Porous stainless steel hollow fiber membranes via dry–wet spinning

Porous stainless steel hollow fibers have been prepared via the dry–wet spinning process, based on phase inversion of a particle loaded polymer solution, followed by sintering. The morphology of the green fibers combines sponge like structures and macro voids, and is related to the dynamics of the phase inversion process. The morphology can be tuned by changing the spinning conditions and the composition of the spinning mixture. In analogy to their ceramic counterparts the morphology of the stainless steel fibers is preserved during sintering, apart from shrinkage due to densification. At a length scale comparable to the diameter of the steel particles the microstructure and related pore size distribution are more strongly affected by the sintering temperature, as compared to their ceramic counterparts. Sintering the stainless hollow fibers at temperatures > 1100 °C results in a sharp decrease in nitrogen permeance and an increase in bending strength, due to densification. The strength (∼1 GPa) and nitrogen permeance (0.1 mmol m−2 Pa−1 s−1 at 21 °C) of stainless steel fibers sintered at 1050–1100 °C are superior as compared to their ceramic counterparts. The excellent properties of the stainless steel hollow fibers make them suitable as membrane (supports) for applications involving harsh environments.

Research highlights
► Porous stainless steel hollow fibers have been prepared with uniform sponge-like structures suitable for coating.
► The morphology of the fibers can be tuned by controlling the amount of particles and water concentration in the spinning mixture, similar to what has been reported for ceramic analogues.
► The microstructure and related pore size distribution, at the length scale of the steel particles, are more strongly affected by the sintering temperature, as compared to their ceramic counterparts.