Fabrication of porous ceramic composites with improved compressive strength from coal fly ash

Abstract

A freeze-gel casting method has been proposed to fabricate porous mullite-alumina composite with controlled 'designer' pore structure and improved compressive strength. In this work, a tertiary butyl alcohol-coal fly ash slurry system with appropriate addition of Al 2 O 3 was used. Unidirectional aligned macropore channels were developed by controlling the solidification direction of the tertiary butyl alcohol solvent. Simultaneously, microsized pores formed in the walls of the pore channels; consequently, the inner section of the walls of the pore channels exhibited a more porous structure than the outer walls. The compressive strength of the sintered porous composite increased as the porosity decreased, i.e. the low porosity gave a high compressive strength. After sintering at 1500uC with 40 wt-% solid loading, the mullite-alumina composite with a porosity of 61?2% exhibited a compressive strength of y64?3 MPa.

Preparation of Fly Ash-Based Porous Ceramic with Alumina as the Pore-Forming Agent

“…At the same time, the mullite (PDF:15-0776) and alumina (PDF:10-0173) increased. It can be explained that the added alumina can increase the diffusion rate of SiO 2 , while it can be reacted with the silica to produce the mullite [28] during the sintering process. Moreover, it has an effect on the bending strength of the porous ceramic, which confirms what was discussed above (as shown in Figure 5).…”

Porous mullite/alumina-layered composites with a graded porosity fabricated by camphene-based freeze casting

“…Such cross-sectional pore morphology is similar to that obtained by unidirectional freeze casting of TBA-based suspensions. 9 However, unlike the linear growth of the TBA solid, the camphene grows to dendritic pattern. Thus, the porous microstructures of both the sintered cast bodies are clearly distinguished.…”

“…In general, the mechanical strength of highly porous ceramics obtained from freeze casting is not sufficient for load-bearing applications; for example, freeze cast mullite-alumina composite sintered at 1300 C with 20 wt% solid loading shows a relatively low mechanical strength of $10 MPa (85% porosity). 9 A promising method for increasing the mechanical strength of porous ceramics is to design layered structures with a gradient porosity. 10,11 Nowadays, researches on the recycling of coal fly ash to produce advanced ceramic materials attract more attention from the resource economy and environmental protection.…”

SiC‐based porous ceramic carriers for heat‐conductive phase change materials through carbothermal reduction method

“…Recently, phase change materials are embedded in porous metal carriers or graphite carriers, producing convenient composite phase change materials 6‐7 . Despite that porous ceramic carriers possesses high porosity, good wettability and high filling rate with phase change materials, they are generally fabricated by natural clay minerals containing metal oxides phases and mineral phases, resulting in low thermal conductivity 8‐9 . Therefore, the porous ceramic carriers with low cost and high thermal conductivity require our attention.…”