The conversion of gibbsite to boehmite via hydrothermal treatment at 200°С in 1.5 wt % HCl is studied by X-ray powder diffraction, IR spectroscopy, Brunauer–Emmett–Teller analysis, scanning (SEM) and transmission (TEM) electron microscopy. The steps of the process are identified. Gibbsite is split in an acidic medium, with its specific surface area increasing up to 150 m²/g, into thin lamellas that have a disordered boehmite structure. Needle-shaped boehmite crystals are formed from thin elongated lamellas of diverse sizes due to the oriented overlaying and cross-linking with the elimination of weakly bound water and structural perfection.

Zinc borates are widely used in industry due to their thermal stability as a flame retardant in the production of plastics, rubber, and other polymer compositions. We have developed a simple and effective approach for the synthesis of zinc borate powders with desired properties, including desired particle size, low bulk density, high reactivity, etc. Zinc borates were prepared by the thermal treatment of a concentrated water–carbohydrate solution of a zinc salt until finely dispersed ZnO was formed, followed by its hydrothermal treatment at 90–300 °C as part of a suspension based on a hot aqueous solution of H₃BO₃. According to X-ray powder diffraction, IR spectroscopy, and TG–DSC data, depending on the temperature of hydrothermal treatment, a decrease in the water content in the structure of synthesized zinc borate particles is observed. TEM and SEM data indicate the formation of isometrically shaped zinc borate particles in the nanometer range during hydrothermal treatment above 250 °C. Varying the temperature of the hydrothermal treatment affects the average size and fineness of the structure of the zinc borate particles.

The hydrothermal conversion of precursors (MDGA hydrargillite/γ-Al₂O₃) to boehmite is studied. It is found that the specific surface area of the precursors increases and the peak of the bending vibrations of molecular water is shifted from 1640 to 1690 cm⁻¹ for hydrargillite at the early stages of hydrothermal treatment. The heats of vaporization of water from a two-phase system (original precursor/resulting boehmite) are found to be 27.5 and 6.5 kJ/mol H₂O, which is less than the tabulated value. Based on the literature data, conclusions are drawn with regard to the state of water in the structure of the treated material in the form of single molecules, dimers, and trimers: the boehmite structure is not perfect, and the heat effects of the dehydration of boehmite in forming γ-Al₂O₃ have values of 13.5 and 21.4 kJ/mol AlOOH. It is found that further hydrothermal treatment leads to the formation of boehmite crystals with perfect structure and, regardless of the composition of the reaction medium used for the treatment, the heat effects of the dehydration of boehmite are 26.9–27.2 kJ/mol AlOOH, which is close to the tabulated value.

In the course of the study, nanocrystalline cobalt monoboride was prepared by thermal decomposition of precursors [Co(DMF)₆][An], where [An] = [B₁₂H₁₂]²⁻ (1), [trans-B₂₀H₁₈]²⁻ (2) or [B₁₀Cl₁₀]²⁻ (3) in an argon atmosphere. Three new salt-like compounds 1–3 were prepared when Co(NO₃)₂ was allowed to react with (Et₃NH)₂[An]. Compound 1 is new; the structures of compounds 2 and 3 have been previously reported. Samples 1–3 were annealed at 900 °C in argon to form samples 1a–3a, which were characterized by single crystal XRD for 1 and powder XRD for 1–3. Powder XRD on the products showed the formation of BN and CoB for 1a in a 1:1 ratio; 2a gave a higher CoB:BN ratio but an overall decreased crystallinity. For 3a, only CoB was found. IR spectra of samples 1a–3a as well as X-ray spectral fluorescence analysis for 3a confirmed these results. The nanoparticular character of the decomposition products 1a–3a was shown using TEM; quite small particle sizes of about 10–15 nm and a quite normal size distribution were found for 1a and 2a, while the decomposition of 3 gave large particles with 200–350 nm and a broad distribution.

A new method of synthesis of nanosized aluminum oxyhydroxide (AlOOH, boehmite) powders has been suggested through a hydrothermal treatment of nanosized γ-Al2O3powder in water and a 1.5 wt % HCl...

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.