## 3 Results
The compressive strength outcomes according to the ball-milling time are shown in Figure 8c. The effect of ball-milling was not visible because the raw particle size was coarse, the densification outcome was poor, and the particle size was not effectively reduced through ball-milling. Figure 8d shows the density values. Overall, this figure shows a trend similar to that of the compressive strength. Controlling the particle size had only limited effects on improving the strength. Therefore, the particle size was fixed with fine alumina, which has higher compressive strength, and the contents of the dispersant and thickener were adjusted to optimize the slurry. A plot of the viscosity vs. the shear rate of ZTA slurries prepared with different amounts of dispersant is shown in Figure 9a. When more dispersant is added, the viscosity of the slurry  
Figure 8: (**a**) Particle size distributions of ZTA for the as-received, coarse, intermediate, and fine cases. (**b**) A plot of the viscosity vs. the shear rate of ZTA slurries used to prepare the reticulated porous ZTA: as-received, coarse, intermediate, and fine ZTA particles, and (**c**) compressive strength outcomes of reticulated porous ZTA specimens prepared from the as-received, coarse, intermediate, and fine ZTA particles (**d**) density levels. is decreased more. The type and amount of dispersant are important when optimizing the slurry. Dispersants with low molecular weights effectively reduce agglomerates because the rate of diffusion within the suspension is rapid and it can easily penetrate between the cracks of the agglomerate, thus affecting the size of the aggregate. Dispersants with higher molecular weight have longer chains and can be adsorbed into several particles, but not to one, causing agglomeration [32]. In addition, as the amount of dispersant increases, more dispersant is adsorbed on the surfaces of the particles to increase the repulsive force, meaning that the slurry is stabilized even if the powder content increases, whereas excess dispersant is present in the solvent, causing cohesion of the dispersants [33]. In contrast, if the amount of the dispersant decreases, it cannot effectively disperse the slurry because the amount of the dispersant is not sufficient to prevent aggregation between the particles by adsorbing the polymer material on the particle surface. Dolapix CE 64 (~660 g/mol) has a low molecular weight compared to other dispersants, completely dissociates in water, and has an electrostatic stabilization effect immediately after it is added [34]. Figure 9b shows the compressive strength and density according to the amount of thickener used. The content of the dispersant at 1 wt. % has the highest compressive strength. Dolapix CE at 64 1 wt. % was reported to have the highest compressive strength [35]. These results were confirmed experimentally to be consistent. When the content of the dispersant is 1 wt. %, it has the highest compressive strength, but there is a limit to the addition of the thickener because it already has high viscosity. Therefore, the content of the dispersant having the second-highest compressive strength at 2 wt. % was fixed. The density trend is similar to that of the compressive strength. Figure 10a shows a plot of the viscosity vs. the shear rate of ZTA slurries prepared with different amounts of a thickener. As the amount of the thickener increases, the viscosity increases. The viscosity of the aqueous solution gradually increases as the amount of the thickener used increases. The compressive strength and density according to the amount of thickener are shown in Figure 10b. When this amount is 1 wt. %, the highest compressive strength of about 4.17 MPa is realized. When the thickener added exceeded 1 wt. %, the compressive strength decreased due to the high viscosity of the ZTA slurry. Overall, the densities show a trend similar to that of the compressive strength. In order to improve the compressive strength of the reticulated porous ZTA, it is most important to optimize the slurry.