Home – Home – Jornals – Chemistry for Sustainable Development 2014 number 4

A short review of research of the transfer mechanism in crystals conducted at the Institute of Solid State Chemistry and Mechanochemistry of the Siberian Branch of the Russian Academy of Sciences over the last 40 years is presented.

For one reactions class of thermal decomposition of the type of crystallohydrate dehydration, decompositions of carbonates, hydroxides and other compounds, we managed to go the entire way – from the starting reagent to the final morphology of the solid product. Possible phase formation mechanisms for this type of processes were considered. A general algorithm that allows theoretically predicting the size and shape of the particles of final product was proposed. The product of thermal decomposition is a porous compact formation that conserves the geometric dimensions and shape of the starting precursor particle (pseudomorphosis). There is a fraction of emptiness inside pseudomorphosis, equal to the difference between the molar volumes of the starting reagent and product. Pseudomorphosis consists of oriented product nanocrystals equally sized and shape interconnected, that is, represents a structured system. It was demonstrated experimentally that pseudomorph obtained by dehydration of CuSO4 x 5H2O monocrystal behaves analogously to liquid crystals as an optically anisotropic medium, i. e., possess birefringence. This is the evidence of the ordered locations of particles composing it. It was established that the spatial distribution of the intensity of small-angle X-ray scattering from pseudomorphosis obtained by dehydration of CuSO4 x 5H2O monocrystal (performed at the synchrotron radiation source of INP, SB RAS, applying a two-coordinate detector) possessed angular anisotropy. Based on the received data, the sizes of the rod-shaped particles were assessed: thickness (~8 nm), length (~100 nm) and their location in pseudomorphosis.

Analysis of the works recently published on the soft mechanochemical synthesis of oxide compounds is presented in the review. Specific features and advantages of this method in comparison with other ones are considered. The possibilities of this method in obtaining materials through easier and readily realizable procedures avoiding solvents are demonstrated. Specific examples of the synthesis of fireproof oxides, spinels, catalysts, lithium-containing compounds, pigments are presented, and the prospects of their implementation are considered.

A strategy of targeted regulating functional properties of perovskite-like oxides with mixed oxygen-electronic conductivity (MOEC) using ferroelectric high-valent dopants (Nb, Ta, Mo, and W) is presented. New research methods of the oxygen stoichiometry and oxygen exchange kinetics in MOEC oxides were proposed. Research results of oxygen permeability of membranes based on the elaborated materials were discussed.

By the mechanochemically stimulated solid-phase synthesis, new nanostructured cathode materials based on vanadium were obtained: Li₃V₂(PO₄)₃, LiVPO₄F and their composites LiVPO₄F/Li₃V₂(PO₄)₃. The crystal structure and electrochemical properties of the synthesized compounds were studied by means of XPA with refinement according to Rietveld and chronopotentiometry. It was demonstrated that Li₃V₂(PO₄)₃ is stably cycling within the voltage range 3.0–4.3 V, in particular at high current density. Improvement of the cathode characteristics of LiVPO ₄F is promoted by obtaining composite materials LiVPO₄F/Li₃V₂(PO₄) ₃ with nanodomain structure. The possibility to use LiVPO₄F in symmetric cells with the voltage of 2.4 V is demonstrated.

The possibility to obtain a zirconium-substituted apatite by the method of mechanochemical synthesis was studied. It was established that zirconium oxide or zirconium hydroxide could be used as the source of zirconium for this synthesis. It is preferable to use zirconium hydroxide, as in the process of the mechanochemical synthesis, the major part of the oxide remains in the initial state. In case of the hydroxide, the intermediate phase of the double oxide contributing to further synthesis is formed.

Research results of the effect of nanodispersed ceramic powders on properties of nanocomposites based on high pressure polyethylene are given. It has been shown that the addition of the nanodispersed modifiers SiC, TiO₂ leads to grinding up polyethylene grains up to the sizes of less than 0.1 μm. Herewith, an increase of the density and fastness to rubbing of polyethylene is observed, as well as the decrease in gas permeability (in 1.5 times) and water vapour permeability (in 1.7 times).

The products formed at the reduction of silver, copper, nickel and bismuth carboxylates were investigated by methods of chemical, X-ray phase, differential thermogravimetric analyses and electronic microscopy at heating in the environment of high-boiling organic liquid. It was shown that powders of silver, copper, nickel, bismuth and of alloys of these metals of the submicron size could be obtained by the way of reduction of these metals carboxylates by ethylene glycol and benzyl alcohol. Structural morphological features of powders obtained, as well as the influence on these parameters of the length of the methylene chain of the starting carboxylate, its morphology and the process of doping by cations of other metals were investigated.

The electrochemical activity of mixed indium-tin oxides (ITO) at the cathode and anode treatment in various solvents was studied. It was established that in case of the anodic polarization at potentials that are more negative than the potential prior to the beginning of hydrogen evolution in appropriate solutions of ITO were reduced to the metals In and Sn followed by the formation of intermetallides. It was shown at the anodic treatment the nature of the acid and current density had a big impact on the rate of the anodic dissolution of ITO. The dissolution rate in HCl is lower than in H₂SO₄ and significantly reduced with the increase of the acid concentration due to the acceleration of the side reaction of the evolution of Cl₂. The electrochemical activity of ITO at the cathode and anodic treatment in solutions allows using electrolysis for the disposal of used magnetron targets or ITO scraps.

Chemical and electrochemical methods of the application of nanolayers of silver metal and its poorly soluble compounds (silver chloride and oxide) on the surface of polymeric fibers were considered. The morphology and phase composition of coatings were studied. A comparative evaluation of the antimicrobial activity of the obtained materials on various bacterial cultures was presented. It was shown that the antimicrobial activity of coatings significantly increased with the rise of their solubility.   Due to the developed surface and a high porosity, synthetic fibres with such coatings are particularly promising for the application as antimicrobial filters in the purification systems and air conditioning, as well as the water treatment system.

Data on the content of uranium and other components in mineralized lakes of Western Mongolia and the adjacent territory of the Russian Federation were generalized. It was revealed that soda lakes of the studied regions were characterized by an increased content of uranium. The assessment of reserves of uranium and other micro- (Li, Br, B, As, etc.) and macroelements in lake waters was performed. Geochemical sources of uranium accumulation in lake systems, and forms of its deposition in water and bottom sediments of lakes were analyzed. Possible variants of the way of extracting uranium and other precious components from lake waters were considered.