Figs. 3 and 4 present typical optical and SEM micrographs of
the prepared bi-layered ceramics. The SEM micrographs
correspond to the porous bottom layer of each sintered disc.
The optical micrographs reveal a perfect interfacial connection
between the dense and porous layer, for all systems studied,
showing that the interface between layers is independent from
the pore forming agent incorporation content, particle size
distribution and nature. The content and particle size distribution
of porogen dictated the volume, number and area of pores in the
bi-layered ceramics bottom layer. Smaller porogen particles
(o250 mm) produced a greater number of small pores, while
larger particles lead to a smaller number of larger pores. For the
studied incorporation contents (up to 25%), no significant
differences were perceived between the two selected polymers.
Optical micrographs did not reveal changes on the porosity of
the dense layer, which could be induced by the release of gases
originated from porogen burn out in the bottom layer. SEM
characterization was performed for all compositions to validate
the above statement. For the sake of clarity only SEM
micrographs for one composition containing pore forming agent
will be shown. Fig. 5a presents SEM micrograph of a fully
dense specimen (prepared without porogen), while Fig. 5b–d
correspond to a sintered disc prepared with 10% PP/250.