The properties of Southern Thailand clay-based porous ceramics fabricated from different pore size templates

• Polyurethane template with larger average pore size contained less solid content.
• The removal of organic portions left holes inside during sintering process.
• Amorphous silica aided a significant densification of ball clay on sintering.
• Porosity levels for all of the sintered porous ceramics were greater than 70%.
• Mullite phase found in the sintered porous ceramics increased compressive strength.

Open cell porous ceramics were produced by low-cost polymeric sponge method using natural clays (Surat Thani clay and Ranong clay) from Southern Thailand and alumina powder as raw materials. Open-cell polyurethane sponges with different pore sizes were used as templates for ceramic slurries. Batch formulations of the samples were formed into green bodies and fired at 1150 and 1200 °C at controlled firing rates. The properties studied include solid content, linear shrinkage, porosity, average pore size, pore size distribution, phase composition, phase morphology and compressive strength. This study found that the composition and pore size of sponge template strongly affected the physical properties and mechanical strength of the synthesized porous ceramics. It was found that porous ceramics could be produced from all ceramic compositions without internal cracking and distortion of the bulk structures. Surat Thani clay acted as a source of ball clay giving a better densification and shrinkage after sintering whereas Ranong clay, which is kaolinitic clay gave a better strength due to the presence of mullite as a major phase after firing at 1200 °C. The interlocking structure of the needle-like mullite phase could add to the evidence for higher compressive strength in the compositions containing higher relative ratio of Ranong clay to Surat Thani clay.