A. P. Barinova

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.

Mechanochemical synthesis of metastable solid solutions: Phase composition and microstructure evolution

The formation of Cu-Sn, Cu-In, Ni-Sn, and Ni-In supersaturated solid solutions during mechanochemical synthesis was studied. It was found that, in the process of synthesis, intermetallic compounds were formed first. Electron-microscopic examination revealed the presence of stacking faults and microstrains nonuniformly distributed in the initial stages of mechanochemical synthesis. Further mechanical activation makes the microstrain distribution more uniform. The microstructure of the metastable solid solutions is well described by models taking into account the major types of structural imperfections—second-order microstrains and deformation stacking faults.

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.

Step-by-step powder composite mechanosynthesis for functional nanoceramics

To study the possibility of Fe2O3 mechanochemical reduction by preliminary mechanically alloyed Fe+20%Al compound their powder mixture was subjected to high-energy ball-milling in Ar atmosphere, with the milling time varying between 2 and 12 minutes. The milled samples obtained at various times of milling were characterized by X-ray diffraction and Mossbauer spectroscopy. As a result gradual α-Fe2O3 reduction via formation of intermediate Fe-Al-O oxides was observed. The presence of the intermediate Fe2AlO4 spinel phases stable over long milling time is stated. Mechanocomposite Fe+20%Al transformation to α-Fe(Al) solid solutions which evolve peculiarly with the milling time, was observed also. The kinetics of α-Fe2O3 reduction process was analyzed in comparison with the same processes in the systems: α-Fe2O3 + Al and α-Fe2O3 + Al + Fe.

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.

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.

Structural transformations upon the mechanochemical interaction between solid and liquid metals

The process of mechanochemical interaction of solid and liquid metals is examined. It is shown that the mechanochemical formation of solid solutions in all the cases occurs through the stages of the formation of stable intermetallic compounds.

Mechanoactivated SHS of FeAl-based nanocomposite powders

FeAl-based nanocomposite powders were prepared by mechanically activated SHS (MASHS) using Fe + Al + Fe2O3 and Fe + Al + Cr2O3 powder mixtures as starting materials. In both the cases, the synthesized powders were found to inherit the structural morphology of mechanocomposites (precursors) formed in the course of mechanical activation.

Microstructural and phase transformations during the preparation of Ni-Ge solid solutions by mechanical alloying

Data are presented on the mechanically activated formation of solid solutions in the Ni–Ge system, where the constituent metals differ sharply in mechanical properties. X-ray diffraction and electron microscopy examination reveals successive formation of layered composites, intermetallic compounds, and fine-particle solid solutions with a highly disordered structure.