Home – Home – Jornals – Chemistry for Sustainable Development 2004 number 3

The main directions of research in the field of solid state chemistry carried out at the Institute of Solid State Chemistry and Mechanochemistry, SB RAS (former Institute of Physicochemical Foundations of Mineral Raw Processing, Institute of Solid State Chemistry and Mineral Raw Processing, SB ASUSSR) since 1974 till present are described.

Possible applications and advantages of mechanochemical technologies are formulated. They include one-stage chemical reactions between solids, preparation of solid disperse systems (aggregates) of chemically interacting solids, formation of solid solutions, formation of solid reagents possessing increased activity in subsequent chemical transformations, and chemical modification of natural polymers. Comparative tests of activator mills have been carried out, recommendations for their application depending on the type of product have been worked out, and methods for ranging some mechanochemical processes for "flow" vibratory centrifugal mills have been developed. An original, readily soluble pharmaceutical of acetylsalicylic acid and its production process have been developed. The advantages of mechanochemical technology include one-stage process (mechanical treatment of the powdered material), absence of solvents and technological operations using them, simplification and increased productivity of technological equipment compared to equipment typically used in liquid-phase processes, and reduced

Publications dealing with theory and practice of harnessing porous flow electrodes (PEs) for electrochemical processing of dilute solutions (extraction of metals, disposal of processing media, electrosynthesis) are reviewed. Peculiarities of this type of PE and brief history of their studies and applications, including research at the Institute of Solid State Chemistry and Mechanochemistry, SB RAS, are considered. It is demonstrated that significant progress has been achieved after 30 years of work; this primarily manifests itself in the development of a wide range of efficient porous materials based on fine carbon and metallic fibers, promoting diffusion controlled electrochemical processes several hundreds (and even thousands) fold. Seeking conditions that ensure the efficient use of the entire surface of a PE available for electrolysis turned out to be a more complicated problem. It is stressed that inhomogeneous porous matrices should be studied from the viewpoint of prospects to substantially increase the effective working depth of the PE (using the variable conductivity of the solid phase) and for better insight into the dynamics of changes in the properties of porous matrices in the course of metal incorporation.

Using various versions of mechanochemical synthesis for the preparation of nanodisperse particles of oxide materials is considered. The results of investigations of some solid-phase reactions in mixtures of reagents subjected to mechanical activation and subsequent thermal treatment are presented. The role of the salt matrix in preventing aggregation of ultradisperse particles has been studied. The efficiency of soft mechanochemical synthesis is compared with that of the sol-gel method. Both methods make it possible to obtain nanodisperse particles close in size.

The possibility of using electrolysis with carbon-graphite flow electrodes of fibrous carbon materials for recovery of gold and silver from solutions formed at various stages of jewellery manufacturing is considered. It is demonstrated that electrolysis with carbon fibrous electrodes ensures high (more than 99%) degree of gold and silver extraction: 1) from sulphuric acid

The "capacity" of layered silicates in mechanochemical neutralization reactions with organic acids has been investigated. It is established that the "capacity" of silicate depends on the nature of the acids and silicate. In reactions with acids readily dissociating in water solutions, the "capacity" of talc is maximum: molar ratio talc:acid=1:2, 1 : 1, and 3 : 2 for unsaturated mono-, bi-, and tribasic acids, respectively. For the same acids, the maximum "capacity" of kaolinite is m. r. kaolinite : acid ≈ 1:0.5. In the case of saturated monocarboxylic acids, m. r. talc : acid < 1 : 1; for aromatic acids, m. r. talc : acid = 1 : 1, kaolinite: acid ≤1 : 0.25.

A method has been developed for producing electroconductive ceramics based on titanium oxides using a reaction TiO₂ + Ti with preliminary mechanical activation of the mixture and subsequent thermal treatment under hydrogen and argon at 1060

Synthesis of the hardening phase in a metal matrix by combined mechanical activation and self-propagating high-temperature synthesis (SHS) has been investigated using the TiB₂

It is demonstrated that combined mechanochemical treatment (CMCT) of a mixture of kaolinite and sulphuric acid may be used for extracting aluminum from layered aluminosilicates. X-ray phase analysis showed that aluminum sulphate crystalline hydrate is formed in the products of CMCT of kaolinite. The effect of CMCT of kaolinites on the degree of aluminum extraction into the liquid phase has been studied in apparatuses with different levels of power supply. The highest degree of aluminum extraction was achieved in an AGO-2 centrifugal planetary mill.

The composition of a fireproof formulation based on liquid glass and alumina and a method for its preparation have been developed. Mechanical activation of alumina changes the phase composition, the structure, and reactivity of the oxide powder and has a favorable effect on the properties of the composition. A flow chart for the production of the composition is suggested.

The transformations that proceed during mechanochemical treatment of the crystalline anomers of
D-glucose have been studied. It is established that a solid organic acid or solid inorganic ampholyte (NaHCO₃) are efficient catalysts of the solid-phase anomerization of D-glucose. It is demonstrated that mechanical activation in the presence of a solid organic acid gives rise to the products of D-glucose dimerization. b-D-glucose shows the highest reactivity in reactions of solid-phase anomerization and dimerization. The difference in reactivity between the two crystalline anomers arises from the efficient mechanism of proton transfer inherent in the b-anomer. Unlike α-D-glucose, the β-anomer shows electrical conduction, which is most likely to be due to proton transfer for this class of substances. Conduction of crystalline β-D-glucose depends on the defectness and correlates with the reaction rate of mechanochemical anomerization.

Synthesis of a series of cathode materials for lithium ion batteries by mechanical activation has been investigated. It is shown that the materials are characterized by submicron particle size and the presence of structural disordering. These characteristics positively influence the electrochemical properties of insertion cathodes (e. g., LiMn₂O₄

Variation of composition and properties of the water-soluble components of peat during mechanochemical treatment has been studied. Mechanochemical treatment affects the composition, quantitative content, and biological activity of the water-soluble components of peat. Mechanochemical treatment of high peat with celloviridine and alkali increases the yield of the water-soluble oxygen-containing compounds, including humic acids. The mineral composition of peat after processing practically did not change. The water-soluble components obtained by the mechanochemical method stimulate germination of seeds and development of wheat sprouts at the early stages of vegetation.

Dissolving nitrogen-containing forage additives based on carbamide, grain, and mechanochemically obtained filling material has been studied. Samples were made by mechanical mixing, processing in an extruder, planetary and centrifugal activator mills. Variation of the grain and filler (straw, fats, bentonite) contents in the additive can serve as an efficient method for controlling the rate of carbamide isolation from forage additives. Conditions of mechanochemical production of forage additives are chosen according to the selection criteria, which are based on the requirement for the maximal admissible disturbance of the internal medium (acidity) of the organism during assimilation of the additive by an animal. The viability of application of mechanochemically obtained carbamide-containing additives has been shown by tests on animals.

This work deals with mechanochemical synthesis of phthalylsulphathiazole involving fluid phases. Model optical microscopy experiments with crystal samples have revealed that sulphathiazole can interact with phthalic anhydride without direct contact of these substances at temperatures of about 100^oC. Scanning calorimetry measurements showed that the synthesis temperature is lowered during mechanical activation of reagents. The reagents do not undergo fusion under the conditions of mechanical activation. Transport of phthalic anhydride through the gas phase was assumed to be the most likely mechanism of synthesis in a mechanochemical reactor.

The nanosized particles of Ni_{1 - x}Co_x alloys encapsulated in a layered template matrix were synthesized by thermal decomposition of precursors - layered binary hydroxides [LiAl₂(OH)₆]₂{(Ni_{1 - x}Co_x(edta)} ^. qH₂O. The morphology and the magnetic properties of the metal component were studied by X-ray phase analysis, electron microscopy (EM), and vibrational magnetometry. It was demonstrated by X-ray phase analysis that the resultant nanoparticles whose coherent scattering region (CSR) is 3-5 nm crystallize as a face-centred cubic (fcc) structure with a lattice parameter characteristic of Ni_{1 - x}Co_x alloys. EM studies revealed that in going from Ni to Ni_{1 - x}Co_x alloys (to x = 0.86) the particle morphology practically does not change; the particles are nearly spherical and do not range widely in size, their diameter increasing monotonously from 5.4 to 14 nm. In passing to Co (x = 100), however, the particles acquire discoid form and range widely in size, the average size being d_av ~ 100nm. The results obtained demonstrated that variation of the composition of the precursor can be considered as a method of controlling the size and morphology of magnetic nanoparticles.

A new method for the synthesis of highly disperse lithium gamma-monoaluminate is suggested. Binary lithium-aluminum hydroxide in carbonate form [LiAl₂(OH)₆]₂CO₃ ^. 3H₂O is used for the precursor. Calcination of a mixture of this hydroxide with lithium carbonate above 800^oC forms γ-LiAlO₂. The sequence of chemical transformations leading to γ-LiAlO₂ has been studied. The first stage of the synthesis yields α-LiAlO₂; when heated to a temperature above 800^oC, the latter is transformed into γ-LiAlO₂. The specific surface of the aluminate product is 3.5m²/g. Test experiments showed that the product may be used as a holder for fuel elements with a melted carbonate electrolyte.

Isomorphic varieties of substituted apatite have been synthesized mechanochemically for evaluating the applicability of the synthesized samples as biologically compatible materials. Mechanical treatment of reaction mixtures in a planetary apparatus for 5-30 min gave the final nanosized crystalline products synthesized directly in an activator. We have synthesized calcium- and phosphorus-deficient nonstoichiometric apatites, stoichiometric hydroxylapatite, hydroxylapatite with superstoichiometric potassium, zinc, and copper ions introduced in its structure, as well as apatites with potassium partially replaced by magnesium and barium. The kinetics of mechanochemical synthesis is affected by water, which stabilizes the structure of apatite. The results of bioactivity and cytotoxicity tests are given. Apatites synthesized mechanochemically may be used as biologically compatible materials.

Syntheses of bismuth compounds having useful properties for medical applications: neutral and basic bismuth nitrate, tartrate, gallate, subsalicylate, phosphate, oxochloride, oxocarbonate, and bismuth-potassium-ammonium citrate are reported. For synthesis of highly pure and reactive compounds it is recommended that hydrolysis and heterogeneous solid-solution reactions be used.

Synthesis of bismuth(III) oxohydroxolaurate by the reaction of lauric acid with bismuth-containing perchlorate or nitrate solutions has been studied by X-ray phase analysis, thermogravimetric analysis, electron microscopy, IR spectroscopy, and chemical analysis. Conditions of the reaction forming bismuth laurate Bi₆O₄(OH)₄R₆, where R is the lauric acid anion, have been determined, and the solubility of the anion in organic solvents has been investigated. It is recommended that highly pure bismuth laurate should be synthesized from metallic bismuth by preliminary oxidation of the latter with atmospheric oxygen, dissolving the resulting Bi₂O₃ in nitric acid (1:1), and purifying bismuth from impurity metals by its precipitation in the form of oxohydroxolaurate by adding a solution of sodium laurate to the solution of bismuth nitrate at (60±10)^oC (molar ratio HR:Bi = 1.0-1.1, concentration of free nitric acid in solution 0.1 mol/l).