## 3 Results and Discussion
### Characterization and Properties of CRMFoams
#### 3.1.2 X-ray Diffraction Patterns and Raman Spectra  
The carbon foams CRMFoam-5 and CRMFoam-2.5 were prepared using red mud as raw material, that was collected from the alumina refining plant Aluminium of Greece MYTILINEOS. Red mud is the main filtered bauxite residue (BR known as ferroalumina), generated during the extraction of alumina from bauxite ore using Bayer process. Chemical analysis of the Greek filtered bauxite residue revealed the following composition for the solid content of BR: 43.59 wt% Fe\({}_{2}\)O\({}_{3}\), 22.78 wt% Al\({}_{2}\)O\({}_{3}\), 8.44 wt% CaO, 6.35 wt% SiO\({}_{2}\), 5.88 wt% TiO\({}_{2}\), 1.93 wt% Na\({}_{2}\)O, 0.56 wt% MgO (LOI 9.30 wt%) [50]. The XRD patterns of the red mud and the CRMFoams, CRMFoam-2.5 (40 wt% in RM), and CRMFoam-5 (20 wt% in RM) are presented in Figure 3. The pattern of RM exhibits a number of sharp diffractions peaks, which can be attributed to crystalline phases of hematite (Fe\({}_{2}\)O\({}_{3}\)- main peaks at 32.2\({}^{\circ}\), 35.7\({}^{\circ}\), JCPD file no. : 33-0664), gibbsite (Al(OH)\({}_{3}\)-main peak at 18.2\({}^{\circ}\), JCPD file no. : 70-2038), dia  
Figure 3: X-ray patterns of red mud (RM) and the CRMFoams, CRMFoam-2.5 (40 wt% in RM) and CRMFoam-5 (20 wt% in RM). No. : 44-1292, austenite (C,Fe-JCPD file no. : 23-0298) and alpha-Fe (Fe, JCPD files no.98-0064). In addition, the phases of gehlenite (Ca\({}_{2}\)Al[AlSiO\({}_{7}\)]—main peak at 31.4\({}^{\circ}\), JCPD file no. : 79-2421), iron silicon carbide (C\({}_{0.17}\) Fe\({}_{0.81}\) Si\({}_{0.02}\))—main peak at 39.5\({}^{\circ}\), 44.7\({}^{\circ}\), JCPD file no. : 19-20628), tricalcium aluminate (Ca\({}_{3}\)Al\({}_{2}\)O\({}_{6}\)—main peak at 33.1\({}^{\circ}\), 47.6\({}^{\circ}\), JCPD file no. : 38-1429) and perovskite (CaTiO\({}_{3}\)—main peaks at 33.0\({}^{\circ}\), 47.2\({}^{\circ}\), JCPD file no. : 82-0239) are easily identified as well. On the other hand, the pattern of carbon foam CRMFoam-2.5, prepared at 1100 \({}^{\circ}\)C, is mainly characterized by sharp and intense diffraction peaks at 20, 44.8\({}^{\circ}\), 43.6\({}^{\circ}\) and 33.5\({}^{\circ}\) and several weaker peaks derived from the crystalline phase of martensite (C,Fe-JCPD file. It is clear, from the comparison of X-ray patterns of CRMFoam-5 and CRMFoam-2.5 samples, that the difference in RM content and heating temperature, between the foams leading to the formation of different crystalline phases (i.e., tricalcium aluminate, martensite, austenite, a-Fe, Fe-Si carbide). Most of the above phases in the pattern of CRMFoam-2.5, constitute evidence of reduction of hematite by carbon. Ferrite (\(\alpha\)-Fe) is the stable form of Fe at room temperature and may contain traces of C dissolved in interstitial sites of its BCC lattice (<0.022 wt%). Austenite (\(\gamma\)-Fe) is stable at temperatures higher than 727 \({}^{\circ}\)C and can dissolve carbon (<2.14 wt%) in interstitial sites of its FCC lattice. Its presence at room temperature can be attributed to rapid cooling that inhibited the transformation of austenite to ferrite. Even, air cooling can suppress the transformation of austenite to ferrite, under the high presence of alloying elements (as in the present case) that inhibit the diffusion of carbon from the austenite lattice to form ferrite and cementie. In the cases where austenite contained high contents of carbon (higher than \(\sim\)0.4 wt%), rapid cooling led to its transformation to distorted \(\alpha\)-Fe, namely martensite, a metastable form of Fe, supersaturated in carbon atoms [51]. In order to investigate the graphitization degree of carbon foams, their Raman spectra were recorded and analyzed. Figure 4 shows the Raman spectra of CRMFoam-2.5 and CRMFoam-5 materials. Both samples showed similar spectral features, which can be mainly attributed to carbon vibrations.