# Glass Ceramic with Improved Structure and Properties Made with Wastes from FeNi Production
## 4 Results and Discussion
### Phase Formation and Structure
It is clear that these drops become finer and finer when moving away from the crystallization field. Figure 5a,b elucidates areas free of \"preliminary\" spinel in samples GC0-1 and GC60-1, respectively. These SEM results demonstrate that without treatment at 650 \({}^{\circ}\)C, the size of iron-rich drops is in the range of 150-250 nm, while after the \"nucleation step\" it decreases to 50-70 nm and the number of drops significantly rises (from 15 \(\pm\) 5 per \(\upmu\)m\({}^{2}\) in GC0-1 to 50 \(\pm\) 10 for GC60-1). This result clarifies that during the nucleation step binodal liquid-liquid separation occurs. Figure 4: SEM images of sample GC0-1 at low magnification (**a**) and sample GC60-1 at high magnification (**b**). The liquid-liquid immiscibility was also confirmed by TEM observations. In Figure 6a, a flake from the parent glass rapidly quenched in water, elucidating a homogeneous amorphous structure, is shown. On the contrary, in Figure 6b, an image from sample GC60-1, where the structure is non-homogeneous and comparable to one obtained by SEM, is presented. In addition, the corresponding electron diffraction (SAED) pattern (shown in the inset) confirms the amorphous structure of GC60-1 and thus the assumption for initial liquid-liquid separation. In samples GC0-5 and GC60-5, variations in the composition and the size of the \"preliminary\" spinel were not detected, which supports the hypothesis that this phase is generally formed during the melt's cooling. In agreement with XRD results, the beginning of pyroxene growth on these spinel crystals was observed. It can be also supposed that at subsequent heat treatments, the iron-rich drops were transformed into tiny magnetite crystals, which than acted as nucleation agents for the pyroxene formation. In sample GC0-60, presented in Figure 7, together with the pyroxene crystals growing on the \"preliminary\" spinel, consistent crystallization (in the form of pyroxene spherulites with of 3-6 \(\upmu\)m size) was also observed in the main matrix. In this figure, EDS spectra of the \"preliminary\" spinel and both pyroxene phases are also reported. The results demonstrate that the first pyroxene phase, growing in the diffusion field on the \"preliminary\" spinel, is characterized by higher concentrations of Ca\({}^{2+}\) and Na\({}^{+}\), while the main pyroxene phase was characterized by higher concentrations of Mg\({}^{2+}\). These results confirm the XRD data for both pyroxene phases and explain the differences in the volumes of their unit cells. In sample GC60-60, due to the effective \"nucleation\", the size of both pyroxene crystals (P1 and P2) is significantly lower [21]; in order to better highlight the structure of the final  
Figure 5: SEM images at high magnification of zones free of “preliminary” spinel for samples GC0-1 (**a**) and GC60-1 (**b**). Figure 6: BF TEM of flake of parent glass (**a**) and area of sample GC60-1 with the corresponding SAED as inset (**b**). glass-ceramic, it was additionally studied by FESEM and EDS mapping of the elements Fe, Cr, Mg, Ca, Na and Si. Figure 8 presents an image of a zone containing two \"preliminary\" spinel crystals and many 0.3-0.6 \(\upmu\)m pyroxene P1 crystals growing on them in a preferential direction. The formation of tiny \"secondary\" spinel and a fine pyroxene P2 phase is also well distinguished in the circumference zone. It is also well seen that the sizes of the \"secondary\" spinel decrease with increased distance from the diffusion zone. The EDS mapping highlights that the concentrations of Si, Na and Ca are higher in the diffusion field, while the ones of Fe and Mg are higher into the main matrix, which is in agreement with EDS data for both P1 and P2 pyroxenes from Figure 7. It was also confirmed that the amount of Cr outside of the \"preliminary\" spinel is negligible, so the \"secondary\" spinel phase (S2) has a composition close to that of magnetite. Figure 7: SEM image of sample GC0-60 with EDS spectra of formed-crystal phases S1, P1 and P2.