Figure : Optical microscope images of the external face a brand new porous stainless steel frit (1 mm thick, 2.1 mm i.d., 0.2 m porosity, and 20% void fraction). (Top left) Voids are observed at the circular joint between the stainless steel frit and the metal ring. (Top right) Zoom in (500 m scale) the central region of the frit showing some defects. (Top right) Zoom in (100 m scale) the central region of the frit revealing that stainless steel grains were wiped off the surface are final polishing step. (Bottom right) Evidence of the final polishing step leaving circular marks on the flattened stainless steel grains. The sizes of the grains varies from 10 m for the smallest to 70 m for the largest.
