## 3 Results and Discussion
### Formation of Nano-Titanium Dioxide as a Precursor
Such AMMCs demonstrate excellent mechanical and physical properties, because coherent (i.e., having a standard atomic layer at the interface) or partially coherent interfaces are formed between the matrix and new phases that arise in \"in-situ\" reactions. The uniform distribution of fine particles of alumina in the aluminum matrix was achieved by the modified method of molten salt synthesis. Molten halides (alkali or alkali-earth chlorides and/or fluorides) are the optimal reactive media for the formation of aluminum-alumina composites, as was shown in our previous papers [26; 36]. The synthesis of alumina particles inside aluminum is carried out by a one-step chemical reaction of titanium dioxide with molten aluminum under the layer of molten halides in air atmosphere by reaction (3); therefore, newly formed alumina nanoparticles are perfectly wetted by the liquid metal. Obviously, these reactions, except for the direct interaction between TiO\({}_{2}\) and molten sodium chloride, are thermodynamically feasible at sufficiently low temperatures of 700-800 \({}^{\circ}\)C. The presented process is a special case of aluminothermy. The interaction between liquid aluminum and fine titanium dioxide particles by reactions (5) and (6) can proceed up to the formation of the intermetallic AITi and Al\({}_{3}\)Ti titanium aluminide compounds. The Gibbs energies of reactions (5) and (6) are more negative than that of reaction (3). It makes reactions (5) and (6) more favorable. Titanium aluminides were not detected in the reaction product by X-ray phase analysis, Raman spectroscopy, EDS spectra of composites, and mapping sample surfaces in X-rays. Intermetallic compounds of aluminum and titanium or titanium species were not detected by means of an inductively coupled plasma optical emission spectrometer OPTIMA 4300 DV (Perkin Elmer, USA) after dissolving the resulting composite in hydrochloric acid. Thus, it can be argued that the interaction occurred according to the mechanism described above by reaction (3). The reason for such a result is the appearance of a side reaction (4) in the system. The interaction between titanium atoms, sodium chloride, and gaseous oxygen according to reaction (4) resulted in the formation of Na\({}_{2}\)Ti\({}_{6}\)O\({}_{13}\) nanowires and nanorods, which was \begin{table}
\begin{tabular}{c c c c c} \hline
**Reaction** & & \(\Delta\mathbf{G_{700}\cdot c}\) & \(\Delta\mathbf{G_{750}\cdot c}\) & \(\Delta\mathbf{G_{800}\cdot c}\) \\ \hline \(13 TiO_{2}+4 NaCl=2 Na_{2}Ti_{6}O_{13}+TiCl_{d}(g)\) & (2) & 333.9 & 326.0 & 318.0 \\ \hline \(3 TiO_{2}+4 Al=3 Ti+2 Al_{2}O_{3}\) & (3) & \(-437.6\) & \(-430.85\) & \(-424.0\) \\ \hline \(13 Ti+4 NaCl+13O_{2}=2 Na_{2}Ti_{6}O_{13}+TiCl_{d}(g)\) & (4) & \(-9642.6\) & \(-9535.7\) & \(-9429.0\) \\ \hline \(3 TiO_{2}+7 Al=3 AlTi+2 Al_{2}O_{3}\) & (5) & \(-643.7\) & \(-643.2\) & \(-624.7\) \\ \hline \(3 TiO_{2}+13 Al=3 Al_{3}Ti+2 Al_{2}O_{3}\) & (6) & \(-804.8\) & \(-788.9\) & \(-773.0\) \\ \hline \end{tabular}
\end{table} 
Table 1: Gibbs energies of some possible reactions in the Al-TiO\({}_{2}\)-NaCl-O\({}_{2}\) system. experimentally proved [37]. The value of Gibbs energy of this reaction is 15 times greater that of all other reactions. The composites obtained in this way were non-porous with a characteristic metallic luster (Figure 3). They exhibited high electrical conductivity and are excellently suited for mechanical processing. It was experimentally proved that the aluminum oxide content did not change from the surface of the aluminum drop to its center. The density of the obtained composite averaged 2.6977 g/cm\({}^{3}\), which is very close to that of pure aluminum (2.6989 g/cm\({}^{3}\)), and indicates the absence of porosity in the composite, which is typical for such samples obtained by traditional methods. According to the X-ray diffraction data, the thus obtained material was composed of Al and \(\alpha\)-Al\({}_{2}\)O\({}_{3}\)[36]. Raman spectra of the oxide inclusions were collected from several crystals inside the aluminum matrix.