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Porous materials with wrinkled surfaces could have broad applications in catalysis and adsorption. However, designing cellular ceramics with similar structures is challenging. Herein, we demonstrated the binary colloidal self-assembly of γ-Al 2 O 3 nanoparticle/silica gelation network for constructing such materials. The competitive effect between volume shrinkage and surface bend during water evaporation of silica gel contributed to wrinkled aperture surface. During calcination, silica nanoparticles were highly active to react with alumina to form mullite nanocrystals, bringing about high compressive strength at low relative densities. After calcining at 1350 °C, resultant products with hierarchical structure exhibited an outstanding compressive strength of 4.2 MPa, a relatively high surface area of 7.23 m2/g at a porosity level of 83.3%. The current strategy provides a feasible and affordable approach for producing high performance ceramic foams towards practical application fields in catalysis and adsorption. [ABSTRACT FROM AUTHOR]

Engineering high performance cellular ceramics with both ultralow density and satisfactory compressive strength for practical applications still represents a grand challenge. Herein, alumina-based cellular ceramics bonded by in-situ formed mullite phase were constructed by Al 2 O 3 –Si-boehmite particle-stabilized foams. The gelation of boehmite sol improved the stability and harnessed the deformation of dried Al 2 O 3 –Si composite foam. The oxidation of silicon and further generation of in-situ mullite phase enhanced the chemical bond between alumina particles on cell walls, resulting in the superior mechanical properties. As an exemplar, the resulting cellular ceramic possessed the robust compressive strength of 2.26 MPa at a high porosity of 87.8%. The gelation-assisted Al 2 O 3 –Si particle-stabilized foams provide a facile and convenient strategy for construction of composite ceramic foams with high porosity and robust strength. [ABSTRACT FROM AUTHOR]

A gelcasting system of alumina utilizing tartaric acid as the dispersant and glutaraldehyde as the crosslinker is reported, in which glutaraldehyde can polymerize itself and react with tartaric acid, thus forming a three-dimensional network. Measurement of zeta potential and viscosity shows good dispersion ability of tartaric acid. Shear modulus during gelation demonstrates its good gelation strength and fast gelation speed at room temperature. Moreover, an effective way to control the gelation speed is provided to improve the feasibility of this method. Results indicate that this gelcasting method has the advantages of low viscosity, small amounts of additives and short forming time and is a promising method to fabricate green bodies with large sizes and complex shapes. [ABSTRACT FROM AUTHOR]

Cellular ceramics with 3D network architecture are attracting ever-increasing attention because of their great application potential in multiple fields. Unfortunately, a daunting challenge still remains for fabricating such materials. A novel methodology is provided in the current work to construct cellular ZrO 2 ceramics with such architecture by combining polyurethane foaming and chemical modification technology. Stearic acid grafted ZrO 2 powder with improved dispersibility allows the successful assembly into the polyurethane porous framework. The obtained cellular materials possess a three-dimensional network architecture with windows on the cell wall. The resulting ZrO 2 cellular ceramic with such unique structure exhibits a relatively high porosity (83.5%) and robust compressive strength (13.5 MPa), which outperforms most of the existing ZrO 2 -based counterparts. With above advantages, we envision that as-prepared products are promising for filter applications. [ABSTRACT FROM AUTHOR]

Ultralight ceramics with striking mechanical properties and improved pore connectivity could have wide applications in areas ranging from catalyst support to hot gas filtration. However, creating such materials has proven to be a challenging target. This work demonstrated a novel methodology to prepare porous MgAl 2 O 4 ceramics by calcining gelled MgO–Al 2 O 3 –SiO 2 particle-stabilized foams. The striking green strength of dried foams can be achieved as a consequence of MgO hydration and subsequent formation of gelled Mg(OH) 2 and MgO–SiO 2 –H 2 O skeleton. The decomposition of colloidal substance at elevated temperature resulted in the formation of small pores on the cell wall, thus forming the hierarchical porous architecture and improving the pore connectivity. The highly porous MgAl 2 O 4 ceramics fired at 1600°C possessed the integrated properties of ultrahigh porosity (87.0%), improved pore connectivity and satisfactory compressive strength (7.93 MPa), showing great potential to be used in multiple industrial fields. [ABSTRACT FROM AUTHOR]

A facile strategy for the fabrication of elongated mullite reinforced porous alumina ceramics (PACs) using carbonized rice husk (CRH) as pore-forming agent and silica source is reported for the first time. A large amount of elongated mullite is synthesized in pores due to the reaction of amorphous silica in CRH skeleton and alumina ceramic powder. Elongated mullite acts as the bridges between pore walls, enhancing the compressive strength of PACs. Furthermore, secondary pores from the intersection of elongated mullite is favor of decreasing of the thermal conductivity. High performance PAC with porosity of 74.3% has been fabricated by employing 25 wt% CRH, which possesses relatively low thermal conductivity of 0.189 W/(m•K) and ultra-high compressive strength of 45 MPa. Its comprehensive performance is much better than that of existing ceramic materials. Our findings present a facile, eco-friendly and effective approach to fabricate high performance PACs as the high-temperature thermal insulation materials. [ABSTRACT FROM AUTHOR]

In order to reduce thermal conductivity but to exhibit better mechanical properties of porous alumina ceramics (PACs), a novel approach, based on the modification of pore structures (i.e. mean pore size, micro-pore proportions and pore shape factor) by impregnation of alumina sol, is reported in the present work. The properties of as-impregnated samples were compared with commercial alumina hollowsphere bricks. Results show that impregnation of alumina sol in PACs has a positive influence on pore structures, leading to a superior strength and a lower thermal conductivity. In particular, when 8 wt% alumina sol solid content is impregnated, the crushing strength (35.3 MPa) and thermal conductivity (0.15 W/m K at 200 °C) of sample are much better than that of the commercial alumina hollowsphere bricks. This novel method for excellent PACs provides promising applications as insulating lining materials in the fields of industrial furnace. [ABSTRACT FROM AUTHOR]

A new gelcasting approach of alumina inspired by Isobam was designed utilizing a polyelectrolyte dispersant named BTT, which is able to form cross-links via thiol-ene reaction with pentaerythritol tetrakis(2-mercaptoacetate). Measurement of zeta potential and viscosity shows good dispersion ability of BTT in 52 vol% alumina suspensions. The flow curves and shear modulus of wet green bodies during gelation demonstrate its high gelation strength in comparison with Isobam. The analysis of effects of addition of ammonium citrate tribasic into the system indicates that a polymer-particle double network is supposed to form during gelation. Elastic part and viscous part of gelation strength of the system are mainly dominated by interaction between polyelectrolyte and particles and cross-linking respectively, which accounts for the existence of both high gelation strength and flexibility of wet green bodies fabricated in this approach. [ABSTRACT FROM AUTHOR]

Sodium zirconium silicon phosphorus with the composition of Na 3 Zr 2 Si 2 PO 12 (NZSP) was prepared by a facile solid state reaction method. The effects of the calcination temperature and rare earth element substitution on the structure and ionic conductivity of the NZSP material were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM) and AC impedance measurement. The results show that the microstructure and ionic inductivity of the NZSP was strongly affected by the aliovalent substitution of Zr 4+ ions in NZSP with rare earth metal of La 3+ , Nd 3+ and Y 3+ . At room temperature, the optimum bulk and total ionic conductivity of the pure NZSP solid electrolyte sintered under different conditions were 6.77×10 −4 and 4.56×10 −4 S cm −1 , respectively. Substitution of La 3+ , Nd 3+ and Y 3+ in place of Zr 4+ exhibited higher bulk conductivity compared with that of pure NZSP. Maximum bulk and ionic conductivity value of 1.43×10 −3 and 1.10×10 −3 S cm −1 at room temperature were obtained by Na 3+x Zr 1.9 La 0.1 Si 2 PO 12 sample. The charge imbalance created by aliovalent substitution improves the mobility of Na + ions in the lattice, which leads to increase in the conductivity. AC impedance results indicated that the total ionic conductivity strongly depends on the substitution element and the feature of the grain boundary. [ABSTRACT FROM AUTHOR]

Herein, the preparation of millimeter-sized poly-hollow alumina spheres (PHASs) with high-surface-area is proposed via an innovative and facile ball dropping method based on particle-stabilized emulsions. The PHASs fabricated by this method possess high specific surface area because of their hierarchical pore structures and high porosity, and exhibit remarkable superiority over the commercially available active alumina materials with specific surface areas of 200–300 m2g-1. The resultant millimeter-sized PHASs have diameters in range of 2–6 mm, average mesoporous sizes of 4–8 nm, and excellent specific surface areas of 400–500 m2 g-1, which are achieved with oil-water volume ratio of 3:1, rotation speed of 900 rpm, and sintering temperature of 500 °C. These high-performance PHASs with ultra-high specific areas and hierarchical pore structures can potentially be useful in various applications. [ABSTRACT FROM AUTHOR]

The generation of PVA hydrogel through freeze-thaw technique has been utilized innovatively to complete the forming process of porous Si 3 N 4 ceramics in the present work. In comparison with gelcasting method, green body with comparable strength has been achieved by this novel forming process, which is owing to the strong function of PVA gel caused by the freeze-thaw cycles. Herein, Si 3 N 4 hollow spheres are employed as pore-forming agent in order to achieve closed pores. The morphology of green body illustrates that pores originate from both hollow spheres and the space occupied by ice crystals, and the latter gives rise to the increase of porosity around 10%. Studies on the mechanical, dielectric and thermal properties of porous Si 3 N 4 ceramics dependent on freeze-thaw cycle and freezing time have been performed. It is found that porous ceramics treated for freeze-thaw 2 cycles with freezing time of 24 h present excellent properties, which are promising to be applied as radome materials. [ABSTRACT FROM AUTHOR]

As a copolymer of isobutylene and maleic anhydride, Isobam, a newly-developed gelling agent, plays a significant role in ceramic forming process. However, dispersion and gelation behavior of Isobam has not been discussed in detail yet. To investigate the influence of other dispersants, pH and electrolytes on dispersion and gelation behavior of Isobam, zeta potential, viscosity and modulus curves during gelation were measured from 50 vol% alumina suspensions with 0.1–0.7 wt% Isobam. A two-step bridging mechanism is proposed to explain the gelation behavior of Isobam, providing guidance on usage of Isobam in combination of other additives to achieve suspensions with high solids loading and adjustable gelation characteristic. [ABSTRACT FROM AUTHOR]

Compressive strength is one of the most important mechanical properties for ceramic foams but the dependence of compressive strength of highly porous ceramic foams on porosity remains unclear up to now, especially for the ceramic foams with porosity above 94%. In this paper, the relationship between compressive strength and porosity of ceramic foams with high porosity in the range of 79–98% was studied for the first time. The alumina ceramic foams and zirconia foams were prepared by particle-stabilized foaming method using sodium dodecyl sulfonate (SDS) as foaming agent. It was found that the function relation between compressive strength and porosity depended on porosity level. Specifically, compressive strength of ceramic foams fitted well with Rice Model when the porosity ranged from 79% to 94%. When the porosity increased above 95%, compressive strength of ceramic foams showed linear relation to porosity, which was probably due to the characteristic of highly porous ceramic foams with thin and lamellate cell wall. [ABSTRACT FROM AUTHOR]