## 3 Results and Discussion  
Crystalline Phases, Chemical Analysis and Particle Size Distributions of the \(Al_{2}O_{3}\) Commercial Powders  
The XRD patterns (Figure 3a-c) and EDX-chemical analysis (Table 2) obtained for Alglass, Vitro-ceram and In-ceram samples show that the \(\alpha\)-alumina (JCPDS standard 10-0173) is the prominent crystalline constituent. Low-intensity ZrO\({}_{2}\) peaks were also identified on the XRD pattern of the Vitro-ceram samples (Figure 3c). In accordance with the XRD results, the chemical analysis indicated a discrete amount of zirconia (0.30 wt.%) in the Vitro-ceram. A minor amount of SiO\({}_{2}\) (0.2 wt.%) and P\({}_{2}\)O\({}_{5}\) (0.2 wt.%) in the Alglass and Vitro-ceram samples, respectively, were also identified. Figure 4 shows the particle size distribution of Alglass, Vitro-ceram and In-ceram powders. The Alglass presented a heterogeneous and trimodal particle size distribution, \begin{table}
\begin{tabular}{c c c c c c} \hline \hline \multirow{2}{*}{**Samples**} & \multicolumn{5}{c}{**(wt.\%)**} \\ \cline{2-6}  & \(\mathbf{Al_{2}O_{3}}\) & \(\mathbf{SiO_{2}}\) & \(\mathbf{P_{2}O_{5}}\) & \(\mathbf{ZrO_{2}}\) &
\begin{tabular}{c} **Other** \\ **Oxides** \\ \end{tabular} \\ \hline Alglass & 99.6 & 0.2 & – & – & 0.02 \\ In-ceram & 99.8 & – & – & – & 0.02 \\ Vitro-ceram & 98.9 & – & 0.5 & 0.3 & 0.30 \\ \hline \hline \end{tabular}
\end{table} 
Table 2: EDX chemical analysis obtained for Alglass, Vitro-ceram and In-ceram. Figure 3: X-ray diffraction spectra of alumina samples: (**a**) Alglass, (**b**) In-ceram and (**c**) Vitro-ceram. A and Z denote \(\alpha\)-alumina and zirconia phases, respectively. in which the maximum sizes measured were 0.5, 11.5 and 50 \(\upmu\)m. This type of particle distribution contributes to excellent compaction in the pressing and sintering process. The In-ceram presented a monomodal particle size distribution ranging from 0.1 \(\upmu\)m to around 30 \(\upmu\)m, where the most significant percentage of particles falls close to 16 \(\upmu\)m. The Vitro-ceram powder also showed a bimodal distribution of particles with a maximum between 0.3 and 5.0 \(\upmu\)m; this sample exhibited the smallest particle size distribution. The mixture of particles with different diameters observed can favor higher compaction, with smaller particles occupying the empty spaces that lie between the larger particles. The systems with a wide range of particle diameters will density better [16]. SEM Investigation and Physico-Mechanical Properties of the Poly(methyl methacrylate)-Infiltered Al\({}_{2}\)O\({}_{3}\) Samples  
Figure 5 shows the Alglass, Vitro-ceram and In-ceram samples before poly(methyl methacrylate) infiltration and sintering at 1400 \({}^{\circ}\)C for 2 h. The color difference among the samples might be due to the impurities contained in the starting powders. Vitro-ceram with a small amount of ZrO\({}_{2}\) was the whitest. Figure 4: (**a**) Distribution and (**b**) cumulative mass of particle size of Alglass, In-ceram and Vitro-ceram powders. As an example, Figure 6a-b show the SEM images acquired from the Vitro-ceram sample cross-section, which was infiltrated with PMMA for 6 h. It seems that the PMMA infiltration is efficient and considerably fills the porosities, but there are some heterogeneous pores still visible at a higher magnification (Figure 6c). Figure 6d shows an SEM image acquired from the cross-section of the sample, which proves enough infiltration of PMMA after 12 h. The depth of infiltrated polymer varies from 173 to 180 \(\upmu\)m, forming a rigid, defect-free surface that could potentially inhibit crack initiation and propagation.