Preparation of porous stainless steel hollow fibers by robotic fiber deposition

Inorganic membranes can be used under harsh operating conditions such as corrosive environments and high temperatures. We propose a new method for producing porous stainless steel hollow fiber membranes using phase-inversion robotic fiber deposition. The method uses a suspension consisting of stainless steel powder, polymer and solvent which is extruded through a concentric nozzle. By a non-solvent induced phase inversion process the hollow fiber is solidified after extrusion. This technique allows the production of accurate continuous patterns in a one-step process. The resulting green stainless steel hollow fibers are quite stiff and the obtained green patterns can easily be transferred without any deformation. A low amount of organic additives (2 wt%) is used resulting only in a limited shrinkage after sintering. The prepared hollow fibers in this study had outer diameters between 1 and 4 mm and wall thicknesses of 200 to 700 μm. It was found that the diameter to wall thickness ratio had an effect on the uniformity of the wall thickness. Therefore this ratio should preferably be larger than eight for stainless steel. The morphology of the obtained fibers was characterized and the effect of the sintering temperature on properties such as porosity, mechanical strength and nitrogen permeation was investigated.