One-step co-sintering of hierarchical mullite whisker/fiber membranes with gradient pore structures for effective filtration of dust-laden gas

Porous ceramic fiber membranes with high gas permeance have shown great potential for the treatment of dust-laden gas. However, a major challenge is posed by the micro or nano-sized solid particles which can easily block the pore channels of the fiber membranes due to the larger surface pore size. Therefore, in this work, a novel method was proposed for the in-situ growth of mullite whiskers around the surface of the mullite fibers. This method aimed to decorate the pore channels of the fiber membranes by using a layer-by-layer construction strategy. For this purpose, a dry-pressing technique was employed to prepare a “green” mullite fiber support. It was followed by the preparation of another “green” fiber layer with the addition of catalysts on this support. After the co-sintering process, hierarchical mullite whiskers with gradient pore structures were produced. The in-situ growth of mullite whiskers around the fibers decorated the pore structure. As a result, it helped in effectively capturing the solid particles in the dust-laden gas. Additionally, the co-sintering process significantly reduced the sintering consumption and fabrication period. Moreover, a detailed investigation was carried out on the construction parameters including the sintering system atmospheres, Si–Al sol addition content, AlF₃ concentration, mechanism of whisker growth and stability. The findings showed that hierarchical mullite whisker/fiber membranes obtained from the proposed method had a mean pore size of 2.7 μm and gas permeance of ∼106 m³ m⁻² h⁻¹·kPa⁻¹. The Darcy's permeability coefficient of the membranes was also higher than the membranes prepared from existing methods. Moreover, the optimized membrane showed 99.9% rejection of the solid particles in the dust-laden gas, including micron-size (2.5 μm) and nano-size (300 nm) solid particles. This work provides a novel method for the fabrication of hierarchical mullite whiskers with gradient pore structures having the capability to filter industrial dust-laden gas.