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Seven binary mixed oxides of V2O5, MoO3, TiO2, B2O3, Bi2O3, In2O3, and Tm2O3, in which V2O5 is a permanent component, were prepared by the method of mechanochemical activation (MCA). All composites have been investigated using EPR spectroscopy, X-ray diffraction, BET analysis and EPR spectra calculations. The results obtained were compared with those for individual V2O5 powder. The kinetic of structural transformations occurring in these binary mixtures under MCA were quantitatively characterized using a developed program of EPR spectra analysis. These structural rearrangements are fitted well by the first-order rate constants. Influence of the oxide nature mixed with vanadium pentoxide, the ratio of the components and time of milling on these transformations are discussed.

The general aspects of the mechanical activation (MA) of Al/CuO thermite compositions based on micron-sized particles and nanopowders of the starting components have been analyzed using X-ray diffraction and hydrogen titration. The latter method has been employed to evaluate the amount of residual oxygen in CuO and Cu2O from the weight loss during heating in H2. The reactivity of the activated mixtures was assessed using DSC and TG in combination with mass spectrometric analysis. In addition, we have measured the ignition temperature, burning velocity, and brightness temperature of the reaction products. The results demonstrate that mechanical activation leads to the fragmentation of the components, mixture homogenization, and the formation of a composite, producing “weakly bound” oxygen in CuOn and causing partial reaction between the components. The total exothermic heat effect in DSC scans, burning velocity, and brightness temperature as functions of specific milling dose (D) have an extremum. The highest reactivity is observed near D = 2 kJ/g, where a sufficient defect density in the components and good mixture homogenization are ensured, but the degree of MA-induced conversion does not exceed 10%. The burning velocity then reaches 400–700 m/s, and the brightness temperature is 3400–3800 °C. The milling dose dependence of the self-ignition temperature has no extremum. The self-ignition temperature steadily decreases with increasing milling dose, even though the ignition knock “power” falls off. The use of nanoparticulate starting components does not appear reasonable.

In this review, the regularities of formation, structure and high reactivity of two types of energetic metal/solid oxidizer nanocomposites (Al(Mg)/X (X = MoO3, (–C2F4–) n )) prepared by mechanoactivation are examined. One reason for the high reactivity is an increase in contact surface between the components occurring after mechanoactivation. Two methods for determination of area of contact surface S C between the components are used, and the values of S C for all the systems are estimated. Considerable attention is paid to the role of highly reactive defects (grain sizes, dislocations and stacking faults, paramagnetic centers, “weakly bound” oxygen in MoO3, etc.), formed in the components under mechanical stress. For the Me/MeO3 systems, the formation of point defects in the oxide is an important factor. It was found that, after mechanoactivation, the evolution of O2 from MoO3 occurs at 230–450 °C. It is argued that this process is associated with the thermal destruction of “weak” Mo–O bonds in the “bridge” oxygen. It was suggested that the formation of defect structure in MoO3 and increasing of the oxygen mobility under heating give rise to a low-temperature peak in DSC curves and initiated self-ignition on the fuel–air mixture. For composites Mg/MoO3, self-ignition occurs at temperature 100 °C lower than that for Al/MoO3: The decreasing of temperature can be connected with larger S C in the first system. In the Mg/(–C2F4–) n system, the reactions of magnesium defects with (–C2F4–) n are accompanied by a weak heat evolution, too low to initiate ignition. In this case, the reaction is initiated by the thermal depolymerization of (–C2F4–) n , while a high values of S C provide a complete conversion. In the case of shock-wave initiation, defects in the components play only a minor role in the conversion, whereas the value of S C remains to be highly important.

Samples of individual and mixed vanadium-molybdenum (V:Mo) oxides xV2O5:(1-x)MoO3, 0 ≤ x ≤ 1, were prepared by the method of mechanochemical activation (MCA). The samples have been characterized by X-ray diffraction (XRD) and X-band electron paramagnetic resonance (EPR) spectroscopy. Prolongation of the treatment duration time in mills led to considerable increase in the V(IV) paramagnetic centers content as well as after additional high temperature annealing at 600 °C. Paramagnetic Mo(V) centers were recorded only in the case of MCA of individual MoO3 oxide. Complexity of the composition of mechanically activated mixed oxides was confirmed with the XRD data. It is shown that in the case of all individual and mixed oxides the content of paramagnetic species increases noticeably with the increase in milling time. The annealing at 600 °C after MCA of mixed oxides forms a new mixed phase of MoV2O8 composition.

Two regimes of oxidation by water are revealed for nanocrystalline aluminum prepared by the mechanical activation of its mixture with graphite and distributed in the matrix of amorphous carbon. At the temperatures 50°C < T < 90°C, nanosized aluminum particles interact with water under quasi-isothermal conditions. The main products are hydrogen and pseudoboehmite AlOOH; a low content of bayerite Al(OH)3 is also formed. After the induction period, the kinetics of interaction can be satisfactorily described by the law of a diminishing sphere. The effective activation energy of the reaction is equal to 61 ± 10 kJ/mol and is identical for the samples of submicron aluminum prepared by different procedures. At temperatures above 90–95°C, the oxidation of mechanically activated aluminum by water is transformed into a thermally self-accelerated explosion process. Under these conditions, the oxidation of aluminum to α-Al2O3 is accompanied by an exothermal reaction between the metal and the carbon matrix during which aluminum carbide Al4C3 is formed.

The structure of active Al/C composite prepared by the mechanochemical method from aluminum and graphite powders (10–30 wt % C) is studied by scanning and transmission electron microscopies, atomic force microscopy, local elemental analysis, X-ray diffraction, as well as by adsorption and sedimentation measurements. It is established that the particles of chemically active Al/C composite represent porous plate-like aggregates with a mean size smaller than 2.5–5 μm and composed of nanocrystalline aluminum blocks with a size of 15–60 nm distributed in a loose amorphous carbon. Single aluminum particles with a size of up to 10 nm are also observed; however, their weight fraction is small.

Changes in the crystal structure and composition of aluminum and graphite powder mixtures in the course of their joint mechanical treatment in a vibration mill were monitored by the adsorption and X-ray diffraction techniques. It was shown that, at absorbed energy doses of 8–10 kJ/g, the grinding and mixing of aluminum with graphite is completed by the formation of an intermediate structure of Al/C composite, where aluminum showed an anomalously high reactivity. The interaction of aluminum with water was used to study its reactivity in the composite. The formation of the composite preceded the stage of chemical interaction between carbon and aluminum atoms.

Mechanical treatment of aluminium with 10-30 wt% graphite in the high-energy vibration mills leads to the formation of a chemically active substance. The structure of active aluminium and its formation are investigated by X-ray diffraction, adsorption, chemical analysis, and DSC. The reactivity of active Al is checked in reactions with graphite, as well as water, oxygen, and nitrogen. At the initial stage of mechanochemical interaction of aluminium with graphite, the dispergation of components and accumulation of defects in Al and C take place. Simultaneously, the surfaces of aluminium nanoparticles are covered with the carbon layer. Then the chemical interaction of aluminium with carbon starts on the surface of particles. At the final stage, aluminium carbide is formed in the volume of particles. The maximal reactivity of Al corresponds to the Al/C nanocomposites, in which chemical interaction of components is not yet realized. The reactivity of mechanochemically activated aluminium significantly exceeds that of standard aluminium powders. Interaction of activated Al with carbon takes place at 450°C, which is 800°C lower than the temperature at which the nonactivated aluminium reacts with carbon. Two types of reactions (“isothermal” and explosive) are observed for mechanochemically activated Al with water and air.

Exothermic effects arising during silicon powder heating after their mechanical treatment were measured by synchronous TG–DSC thermal analysis method. Silicon samples possessed semicrystalline structure. As temperature varied from room temperature to 1200°C at a rate of 10 and 50 deg/min, the heat was released in the range 550–800°C. The crystallization of amorphous phase was also observed in the same temperature range using the X-ray diffraction. As the amount of energy consumed during the mechanical treatment of powders increased, the value of the heat effect rose synchronously with the degree of amorphization. In this case, the ratio of the released heat to the content of X-ray amorphous phase was constant and equal to 6 ± 2 kJ/mol.

The kinetics of silicon amorphization in the process of mechanical treatment of powders in a vibrating micromill was studied by the X-ray diffraction. The treatment was carried out in the argon atmosphere, the apparatus energy intensity was equal to 18 W/g, and the amount of consumed energy (dose) was as high as 510 kJ/g (14 MJ/mol). The analysis of the shape of X-ray diffraction patterns and the dynamics of the changes in silicon atomic structure were described within the framework of three-fraction model. Fraction 1 composed of large crystalline blocks comprising particles of initial powder; the second fraction is represented by nanocrystalline blocks with the dimensions of not less than 8 nm; and the third fraction is an amorphous phase. A decrease in the content and sizes (from 102to 25 nm) of initial microcrystals of fraction 1 is accompanied by the formation of X-ray amorphous phase 3. Nanocrystalline blocks of fraction 2 are none other than the intermediate products. They are first accumulated synchronously with the amorphous phase and then disintegrated with a decrease in their sizes from 8 to 4 nm. At the initial stage of experiment, at the dose up to 15 kJ/g and the degree of amorphization up to 40%, the energy yield of the formation of amorphous phase amounts to 1 ± 0.1 mol/MJ. At the end of experiment (the dose varies from 20 to 510 kJ/g), the yield drops by tens of times, and the content of amorphous phase reaches 70–80%.

Several series of adsorption measurements were made for a more detailed analysis of the processes resulted in the amorphization of silicon during the mechanical treatment of its powder. Among these measurements are the determination of the specific surface area by the BET method and the registration of “instantaneous” sorption of hydrogen and oxygen directly during the mechanical treatment of powders in the atmosphere of these gases. The sorption of hydrogen is low corresponding approximately to the monomolecular coverage of a freshly formed silicon surface. The sorption of oxygen (P> 100 Torr) is significantly higher than that of hydrogen and its yield is close to that of amorphous phase in the inert environment. The presence of oxygen slows down the formation of amorphous phase. To explain this result, it was suggested that, in the regions of the concentration of mechanical stresses, silicon is active, disordered, and possesses a high sorption capacity. In the oxygen atmosphere, the sorbed molecules tend to oxidize the active silicon, whereas, in an inert atmosphere, the amorphous phase that is stable up to 800°C is formed from active silicon.

Nanocrystalline aluminium powder has been prepared by high-energy ball milling of flaked micron-sized aluminium powder in the presence of 10 wt% of graphite under argon atmosphere. The structure and chemical composition of as-prepared nanocomposites and the their thermally induced changes are studied by X-ray diffraction (XRD), transmission electron microscopy (TEM), and simultaneous TG-DTA technique (SDT). TEM studies reveal that the aluminum nanoparticles have a size of 20-50 nm and they are randomly distributed within graphite “threads,” which in turn form aggregates of 3-5 μm. The oxidation behaviour of nano-Al in air was studied and compared to a precursor mixture of Al powder with average particle size of 21 μm and 10 wt% of graphite. For both powders, two stages of oxidation were observed in the temperature range 500-660°C and beyond 750°C. The mass gain for the first oxidation stage of the nano-powder is 3.5 times higher than that of the micron-sized one. A decrease of the activation energy of Al oxidation has been found for the nano-Al powder in comparison to the precursor aluminium. The evolution of crystal structure of aluminium oxide during oxidation of the Al/C composite powder has been followed by XRD.