Том 483, № 1 (2018)

A new method (AA approximation) is proposed for obtaining approximate analytical solutions of a system of equations describing the transport of the basic reagents for the electroreduction process of the BrO\(_{3}^{ - }\) anion on a rotating disc electrode in an acid medium in the presence of very small additions of molecular bromine. This process is of significant interest both from the fundamental point of view (as an example of a new electrochemical EC'' mechanism with autocatalytic properties) and from the applied point of view in the context of prospects to create, on its basis, innovation power sources—bromate redox flow batteries. Since the previously proposed method for solving the system of kinetic transport equations for this system turned out to be inapplicable for very large diffusion layer thicknesses and very strong currents, here a new method of obtaining approximate analytical expressions for concentration profiles and maximum current is proposed. It has been shown that its predictions are in good agreement with the results of the numerical solution of the same problem in a wide range of system parameters, including the region of very large diffusion layer thicknesses, which confirms the validity of the used analytical approximations.

New methods of creation of cyclic bridging and terminal exopolyhedral sulfur-containing substituents in the closo-decaborate anion have been suggested. It has been shown that the reaction of [B₁₀H₉SH]^2– with 1,2-dibromoethane leads to crosslinking of two cluster anions to give the [B₁₀H₉S(CH₂)₄SB₁₀H₉]^2– dimer. An analogous reaction with 1,4-dibromobutane yields a derivative with the cyclic tetrahydrothiophene substituent [B₁₀H₉S(CH₂)₄]^–. Its interaction with tetrahydrothiophene in the presence of a small excess of trifluoroacetic acid leads to the formation of the neutral disubstituted derivative [B₁₀H₈(S(CH₂)₄)₂].

A procedure for tritiation of predominantly the cyclohexene moiety of abscisic acid was developed. Tritium was introduced by isotope exchange reaction with 100% tritiated water at 220°C in the presence of diisopropylethylamine. The yield of abscisic acid was 50%, and the specific activity was 30.5 Ci/mmol. The labeled product was tested. It was shown that tritiated abscisic acid synthesized by the proposed method did not differ from the unlabeled precursor and could be used for biological assays.

Based on tricalcium phosphate, new high-strength composite materials were synthesized, in which the strengthening phase was ZrO₂. To reduce the sintering temperature and obtain a fine crystalline structure, a special additive based on sodium silicate was developed, which favored the formation of low-temperature melts. It was studied how the ratio between the initial components and the sintering conditions affect the phase composition, microstructure, and mechanical properties of the obtained composite materials. By improving technology and optimizing composition, strong ZrO₂-rich composites were produced in the tetragonal modification with a low sintering temperature of 1250–1350°C and a flexural strength to 260 MPa. The composites had microstructure with tricalcium phosphate and ZrO₂ crystal sizes to 500 nm and to 5 μm, respectively. Such materials can be used in medicine for manufacturing bone implants capable of withstanding physiological loads.

The high-temperature solid-phase interaction of hydroxyapatite (HA) with magnesium, strontium, and zinc nitrates at the stage of annealing of ceramics was investigated. The phase composition and unit cell parameters of the obtained materials were studied for various metals introduced into the structure to different concentrations. The introduction of Mg led to partial decomposition of HA to tricalcium phosphate and tetracalcium phosphate, the addition of Sr caused partial formation of tetracalcium phosphate from HA, and the doping with Zn gave rise to single-phase HAs.