## 3 Results
Figure 3: SEM images of a fractured strut wall of (**a**) the sacrificial polymer template and (**b**) the reticulated porous diatomic–kaolin composite. Figure 5 shows the pore size distributions of the reticulated porous diatomite-kaolin composite specimens (pore density = 45 PPI), prepared from the composite particles ball milled for 0, 4, 8, and 24 h. As the ball-milling times increased, the pore size and pore volume fraction of the reticulated porous diatomite-kaolin composite specimens showed a slight decrease. Because the number of strut walls is fixed (it only depends on the pore density of the sacrificial polymer template), any difference in the pore size distributions can only be ascribed to the different ball milling times, resulting in diatomic-kaolin composite particles with different amounts of internal pores and average sizes. Figure 4: (**a**) 3D microstructure of typical reticulated porous diatomite–kaolin composite with a pore density of 45 PPI, reconstructed by micro-computed tomography (micro-CT). (**b**) Representative slice extracted from the micro-CT reconstructions. (**c**) 3D microstructure of typical reticulated porous diatomite–kaolin composite with a pore density of 80 PPI, reconstructed by micro-CT. (**d**) Representative slice extracted from the micro-CT reconstructions. Figure 5: Pore size distributions of reticulated porous diatomite–kaolin composites prepared from diatomic–kaolin composite particles ball milled for 0, 4, 8, and 24 h.  
In Figure 5, the pore size distributions of the reticulated porous diatomic-kaolin composite specimens covered the range from 0.5 to 5 \(\upmu\)m, which reflects the pore size distribution of the strut walls. The size of the voids generated by the burn-out sacrificial polymer template ranged from 50 to 100 \(\upmu\)m, whereas that of the large cell composed by the strut walls was in the sub-millimeter range. Figure 6a shows a viscosity vs. shear rate plot of the diatomic-kaolin composite slurries prepared with different ball milling times at a solid loading of 50 wt.%. Upon comparing the viscosity of the diatomic-kaolin composite slurry ball milled for 24 h to those of the samples ball milled for 0, 4, and 8 h, it was observed that the viscosities of the slurries were affected more strongly by the solid loading. For a solid loading of 50 wt.%, although the viscosities did not increase significantly as the ball milling time increased from 0 to 8 h, a drastic increase was observed at a critical point (24 h under these conditions). However, Figure 6b shows that the viscosities increased as the ball milling time was increased from 0 to 24 h; this can be understood by assuming that, until the solid loading reaches a certain point, the effect of the particle size decrease is marginal. In addition, the viscosities were still found to be significantly low, implying that the slurry may penetrate more easily the excessively narrow cells of a sacrificial polymer template with a pore density greater than 45 PPI. These correlations are in good agreement with established literature data [13]. For comparison, Figure 6c display a viscosity vs. shear rate plot of diatomic-kaolin composite slurries ball milled for 0 h with different solid loadings. The viscosity of slurries ball-milled for 0 h with solid loadings from 50 to 80 wt.% (Figure 6c) were then compared to those of slurries ball  
Figure 6: Viscosities of diatomic–kaolin composite slurries used for the preparation of reticulated porous diatomic–kaolin composite: ball milled for 0, 4, 8, and 24 h at a solid loading of (**a**) 50 wt.%, (**b**) 80 wt.%, (**c**) ball milled for 0 h at solid loadings ranging from 50 to 80 wt.%, (**d**) ball milled for 24 h at solid loadings ranging from 50 to 80 wt.%.