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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]

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]

Isobam, a copolymer of isobutylene and maleic anhydride, is a newly developed gelling agent for ceramic colloidal forming. However, the Isobam system exposes a weakness of high viscosity when solids loading exceeds 54 vol%. Suitable additives to effectively decrease viscosity and have minimal impact on gelation strength were discovered from various dicarboxylic acids through investigation on zeta potential, viscosity of suspensions, shear modulus during gelation and yield stress and modulus of elasticity of wet green bodies. Alumina ceramics with flexural strength of 442 ± 49 MPa and a Weibull modulus of 10.8 were produced from 54 vol% suspensions with 0.5 wt% Isobam assisted by 0.04 wt% phthalic acid and 0.03 wt% oxalic acid after pressureless sintering. [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]