## 3 Results  
According to the XRD analysis shown in Figure 2 and summarized in Table 2, the phase composition is very similar for each sample. The XRD spectra indicate the presence of a number of hydrated phases in each sample. Brucite (Mg(OH)\({}_{2}\)) is the first of the phases connected with magnesium oxide, the second identified phase is double magnesium and aluminum hydroxide hydrate (Mg\({}_{6}\)Al\({}_{2}\)(OH)\({}_{18}\)-4.5H\({}_{2}\)O). In the samples, aluminum oxide hydroxide (AlO(OH)) and a form of hydrated aluminum oxide with a formula close to 11 Al\({}_{2}\)O\({}_{3}\)-1.79H\({}_{2}\)O were also observed. The non-hydrated oxides in the studied samples were aluminum oxide (Al\({}_{2}\)O\({}_{3}\)), present in each sample, and traces of MgO for the sample with the addition of chelates. Based on this result, it can be stated that magnesium oxide, in the experimental conditions, completely reacted with water for sample 1 while some traces of it remained in the sample with the addition of citric and tartaric acids. According to the XRD analysis, there were no traces of aluminum hydroxide in the samples, although, in the experimental conditions, bayeriteshould have probably appeared [13]. In the place of aluminum hydroxide, boehmite can be identified, and magnesium aluminum hydroxide \begin{table}
\begin{tabular}{c c c} \hline \hline
**Sample Designation** & **Identified Phase** & **Reference Pattern** \\ \hline \multirow{8}{*}{\(1\)} & \(\alpha\)-Aluminum oxide Al\({}_{2}\)O\({}_{3}\) & 01-088-0826 \\ \cline{2-3}  & BoehmiteAlO(OH) & 01-083-2384 \\ \cline{2-3}  & Aluminum oxide hydrate 11 Al\({}_{2}\)O\({}_{3}\)*1.79H\({}_{2}\)O & 01-070-0384 \\ \cline{2-3}  & Double magnesium aluminum hydroxide & 00-035-0965 \\ \cline{2-3}  & Brucite Mg(OH)\({}_{2}\) & 00-044-1482 \\ \hline \multirow{8}{*}{2} & Aluminum oxide Al\({}_{2}\)O\({}_{3}\) & 01-088-0826 \\ \cline{2-3}  & BoehmiteAlO(OH) & 01-083-2384 \\ \cline{2-3}  & Aluminum oxide hydrate 11 Al\({}_{2}\)O\({}_{3}\)*1.79H\({}_{2}\)O & 01-070-0384 \\ \cline{2-3}  & Double magnesium aluminum hydroxide & 00-035-0965 \\ \cline{2-3}  & hydrate Mg\({}_{6}\)Al\({}_{2}\)(OH)\({}_{18}\)*4.5H\({}_{2}\)O & 00-044-1482 \\ \cline{2-3}  & PericlaseMgO & 00-004-0829 \\ \hline \multirow{8}{*}{3} & Aluminum oxide Al\({}_{2}\)O\({}_{3}\) & 01-088-0826 \\ \cline{2-3}  & BoehmiteAlO(OH) & 01-083-2384 \\ \cline{2-3}  & Aluminum oxide hydrate 11 Al\({}_{2}\)O\({}_{3}\)*1.79H\({}_{2}\)O & 01-070-0384 \\ \cline{1-1} \cline{2-3}  & Double magnesium aluminum hydroxide & 00-035-0965 \\ \cline{1-1} \cline{2-3}  & hydrate Mg\({}_{6}\)Al\({}_{2}\)(OH)\({}_{18}\)*4.5H\({}_{2}\)O & 00-044-1482 \\ \cline{1-1} \cline{2-3}  & Brucite Mg(OH)\({}_{2}\) & 00-044-1482 \\ \cline{1-1} \cline{2-3}  & PericlaseMgO & 00-004-0829 \\ \hline \hline \end{tabular}
\end{table} 
Table 2: Phase composition of the studied samples. hydrate can be observed. However, the amount of the double magnesia alumina hydroxide is rather low in respect to beonhtite, it suggests that that if aluminum hydroxide appears during the hydrothermal treatment, it converts into boehmite rather than into double magnesium and aluminum hydroxide. Depending on the author, gibbsite formation takes place in the temperature of at least ca. 130-150 \({}^{\circ}\)C (these are the lowest values provided in the literature). When the temperature exceeds these values, direct formation of boehmite starts to be preferable [18; 19; 20; 21]. According to [22], gibbsite in the experimental conditions could be decomposed with the creation of boehmite around 230 \({}^{\circ}\)C, but bayerite with the temperature of decomposition around 280-300 \({}^{\circ}\)C should still be stable. This suggests that when increasing the temperature to the maximum assumed value (240 \({}^{\circ}\)C) in the experiment, the hydration process proceeds with gibbsite synthesis as an intermediate stage. It should also be noted that in the temperature range of this experiment, the water vapor pressure does not affect the alumina hydration [18; 21].