## 3 Results  
### Characterization of Diatomic Powders, Diatomite/Sodium Alginate Dispersions and Resultant Granules  
The particle size distributions of the diatomic powders with a major SiO\({}_{2}\) composition, as shown in Table 1, were compared before (as-received diatomite) and after ball-milling for four hours, as presented in Figure 2. The results indicate that the average particle size of the diatomic powders decreased from 13.92-14.25 \(\upmu\)m (average particle size: -13.96 \(\upmu\)m, D\({}_{10}\): 5.57 \(\upmu\)m, D\({}_{50}\): 11.14 \(\upmu\)m) for the as-received-diatomite to 5.48-5.77 \(\upmu\)m (D\({}_{10}\): 0.26 \(\upmu\)m, \begin{table}
\begin{tabular}{c c c c c c c} \hline \hline
**SiO\({}_{2}\)*** & **Al\({}_{2}\)O\({}_{3}\)** & **Fe\({}_{2}\)O\({}_{3}\)** & **CaO** & **MgO** & **Na\({}_{2}\)O + K\({}_{2}\)O** & \multicolumn{2}{c}{**Loss**} \\  & & & & & & **of Ignition (1000 \({}^{\circ}\)C)** \\ \hline
92.0 & 1.0 & 1.5 & 0.3 & 0.3 & 2.5 & 0.2 \\ \hline \hline \end{tabular}  
* Up to 72.5% of crystalline phase (<70.0% cristobalite, <2.5% quartz).  
\end{table} 
Table 1: Typical chemical analysis results of diatomite (%). D\({}_{50}\): 5.42 \(\upmu\)m) for the ball-milled diatomic powders. The ball-milling process resulted in a narrowed particle size distribution and increased uniformity of the diatomic particles by reducing agglomerates [45; 46]. According to the literature, this improved particle size distribution is beneficial for optimizing the viscosity of processing dispersions [46] and for enhancing the mechanical strength of the resultant ceramics [45] due to the formation of ordered particle domains. The described trends were observed in our previous studies of reticulated porous ZrO\({}_{2}\) and ZrO\({}_{2}\)-toughened Al\({}_{2}\)O\({}_{3}\) ceramics [47; 48], where ball-milling enabled the tailoring of the particle size distribution of the raw materials, resulting in the optimized viscosity of the processing slurries and improved compressive strength capabilities of the ceramic materials. Furthermore, the ball-milled diatomic powders exhibited a bimodal particle size distribution (average particle size: \(\sim\)5.70 \(\upmu\)m), which resulted from the breakup of large diatomic particles originating two maximum values of modes, a primary peak at around D\({}_{50}\): 5.35-5.47 \(\upmu\)m and a secondary peak at around 0.31-0.54 \(\upmu\)m, corresponding to the D\({}_{10}\) value of the distribution (\(\sim\)0.26 \(\upmu\)m). Earlier works focusing on Al\({}_{2}\)O\({}_{3}\) ceramic materials found that bimodal particle size distributions of Al\({}_{2}\)O\({}_{3}\) with a smaller fraction (10-30%) of finer particles can enhance the packing density, i.e., the bulk density of the green body, in systems with a fixed solid content. This fraction of finer particles promoted the optimization of the viscosity of the processed slurries and enhanced the inter-particle bonding by filling the gaps between the grains, resulting in improved mechanical properties [49; 50]. Based on the analysis above, it is proposed that the applied milling processing conditions, as determined from our previous research (4 h, 200 rpm) [37], which prevent the pulverization of the diatomic frustules, are likely to improve the regularity of the particle size distribution of the diatomic powders. Consequently, the use of ball-milled diatomic powders is expected to optimize the properties of the diatomic/sodium alginate dispersions and porous diatomic granules, compared to using as-received diatomic powders without prior processing. Figure 3 presents the viscosity of diatomic/sodium alginate dispersions prepared with diatomic contents ranging from 3.8 to 30.5 wt.% (D04-D44) as a function of the shear rate (Figure 3a) and rpm (Figure 3b). The suspensions of diatomic and sodium alginate are created by mixing the milled diatomic slurries and sodium alginate at a fixed content to ensure the homogeneity of the mixture.