# Effect of the Sintering Temperature on the Compressive Strengths of Reticulated Porous Zirconia
## 3 Results  
In this study, reticulated porous zirconia specimens of 25, 45, 60, and 80 PPI (pores per inch) were prepared using the replica template method. Figure 1a shows the polymer templates of the sacrificial polymer template (commercial polyurethane foam) specimens with pore densities of 25, 45, and 60 PPI. The as-prepared reticulated porous zirconia specimens with pore densities of 25, 45, and 60 PPI, prepared using the replica method, are shown in Figure 1b. Typical SEM images of the fractured strut walls of the sacrificial polymer template and the reticulated porous zirconia are shown Figure 2a,b, respectively. The triangular voids obtained after the heat treatment and sintering of the sacrificial polymer template, shown in Figure 2b, strongly affect the overall mechanical properties of the reticulated porous ceramics. It is also well known that these inevitable triangular voids lower the compressive strength of reticulated porous ceramics, significantly hindering their application potential. Figure 2b shows the microstructure by which the reticulated porous zirconia with a uniform thickness of the strut wall is formed. Figure 1: Optical images of (**a**) the sacrificial polymer templates (commercial polyurethane foam), with pore densities of 25, 45, and 60 PPI, and (**b**) the reticulated porous zirconia specimens, with pore densities of 25, 45, and 60 PPI, prepared through the replica method. The viscosities of the zirconia slurry used for the preparation of the reticulated porous zirconia and the compressive strengths with solid loading rates of 60-67.74 wt.% and with 0.95\(-\)1.90 wt.% MC are shown in Figure 2(a),2(b), respectively. This figure shows part of the preliminary experiment, and because it is impossible to proceed with the experiment while changing all of the variables from the beginning, these values function as the basis of how the variables were measured, with the solid loading and MC value used here as variables. The sample with the highest strength was selected as the most optimized slurry (based on 45 PPI). Considering the amount of solid loading as a variable, the compressive strength at a solid loading rate of 67.74 wt.% was the highest. However, this sample did not have enough viscosity to tightly coat the strut walls of the sacrificial polymer template. To control the viscosity only by solid loading, zirconia particles must be added indefinitely until the desired viscosity is reached, though this approach is not efficient. Therefore, after fixing the solid loading amount (67.74 wt.%), the viscosity was controlled by the MC. The MC acts as a thickener that increases in uniformity when mixed with water [25]. It can be seen that the viscosity increased considerably when MC was added. Sintering was performed at 1600 \({}^{\circ}\)C to compare the compressive strength of the reticulated porous alumina to that in a previous experiment. In this study, preliminary experiments were conducted based on reticulated porous zirconia with a pore density of 45 PPI because it is difficult to prepare reticulated porous  
Figure 3: Viscosity at a shear rate of 0.01 s-1 of the zirconia slurry, and the compressive strengths: (a) 60–67.74 wt.% solid loading; and (b) 0.95–1.90 wt.% MC. Figure 2: Typical SEM images of a fractured strut wall of (a) the sacrificial polymer template, and (b) a reticulated porous zirconia specimen prepared from fine particles. ceramics with a pore density that exceeds 45 PPI with a sacrificial polymer template. As the pore density of the reticulated porous ceramics approaches 80 PPI, the increase in pore density makes it difficult to coat the internal strut walls of the sacrificial polymer template completely as well. Voids can be generated inside the sacrificial polymer template, reducing the compressive strength. It is uncertain as to whether the slurry was evenly distributed deep inside the reticulated porous zirconia specimens. Therefore, in this study, a non-destructive \(\upmu\)-CT analysis was utilized to investigate the prepared reticulated porous zirconia specimens.