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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]

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]

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]

In the present work, carbon black (CB) works as a pore-forming agent in the preparation of alumina porous ceramics. The pore structures ( i.e. mean pore size, pore size distribution and various pores size proportions) were characterized by means of Micro-image Analysis and Process System (MIAPS) software and mercury intrusion porosimetry. Then their correlation and thermal conductivity as well as strength were determined using grey relation theory. The results showed that the porosity and mean pore size increased against the amount of CB, whereas the thermal conductivity, cold crushing strength and cold modulus of rupture reduced. The <2 μm pores were helpful for enhancing the strength and decreasing the thermal conductivity whereas the >14 μm pores had the opposite effects. [ABSTRACT FROM AUTHOR]