N. Z. Lyakhov

Solid‐State Combustion in Mechanically Activated SHS Systems. I. Effect of Activation Time on Process Parameters and Combustion Product Composition

The factors responsible for the transition from reagent interaction involving a liquid phase in ordinary SHS powder mixtures to solid‐state combustion after preliminary activation of these mixtures in an energy‐intensive planetary mill were studied for Ni + 13 wt. % Al and Ni + 45 wt. % Ti compositions. The dependences of the burning rate and temperature on the duration and conditions of mechanical activation were determined. It is found that the occurrence of solid‐state SHS in a powdermixture is due to the formation of “laminated composites,” in which the reagents are ground to ultrafine size, the area of their contact increases severalfold, and the concentration of nonequilibrium defects is high. In activated samples, heat release proceeds in several stages and at lower temperature than in powder mixtures.

Solid‐State Combustion in Mechanically Activated SHS Systems. II. Effect of Mechanical Activation Conditions on Process Parameters and Combustion Product Composition

The effect of mechanical activation conditions in a planetary ball mill on the main parameters of SHS‐processes and combustion product composition was studied for Ni + 13 wt. % Al and Ni + 45 wt. % Ti compositions. From results of experiments at elevated initial temperatures, it is concluded that because of reverse quenching, the defects produced by mechanical activation are not annealed in the heating zone and are retained in the sample until the beginning of chemical interaction in the leading zone of the SHS wave. The process of annealing of the activated samples was studied in situ on a transmission electron microscope and a synchrotron radiation diffractometer. The energy stored in the samples as a result of mechanical activation is estimated by calorimetric studies.

Study of the products of interaction between iron and gallium during mechanical activation

Mechanochemical interaction between iron and gallium has been investigated. The multistage character and the dynamics of mechanochemical formation of the gallium solid solution in iron have been established. X-ray diffraction, electron microscopy, and atomic force microscopy have been used for studying structural and morphological peculiarities of products formed at various stages of mechanical activation. Mössbauer spectroscopy has been used for the investigation of local variations in the nearest surroundings of iron atoms during phase transformations.

Thermal explosion in mechanoactivated 3Ni + Al mixtures

Explored was thermal explosion in mechanoactivated 3Ni + Al mixtures. Mechanoactivation was found to result in an abnormal decrease in the effective activation energy E and ignition temperature Tign for thermal explosion. Analysis of reaction thermogram allowed us to find out the kinetic function. Mechanoactivation conditions for synthesis of Ni3Al in thermal explosion mode have been optimized. SHS reaction in 3Ni + Al mixtures mechanoactivated for 180 s was found to obey the first-order kinetics.

Mechanochemically synthesized powder precursors local structure influence on the microstructure of SHS Fe2O3/Fe/Zr/ZrO2 composites

Composite powder materials containing zirconia and iron oxide nanoparticles, as well as iron-zirconium intermetallic compounds, are of great interest for use as high-temperature functional coatings, in catalysis, and for medical and biotechnological purposes. In this work the influence of the forming local structure of particles during the mechanical activation of Fe/Zr and Fe2O3/(Fe/Zr) powder precursors on the microstructure of Fe2O3/Fe/Zr/ZrO2 nanocomposites, synthesized in a SHS combustion mode, is investigated.

Study of high-temperature oxygen permeability in Sr1 − xLaxCo0.8 − yNbyFe0.2O3 − z perovskites

The oxygen permeability of ceramic SrCo0.8 − yFe0.2NbyO3 − z (0 ≤ y ≤ 0.2) and La0.3Sr0.7Co0.6Fe0.2Nb0.2O3 − z disc membranes as a function of temperature and oxygen partial pressure was studied. Kinetic analysis was performed based on the experimental data on oxygen permeability as a function of oxygen partial pressure.

Mechanochemical production of nanocomposites of metal/oxide and intermetallic/oxide systems

Addition of nanosized intermetallic or metallic phases into corundum considerably raises mechanical behavior of the material. In this work, the nanocomposites of α-Al2O3/intermetallic and α-Al2O3/metal systems were obtained by mechanochemical reduction of α-Fe2O3 by Al (and by solid solution of Al in Fe). The mechanochemical reduction process of hematite by various amount of metal-reducer was studied by IR and Mossbauer spectroscopies, and by X-ray synchrotron radiation diffraction technique.

Anomalous decrease in the activation energy and initiation temperature of a thermal explosion in the mechanically activated composition 3Ni + Al

277 † In recent years, increasing interest in combination of the methods of self-propagating high-temperature synthesis (SHS) and mechanical activation (MA) has been observed [1–4]. This is explained by the fact that the preliminary MA of the powdered reaction mixtures provides a substantial expansion of the possibility of gasless combustion for the high-temperature synthesis of inorganic materials, specifically, to extend the concentration limits of combustion, to use for synthesis such compositions that do not combust under usual conditions, to avoid the necessity of pressing the starting samples [3, 4], and to realize the solid-phase combustion mode even in compositions with a low-melting reagent such as aluminum [4]. It should be noted that the synthesis in most of the investigated activated compositions was performed in the mode of frontal propagation of the SHS wave. However, the features of the dynamics of the self-heating process in the thermal explosion mode in activated systems and the corresponding interrelation of the processes of structure and phase formation with the MA modes are almost unknown. The thermograms of the synthesis of activated samples can give a lot of useful information with respect to the synthetic parameters and, first of all, the effective activation energy and critical conditions of interaction initiation.

Dynamic diffractometry of phase transformations during high-temperature synthesis in mechanically activated powder systems in the thermal explosion mode

High-temperature synthesis of mechanically activated powders of the Ti-Al system are studied by means of induction heating in an inert atmosphere and vacuum. The effect of the duration of preliminary mechanical activation of the original mixture on the main synthesis parameters (e.g., time and temperature at the onset of reaction between components, the combustion rate, and the temperature of synthesis initiation) is investigated experimentally.

Producing Cu/ZrO2 composites by combining mechanical activation and self-propagating high-temperature synthesis

The possibility of producing Cu/ZrO2 composites by combining mechanical activation and self-propagating high-temperature synthesis (SHS) is studied using x-ray diffraction and electron microscopy. It is shown that Cu/ZrO2 composites are formed in SHS using CuO/Cu/Zr mechanocomposite as a precursor.