A. A. Rogozinskaya

Production and Properties of Thick Magnetoresistive Films from Fine Ni3B Powders

Pastes and films are produced from Ni3B powders of different particle sizes using thick-film technology: screen printing of pastes on a dielectric substrate and subsequent heat treatment in air without any protection. The phase composition and structure of the films are examined by X-ray diffraction and electron microscopy; the size of nanostructured elements (ferromagnetic Ni and dielectric layer of B2O3) formed during heat treatment of the films is determined. The magnetoresistance of the films in a 0−2 T magnetic field is measured. The influence of the external magnetic field on the magnetoresistance of the films is determined by spin-dependent tunneling of charge carriers.

DEFORMATION BEHAVIOR OF REFRACTORY METAL CARBIDES DURING RUBBING IN A WIDE TEMPERATURE RANGE

Conclusions1.It is shown that the processes of strengthening (and strength loss) take place in the surface layers of titanium, niobium, and tungsten carbide specimens during high-temperature rubbing in a vacuum are linked with charges in fine crystal structure and phase composition experienced by these carbides in their surface layers.2.It has been established that the strengthening of the surface layers of these carbides observed in the range from room temperature to 400–800°C increases their wear resistance. The strength loss exhibited by the surface layers of the carbides in the range 900–1400°C is a result of the effect of the temperature factor becoming stronger than that of the deformation factor.

Porous Structure of Powders Prepared with Heat Treatment of Gels from Tin (IV) and Antimony (III) Hydroxides

The effect of heat treatment on the parameters of the porous structure of powders in the system Sn(IV) ― Sb ― O is studied. It is established that xerogels of coprecipitated tin and antimony hydroxides dried at 360 K are microporous adsorbents containing particles of both crystalline and amorphous phases. During powder heat treatment there is formation of solid solutions based on tin dioxide and there is redistribution of the microporous structure into a mesoporous structure. This is accompanied by a reduction in specific surface and an increase in pore size.

Effect of Electrode Material on the Electrical Properties of Tin Dioxide Thick Films

The influence of electrode materials made of Ag-containing paste and Ni3B-based paste on the properties of fine SnO2 thick films is studied. The Sn0.97Sb0.03O2 nanopowder is introduced into the thick-film composite to intensify film consolidation during heat treatment, enhance film adhesion to the substrate, and control the resistivity. X-ray diffraction and electron microscopy are applied. The dependences of film resistivity on composition of the conducting phase are established. The effect of heat treatment temperature on the resistivity and current-voltage characteristics of films on silver and nickel electrodes is examined. It is shown that the electrodes made of powdered Ni3B paste can be used for SnO2 films whose heat treatment temperature does not exceed 1073 K, in particular, for gas sensors.

Effect of Pulsed Laser Radiation on the Properties of Resistive Thick Films Based on Nickel and Barium Borides

We have used atomic force microscopy to study the surface morphology of resistive thick films based on powders of nickel and barium borides and a glass binder, treated with laser radiation. We used x-ray phase analysis to study the phase composition of these films. We have observed a change in the surface morphology, the phase composition, and the electrical resistance of the studied films as a function of the laser radiation energy.

COMPOSITE CERAMICS BASED ON ALUMINUM NITRIDE: CATALYST SUPPORT FOR METHANE CONVERSION

We have investigated the feasibility of using a high-temperature support based on AlN for a nickel catalyst in the reaction of methane conversion. We have conducted a comparative study of the basic characteristics of the support based on AlN and Al2O3 in the temperature range from 600°C to 800°C. We have demonstrated that a promising approach is to use a composite AlN-based support for the catalyst in high-temperature catalytic processes.

Structure and Properties of Titanium Carbide Based Cermets with Additives of Other Carbides

The properties of wear-resistant cermets based on titanium carbide with additives of other carbides produced by two techniques are investigated. These techniques are: pressure sintering of powder mixture of the starting components (TiC, VC, Mo2C, NbC, Ni, and Cr) and pressure sintering of powder mixture of pre-synthesized solution of the starting carbides ((Ti, V, Mo, and Nb)C with additives of Ni and Cr. It is determined that cermets produced by the second technique possess more homogenous and fine-dispersed structure. The latter determines its higher mechanical strength, hardness, crack resistance, heat stability, and wear resistance, in comparison with the properties of cermets produced by the first technique.

Features of Brittle Material Powder Compaction During Pressing

The compaction of (i) titanium, vanadium, and molybdenum carbide powders, (ii) mixtures of these powders with the addition of nickel, chromium, and niobium carbide powders, and (iii) coarse titanium and tungsten carbides as well as diamond powders clad with cobalt under compressive loading with a constant rate on the powder in a die at room temperature is studied. Based on the variation of the relative density of the compacts with current pressure, the variation of stresses in the matrix (forming a porous body) with its strain is determined. This enables to reveal the features of compaction, strain hardening, and fracture of brittle powder particles during pressing. It is established that for the molybdenum carbide powder, consisting of powder particles with pronounced irregular shape, the initial elastic deformation of the matrix abruptly transits into the stage of plastic deformation with almost linear strain hardening. At the final stage of the powder compaction, the particles are fractured. At the initial stage of pressing, an increase in the packing density of the powder particles and in their strain hardening occurs for titanium and vanadium carbide powders, whose particle shape is close to the rounded. With the increase in the density of the porous body, it is observed an almost linear strain hardening of the matrix, which changes into decay with decreasing shear stress, when the powder body approaches its non-porous state. As a result of pressing, the size of the coherent X-ray scattering areas decreased to 62 nm and the dislocation density in the titanium carbide particles grew to 8.3 · 1010 cm–2. With an increasing content of plastic metallic particles in the matrix with the particles of brittle materials, it is the metallic particles that predominantly undergo the plastic strain with strain hardening. This causes a sharp increase in the total strain hardening, reducing the density of the porous body during pressing. It is established an effective compacting of coarse titanium and tungsten carbide powders with cobalt-clad particles 200–600 μm in size. In this case the variation of the stress in the matrix with the strain of the matrix has a sharp yield point associated with high elastic limit, significantly exceeding the yield stress, and the time delay in the transition from a purely elastic deformation of the body to its plastic flow.

The Surface Morphology and Electrophysical Properties of Thick SnO2–Sb Films After Laser Processing

The influence of laser pulses on the structure and electrophysical properties of resistive thick films based on the Sn0.9Sb0.1O2 solid solution is studied. Scanning electron microscopy, atomic force microscopy, and X-ray diffraction are used to examine the structure of resistive thick films and determine the distribution of Sn0.9Sb0.1O2 solid solution in surface layers and across the film. Exposure of thick resistive films to nano- and microsecond laser pulses changes their currentvoltage characteristics compared to samples subjected to millisecond pulses. The current-voltage characteristics become practically linear in the range from 1 to 10–11 V, thus allowing one to determine the optimum (α = 1) operating voltage range for resistors. The temperature coefficient of resistance depends on the length and energy of pulses.

Effect of substrate temperature on the electrospark deposition, structure, and mechanical properties of coatings. III. effect of substrate preliminary treatment on the electrospark deposition and phase composition of coatings

The effect of preliminary treatment of a steel substrate on the dynamic properties of cathode jets during electrospark deposition is studied. The energy of cathode jets is determined indirectly using the strain hardening of the electrode surface layer. It is established that the dynamic properties of cathode jets are determined by the electrode gap and structural and heat-transfer properties of the cathode material.