## 3 Results and Discussion
### Slag Microstructure  
The microstructure of the samples was studied by EDS-SEM analysis. Different phases were, observed under backscattered electron imaging, and they were compared with the phases obtained by XRD, as shown in Table 3. All the samples contained pseudobrookite as the major phase. The M\({}_{3}\)O\({}_{5}\) phase formed in the slag samples consisted of a mixture of Ti\({}_{2}\)FeO\({}_{5}\), Mg\({}_{0.5}\)Ti\({}_{2}\)O\({}_{5}\), and Mg\({}_{2.5}\)Ti\({}_{0.5}\)O\({}_{5}\), according to the XRD analysis. As all of them were of the M\({}_{3}\)O\({}_{5}\) composition, they are represented as pseudobrookite in this discussion for simplicity. The other common phases observed were the ilmenite, rutile, and silicate glass phases, as discussed using the figures below. Figure 6 shows the ilmenite slag sample after it was quenched in water. The cross-section of the sample could be seen to have a hollow tube-like area, which might have formed during the quenching for air passage. Three regions of the cross-section were analyzed using EDS-SEM to understand the phase composition and the differences as we move from the outer surface towards the hollow inner surface. In this study, the region near the outside surface was called as outer area, and the region near the hollow part, as the inner area. The region in between these two was referred to as the center, which represents the bulk material. Figure 5: X-ray powder diffraction (XRD) patterns of three synthetic slags. \begin{table}
\begin{tabular}{c c c c c c} \hline \hline \multirow{2}{*}{**Slag**} & \multicolumn{6}{c}{**Phases (wt\%)**} \\ \cline{2-6}  & **Pseudobrookite** & **Silicate** & **Rutile** & **Ilmenite** & **Titanium Oxide** & **Iron Titanium Oxide** \\ \hline
1 & 51.2 & 36.0 & & 12.9 & \\
2 & 64.0 & 4.1 & & 5.9 & 26.0 \\
3 & 57.8 & 7.0 & & 35.2 & \\
4 & 84.8 & 12.3 & 2.9 & & \\
5 & 68.2 & 14.6 & 10.3 & & \\
6 & 95.2 & 1.0 & 3.0 & & \\
7 & 85.1 & 7.0 & 4.6 & & \\
8 & 51.1 & 1.9 & 29.0 & & 18.0 \\
9 & 88.2 & 11.5 & 0.3 & & \\
10 & 78.0 & 13.0 & 8.6 & & \\ \hline \hline \end{tabular}
\end{table} 
Table 3: Phases in weight (percentage) detected by X-ray powder diffraction (XRD) for each sample using the Rietfeld refinement. Figure 7 shows the microstructure of sample 1, where three different phases can be observed. Similar phase formation is observed in sample 3 (Figure 8) and the other samples. In some samples, two types of silicates were observed, as shown in Figure 8: S\({}_{1}\) appeared lighter than the S\({}_{2}\) in the backscattered electron image, indicating the presence of a higher average atomic number within the silicate phase. The amount of silicon dioxide present in the darker silicate (S\({}_{2}\)) phase was higher than, the lighter silicate (S\({}_{1}\)) phase. All the slag samples consisted of three to four phases where the pseudobrookite and silicate phases were consistent with the other phase consisting of ilmenite, rutile, or magneli phases. This can be observed throughout the microstructure images for samples. Figure 6: (**a**) Water quenched slag sample. (**b**) The cross-section of the slag sample showing the inner and outer surface regions. Figure 7: Microstructures of slag sample 1 analyzed by scanning electron microscopy (SEM). The rutile phase is represented as R, the silicate phase as S, and the pseudobrookite phase as psb. Among the impurities present in the slag, nearly all the SiO\({}_{2}\) and a majority of Al\({}_{2}\)O\({}_{3}\) were in the glass phase, whereas the other impurities oxides, such as MnO and MgO, were present majorly in the M\({}_{3}\)O\({}_{5}\) solid solution and also in the silicate phase [23]. The amount of Al\({}_{2}\)O\({}_{3}\) that went to the silicate phase was almost equal to a third of the amount of SiO\({}_{2}\)[32]. Within the slag, the divalent impurities (Mg\({}^{2+}\) and Mn\({}^{2+}\)) substituted the Fe\({}^{2+}\), whereas the trivalent impurities (Al\({}^{3+}\)) substituted the Ti\({}^{3+}\)[31].