Direct foaming of macroporous ceramics containing colloidal alumina

Liquid foams containing Al2O3 nanoparticles were obtained after direct foaming of a colloidal alumina suspension with ammonium stearate. These systems were stable for at least 24 h and were comprised by small cells (35 mu m). Up to 10 wt% of these foams were added to an ultrastable Al2O3-stabilised one and resulted in macroporous samples with high total porosity (>70%). Their green mechanical strength was proportional to the amount of colloidal alumina added, but lower than a composition with calcium aluminate cement. When compared with compositions prepared with colloidal alumina suspension, the colloidal foams resulted in samples with a higher number of small pores (<30 mu m) and lower linear shrinkage after firing at 1600 degrees C for 5 h (similar to 9%). Thus, colloidal alumina foams can be used for processing macroporous refractory ceramics with smaller pores, lower dimensional changes after firing and higher porosity.

Automated summary

Liquid foams containing Al2O3 nanoparticles can be used to process macroporous refractory ceramics with higher porosity, a higher number of small pores, and lower linear shrinkage after firing at 1600 degrees C for 5 hours.