New insight into the modification of pore structure in porous ceramics prepared from fly ash rich in CaO

Porous ceramics with high open porosity and good mechanical properties were successfully prepared from fly ash rich in CaO. An addition of 30-50wt.% dolomite decreased the average pore diameter from similar to 11.79 mu m to similar to 2.82 mu m due to the decrease of viscosity with high dolomite addition, while there is an increase in open porosity from 48.63% to 53.23%. SEM results suggested that pores were firstly surrounded by glassy phase. With the addition of more than 30 wt.% of dolomite, pores were covered by loose structure. XRD results showed the changes in crystal phases of sintered ceramics, from anorthite sodian to alkaline basalt and then to calcium magnesium silicate. CaO and MgO from decomposed dolomite were proposed to be the main reason on modification closed pores to open ones. Except this, CO2 emission and crystalline water emission during sintering were also contributed to the formation of open pores in porous ceramics.