The effect of coarse particles on the microstructural evolution of porous alumina sintered at 1375 °C

Fabrication of porous alumina ceramics from powder mixtures with sol–gel derived nanometer alumina: Effect of mixing method

“…However, as the nanomaterial percentage continues increasing above the threshold value, which was measured at around 8 wt% in our case, the combination of faster sintering kinetics and of better packing of particles results in the gradual decrease of porosity in consistency with literature results. 3,4,6,7,16 The better packing in case of bimodal distributions has been long discussed and an optimum packing at a fine powder content at around 20-30 wt% is reported 3,[5][6][7]12,[16][17][18] attributed to the filling of voids among the coarse particles with the small ones. It becomes obvious that the homogeneity has to play an important role in this combined phenomenon of both porosity and strength increase, because as the nanoparticles form large agglomerates, these would concentrate on the voids of coarse particles (even for low nanomaterial addition) and the effect on porosity increase would be less pronounced from the beginning.…”

“…characteristics have been developed by using bimodal powder consisting of coarse and very fine particles, 3,5,11,12 whereas many researchers are also investigating the effect of bimodal powder mixtures on final ceramic microstructure. 4,6,7 The basic assumption made is that the use of such mixtures results to better particle packing, more homogeneous microstructures, enhanced surface and grain boundary diffusion at intermediate temperatures and retarded densification at high temperatures.…”

Effects of Coarse Particles on the Gelcasting of Ceramic Foams

“…A feasible approach to evaluate these effects is to characterize and test the final materials after a certain sintering processing. However, the sintering ability of coarse particles is lower than that of fine particles, which also influences the properties of the final foams 10 . Hence, it becomes difficult to evaluate the effects of coarse particles on the gelcasting of ceramic foams.…”