# Effect of the Sintering Temperature on the Compressive Strengths of Reticulated Porous Zirconia
## 3 Results
The results of measurements of the compressive strength at 1400 \({}^{\circ}\)C, 1500 \({}^{\circ}\)C, and 1600 \({}^{\circ}\)C indicate that the compressive strength when the specimens are sintered at 1600 \({}^{\circ}\)C is the best. In this case, 80 PPI was utilized only at 1600 \({}^{\circ}\)C to obtain the maximum compressive strength. To maximize the compressive strength, samples of 80 PPI sintered at 1600 \({}^{\circ}\)C were measured, but at 80 PPI, a decrease in the compressive strength was noted. As the pore density of reticulated porous zirconia approaches 80 PPI, it is difficult to coat the strut walls inside the sacrificial polymer template completely and to remove the excess zirconia slurry. In addition, several blocked, interconnected pores form, and voids are caused inside the sacrificial polymer template, lowering the compressive strength. Figure 11b shows the density levels when the reticulated porous zirconia is sintered at 1600 \({}^{\circ}\)C. Overall, this trend is identical to that of the compressive strength. The pore size distributions of the reticulated porous zirconia specimens (pore density = 45 PPI) prepared from the as-received, coarse, intermediate, and fine zirconia particles when sintered at 1400, 1500, and 1600 \({}^{\circ}\)C are correspondingly shown in Figure 12a-c. Because the number of strut walls is fixed, the difference in the pore size distribution varies with the average particle size. The pore size and the pore volume of the reticulated porous zirconia did not decrease significantly because the average particle size difference was not significant. However, the number of pores decreased; thus, the compressive strength outcomes were found to have increased. Figure 3:0 (**a**) Compressive strength outcomes of the reticulated porous zirconia prepared from the as-received, coarse, intermediate, and fine zirconia particles when sintered at 1500 \({}^{\circ}\)C, and (**b**) the corresponding density levels. Figure 3:1 (**a**) Compressive strength outcomes of the reticulated porous zirconia prepared from the as-received, coarse, intermediate, and fine zirconia particles when sintered at 1600 \({}^{\circ}\)C, and (**b**) the corresponding density levels. Figure 3:2 Pore size distributions of the reticulated porous zirconia prepared from the as-received, coarse, intermediate, and fine zirconia particles when sintered at **(a)** 1400 \({}^{\circ}\)C, **(b)** 1500 \({}^{\circ}\)C, and (**c)** 1600 \({}^{\circ}\)C.  
Several conclusions can be drawn based on the results of the experiments conducted to obtain reticulated porous zirconia with high compressive strength outcomes. The main factors that can affect the compressive strength are the average particle size, the viscosity of the zirconia slurry, the sintering temperature, and the PPI of the sacrificial polymer template. First, it is possible to improve the compressive strength by controlling the average particle size of the zirconia. Fine particles generally consist somewhat of agglomerated particles and cause non-uniformity, thus reducing the degree of densification when sintering takes place. However, in this study, the compressive strength increased when the average particle size was fine because the average particle size was in the sub-micron range. Second, if the zirconia slurry viscosity is too high in the case of a sacrificial polymer template with a low PPI value (such as 25 PPI), the strut wall thickness increases, resulting in an increase in the compressive strength. However, at a high PPI value (such as 80 PPI), the zirconia slurry cannot be uniformly coated onto the sacrificial polymer template strut walls, resulting in macro-voids forming deep inside (as shown in Figure 8b). Conversely, if the viscosity of the zirconia slurry is too low, the likelihood of the generation of macro-voids is reduced but the thickness of the sacrificial polymer template strut walls becomes too thin and nonuniform, resulting in an expected decrease in the compressive strength.