## 3 Results and Discussion  
According to the reactions in Equations (1) and (2), two samples of MOB were prepared and then characterized. Firstly, the purity of both samples was determined using XRD (see Figure 3). This analysis was performed after five weeks of hardening, and showed a single-phase composition for both MOB-318 (3 Mg(OH)\({}_{2}\cdot\)MgBr\({}_{2}\cdot\)8H\({}_{2}\)O, ICDD 00-007-0411) and MOB-518 (5 Mg(OH)\({}_{2}\cdot\)MgBr\({}_{2}\cdot\)8H\({}_{2}\)O, ICDD 00-012-0121). As can be seen from both diffractograms, there was a strong background due to the amorphous nature of the samples. Some minor reflections in both diffractograms were present due to the hydroxycarbonates, which were formed on the MOB surface. Let us note that a slight discrepancy was found for 20 positions of MOB-518 compared to the reference ICDD 00-012-0121. SEM analysis was performed to study the microstructure, showing the typical needle-shaped crystals of both MOB phases (see Figure 4). The needles were visible at high magnification, with dimensions between 1 and 5 \(\upmu\)m in length and approximately 0.5 \(\upmu\)m in width. Overall, the samples were non-defective, and their structures held together very well. In the next step, EDS was used to determine the chemical composition of the samples. In both samples, magnesium, oxygen and bromine were detected, as well as a small amount of carbon. The presence of carbon was caused by the absorption of CO\({}_{2}\) from the atmosphere while forming magnesium carbonates. The results of the EDS can be seen in Figure 5. EDS maps confirmed a  
Figure 4: SEM micrographs of MOB-318 and MOB-518. Figure 3: XRD patterns for MOB-318 and MOB-518 after five weeks. homogenous distribution of detected elements which corresponded to the results obtained by XRD. Bromine content was slightly lower in sample MOB-518, which was in agreement with the composition of both phases. The shape and size of the individual MOB crystals was studied using TEM. The results showed a structure typical for magnesium oxychlorides. Additionally, the magnesium oxybromides had needle-like crystals that were approximately 1-5 \(\upmu\)m long and less than 0.5 \(\upmu\)m wide. The results are shown in Figure 6.  
The collected FT-IR spectra (see Figure 7) of the tested magnesium oxybromide phases signed as MOB-318 and MOB-518 contain the bands arising from the fundamental vibrations of structural H\({}_{2}\)O and the lattice vibrations of MgBr\({}_{2}\) and Mg(OH)\({}_{2}\) (Table 2). As originally reported by [PERSON] et al. [32], the absorption bands near 1600 cm\({}^{-1}\) are associated with H\({}_{2}\)O bending mode vibration; the bands in the range of 2000-3700 cm\({}^{-1}\) are caused by the symmetric and asymmetric stretching mode of O-H bonds in H\({}_{2}\)O and Mg(OH)\({}_{2}\). The series of modes in the range of 1000-400 cm\({}^{-1}\) are the result of  
Figure 5: (**a**) Elemental maps of MOB-318 and MOB-518, (**b**) chemical composition obtained by EDS. Figure 6: TEM micrographs of MOB-318 and MOB-518. the existence of lattice translation modes (Mg-OH) and vibrational modes of the lattice showing the Mg-O/Mg\({}^{2+}\), O/O-Mg-O/O-Mg\({}^{2+}\)-O bonds [33]. The absorption band at 853 cm\({}^{-1}\) could be attributed to the characteristic absorption peak of cubic Mg-O. Lattice vibration modes of Mg-O/Mg-Br bonds were observed near 500 cm\({}^{-1}\) in the absorption spectrum. Translation vibrations of Mg/Mg-O and Mg-OH observed at about 500 cm\({}^{-1}\) were overlapped with strong deformation and stretching vibrations of Mg-Br. Let us note that the band at 1150 cm\({}^{-1}\) were visible due to the surface carbonation of both samples. This was further confirmed by STA-MS.  
To determine the thermal stability of the samples, we used simultaneous thermal analysis combined with mass spectrometry (Figure 8). During the heating of the sample MOB-318, a number of thermal effects were observed. The first one began around \(\sim\)90 \({}^{\circ}\)C and could be attributed to a release of two molecules of water.