## 3 Results  
Typical sacrificial polymer templates (in this study, commercial polyurethane foams) with pore densities of 10, 25, 45, 60, and 80 PPI are shown in Figure 1a. Figure 1b shows the as-prepared reticulated porous diatomite-kaolin composite specimens with pore densities of 10, 25, 45, 60, and 80 PPI, which were prepared using the polyurethane foams and diatomite-kaolin composite slurry. The sintering temperature of the reticulated porous diatomite-kaolin composite specimens was determined to be 1200 \({}^{\circ}\)C. Based on our previous study and other reports in the literature [23; 24; 49; 50], it is well known that the reticulated porous diatomite-kaolin composite maintains a similar microstructure up to 1200 \({}^{\circ}\)C after that it begins to melt because of impurities such as Na2O, K2O, Al2O3, CaO and MgO [50], which can damage the characteristic porous morphology of diatomite particles. To control the average particle size of diatomic particles, ball-milling was carried out for 0, 4, 8, and 24 h. Typical scanning electron microscopy (SEM) images of diatomic particles after the corresponding ball-milling processes are shown in Figure 2a-d, respectively. Obviously, the average particle sizes of diatomic decreased as the ball milling time increased, until a certain saturation point was reached. The particle size distributions of diatomic samples after being ball milled for 0, 4, 8, and 24 h are shown in Figure 2e, and the corresponding average particle sizes were 12.79, 10.54, 8.77, and 8.36 \(\upmu\)m, respectively. The diatomic particles were also ball milled for 1 and 2 h (with corresponding average particle size of 11.66 and 11.11 \(\upmu\)m, respectively); however, because of the negligible particle size difference, further experiments were carried out using only diatomic particles ball milled for 0, 4, 8, and 24 h.  
It is well known that reticulated porous diatomite is too weak to handle, owing to the high porosity of the reticulated porous ceramic and the inherent porous nature of diatomic particles [20,21,23]. Therefore, to the best of our knowledge, only a few applications of reticulated porous diatomite prepared by the replica method have been reported. To expand the application fields of reticulated porous diatomic beyond its typical applications (porous diatomic filters prepared by the extrusion method and porous diatomite foot mats prepared by slip casting), we introduced kaolin to form a diatomite-kaolin composite and determined the optimal processing conditions to obtain the maximum compressive strength while maintaining the advantageous properties of diatomic. The average particle size of the as-received kaolin (1.53 \(\upmu\)m) was approximately 12% that of the as-received diatomic (12.79 \(\upmu\)m). Therefore, we suggested that the plate-like kaolin particles could strengthen the coarsely and partially inter-connected pore channels generated by diatomite particles [24]. It should also be mentioned that the pore structure characterization of a reticulated porous ceramic should be based on the results of several complementary techniques such as (1) SEM, (2) micro-CT, and (3) mercury porosimetry [51]. Typical fractured strut walls of the sacrificial polymer template (a commercial polyurethane foam) and of the reticulated porous diatomite-kaolin composite are shown in Figure 3a,b, respectively. The macroscale voids generated after the pyrolysis of the polymer template (during the burn-out process in the replica method), shown in Figure 3b, are common features that strongly affect the overall mechanical properties. It is well known that these inevitable macroscale voids and defects make any kind of reticulated porous ceramics prone to external load bearings, and significantly reduce their application potential. If the cross-section of the strut walls of the sacrificial polymer template is circular, unlike the triangular shape of the commercial polymer template in Figure 3a, it can improve the mechanical properties of reticulated porous ceramics [52].