Diatomite-based porous ceramics with high apparent porosity: Pore structure modification using calcium carbonate

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

“…With increased dolomite content up to 20 wt.%, glassy phase in the ceramics significantly decreased and the closed pores (Figure a, Figure b) were modified to become interconnected pores. Moreover, a large number of newly generated large‐size pores appeared in the ceramics due to CO 2 emission from the decomposition of dolomite, which may explain an obvious increase in open porosity and average pore diameter of ceramics with addition of 20 wt.% dolomite in Figure and Figure b. With the further increasing addition of dolomite, the interconnected pores (Figure c) were gradually modified to become isolated small‐size ones (Figure d, Figure e, Figure f).…”

“…The decrease in density caused by the loss of mass due to the increase in dolomite could actually decrease the bending strength of ceramics . Moreover, the increased dolomite concentration affected the formation of sintering necks, which was beneficial in the improvement of bending strength of ceramics . Previous literature also stated that with the increase of the relative diameter of sintering neck, strength of the material is constantly increased…”

“…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.…”

“…An addition of 0–50wt.% dolomite initially enlarged the average pore diameter from ∼8.17 μm to ∼12.98 μm and then decreased to ∼2.82μm, which was consistent with the change of the pore size distribution of ceramics. This phenomenon might be explained as follows: the release of CO 2 from decomposition of dolomite generated new pores, while higher dolomite addition could introduce more CaO and MgO (alkaline‐earth oxides) to decrease melt viscosity, thereby further promoting the flowability of the melt among pores and the formation of small‐size pores …”

“…Notably, when the added dolomite exceeded 20 wt.%, the open porosity and bending strength of ceramics exhibited different trends due to the fact that the bending strength of ceramics could be also affected by other factors. The decrease in density caused by the loss of mass due to the increase in dolomite could actually decrease the bending strength of ceramics . Moreover, the increased dolomite concentration affected the formation of sintering necks, which was beneficial in the improvement of bending strength of ceramics .…”