

Abstract In this article we are reporting the optimization of gelcasting process which enabled us to manufacture silicon nitride bodies with around 30–37% porosity and 182–250 MPa flexural strength. Owing to their potential applications mainly in biomedical and aerospace, porous Si 3 N 4 ceramics have gained ever increasing interests. However, the main challenge has been ensuring their high strength while maintaining high porosity. Si 3 N 4 bodies were prepared via a controlled gelcasting followed by pressureless sintering in a coke bed. Monomers including acrylamide (AM) and N , N ' -methylenebisacrylamide (MBAM) were employed to formulate the primary slurry. Sub-micron Si 3 N 4 powder of 35 vol% was used as solid loading where ammonium persulfate (APS) and N , N , N ' , N ' -tetramethylethylenediamine (TEMED) were added to initiate and catalyze polymerization reactions. Sintering was carried out at 1650 °C for 2–6 h and at 1750 °C for 2 h where 6 wt% mixture of Al 2 O 3 − Y 2 O 3 was included as a sintering aid. Phase characterization and microstructural evolution were studied by X-ray diffraction (XRD) and scanning electron microscopy (SEM), respectively; while mechanical evaluation was based on bending test. It was found that by optimizing the viscosity of slurry and the idle time of gelation, a well distribution of high porosity structure is developed. The high strength of the sintered bodies is related to a high volume and unique microstructure of fine and elongated β- Si 3 N 4 grains evolved during optimized sintering conditions. At temperatures above 1650 °C and sintering times of more than 4 h, the strength is decreased due to coarsening of β- Si 3 N 4 grains, however. [ABSTRACT FROM AUTHOR]

Highlights • The effect of the content of mullite on the tribological properties of Mullite/3Y-TZP composite ceramics was investigated in depth. • The relationship among microstructure, mechanical properties and tribological properties of Mullite/3Y-TZP composite ceramics was revealed. • A theoretical model of wear mechanism was established based on the wear surface morphology, revealing the wear mechanism of Mullite/3Y-TZP composite ceramics. Abstract In-situ mullite toughened 3Y-TZP ceramics (Mullite/3Y-TZP ceramics) with different content of mullite were prepared by gel-casting combined with pressureless sintering to study effects of the content of mullite on their microstructure and tribological properties. The results indicated that the mullite uniformly distributed in the zirconia matrix had a complete columnar structure and a moderate content in S2 (the sample containing 4 mol% mullite), and the smooth surface caused by low porosity combined with the good mechanical properties significantly reduced the coefficient of friction and wear rate of S2. A high proportion of irregular mullite destroyed the overall structure of S3-S5 (the samples containing 6, 8 and 10 mol% mullite, respectively), combined with high porosity not only reduced the mechanical properties of them, but also led to an increment in surface roughness, which significantly lowered the wear resistance of the material. Studies of worn surfaces showed that micro-cutting was present in every sample, but the degree of micro-cutting and adhesive wear in S2 were minimal due to its good structure and properties. However, the micro-cutting and adhesive wear of S3-S5 were exacerbated. [ABSTRACT FROM AUTHOR]

Abstract Solid loading as a key parameter in gel casting influence both rheological behavior and stability of slurry. It also has strong impacts on microstructure and final properties of porous FeAl intermetallics. In this study, a designed non-aqueous gel casting has been developed for fabrication of porous FeAl intermetallics. The SEM analysis, bubble point method and compression test were used to investigate pore structure and properties of porous FeAl intermetallics. Results reveal that higher solid loading will improve the uniformity of pore structure and lead a decrease in maximum pore size. Gas permeability decreases but compressive strength increases with increasing solid loading. The quantitative relationship between maximum pore size (d m) and solid loading (φ) is d m = 10.52 − 0.15 φ (35 ≤ φ ≤ 50); the relationship between gas permeability (K) and solid loading (φ) is K = 13.99 − 0.22 φ (35 ≤ φ ≤ 50). Further, the distinctive phase transformation and pore formation mechanism are the main reasons for tiny volume expansion and highly open porosity of final products, respectively. Altogether, this work provides a strategy to fabricate porous FeAl intermetallics with adjustable pore structure and properties by controlling the solid loading, suggesting that the non-aqueous gel casting is a promising candidate for the preparation of porous FeAl intermetallics. Graphical abstract Unlabelled Image Highlights • Porous FeAl intermetallics were fabricated using a non-aqueous gel casting. • Higher solid loading can improve the uniformity of pore structure. • Maximum pore size and gas permeability decrease with increasing solid loading. • Compressive strength increases with increasing solid loading. • Pores are formed by removal of gel network and phase transformation. [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 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]

Abstract The effects of different content of mullite on the microstructure and mechanical properties of in-situ mullite toughened 3Y-TZP ceramics (Mullite/3Y-TZP composite ceramics) prepared by gel-casting combined with pressureless sintering were observed in this study. The results indicated when the content of mullite was low (2–4 mol%), especially in 4 mol%, mullite showed regular columnar structure and the size of columnar mullite was larger. When the content got higher (> 6 mol%), mullite showed a granular or even fluid shape and was connected to each other. In addition, the bending strength and fracture toughness of the samples showed a trend of rising first and then decreasing with the increase of the content of mullite, but the hardness had been declining. The sample containing 4 mol% mullite had the best mechanical properties (hardness reached 13.02 GPa, bending strength reached 907.31 MPa and fracture toughness reached 10.38 MPa m1/2). Furthermore, mullite, alumina and zirconia particles played an important role in toughening reinforcement due to pinning effect. [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]

In ceramic forming techniques high particles packing can provide better properties of the final ceramic products. The high quality of the material coupled with the shape complexity of the ceramic product is still challenging. The aim of this work was the optimization and preparation of the ceramic samples based on two alumina powders of different particle size (AA05: 0.5 μm and TM-DAR: 0.15 μm). Firstly, ceramic suspensions of 50vol.% solid loading and the volumetric ratio of AA05 to TM-DAR 1:1, 2:1, 3:1, 4:1, respectively have been prepared. The 2-carboxyethyl acrylate was applied as the new monomer limiting the negative effect of oxygen inhibition. Additionally, the cold isostatic pressing (CIP) was used in order to increase relative density of green bodies. The results of presented research have shown that samples with the ratio of AA05 to TM-DAR 2:1 were characterized by the highest green density (62%). Moreover, CIP process proved to be effective and increased the density of green bodies from 62% to 67%. The pore size distribution of the green bodies has been measured. Samples were sintered at different conditions (1400°C, 1450°C and 1500°C for 1h and 1300°C, 1400°C, 1450°C and 1500°C for 5h). [ABSTRACT FROM AUTHOR]

Gel-casting is a promising preparation technology of Si 3 N 4 structural ceramics. The process involves drying of the “green” gel-cast parts before densification. And the drying of green gel-cast bodies is an important step in the gel-casting manufacturing process. In this work, the Si 3 N 4 gel-cast green bodies were dried in polyethylene glycol (PEG) solution with the purpose of obtaining Si 3 N 4 ceramics with good mechanical properties. The effect of the molecular weight and concentration of PEG solution on drying rate, microstructure and mechanical properties of Si 3 N 4 ceramics was studied. The results indicated that with the increase of molecular weight of PEG, the drying rate increased obviously and the structure became more uniform and dense when the concentration of solution was 20 wt%. The Si 3 N 4 ceramics after sintering have the excellent flexural strength (662.6 MPa) under PEG600 drying condition. Furthermore, the concentration of PEG600 solution had a positive effect on drying and sintering of the green body. Therefore, the bending strength reached 871.1 MPa under 65 wt% PEG 600 solution drying condition. Overall, the drying process (drying in 65 wt% PEG600 solution) promotes the efficiency and quality of drying of Si 3 N 4 gel-cast green bodies, which is beneficial for the subsequent drying and sintering process. [ABSTRACT FROM AUTHOR]

A low-toxic and water-soluble monomer N, N-dimethylacrylamide (DMAA) was employed as a gelling agent in the gelcasting of porous Si 3 N 4 ceramics. The process conditions and composition for slurry preparation (with a solid loading of 36 vol%), the consolidation and sintering of green bodies were investigated and optimized. The effects of various factors such as zeta potential, pH value of the premix solution, dispersant dosage and ball milling time on the rheological properties of the slurries were investigated. The results suggest that the best rheological properties (66.5 mPa.s at a shear rate of 96.3 s −1 ) of the slurries were obtained when pH value ranged between 9 and 11, dispersant dosage reached 1 wt%, and ball milling time was 6 h. All the as-prepared green bodies showed a homogeneous microstructure and high flexural strength ≥ 26 MPa with a maximum up to 46.3 MPa when the ratio of DMAA to MBAM, initiator dosage, polymerization temperature and time were 14, 1 wt%, 70 °C and 90 min, respectively. The sintered bodies had a homogeneous microstructure, excellent and regulatable properties, a flexural strength of 216.3–327.3 MPa, and a porosity of 39.6–29.1% by varying the sintering temperature from 1710 °C to 1810 °C and the holding time from 1 h to 3 h. The superior comprehensive effect makes DMAA a promising candidate for an environmentally friendly gelling agent in gelcasting of porous Si 3 N 4 ceramics. [ABSTRACT FROM AUTHOR]

In-situ grown mullite toughened zirconia ceramics (mullite-zirconia ceramics) with excellent mechanical properties for potential applications in dental materials were fabricated by gelcasting combined with pressureless sintering. The effect of sintering temperature on the microstructure and mechanical properties of mullite-zirconia ceramics was investigated. The results indicated that the columnar mullite produced by reaction was evenly distributed in the zirconia matrix and the content and size of that increased with the increase of sintering temperature. Mullite-zirconia ceramics sintered at 1500 °C had the optimum content and size of the columnar mullite phase, generating the excellent mechanical properties (the bend strength of 890.4 MPa, the fracture toughness of 10.2 MPa.m 1/2 , the Vickers hardness of 13.2 GPa and the highest densification). On the other hand, zirconia particles were evenly distributed inside the columnar mullite, which improved the mechanical properties of columnar mullite because of pinning effect. All of this clearly confirmed that zirconia grains strengthened columnar mullite, and thus the columnar mullite was more effective in enhancing the zirconia-based ceramics. Simultaneously, the residual alumina after reaction was distributed evenly in the form of particle, which improved the mechanical properties of the sample because of pinning effect. Overall, the synergistic effect of zirconia phase transformation toughening with mullite and alumina secondary toughening improved the mechanical properties of zirconia ceramics. [ABSTRACT FROM AUTHOR]

Gelcasting method with nontoxic biopolymer as gel former can be used to prepare ceramics with complex shape. AlN ceramic bonded carbon (AlN/CBC) composites with light weight were fabricated by gelcasting and pressureless sintering method using nontoxic agarose as gel former with Y 2 O 3 + CaF 2 as sintering additive. The effect of sintering additive content and sintering temperature on the microstructure, flexural strength and thermal conductivity of composites was investigated. The results reveal that, as the temperature decreases, the raw powders solidify into three-dimensional net structures through abundant hydrogen bonds in the agarose. High sintering temperature facilitates densification and improves mechanical and thermal properties of the composites. Increasing sintering additive content can also tune the density and raise flexural strength. The AlN/CBC composite containing 7 wt% sintering additive content, which was sintered at 2000 °C, exhibits the highest thermal conductivity. Relative density, C content and microstructure uniformity have effects on properties of AlN/CBC composite. [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]

Hierarchically pore-structured porous diatomite ceramics containing 82.9∼84.5% porosity were successfully prepared for the first time via foam-gelcasting using diatomite powder as the main raw material. Sizes of mesopores derived from the raw material and macropores formed mainly from foaming were 0.02∼0.1 μm and 109.7∼130.5 μm, respectively. The effect of sintering temperature, additive content and solid loading of slurry on pore size and distribution, and mechanical and thermal properties of as-prepared porous ceramics were investigated. Compressive strength of as-prepared porous ceramics increased with sintering temperature, and the one containing 82.9% porosity showed the highest compressive strength of 2.1 ± 0.14 MPa. In addition, the one containing 84.5% porosity and having compressive strength of 1.1 ± 0.07 MPa showed the lowest thermal conductivity of 0.097 ± 0.001 W/(m·K) at a test temperature of 200 ̊C, suggesting that as-prepared porous ceramics could be potentially used as good thermal insulation materials. [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]

Porous alumina ceramics with inter-locked plate-like structure were successfully fabricated by the tert -butyl alcohol-based gel-casting method. The effects of Al/Si mole ratio on the structure and properties of the obtained products were investigated. The formation process of the inter-locked structure was analyzed. The products fabricated with the one-step method, in which the growth of plate-like alumina and the formation of the inter-locked structure were combined together, exhibited a high porosity of 76.21%, a compressive strength of 0.525 MPa and a low thermal conductivity of 0.495 W/mK, while the products fabricated by the two-step method after sintered at 1500 °C using the grinded powders after 700 °C heat-treatment as the starting materials possessed a relatively high compressive strength of 4.80 MPa. The obtained porous alumina ceramics were promising flexible insulant materials for the application in high-temperature field. [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]

Epoxy Gel Casting (EGC) was recently coined to designate a setting mechanism based on the in situ polymerization of epoxy resins dissolved in the aqueous dispersion media of ceramic powder suspensions upon adding suitable amine-based crosslinking agents. The specific interactions between the surface of the powder particles and the processing additives are likely to determine different partitions of the crosslinking species, dissolved in the bulk solution, or adsorbed at the surface of the particles, and affect the EGC process. The present work aims at evaluating the influence of surface chemistry on the extent of the specific interactions at the solid/liquid interface and how it affects the polymerization kinetics and the properties of ceramic green bodies consolidated by EGC. Three different ceramic oxides (alumina, zirconia and fused silica) having similar particle size distributions were used. Stable colloidal suspensions with 45 vol.% solids were prepared by dispersing the powders in aqueous solutions containing a fixed amount of a common dispersant and various dissolved amounts of an epoxy resin. Zeta potential, rheological measurements and calorimetry were used to assess the specific interactions and their effects on the consolidation kinetics upon adding a polyamine hardener, and on the final properties of consolidated parts. With the isoelectric point of the naked particle surface decreasing, there were noticeable decreases in gelation time, shrinkage, green density, and flexural strength of the green ceramic body’s properties. An interaction model is proposed to explain the observed differences. The potential of EGC to consolidate ceramic microneedles cast in soft rubber moulds was demonstrated. [ABSTRACT FROM AUTHOR]

Inter-locked mullite frameworks (IM frameworks) were prepared by the tert butyl alcohol (TBA) -based gel-casting method. The inter-locked structure formed through fluorine-catalyzed gas-phase reaction. Inter-locked topaz structure first formed in the samples and then it transformed into inter-locked mullite structure. TBA's volatilization and gaseous reactants' running off, which acted as two kinds of “pore formers” in the gel-casting process, offered enough space for the mullite grains' anisotropic growth, and led to the porous structure's formation. The volume density, apparent porosity, specific surface area and compression strength of the samples that formed at 1100–1500 °C were found to be 0.53–0.59 g/cm 3 , 82.1–76.1%, 12.3–4.6 m 2 /g and 1.6–3.6 MPa, respectively, indicating that the IM frameworks are promising as high-temperature catalyst supports. [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]

Porous mullite fiber/silica composite was successfully fabricated by a TBA-based gel-casting, and the influence of mullite fiber content on the composite microstructure and properties were investigated. The results show that the mullite fiber content played an important role in tailoring the microstructure of the composite, consequently influencing the sample properties. The composite fabricated with high fiber content showed a porous fibrous structure with mullite fibers as the fiber skeleton and silica as the binder, and exhibited a low density, high porosity, excellent elasticity and low thermal conductivity. On the contrary, the sample fabricated with low fiber content possessed a high density and high strength due to its dense microstructure which is similar with that of the fiber reinforced ceramic matrix composite. [ABSTRACT FROM AUTHOR]

A novel temperature resistance buoyancy material with hollow glass microspheres (HGMs) as the filler and borosilicate glass (BG, similar chemical composition to the HGMs) as the high temperature matrix was prepared by a tert-butyl alcohol based on gelcasting process. The effect of solid loading and sintering temperature on microstructure and mechanical properties were investigated. The results showed that HGMs were bonded together by borosilicate glass and 45 wt.% solid loading and 700 °C were the optimal processing parameters to fabricate the samples with the best mechanical and thermal properties, and the corresponding bulk density, compressive strength, thermal conductivity and Young’s modulus were 0.92 g/cm 3 , 14.46 MPa, 0.15 W/m K and 1.24 GPa, respectively. The exponent m value for the samples fabricated in this work was 1.18, lower than that of open- or closed-cell foams, because the sample possess both the closed and open pores. The experimental values of thermal conductivity from 0.07 to 0.16 W/m K were lower than the prediction with the Hashin–Shtrikman upper bound and almost close to that predicted by the Landauer’s relation. Only modulus value of SSL45 sample which possessed the maximum value was closer to Hashin–Shtrikman upper bound, while the modulus value of other samples agreed well with Ashby–Gibson model applied for a porosity ranging from 65% to 89%. The HGMs/BG composite exhibited a low density, low thermal conductivity and excellent temperature resistance, and can be used as the thermal insulation for undersea pipeline or submarine. [ABSTRACT FROM AUTHOR]

A combination of gel-casting and polymeric foam infiltration methods is used in this study to prepare porous bodies of hydroxyapatite (HA), to provide a better control over the microstructures of samples. These scaffolds were prepared by impregnating a body of porous polyurethane foam with slurry containing HA powder, and using a percentage of solids between 40% and 50% w/v, and three different types of monomers to provide a better performance. X-Ray Diffraction (XRD), and Fourier Transformed Infrared (FTIR) and Scanning Electron Microscopy (SEM) were employed to evaluate both the powder hydroxyapatite and the scaffolds obtained. In addition, porosity and interconnectivity measurements were taken in accordance with the international norm. Bioactivity was checked using immersion tests in Simulated Body Fluids (SBF). After the sintering process of the porous bodies, the XRD results showed peaks characteristic of a pure and crystalline HA (JCPDS 9-432) as a single phase. SEM images indicate open and interconnected pores inside the material, with pore sizes between 50 and 600 μm. Also, SEM images demonstrate the relatively good bioactivity of the HA scaffolds after immersion in SBF. All results for the porous HA bodies suggest that these materials have great potential for use in tissue engineering. [ABSTRACT FROM AUTHOR]

A nontoxic, water-soluble copolymer consisting of isobutylene and maleic anhydride (PIBM) was used as both dispersant and gelling agent to mold MgAl 2 O 4 green body by gelcasting at room temperature in air. In this paper, MgAl 2 O 4 slurries with solid loadings from 43 vol% to 50 vol% were prepared by adding PIBM. The rheological properties of the slurries were investigated. As the solid loadings increased from 43 vol% to 50 vol%, the linear shrinkage in the drying and pre-sintering process decreased from 6.9% to 2.8% and from 16.0% to 14.7%, respectively. The bending strength of the green body with 50 vol% solid loading can reach 2.62 MPa. The in-line transmission of the MgAl 2 O 4 ceramics gradually increased from 61% to 86.9% (1100 nm) with the solid loadings increasing. [ABSTRACT FROM AUTHOR]

ZrB 2 –SiC foams were prepared from composite poring mechanisms of foaming and solid poring (PAA beads) by the application of a gelcasting technique. The porosities and microstructures of sintered bulks were tailored through changing the solids loading of slurries and the amount of added PAA beads. The increase in solid loading caused high viscosities of slurries, and thus resulted in the reduction of porosity and a tendency to form close pores. With increasing the amount of PAA beads, high porosities (up to 91.4%) and obvious connectivity improvement between bubble-derived pores emerged owing to efficient foaming and presence of bead-derived pores. As the porosity increased, the compressive strength (0.4–8.2 MPa) decreased, and the gas permeability (9.7–62.1×10 −12 m 2 ) augmented because of the effects of bead-derived pores and the increase in window number and size of bubble-bead pores. [ABSTRACT FROM AUTHOR]

Porous γ -Y 2 Si 2 O 7 ceramic with good mechanical and thermal properties is prepared by the in situ reaction sintering foam-gelcasting method using Y 2 O 3 and SiO 2 as the starting powders and non-toxic gelatin as the gel former. The porous sample has interconnected large pores (40–230 μm) and small pores (0.1–2 μm) in the skeleton. The porosity can be controlled from 64.3% to 89.3% by adjusting the solid content and amount of the slurry. The corresponding strength ranges from 46.5 to 3.4 MPa. Porous γ -Y 2 Si 2 O 7 with a porosity between 57.2% and 90.0% shows a low thermal conductivity in the range of 0.918–0.147 W/(m K) at room temperature. Porous γ -Y 2 Si 2 O 7 has excellent mechanical property at high temperature (the strength at 1100 and 1200 °C is maintained above 71% and 50%, respectively, of the value at room temperature) and good thermal stability (the reheating shrinkage is 1.3–1.7%). This work indicates that lightweight porous γ -Y 2 Si 2 O 7 ceramic could be applied as a promising high-temperature thermal insulator with low thermal conductivity and high temperature reliability. [ABSTRACT FROM AUTHOR]

Inorganic scintillators are very important in medical and industrial measuring systems in the detection and measurement of ionizing radiation. In addition to Ce 3+ , a widely used dopant ion in oxide scintillators, divalent Europium (Eu 2+ ) has shown promise as a high-luminescence, fast-response luminescence center useful in the detection of ionizing radiation. In this research, aluminum oxide (Al 2 O 3 ) was studied as a host material for the divalent europium ion. Polycrystalline samples of Eu 2+ -doped translucent Al 2 O 3 were fabricated, and room temperature luminescence behavior was observed. Al 2 O 3 ceramics doped with 0.1 at% Eu 2+ were fabricated with a relative density of 99.75% theoretical density and in-line transmittance of 22% at a wavelength of 800 nm. The ceramics were processed by a gel-casting method, followed by sintering under high vacuum. The gelling agent, a copolymer of isobutylene and maleic anhydride, is marketed under the commercial name ISOBAM, and has the advantage of simultaneously acting as both a gelling agent and as a dispersant. The microstructure and composition of the vacuum-sintered Eu 2+ :Al 2 O 3 were characterized by Scanning Electric Microscopy (SEM), Transmission Electron Microscopy (TEM), and Energy-dispersive X-ray spectroscopy (EDS). The phase composition was determined by X-ray diffraction measurements (XRD) combined with Rietveld analysis. The photoluminescence behavior of the Eu 2+ :Al 2 O 3 was characterized using UV light as the excitation source, which emitted blue emission at 440 nm. The radio-luminescence of Eu 2+ :Al 2 O 3 was investigated by illumination with X-ray radiation, showing three emission bands at 376 nm, 575 nm and 698 nm. Multiple level traps at different depths were detected in the Eu 2+ :Al 2 O 3 by employing thermoluminescence measurements. [ABSTRACT FROM AUTHOR]

Wet alumina green bodies with a dimension of 400 mm ×50 mm ×10 mm, respectively gelcast by PIBM (a copolymer of isobutylene and maleic anhydride) and EA (epoxy-amine) gel system, were dried at controlled temperature and humidity. Microstructure evolution and drying behavior of the green bodies with different solids loading and organic network were investigated. Pores among alumina particles became smaller and the constant rate period (CRP) became shorter with the increased solids loading or organic network. Further, the shrinkage of the body using PIBM ceased earlier and was smaller than that of the body using EA gel system. The typical microstructure of the body using PIBM gel system was thin organic networks on the particles and gradually a cocooned structure evolved during drying. While, the body using EA gel system had dense organic networks which evolved into a dense layer and strand-like structure around the particles. Such microstructures played different roles in water transportation and stress relaxation. As a result, the PIBM body was successfully dried without malformation but the EA body was bowing. [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]

C/SiC composites were prepared by infiltrating molten Si into gelcasted pure porous carbon preforms derived from mesocarbon microbeads (MCMBs). First large size flaw-free carbon preforms with smooth surfaces were produced by gelcasting method. The porosity and pore size of the carbonized preforms can be adjusted by changing the solid loading (MCMBs) ranging from 40 to 65 wt%. Subsequently, C/SiC composites were fabricated by liquid silicon infiltration of the porous carbon preforms. The results show that the preforms with solid loading from 40 to 50 wt% were completely infiltrated with Si and formed a C/SiC with homogeneous microstructure. While “SiC shell—black carbon core” structures were observed for the C/SiC composites with solid loading above 50 wt%, indicating that the Si infiltrating process was stopped in the surface of the preform. Reaction and infiltration mechanism analysis reveals that the siliconization process of porous carbon preform and the microstructures of the C/SiC samples were mainly affected by the reaction activity of carbon materials and pore structures of carbon preforms. [ABSTRACT FROM AUTHOR]

TiAl intermetallic and SiC ceramic are two kinds of important high-temperature structural material, but it is difficult to fabricate complex high-performance composites of them by traditional methods. In the paper, it is a pioneer study to prepare their composites so as to fabricate turbine blade by the hybrid technology of Stereolithography and gelcasting. Impregnation and pyrolysis behaviors of polycarbosilane were explored for SiC ceramic preparation, and the microstructure evolution and mechanical properties of TiAl-based composites were mainly analyzed. The results showed that adding trace amount of nickel and aluminum could remarkably promote the sintering of gelcasting TiAl intermetallic samples, the micropores inside TiAl samples were connected after debinding, and the metallurgical structures were all intermetallic. After the porous TiAl samples impregnated with polycarbosilane were then pyrolyzed three times, the final metallurgical structures were TiAl-based composites of TiAl, NiAl, SiC, TiC and Ti 3 SiC 2 . Ti 3 SiC 2 was the interface layer formed between TiAl intermetallic and SiC ceramic, and their high-temperature bending strength was between 82 MPa and 90 MPa at 1100 °C. Therefore, it was a promising method for the fabrication of complex high-performance TiAl-based parts such as turbine blade. [ABSTRACT FROM AUTHOR]

C/SiC composites were prepared by infiltrating molten Si into gelcasted pure porous carbon preforms derived from mesocarbon microbeads (MCMBs). First large size flaw-free carbon preforms with smooth surfaces were produced by gelcasting method. The porosity and pore size of the carbonized preforms can be adjusted by changing the solid loading (MCMBs) ranging from 40 to 65 wt%. Subsequently, C/SiC composites were fabricated by liquid silicon infiltration of the porous carbon preforms. The results show that the preforms with solid loading from 40 to 50 wt% were completely infiltrated with Si and formed a C/SiC with homogeneous microstructure. While “SiC shell—black carbon core” structures were observed for the C/SiC composites with solid loading above 50 wt%, indicating that the Si infiltrating process was stopped in the surface of the preform. Reaction and infiltration mechanism analysis reveals that the siliconization process of porous carbon preform and the microstructures of the C/SiC samples were mainly affected by the reaction activity of carbon materials and pore structures of carbon preforms. [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]

Highly transparent yttrium aluminum garnet (YAG) ceramic was prepared through spontaneous gelcasting with an aqueous mixture of commercial Al2O3 and Y2O3 powders and a water soluble co-polymer of isobutylene and maleic anhydride (commercial name Isobam) as the dispersant and gelling agent. The rheological behaviors of the slurries were investigated as a functions of Isobam concentration and solids loading. The optimized formula of the slurry was obtained with a solids loading of 68 wt% and Isobam addition 0.3 wt% (per powder). The in-line transmittances of the resulted YAG ceramic (thickness: 7.5 mm) were about 82.3% and 79.2% at the wavelengths of 1000 nm and 400 nm respectively. Microstructure observation exhibited a nearly pore-free structure with the average grain size about 15 µm. The new gelling system may have potential use for the fabrication of large and complexly shaped high quality YAG transparent ceramics. [ABSTRACT FROM AUTHOR]

Abstract: A mini alumina ceramic turbine rotor has been successfully fabricated using a tailored colloidal process based on gelcasting technology. A specialized forming, drying and sintering approach was developed for the complex-shaped component with both large volume (90mm in diameter and 20mm in height) and submillimeter geometry (0.42mm at the blade tip with curvature), to assure a highly dense product without warpage and cracks. The effects of solid content and temperature on the rheological behaviors of the prepared slurry were investigated to identify the best pourability. A novel approach using radius of curvature and overlapped area was adopted to compare the blade contour similarity under different sintering strategies and solid contents. In addition, the different physical and mechanical properties between main body and blade regions were discussed and their microstructures were analyzed. The preparation route for highly dense alumina rotor with minimum contour distortion was finally summarized. [Copyright &y& Elsevier]

Abstract: In this paper, novel porous Si3N4 ceramics were prepared by aqueous gelcasting using Si3N4 poly-hollow microspheres as pore-forming agent. The effect of Si3N4 poly-hollow microsphere content on the phase composition, microstructure, shrinkage, porosity and mechanical properties of the prepared porous Si3N4 ceramics were investigated. It is found that there is only β-Si3N4 phase in all the prepared porous Si3N4 ceramics. Meanwhile, the SEM results show that the pores in the porous Si3N4 ceramics distribute uniformly, the added Si3N4 poly-hollow microspheres and the basal body contact closely. With the increase of Si3N4 poly-hollow microsphere content, the shrinkage of the porous Si3N4 ceramics decreases gradually, and the porosity of the porous Si3N4 ceramics decreases firstly and then increases. Furthermore, the flexural strength and fracture toughness of the porous Si3N4 ceramics decrease with the increase of the Si3N4 poly-hollow microsphere content. [Copyright &y& Elsevier]