This review is devoted to describing the main synthesis methods, the properties of MgO nanoparticles, and their areas of application, such as the creation of coatings for transformer and other types of steels, coatings on glass to control the energy of transmitted solar radiation, the creation of transparent and translucent one-component ceramics, the creation of multicomponent ceramic compositions, in medicine to make antibacterial agents, etc. The main methods of obtaining MgO nanoceramics are considered: sintering at low temperatures under high pressure, high-temperature sintering, the spark plasma sintering (SPS) method, and obtaining MgO melt in plasma in a cooled crucible followed by crystallization and the formation of dense ceramics. It is shown that variations in the conditions for the synthesis of nanosized MgO powders make it possible to obtain precursors that, upon sintering, form ceramics with a density close to the theoretical one.

A method is proposed for the synthesis of nanoscale boehmite powder at low temperatures of hydrothermal treatment in 1.5 wt % HCl solution at 150 and 170°C and in water at 80, 100, and 130°C. The optimal parameters of hydrothermal treatment are found. The conversion stages of γ-Al2O3 to boehmite (AlOOH) are found; the process is solid-phase (topochemical). The physical and technological properties of boehmite nanopowder are studied. We have found that boehmite possesses similar properties despite the temperature of hydrothermal treatment.

We have developed a method for the preparation of boehmite (AlOOH) nanopowder with tailored properties (particle size from 10 to 40 nm, thermal conductivity below 0.02 W/(m K), specific surface area on the order of 65 m 2 /g, and loose bulk density in the range 0.02–0.04 g/cm 3 ) by hydrothermal treatment of γ‑Аl 2 О 3 nanopowder in a 1.5% HCl solution at 200°C. The steps of the process have been identified and it has been shown to be a solid-state (topochemical) transformation.

Methods for the preparation of raw materials to produce leucosapphire are considered. It is shown that the main directions in the production of high-purity aluminum oxide raw materials are: electrochemical oxidation of aluminum, decomposition of alkoxides, high-temperature treatment of aluminum oxide in a halogen-containing atmosphere, and preliminary purification of aluminum-containing compounds followed by their decomposition. It is shown that methods of the purification of aluminum hydroxide and oxide obtained by the Bayer process are the most promising for industrial use. These methods include the complex purification and simultaneous preparation of ceramic preforms starting from aluminum hydroxides or oxides by their treatment in subcritical or supercritical steam and the following heat treatment in a halogen-containing medium.

— We have studied the kinetics of boehmite nanopowder formation during hydrothermal treatment of γ-Al 2 O 3 nanopowder in a 1.5% HCl solution at 200, 170, and 150°C. The results demonstrate that the temperature-dependent reaction rate constant follows the Arrhenius equation. The E a of the process has been determined to be 84 kJ/mol. The thermodynamics of γ-Al 2 O 3 nanopowder conversion into boehmite during hydrothermal treatment at 150°C has been studied by differential scanning calorimetry. The heat of vaporization of water from a two-phase nanosystem (γ-Al 2 O 3 + forming boehmite) has been determined to be 8, 16, and 22 kJ/mol H 2 O, which points to an active role of water with a low heat of vaporization in the initial stages of the hydrothermal treatment of the γ-Al 2 O 3 nanopowder. The heat effect of the АlООН → γ-Al 2 O 3 conversion in the nanopowders is lower than the reference value by 7 kJ/mol AlOOH, which is attributable to the small particle size and low structural perfection of the synthesized boehmite (AlOOH).

We propose a mechanism capable of describing phase transformations during the hydrothermal treatment of micron- and nanometer-sized γ-Al2O3 and Al(OH)3 powders, identify the steps of the process, and demonstrate the role of water with a small heat of vaporization in the hydrothermal treatment process.

A new method was proposed to produce high-flexural-strength corundum ceramics from α-Al2O3 samples synthesized by heat treatment of boehmite AlOOH at 1300 °C for 5 h. It was shown that hydrothermal treatment of MDGA-grade hydrargillite at 200 °C in a 0.4 wt % magnesium acetate solution for 3 days gives finely crystalline boehmite, which is a feedstock for synthesizing corundum ceramics with a flexural strength of 400 MPa.

A method for the preparation of nanosized powder metal oxides (Al2O3, MgO, and ZnO) has been developed by the sequential heat treatment of saturated solutions of salts of these metals and sucrose at a temperature of 350°C and then 800°C. The application fields and physicochemical and technological properties of the materials synthesized are determined.

The processes of obtaining fine-grained corundum with a given crystal size and habit are considered. It is shown that thermocouple treatment in aqueous supercritical fluid allows one to obtain corundum from various precursors in a wide range of crystal sizes (0.01–500 μm). Powders with a crystal size in the range 20–500 μm can be obtained directly from hydrargillite prepared in the course of the Bayer Process. The size and habit of the crystals are determined by the parameters of the thermocouple treatment and properties of the process activators used. Powders with a crystal size falling in the range 30–1000 nm can be obtained by using synthesized or commercially available boehmite as a precursor for the thermocouple treatment. The crystal habit is determined by the habit of the boehmite crystals used. New methods of boehmite synthesis have been developed that allow one to obtain nonaggregated crystals with a size of 10 nm with a narrow distribution curve.

A new method for producing a nanosized γ-Al 2 O 3 powder was proposed, by which a saturated solution of aluminum oxychloride and sucrose was subjected to sequential heat treatment to 350°C to form a transient species and then to 800°C to form a nanosized γ-Al 2 O 3 powder. The optimal treatment parameters were determined. Stages of the process were identified. The transient species and the nanosized γ-Al 2 O 3 powder were studied.

A new method was proposed to increase the crystallization rate in growing single crystals of quartz. In this method, the crystallization is accelerated by using surfactants (polyethyleneamine, tetramethylammonium base, and polyethyleneimine) added to a soda-alkaline solution of standard concentration. Within studied ranges of pressures and concentrations of components of the solution, polyethyleneimine at a concentration of 0.002–0.05 wt % is the most efficient crystallization accelerator, which can increase the quartz crystal growth rate on the average by a factor of 2.

A new method of synthesis of nanosized aluminum oxyhydroxide (AlOOH, boehmite) powders has been suggested through a hydrothermal treatment of nanosized γ-Al 2 O 3 powder in water and a 1.5 wt % HCl solution at different temperatures. It has been found that hydrothermal treatment in a 1.5 wt % HCl solution leads to the purification of the starting material; different treatment durations allow one to obtain boehmite particles of different shape. It has been demonstrated that a nanosized boehmite powder is obtained upon the hydrothermal treatment of a nanosized γ-Al 2 O 3 in water above 80°С. The nanosized boehmite powders synthesized at different temperatures have been studied by various methods.

The process of obtaining silicon dioxide upon the interaction of fluorosilicic acid with an aqueous solution of ammonia is studied. The fluorine-containing compounds in synthesized dioxide are identified by 19 F NMR spectroscopy. It is shown that the two-stage method of precipitation followed by washing, allows producing silicon dioxide with a fluorine content of units of ppm.