Production of Aluminum Oxide/Iron Oxide Composite Particles in Sub- and Supercritical Water

Composite materials play a key role in modern technologies, providing lightness, strength, and corrosion resistance. They are used in various industries, including aviation, the automotive industry, construction, oil and gas processing, petrochemistry, etc. In this paper, it is proposed to study the production of aluminum oxide/iron oxide composite particles in sub- and supercritical water environment. The high heat- and mass-transfer characteristics inherent in supercritical water ensure the implementation of chemical reactions in this environment at a high rate. The studies in this paper are carried out in the temperature range T = 350–410°C and reaction time τ = 180–420 min. The volume of loaded water corresponds to the critical value at the critical point (in our case, V = 326 mL). Composite particles obtained in the processes of sub- and supercritical water oxidation are analyzed using a Nova 2200e analytical analyzer for changes in the specific surface area and pore size. The analysis results show that an increase in the process temperature leads to a decrease in the specific surface area and the specific surface area of the micropores of the samples. Changing the time of sample treatment in supercritical water did not lead to significant changes in the surface of composite particles. The results of X-ray quantitative phase analysis showed that during sub- and supercritical water oxidation, metallic aluminum can transform into various phases of aluminum oxide: $${{\gamma - A}}{{{\text{l}}}_{2}}{{{\text{O}}}_{3}}$$ ; $${{\chi - A}}{{{\text{l}}}_{2}}{{{\text{O}}}_{3}};$$ and α $${\text{ - A}}{{{\text{l}}}_{2}}{{{\text{O}}}_{3}}$$ . An increase in the temperature of the sub- and supercritical water oxidation process leads to a decrease in the formation of the $${{\gamma - A}}{{{\text{l}}}_{2}}{{{\text{O}}}_{3}}$$ phase, and the amount of the α $${\text{ - A}}{{{\text{l}}}_{2}}{{{\text{O}}}_{3}}$$ phase increases. With an increase in the time of supercritical water oxidation, the amount of the α $${\text{ - A}}{{{\text{l}}}_{2}}{{{\text{O}}}_{3}}$$ phase increases. Photographs obtained using a scanning electron microscope with an energy-dispersive spectrometer identify the formation of micron-sized porous aluminum oxide particles and nanosized iron oxide particles deposited on their surfaces.