## 3 Results and Discussion  
At the beginning, the kinetics of formation of MOC 5-1-8 was determined using the XRD analysis on the test samples taken every 12 h for seven days (see Figure 1). The first measurement showed that only MgO (ICDD 01-075-0447) was present in the sample because of its insolubility in water, whereas magnesium chloride was completely dissolved. The reflections of MgO were found at 2\(\theta\) = 42.9 (reflection 400) and at 2\(\theta\) = 62.2 (reflection 440). The formation of Phase 5 (ICDD 00-007-0420) occurred rapidly; after 12 h, almost 69% of MgO already reacted. The strongest reflection (100) of MOC 5-1-8 was detected at 2\(\theta\) = 12.0. Figure 2 demonstrates a gradual decrease in MgO amount with increasing time, while the amount of phase MOC 5-1-8 increased. After 48 h, 89% of phase 5 was present in the sample. After 96 h, less than 5% MgO remained unreacted. Moreover, the sample was also subjected to phase analysis after 28 days, revealing the majority phase MOC 5-1-8 with a low amount of magnesium carbonate (2\(\theta\) = 7.8 for reflection 110; see Figure 3). The presence of carbonate can be explained in terms of the MOC 5-1-8 surface reaction with CO\({}_{2}\) in air, resulting in a thin surface layer of this impurity phase. Figure 1: X-ray powder diffraction (XRD) measurements of magnesium oxychloride cement (MOC) 5-1-8 suspensions for 168 h.  
Figure 3: X-ray diffraction pattern of MOC 5-1-8 after 28 days. Figure 2: Sample composition over time obtained by Rietveld analysis. The morphology and the chemical composition of the sample were characterized using SEM and EDS after 28 days. The typical needle-like crystalline structure of Phase 5 was observed by SEM at high magnification (see Figure 4). The needles were 1-2 \(\upmu\)m long and approximately 0.5 \(\upmu\)m wide. For a detailed description of Phase 5 needles, TEM was used (see below). It is apparent from the SEM micrographs that this structure is very compact, which is further supported by the lack of defects detected in the sample. High purity of this sample was confirmed by EDS where only magnesium (29.9 wt. %), oxygen (46.5 wt. %), chlorine (14.2 wt. %), and carbon (9.3 wt. %) were detected. Carbon was present due to the reaction of Phase 5 with CO\({}_{2}\) forming magnesium carbonate. Moreover, the chemical composition was also determined by XRF, where 22.3 wt. % magnesium, 23.0 wt. % chlorine and 54.6 wt. % light elements (hydrogen, oxygen, and carbon) were detected. Impurities like sulfur and calcium were observed in very low amounts (lower than 0.05 wt. %). Transmission electron microscopy was employed in order to determine the morphology of the selected needles that were seen in SEM micrographs. TEM confirmed the needle-like structure of MOC 5-1-8; the typical length of individual needles was 1-3 \(\upmu\)m and the width was 50-150 nm (see Figure 5). Figure 4: Scanning electron microscopy micrographs and energy-dispersive X-ray spectroscopy (EDS) elemental maps of MOC 5-1-8. Figure 5: Micrographs obtained by transmission electron microscopy of MOC 5-1-8. Furthermore, we tested the reference sample and samples after thermal exposure in order to analyze the thermal stability of MOC 5-1-8 phase. The collected FT-IR spectra are presented in Figure 6, and assignments of the major absorption bands of reference sample are summarized in Table 1. It can be seen that the tested magnesium oxychloride cement phase 5-1-8 contains the bands from the fundamental vibrations of structural H\({}_{2}\)O and the lattice vibrations of MgCl\({}_{2}\) and Mg(OH)\({}_{2}\). The absorption bands between 3700 and 3300 cm\({}^{-1}\) were assigned to the stretching modes of O-H bonds in hydroxyl groups and in water. The water release is clearly visible on the bands in the range of 2000-3700 cm\({}^{-1}\), which were contributed by the symmetric and asymmetric stretching mode of O-H bonds in H\({}_{2}\)O and Mg(OH)\({}_{2}\)[31] after thermal exposure.