Preparation of porous stainless steel hollow-fibers through multi-modal particle size sintering towards pore engineering

The sintering of metal powders is an efficient and versatile technique to fabricate porous metal elements such as filters, diffusers, and membranes. Neck formation between particles is, however, critical to tune the porosity and optimize mass transfer in order to minimize the densification process. In this work, macro-porous stainless steel (SS) hollow-fibers (HFs) were fabricated by the extrusion and sintering of a dope comprised, for the first time, of a bimodal mixture of SS powders. The SS particles of different sizes and shapes were mixed to increase the neck formation between the particles and control the densification process of the structure during sintering. The sintered HFs from particles of two different sizes were shown to be more mechanically stable at lower sintering temperature due to the increased neck area of the small particles sintered to the large ones. In addition, the sintered HFs made from particles of 10 and 44 µm showed a smaller average pore size (<1 µm) as compared to the micron-size pores of sintered HFs made from particles of 10 µm only and those of 10 and 20 µm. The novel HFs could be used in a range of applications, from filtration modules to electrochemical membrane reactors.