## 3 Results and Discussion  
The impregnation of MgO resulted in the samples containing ca. 10 and ca. 25 mol.% MgF\({}_{2}\). The results of the quantitative analyses are presented in Table 1. In the case of the 10 MF sample, the actual MgF\({}_{2}\) content was a little higher than intended, whereas in that of the 25 MF sample it was a little lower. The values obtained from x-ray diffraction were about 1% lower compared to those from the pyrohydolytic method. Table 1 also shows values of the surface area determined by the BET method, average pore diameter, and the pore volume calculated by the BJH method on the basis of the desorption branch of isotherms for the samples calcined at different temperatures. Surface areas of the samples subjected to the impregnation treatment were several times lower compared to bare MgO. The higher the magnesium fluoride content, the greater the reduction in the surface area, which suggests that the reason for such a trend is the deposition of MgF\({}_{2}\) on the surface of magnesia. The surface area of bare MgF\({}_{2}\) calcined at 500 \({}^{\circ}\)C is comparable to the surface areas of MgO samples impregnated with MgF\({}_{2}\). After the calcination at higher temperatures (600 and 700 \({}^{\circ}\)C), the surface area of magnesium fluoride decreased rapidly, but this was not observed in the case of the impregnated samples. It was proven in an earlier study [9] that the surface texture in the MgF\({}_{2}\)-MgO system undergoes stabilization compared to that of bare components. We believe that a similar effect occurred in the present case. At the same time, we observed a decrease in the porosity of the samples with an increasing calcination temperature, which is a result of the sintering of narrower pores. For instance, in the case of the 10 MF sample calcined at 500 \({}^{\circ}\)C, the average pore diameter was 18.6 nm and after the calcination at 700 \({}^{\circ}\)C it increased to 26.8 nm. The isotherms of low-temperature N\({}_{2}\) adsorption on MgF\({}_{2}\), MgF\({}_{2}\)/MgO, and MgO calcined at 500 \({}^{\circ}\)C in air are shown in Figure 1. All the isotherms can be classified as IV(a), according to the International Union of Pure and Applied Chemistry (IUPAC) classification [12], i.e., the type that is characteristic of mesoporous materials. The isotherm measured for MgO calcined at 500 \({}^{\circ}\)C exhibits a hysteresis loop of type H2(b), which indicates capillary condensation occurred in the mesopores. \begin{table}
\begin{tabular}{c c c c c c c} \hline \hline
**Sample** & \begin{tabular}{c} **MgF\({}_{2}\) Content \({}^{\star}\)**, \\ **(Pyrohydrolysis)** \\ **mol.\%** \\ \end{tabular}  & \begin{tabular}{c} **MgF\({}_{2}\) Content,** \\ **(XRD) mol.\%** \\ \end{tabular}  & \begin{tabular}{c} **Calcination** \\ **Temperature,** \\ **\({}^{\circ}\)C** \\ \end{tabular}  & \begin{tabular}{c} **BET Surface** \\ **Area \#, m\({}^{2}\)** \\ **\({}^{\circ}\)C** \\ \end{tabular}  & \ \begin{tabular}{c} **Total Pore** \\ **Volume \#,** \\ **cm\({}^{3}\) g\({}^{-1}\)** \\ \end{tabular}  & \begin{tabular}{c} **Average Pore** \\ **Diameter \#, nm** \\ \end{tabular}  \\ \hline MgO & 0 & 0 & 600 & 164 & 0.45 & 22.6 \\  & & & 700 & 130 & 0.49 & 42.3 \\  & & & 500 & 43.4 & 0.17 & 18.6 \\
10 MF & \(11.7\pm 0.6\) & 10.5 & 600 & 52.3 & 0.28 & 22.0 \\  & & & 700 & 51.3 & 0.35 & 26.8 \\  & & & 500 & 38.9 & 0.26 & 26.3 \\
25 MF & \(22.9\pm 1.1\) & 21.8 & 600 & 44.7 & 0.31 & 27.9 \\  & & & 700 & 36.9 & 0.31 & 29.4 \\  & & &Such a shape of the hysteresis loop is characteristic of mesoporous adsorbents containing ink-bottle shaped pores with varied neck sizes. A somewhat different shape of the hysteresis loop occurred in the case of the MgF\({}_{2}\)/MgO samples. The nitrogen physisorption isotherm was type IV(a), however, the hysteresis loop of type H1 indicates the presence of wide mesopores.