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The possibility of producing ultra-high-temperature composite Ta4ZrC5 by a single-stage method was experimentally studied. The method combines the exothermic synthesis by electrothermal explosion and the consolidation of the hot product under quasi-isostatic compression. The effect of the mechanical activation of the reaction mixture of powders of tantalum, zirconium, and carbon on the formation of the phase composition of Ta4ZrC5 ceramic composite was investigated. The conditions for producing single-phase ultra-high-temperature composite were determined. Composites with an average particle size of 1–2 μm and a residual porosity of 8–10% were obtained. [ABSTRACT FROM AUTHOR]

Reactive multilayer nano-foils possess high heat release and combustion temperature, which makes them very attractive for advanced applications, such as materials joining materials, tuning ignition and actuation, energy microsources, and others. The combustion mechanism of CuO/Al foils has not been adequately described yet. In this work, we report experimental evidence of an amazing combustion mode in CuO/Al reactive multilayer nano-foils. A set of droplets of molten combustion products forms behind the reaction front and "rides" this front under the action of surface tension. When the combustion front arrives at the edge of substrate and stops, the droplets start to fly-by inertia along-track direction of the combustion propagation. Thus, the combustion front can throw hot micro-droplets toward a predetermined target to perform some specific action, e.g., distance ignition, actuating pulse, or energy transfer. [ABSTRACT FROM AUTHOR]

Various macrokinetic modes of interaction (self-ignition or combustion) of compact samples from nonpassivated (pyrophoric) and passivated iron nanopowders with air are under study. Experiments show that the modes of interaction with air depend on the type of the used gaseous medium (argon or air), previously containing weighting cups with samples, and on how long the bottles remain in air. The possibility of passivation of pressed samples from pyrophoric iron nanopowder is experimentally established for the first time in the case where the weighting cups with samples remain in air. Various experimental methods are used to investigate the sample heating dynamics and the effect of density inhomogeneity along the length of the sample. It is revealed that pyrophoric samples are heated nonuniformly, although heating begins simultaneously over the entire surface of the sample. [ABSTRACT FROM AUTHOR]

The use of nanopowders implies the ability to safely store them without changes in their physicochemical parameters ensured by passivation. In this work, we have determined the thermal stability range in air for compact samples of different diameters prepared from pyrophoric nickel nanopowders and then passivated. The results demonstrate that compact samples prepared from nickel nanopowder can be safely stored in air at temperatures of up to about 200°C without additional oxidation, which points to their high thermal stability. The lack of a noticeable heat release during slow heating to 200°C and the presence of only Ni in both the passivated and heat-treated samples according to X-ray diffraction data suggest that the oxide layer is very thin or that there are noncrystalline oxide phases. The observed uniform oxygen and nickel distributions over fracture surfaces of samples after heating suggests that their interaction with air during both the passivation process and heating to temperatures on the order of 200°C is a bulk process. [ABSTRACT FROM AUTHOR]

An experimental apparatus was developed and manufactured to simulate the processes of electric spark plasma sintering. The apparatus allows direct observation and high-speed video recording of chains of powder particles in the channels of a dielectric matrix when passing short pulses of electric current. Tests performed using chains of titanium spherical particles with a diameter of up to 300 μm as an example showed the significant overheating of the contact area at the moment of transmission of a short (~1 ms) electric current pulse that is characteristic of spark plasma sintering. Thus, the developed methodology and installation provide the ability to study the mechanisms of modern technologies for the consolidation of powder materials based on pulsed electricity. [ABSTRACT FROM AUTHOR]

The amorphous-crystalline transition in Fe84B16 alloys prepared by melt spinning and high-energy ball milling was studied. Time-resolved X-ray diffraction showed that the kinetics of transition into a crystalline state depends on the method of preparing a metastable alloy. In amorphous Fe84B16 alloy prepared by melt spinning, crystallization proceeded within a time period of below 1 s and was accompanied by the formation of eutectic α-Fe–Fe3B. At temperatures above 600°C, metastable phase Fe3B was found to transform into Fe2B and α-Fe. In the high-energy ball milling produced alloy, structural changes were accomplished in 4–8 s and the transition into a state with a perfect crystalline structure was caused by the growth of nanocrystallites formed during processing. [ABSTRACT FROM AUTHOR]

This paper presents a study of direct conversion of chemical energy into electrical energy during the combustion of a (80Zr + 20CuO)–(LiF + CaF2 + MgF2)–(15Zr + 85CuO) thin three-layer condensed energy system, which is a high-temperature galvanic cell. It is determined that this cell during combustion generates an electric signal with an amplitude of 1.6 V and a half-width of 15 s. Its formation mechanism is proposed. A time-resolving X-ray diffraction method is used to identify the phases formed. [ABSTRACT FROM AUTHOR]

The possibility of producing ultra-high-temperature composite Ta4ZrC5 by a single-stage method was experimentally studied. The method combines the exothermic synthesis by electrothermal explosion and the consolidation of the hot product under quasi-isostatic compression. The effect of the mechanical activation of the reaction mixture of powders of tantalum, zirconium, and carbon on the formation of the phase composition of Ta4ZrC5 ceramic composite was investigated. The conditions for producing single-phase ultra-high-temperature composite were determined. Composites with an average particle size of 1–2 μm and a residual porosity of 8–10% were obtained. [ABSTRACT FROM AUTHOR]

A family of high-entropy alloys (HEA) composed of 3d-transitional metals is attracting great interest due to the mechanical, magnetic, and electrical properties that are valuable in the development of advanced structural and functional materials. In this work, we studied X-CoCrFeNi HEAs, where X = Al, Ti, or Cu, produced by mechanical alloying by means of high-energy ball milling. Powder mixture composed of elemental metal powders transforms in a homogeneous alloy (super-saturated solid solution) due to the intense diffusion which takes place during friction and shear deformation of the metal particles during the mechanical alloying. The thermal stability of the HEA phases was experimentally studied in the range 873-1273 K using high-temperature X-ray diffraction and compared with the results of thermodynamic calculations (Calphad). [ABSTRACT FROM AUTHOR]

We proposed a new method to increase the biocompatibility of porous materials that were synthesized from titanium and cobalt allows by the method of self-propagating high-temperature synthesis. This method suggested the introduction of calcium hydroxyapatite into the reaction mixture. Administration of calcium hydroxyapatite into the reaction mixture had a modifying effect on the structure and surface of the pore space and biocompatibility of composite materials. Administration of calcium hydroxyapatite crystals was followed by a significant decrease in the size of pores and appearance of water-soluble fractions, which inhibited the activity of cells. However, treatment with amorphous nanodispersed calcium hydroxyapatite increased the biocompatibility and adhesiveness of materials for mesenchymal stem cells. The pore space and mechanical characteristics of materials obtained with amorphous nanodispersed calcium hydroxyapatite were similar to the properties of natural bone. Moreover, these materials surpassed titanium-cobalt allows in biocompatibility. Our results indicate that the introduction of amorphous nanodispersed calcium hydroxyapatite into the reaction mixture during self-propagating high-temperature synthesis has a modifying effect on the pore space of composite materials and increases their biocompatibility and adhesiveness for cells. We conclude that these materials may be used as a carrier of stem cells and progenitor cells in hybrid implants.