Experimental verification of discrete models for combustion of microheterogeneous compositions forming condensed combustion products (Review)

Combustion, Explosion, and Shock Waves - This paper presents an analytical review of modern quasihomogeneous and discrete models of gasless combustion. Particular attention is given to experiments...     

NANODEV: A Nanoelectronic-Device Simulation Software System

The concept and structure of the NANODEV simulation software are described. NANODEV deals with nanoelectronic devices that exploit single-electron tunneling, resonant tunneling, or quantum interference. It can use both simplified and sophisticated models and enables one to evaluate a wide variety of devices and configurations. The capabilities of NANODEV are illustrated by examples.     

Deformation Dynamics of a Reactive Medium During Gasless Combustion

Deformation during gasless combustion of 5Ti + 3Si and Ti + C samples was studied experimentally. The dynamics of motion of the material in a gasless combustion wave was studied using highspeed video recording (500 frames/sec) with a spatial resolution of the order of 10 m. It was shown that behind the combustion front, the medium was first expanded and then compressed. The dimensions of the expansion and compression zones were determined.     

Combustion and structure formation in the Ti-Ta-C-Ca<Subscript>3</Subscript>(PO<Subscript>4</Subscript>)<Subscript>2</Subscript> system

Biocompatible composites (Ti, Ta)C _x + Ca₃(PO₄)₂ for deposition of nanofilms onto load-bearing implants by ion-plasma sputtering were prepared from Ti + Ta + C + Ca₃(PO₄)₂ mixtures by forced SHS compaction. The effect of Ta + C addition to green mixtures (characterized by parameter z) on the structure/phase formation in combustion products was explored. The addition of tantalum and carbon was found to have little or no influence on the burning velocity U and combustion temperature T _c. Two thermal spikes exhibited by thermograms were associated with the occurrence of two consecutive reactions leading to formation of titanium and tantalum carbides. With increasing z, the grain size of (Ti, Ta)C was found to diminish, its relative density to decrease, while the hardness to markedly grow.      

Mo/Ni and Ni/Ta–W–N/Ni thin-film contact layers for (Bi,Sb)<Subscript>2</Subscript>Te<Subscript>3</Subscript>-based intermediate-temperature thermoelectric elements

We have examined the possibility of utilizing thin-film contact layers for producing reliable Ohmic contacts to proposed intermediate-temperature (Bi,Sb)₂Te₃-based thermoelectric materials with improved thermoelectric properties, which allow the working temperature range to be extended to 600 K. Three contact configurations have been produced by ion-plasma magnetron sputtering: a single Ni layer, Mo/Ni bilayer, and Ni/Ta–W–N/Ni three-layer system. It has been shown that reliable contacts can be produced using Mo/Ni and Ni/Ta–W–N/Ni layers, which prevent interdiffusion between the materials to be joined and ensure good adhesion to the thermoelectric element.     

Microstructure,Phase Composition,and Thermal Stability of Two Zirconium Alloys Subjected to High‐Pressure Torsion at Different Temperatures

The structure, phase composition, and thermal stability of the industrial zirconium alloys, namely, E110 (Zr–1% Nb) and E635 (Zr–1% Nb–0.3% Fe–1.2% Sn), which are subjected to high‐pressure torsion (HPT) at room temperature (RT), 200, and 400 °С have been studied. HPT of Zr‐alloys at RT (10 revolutions) leads to the formation of grain–subgrain nano‐sized structure and to increase the microhardness by 2.1…2.8 times. The increase in the HPT temperature to 200–400 °С leads to the increase in the structural‐element average size. The structural‐element size in the complexly alloyed E635 alloy in all cases is lower compared with the E110 alloy. The hardening of the alloys after HPT at RT and 200 °С is close, and at 400 °С is much less. HPT initiates the α‐Zr → (ω‐Zr + β‐Zr) transformation, which is the main factor for alloys hardening. The α‐Zr → (ω‐Zr + β‐Zr) transformation in the E635 alloy occurs less quickly. The maximum amount (ω‐Zr + β‐Zr) phase in the structure of the alloys is observed after HPT at RT and 200 °C, and the minimum ? at 400 °C. During heating, the alloys undergo the reverse (ω‐Zr + β‐Zr) → α transformation which depends on both the alloy composition and HPT temperature.

     

Structure and properties of a layered steel/vanadium alloy/steel composite prepared by high-pressure torsion

The microstructure and hardness of a layered steel 08Kh17T/V–10Ti–5Cr/steel 08Kh17T composite, which was prepared by torsion under a high hydrostatic pressure at temperatures of 20, 200, and 400°C, have been studied. Severe plastic deformation under used conditions is shown to provide good joining of layers, which is accompanied by their substantial hardening (from 2.0 to 3.5 times). During deformation at temperatures of 20 and 200°C, fragmentation of the vanadium alloy layer into thinner layers is observed; at 400°C, mainly a plane interface between the vanadium alloy and the steel layers is formed.     

Structure and mechanical properties of oxide films on zirconium alloys upon oxidation under different conditions

The structure and mechanical properties, as well as the mechanism and kinetics of the destruction of oxide films formed on tube specimens of E110 zirconium alloy based on electrolytic or sponge zirconium upon corrosion testing in an autoclave and high-temperature oxidation in steam (LOCA conditions), were studied with the use of transmission and scanning electron microscopy, microhardness measurements, acoustic emission, and fractography. Oxide films on specimens made of electrolytic zirconium upon testing in an autoclave are found to be composed of extended grains with a thickness of 100 nm, while those on sponge specimens are composed chiefly of equiaxial grains with a diameter of 30 nm. After high-temperature oxidation, the structure of oxide films consists of extended grains of a variable thickness, which increases from the surface to the film-metal boundary from 600 nm to 2.5 μm on specimens made of electrolytic zirconium and from 250 nm to 2 μm on sponge-zirconium specimens. The microhardness of films after testing in an autoclave is 1200 ± 50 HV on electrolytic zirconium and 2000 ± 50 HV on sponge zirconium. The hardness of films on sponge-zirconium specimens upon high-temperature oxidation is 1600 ± 50 HV. The combined analysis of deformation diagrams, fractures, and acoustic emission data showed that the destruction of thin oxide films after testing in an autoclave and that of thick films after high-temperature oxidation begins with the formation of transverse brittle ruptures at the same load of 12–15 MPa. The number of cracks in the films on specimens that underwent high-temperature oxidation increases under loading especially rapidly on electrolytic zirconium.     

Reactive nanofoils for joining refractory and dissimilar materials

Heterogeneous nanostructured foils produced by magnetron deposition or mechanical processing represent a new class of reactive materials. They are composed of layers or clusters of different phases (typically with a size of 10–100 nm) that can react with each other with strong heat release. The reaction, being initiated locally, spontaneously propagates across the entire foil in the form of high-temperature wave. Some examples of promising practical applications of these foils in advanced technologies, such as joining dissimilar materials, were presented.