Home – Home – Jornals – Chemistry for Sustainable Development 2002 number 1-2

The history of origination and development of mechanochemistry in Siberia is outlined. Three main stages are revealed: 1. Early works in mechanochemistry (Tomsk period, 1950-1961). 2. Mechanochemistry in the Siberian Branch of the AS  USSR (1961-1990). 3. Post-perestroika period (1990-2002).

Mechanisms restricting the possibility to increase dispersity of powders produced by mechanical grinding method have been considered. Transformation of nanocrystal powder particles into super-plastic state has been demonstrated to be the main mechanism, whereupon disintegration stops, and all further treatment amounts to change in the shape of particles. Through introduction the notion of macro-dislocation - the linear defect of irregularity in the nanocrystal grain packing - both the process of transformation into super-plastic state and the process of disruption are described. Estimations of disintegration limit for metal powders have been made. Results are in good agreement with experimental data obtained by atomic power microscopy method (APM) on the iron powder ground with surface-active substances (SAS) added. A sketch of formation and development of nanostructure and phase constitution of powder particles being ground in ball mills in liquid organic media has been suggested, which takes account of the process features connected with multiple high-velocity cold-hardening, high temperature polygonization and re-crystallization, and multiple re-chill in liquid media.

An analysis of thermal processes occurring during mechanical treatment (MT) is presented. A two-stage scheme of development of thermal processes in ZnO, ZnO - TiO₂ systems is proposed and their role in the formation of the resulting defect structure is discussed. At the first stage of the MT, the collectivized processes of destruction of individual particles are observed. The second stage of processing is connected with the development of annealing effects caused by heat accumulation processes by the whole sample. The annealing processes favour the formation and accumulation of a set of associates of simple defects that accelerate diffusion processes in components of the mixtures. The processes of accumulation of associates of defects in the sample and a significant rise in the average temperature of the sample are major factors determining the progress of a mechanochemical reaction of the type ZnO + TiO₂

Results of the investigation of mechanochemical reactions of the synthesis of diborane (6) B₂H₆ from M*BH₄ (M* = Li, Na, K) and halides of polyvalent metals MX_n , adducts of BH₃ borane with nitrogen-containing organic Lewis bases (L) of the L ^. BH₃ type, borazine H₃B₃N₃H₃ from M*BH₄ and NH₄Cl, tetrahydroborates of transition metals M(BH₄) _n (M = Zr, Hf, U, Ti) from MX_n and M*BH₄ are generalized. Reactions were performed under mechanical activation of mixtures of crystalline reactants in vacuum ball mills in the absence of solvents. Rotary and vibratory mechanical activators were used. The listed reactions can serve as the basis for mechanochemical technologies. Technological aspects of the application of borane compounds are considered.

The influence of mechanochemical activation (MCA) on physicochemical, adsorption, and catalytic properties of a zeolite in refining low-octane gasoline fraction and aromatization of propane-butane fraction is studied. It is shown that MCA of a zeolite leads to the decrease in its crystallinity degree, specific surface, and acidity. In the composition of the products obtained at the conversion of directly distilled gasoline fractions over activated catalysts the concentration of aromatic hydrocarbons decreases, the content of alkenes, naphthenes and isoalkanes increases, the yield of the desired product enhances. The yield of aromatic hydrocarbons during the conversion of C₃-C₄ saturated hydrocarbons over a zeolite catalyst subjected to mechanical activation for 12 h increases by almost 10 %, its life between regenerations is 1.5-2 times longer.

The behaviour of Fe(100 - x)C(x) systems under mechanical alloying (MA) of elemental components within the concentration range up to x = 32 is studied by X-ray diffraction and Mossbauer spectroscopy. At carbon content x < 20 the amorphous phase is observed. At x ≥ 20 the Fe₃C and Fe₇C₃ carbides are formed. For the high-carbon composition Fe(68)C(32) the kinetics of solid state reactions is studied. The amorphous phase, Fe₃C cementite and Fe₇C₃ are formed sequentially in MA process. Solid-state reaction mechanism including the penetration of carbon along the grain boundaries of Fe, the formation of amorphous phase and carbides depending on C content and milling time is discussed.

The processes of mechanical alloying in the Fe - M (M = C, Si, Ge, Sn) systems at the atomic ratios of 68 : 32 and 75 : 25 under identical conditions of mechanical treatment are studied by X-ray diffraction, M

The paper deals with the effect of mechanical treatment on chitin and chitosan isolated from Gammarus (Amphipoda) of Altay. Water-soluble carboxy-methyl ethers of chitin and chitosan in the solid phase were obtained using mechano-chemical activation in planetary centrifugal mill SPEX 8000. The obtained samples were characterized by means of IR spectroscopy, carboxy-methyl group content was determined, as well as molecular masses, solubility in water, relative viscosity of alkaline solutions.

XRD, SIMS, BET, MDPD, TPR, and HREM were used to study the effect of time of mechanical treatment (MT) of the mixture of simple La₂O₃, CaO and Fe₂O₃ oxides and the temperature of subsequent calcination on the phase composition, real structure and catalytic properties of substituted La_1-x Ca_xFeO_3-0.5x (0 ≤ x ≤ 1) perovskites in CO catalytic oxidation. The phase composition and microstructure of MT samples differ significantly from those of ceramic samples: no Grenier phase La_0.33Ca_0.67FeO_2.67 were and micro-heterogeneous solid composite La_0.5Ca_0.5FeO_2.75 found in ceramic samples; independently of the time of treatment and Ca content, the MT samples are composed of the perovskite and brown mille rite phases. The microstructure of MT samples (T_calc < 1100 °C)

The scheme is presented describing the complex of principal physicochemical processes under intensive mechanical treatment of inorganic oxides as dynamic equilibrium between particle powdering and coalescence, and its graphic illustration is given. A large body of experimental results on superfine grinding of α-Al₂O₃ and ZrO₂

In the present work, mechanical alloying technique was applied to prepare hard magnetic Sm₂Fe₁₇N_x powders. Starting from pure Fe and Sm powders, the formation process of hard magnetic Sm₂Fe₁₇N_x phase by mechanical alloying and subsequent solid-gas reaction was studied. At as milled condition powders were found to consist of Sm-Fe amorphous and a-Fe phases in all compositions of Sm_xFe_100-x (x = 11, 13, 15, 17). The effects of starting composition on the formation of Sm₂Fe₁₇ intermetallic compound was investigated by heat treatment of mechanically alloyed powders. When Sm content was 15 at. %, heat-treated powders consisted of nearly Sm₂Fe₁₇ single phase. For preparation of hard magnetic Sm₂Fe₁₇N_x powders, additional nitriding treatment was performed under N₂ gas flow at 450

The analysis of some cross effects accompanying solid-phase transformations is performed within the frame of the thermodynamics of irreversible processes. Solid-phase systems capable of chemical transformations belong to complicated thermodynamic systems the state of which, unlike the one thermodynamically equilibrium, can be described by introducing additional thermodynamic parameters. Methods of describing additional parameters may be different depending on specific physicochemical situation and required detailing degree. Many cross effects discussed during thermodynamic analysis are known from experiment even if this is not mentioned. Partial models taking account of different crosse effects are known in continuum mechanics. Examples are presented that illustrate the principal role of interconnections between different phenomena, which is necessary to take into account in mathematical description of solid-phase transformations.

Thermostability of the structure, diffusion permeability and the features of the mechanical properties of nanostructured copper, nickel and composite Cu

The interaction of the sample with wear products from milling bodies made of stainless steel, tungsten carbide and strengthened ball bearing steel (ShKh15) is investigated by means of M

Mechanical activation (MA) in high-energy planetary activators is used to prepare disperse and disordered cathode (LiMn₂O₄, LiCoO₂ and Li_1+x V₃O₈) and anode (Li₄Ti₅O₁₂) materials, as well as solid oxide electrolytes (La_0.67-xLi_3xTiO₃) for rechargeable lithium accumulators. The effect of various factors including mechanical and structural properties of initial reagents, oxidation degree of transition metal ions, etc., on mechano-chemical synthesis is investigated. The features of the crystal and electronic structure of the synthesized compounds are studied using different methods in comparison with the materials obtained by the traditional ceramic method.

A high-rate synthesis ofnano-crystal zirconium oxide of tetragonal modification is performed by activation of amorphous zirconium hydroxide in mechano-chemical apparatus. Preliminary short-time mechano-chemical treatment of the hydroxide also allows one to decrease substantially (by 150-200

The corrosion stability of finely dispersed iron powder obtained by grinding in heptane and in heptane with a surfactant added (oleinic acid) in a 0.85 % NaCl solution at a temperature of 37 ?C is investigated. It is shown that corrosion stability increases with increasing grinding time; it also increases in the presence of the surfactants (SAS), in spite of the increase of powder dispersivity. The increase of corrosion stability is connected with the formation of a thin (up to 10 nm thick) protective surface layer containing graphite-like and oxide layers, as well as complex organic compounds. The composition and structure of these layers depend on grinding time and on the presence of SAS.

The mechanochemical method of active aluminium preparation was developed. Also technique of preparation of aluminiumorganic derivatives from unsaturated hydrocarbons is fulfielled. Possibility of realization of hydroalumination under the conditions of mechanochemical activation in drums of planetary mills was demonstrated for the first time. Butillithium via reaction of a butenes mixture with a lithium hydride in conditions of a mechanochemical activation was synthesized.

An equimolar ZnO and Cr₂O₃ powder mixture was mechanically activated by grinding using a high-energy vibrational mill for 0-180 min. Structural changes of the material that occur during mechanical treatment were analyzed using the surface characterization method (specific surface area, and based on the latter the calculated mean particle size) and X-ray diffraction line broadening theory. The characteristic temperatures within in the temperature range of 20-1100

The result of structural investigation of BaO₂ powder samples exposed to intensive mechanical treatment in the disintegrator are presented. X-ray patterns of the powders under study displayed features involving significant broadening and changes in positions of X-ray peaks at the certain stage of treatment. The structural instability which manifested in discontinuous jump of lattice parameters, is observed. Assumptions of the reasons causing a sharp leap of lattice parameters and broadening of X-ray lines have been made. Correlation between structural instability and solubility of BaO₂ has been established.

The phenomenon of mechanical impact has been studied to determine the response of solids to the intensive mechanical disturbance.  The process of blow is considered as sudden simultaneous change of velocities of all atoms of striking particle. The probabilities of lattice excitation and prerequisites to structural imperfections have been investigated. The calculations for cubic germanium, silicon, and diamond crystals were performed.

It is demonstrated with many examples that conducting mechano-chemical reactions at increased pressure of the gas medium allows one to synthesize new compounds, to conduct catalytic reactions in solid, to find new more efficient routes for reactions, both in inorganic and in fine organic synthesis. At hydrogen pressure of 2-10 MPa, the hydrides of magnesium and intermetallic compounds are synthesized, including previously unknown hydride of the magnesium-copper intermetallide. At increased oxygen pressure, lower oxides of manganese are transformed into active manganese dioxide, which is efficient oxidizer for the processes of fine organic synthesis. Catalytic reactions are conducted under the conditions of mechanical activation at increased pressure of hydrogen, oxygen, and ammonia. Solid-phase hydrogenation of a series of organic compounds allows one to selectively reduce functional groups and unsaturated bonds. Hydro-dechlorination of toxic chlorinated aromatic compounds has been performed, including complete destruction of 1,2,3,4-tetrachlorodibenzo-p-dioxin. At increased oxygen pressure, oxidative transformations of ursolic acid are performed. At increased ammonia pressure, the amide of ursolic acid is obtained. At increased temperature and increased hydrogen pressure, hydro-alumination of heptene-1 and dihydromyrcene is performed, leading to the formation of the corresponding aluminum derivatives R₃Al.

The investigation of phase composition in Y₂O₃-Ta₂O₅ and La₂O₃-Ta₂O₅ systems is carried out at mechanical activation and subsequent heat treatment. In Y₂O₃-Ta₂O₅ system the interaction of components is observed during mechanical activation. Heating of mechanically activated intermixtures of oxides leads to the formation of orthotantalates of yttrium and lanthanum. Temperature and time of complete interaction of components is much less than in a traditional ceramic method. The new convenient method of synthesis of tantalates of rare-earth metals is developed.

Effect of mechanical activation on the structural transformations in zirconium - graphite - hydrogen system was studied using X-ray powder diffraction, scanning and transmission electron microscopy and kinetic techniques. Experiments with zirconium - graphite mixture were carried out under high-energy impact milling in a permanent hydrogen flow. Mechanically induced process of two stages was observed: (1) formation of the tetragonal ε-ZrH_x (x = 1.8-2); (2)

The influence of mechanical activation on synthesis processes and magnetic properties of hexagonal ferromagnetics of the structural type W has been studied. It is shown that in case of mechanical activation after preliminary annealing the optimal synthesis temperature reduces by 80-100

The effect of mechanical activation on high-temperature synthesis in the regime of thermal explosion in Fe

Zinc stannate ceramics has characteristic electrical properties widely used in fabrication of various types of sensors. It is well known that the properties of materials are mostly preparation-dependent and that the structure of ceramic sensor material should be porous. That is just one of the problems that has to be solved, along with the basic one - the obtaining of specific chemical compound, zinc stannate. The subject of this work is the influence of mechanical activation on solid state chemical reaction, e. g., the formation of porous zinc stannate ceramics during different thermal treatments of compact samples obtained from ZnO and SnO₂ powder mixtures activated for various times. Mixture of ZnO and SnO₂ powders (molar ratio 2 : 1) was ac-tivated by milling in a vibratory mill with a continual regime in air, for different time periods. The shrinkage behaviour of samples during heating was followed by sensitive dilatometer. X-ray powder diffraction analysis of activated powders and thermally treated samples and SEM analysis were also performed. The main conclusion of the performed analyses is that porous, fine-grained zinc stannate ceramics could be obtained for certain time of activation at much lower temperatures than the ones reported in the literature, with simultaneous acceleration of the chemical reaction.

The effect of the preliminary mechanical treatment of metal powders on the quality of coatings obtained by plasma deposition is investigated. Substantial improvement of the inner structure and strength properties of the coatings is demonstrated. It is stated that the specific heat effect of the interaction of mechanically treated copper powder with acetic acid increases for mechanical treatment up to 15 min, which is likely to be due to the accumulation of defects in metal volume. The chemical reactivity of the mechanically activated copper powder and of the copper powder obtained by means of the electric explosion of wires is demonstrated to correlate with interplane distances between the planes with (111) Miller indices.

Results of systematic studies of framework zirconium phosphates synthesis via  mechanical activation (MA) of the mixture of solid salts followed by the hydrothermal treatment (HTT) in the presence of surfactants, drying and calcination in air are considered. Application of modern physical methods sensitive to the state of bulk and surface of nano-systems (XPD, SAXS, TEM, EXAFS, FTIRS, SIMS, UV-vis) allowed to elucidate genesis of those complex systems containing different stabilizing/modifying cations and anions. The local structure of zirconium phosphate nuclei formed in the course of MA and spatial distribution of guest cations within those nanoparticles strongly depend on the composition of starting solid reagents, which determines a mode of the acid-base interaction in the activated mixture. These properties determine in turn realization of different mechanisms of complex framework phosphates crystallization under HTT - either via oriented stacking of primary particles (occurs even in neutral or alkaline solutions) or by dissolution-precipitation route in acid solutions. Factors determining the structural type, thermal stability, surface composition and solubility of crystalline complex zirconium phosphates prepared via MA route were elucidated and analyzed as dependent upon the composition and genesis of those systems.

Deformed molecules exhibit anomaly in various aspects. Mechanical stressing, being anisotropic in nature, on the molecular crystals inevitably brings about quenched deformation of constituent molecules. When we deal with coordination compounds, deformation of the molecule results in disproportionation of ligands to change them into asymmetric, and hence develops distribution of ligand field strength. Consequences of introducing such asymmetry are very diverse. Gradual spin crossover and substitution of ligands by counter ions are only a few examples. Solid state ligand exchange is particularly of importance, since this opens up a new way for synthesizing various coordination compounds using neither solvents nor catalysts. Evidences of distribution of ligand field strength are shown for ferrous coordination compounds. Subsequently, application to the synthesis of some ferrous pyridyl compounds is demonstrated.

Defect formation and activation of agglomeration during mechano-chemical treatment of tungsten powder and its mixtures with copper and nickel are considered. Mechano-chemical activation in high-energy strain mills is accompanied by the decrease of coherent lengths (to 10 nm), accumulation of microdeformations (up to 0.2-0.3 %) and increase of tungsten lattice parameter, as well as by profound mixing of the components. Besides, the system gets contaminated with iron impurities. Chemical transformations during the annealing of samples with different doses of mechanical treatment are analyzed. The application of mechanochemical activation allowed us to obtain well agglomerated W/Ni/Cu alloys at annealing in the absence of hydrogen (density: up to 16 g/cm³; Wickers' hardness: up to 550 kg/mm²). Optimal dose of mechano-chemical activation is determined (10-115 kJ/g); optimal regime of powder pressing is revealed. The effect of iron impurities on the hardness of agglomerated tablets is investigated.

An investigation of mechanically stimulated self-propagating reactions (MSR) has been carried out for different conditions of mechanical activation in the system Zn-Sn-S using a SPEX 8000 mill. Both the earlier obtained and new results are generalized, with focus on the determination of induction period preceding the ignition of exothermal reaction. The discovered features and some hypotheses concerning the mechanism of MSR are discussed.