Formation mechanism of high apparent porosity ceramics prepared from fly ash cenosphere

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

“…EDS analysis further exhibited that the surface of pores mainly consisted of O, Si, Al, Ca, Na and few Mg, which was consistent with the XRF analysis results of alkali pretreated fly ash in Table . Our previous work suggested that the introduction of CaO could modify the dense shell of fly ash cenosphere into porous shell and increase open porosity of porous ceramics . However, even though there was element of Ca on the surface of pores, the pores shown in Figure were still in closed status.…”

“…The decrease in open porosity can be explained by the formation mechanism of ceramics: at room temperature, there were a lot of pores in green compacts due to the gaps between the particles; with the increase of sintering temperature, the open porosity decreased through two pathways: one was that these particles were gradually bonded together via mass transfer; the other was that the reduced surface viscosity of particles promoted rearrangement of particles and narrowed the space between particles . Thus, the open porosity of the samples partly came from the gaps between particles . The linear shrinkage of ceramics increased with increasing sintering temperature, which was consistent with the above explanation.…”

“…Our previous work suggested that the introduction of CaO could modify the closed pores of fly ash cenosphere into open pores. With the addition of CaO, porous ceramics with high open porosity were successfully prepared . For porous ceramics prepared from fly ash, the influence of dolomite in pore structure was confirmed to be obvious.…”

“…Traditional techniques for improving the open porosity of porous ceramics include the addition of pore‐forming agents, gel‐casting, direct foaming, and freeze‐casting . Among them, directly addition of pore‐forming agent is a simple strategy to increase the open porosity of ceramics . Moreover, the pore structure of porous ceramics, which is the key parameter in their applications, can be effectively modified using pore‐forming agents …”

“…[9][10][11][12][13][14] Among them, directly addition of poreforming agent is a simple strategy to increase the open porosity of ceramics. [14] Moreover, the pore structure of porous ceramics, which is the key parameter in their applications, can be effectively modified using pore-forming agents. [15][16][17] Fly ash is a type of solid waste discharged from coal fired power plants with an annual worldwide emission of nearly 750 million tons.…”