## 3 Results and Discussion  
Two MCC phases were prepared and characterized. The phases under study with the compositions 3 Mg(OH)\({}_{2}\)-MgCl\({}_{2}\)-8H\({}_{2}\)O and 5 Mg(OH)\({}_{2}\)-MgCl\({}_{2}\)-8H\({}_{2}\)O are referred to as Phases 3 and 5, respectively. The phase purities of both phases were determined using XRD analysis after 7 days (see Figure 3). A fast formation of Phase 3 was confirmed, and a single-phase composition was obtained (ICDD 00-007-0412). Similar results were also obtained for Phase 5. The formation of Phase 5 (ICDD 00-007-0420) was confirmed with no significant impurities. Figure 3 shows the XRD patterns measured after 7 days for MOC Phases 3 and 5. Another XRD measurement was performed after 50 days of samples maturing. In both samples, chlorartinite was formed on the surface due to carbonation (see Figure 4). Phase 3 reacted with carbon dioxide forming Mg\({}_{2}\)(CO\({}_{3}\))(OH)Cl:2H\({}_{2}\)O (ICDD 00-061-0391), while Phase 5 formed Mg\({}_{2}\)(CO\({}_{3}\))(OH)Cl:3H\({}_{2}\)O (ICDD 00-00-0278). A tubular crystal structure of the dihydrate formed by MgO\({}_{6}\) octahedra interconnected by carbonate anions with chloride anions and water molecules  
Figure 3: XRD patterns for magnesium oxychloride cement (MOC) Phases 3 and 5 after 7 days. Figure 2: Photography of prepared samples in XRD holders: Phase 3 (left) and Phase 5 (right). located inside the channels is depicted in Figure 5. It is apparent from the comparison with the initial structures of Phases 3 and 5 (Figure 1) that the CO\({}_{2}\) incorporation into the system required a complete reconstruction of the MgO\({}_{6}\) network and, in the case of Phase 5, the formation of another phase (see Equation (4) below). Hence, a relatively slow kinetics of the carbonation process can be anticipated. Figure 4 shows the XRD pattern of MOC Phases 3 and 5 after 50 days of maturing. Figure 5 shows the crystal structure of the chlorartinite phase. XRD measurements with subsequent Rietveld analysis were performed again after 100, 150, 200, and 250 days of maturing. In both samples, the content of chlorartinite increased with the aging time of the samples. However, as can be seen from Figure 6, the rate of chlorartinite formation was different for Phases 3 and 5. In the case of Phase 3, MOC almost disappeared after 250 days, while chlorartinite represented the dominant phase. The carbonation of Phase 5 was slower than Phase 3, likely due to the phase separation. After 150 days, the surface of the sample contained similar amounts of Phase 5 and chlorartinite. After 250 days, this sample contained 46% of Phase 5 and 54% of chlorartinite. The XRD patterns acquired on 250-day samples are shown in Figure 7 for both surfaces and bulk. It is  
Figure 4: XRD patterns of MOC Phases 3 and 5 after 50 days. Figure 5: Crystal structure of the chlorartinite phase. Color scheme is the same as in Figure 1; carbon atoms located in the centers of triangular carbonate molecules are in red. SEM micrographs were acquired to study the microstructure of the 250-day MOC samples. The typical needle-like crystalline structure of Phases 3 and 5 were obtained in the bulk at high magnification (see Figure 8). The needles were 1-5 \(\upmu\)m long and approximately 0.5 \(\upmu\)m wide. On the other hand, the morphology of the surface was different. Due to carbonation (formation of chlorartinite), the surface contained a lower amount of needles in both samples. More needles (MOC phase) were detected in Phase 5 than Phase 3, which is in good agreement with the XRD results. The EDS chemical composition was also measured at three different locations in the sample (surface, center, and bottom). High purity of both samples was confirmed when only magnesium, oxygen, chlorine, and carbon were detected. The EDS data confirmed the highest carbon content on the surface of the tested samples. The carbon content in the center and on the bottom of the analyzed samples was significantly lower.