Search

Abstract The mechanical strength of highly porous ceramic foams shows significant attenuation with the increase of porosity, especially for ceramic foams with very high porosity level above 95%. Ultra-light bulk composite ceramic foams were fabricated via introducing 20 wt% zirconia in alumina-based cell wall, aiming at improving mechanical strength of alumina based ceramic foams. The preparation and stability of alumina and zirconia particles synergistically stabilized foams were investigated. The obtained bulk ceramic foams manifested an exciting combination of both high porosity above 96% and excellent specific compressive strength, due to their closed pore structure, defect-free cell wall with uniform thickness, and uniformly distributed zirconia grains in alumina matrix. The alumina/zirconia composite ceramic foams with porosity of 96.7% exhibited compressive strength of 1.11 ± 0.07 MPa, which was much higher than that of alumina ceramic foams in the case of same porosity. [ABSTRACT FROM AUTHOR]

An innovative approach for fabricating porous alumina ceramics (PACs) with improved mechanical and thermal properties using walnut shell powders as pore-forming agent combined with alumina sol impregnation is reported in the present work. It is demonstrated that uniform distribution of spherical pores can be observed in as-prepared PACs by using above technical route. The decrease of walnut shell powder sizes significantly promotes the enhancement of crushing strength and reduction of thermal conductivity of the PACs. Meanwhile, the impregnated alumina sol is favoring for the formation of spherical micro-pores, then further improves their mechanical and thermal insulation performances. The lowest thermal conductivity and highest crushing strength of resulting sample reach 0.16 W/m K and 29.2 MPa, respectively. This novel method offers new possibilities to fabricate high-quality PACs. [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]

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]

Mechanically robust alumina ceramics with low shrinkage were successfully prepared via gelcasting using Isobam as the gelling agent and pre-sintered alumina powder as the raw material for the first time. The influence of amount of pre-sintered alumina powder and powder's pre-sintering temperature on the viscosity of suspension and mechanical properties of low-shrinkage alumina ceramics were systematically investigated. The results showed that low-shrinkage alumina ceramics with flexural strength of 294.5 ± 33.0 MPa, linear shrinkage of 7.79% and relative density of 91.5% can be obtained with the addition of 60 wt% alumina powder pre-sintered at 1600 °C. This convenient and facile approach is promising to fabricate low-shrinkage alumina ceramics with large sizes, high dimensional accuracy and complex shapes. [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]