Analysis of the Stress State at the Contours of Underground Horizontal Mine Workings Exposed to Uniform Pressure and Determination of the Safe Laying Depth

Soil Mechanics and Foundation Engineering - The results of constructing an underground horizontal mine working of the given size and the specified shape of the cross section are presented based on...     

Ceramic and transport properties of halogen-substituted strontium ferrite

An attempt of fluorine and chlorine substitution for oxygen in strontium ferrite SrFeO_3–δ was undertaken in search of a new means of influence on the oxide properties. An uncontrollable removal of halogen-ions from oxides during synthesis was detected. Nevertheless, residual halogens were found to provide a notable impact on ion conductivity and oxide stability under reducing conditions. More than twice higher ion conductivity relative to SrFeO_3–δ was recorded in materials with nominal compositions SrFeO_2.8–δF_0.2, SrFeO_2.6–δCl_0.4, and SrFeO_2.4–δCl_0.6. The strong effect of halogen addition on ceramic properties of oxides was revealed. While SrFeO_3–δ was known for its poor sinterability, adding 0.2?mol of fluorine or chlorine during the synthesis of SrFeO_3–δ was shown to result in successful obtaining gas-tight ceramics.     

In-situ determination of the HfO2–Ta2O5-temperature phase diagram up to 3000°C

The previously unknown experimental HfO₂–Ta₂O₅-temperature phase diagram has been elucidated up to 3000°C using a quadrupole lamp furnace and conical nozzle levitator system equipped with a CO₂ laser, in conjunction with synchrotron X-ray diffraction. These in-situ techniques allowed the determination of the following: (a) liquidus, solidus, and invariant transformation temperatures as a function of composition from thermal arrest experiments, (b) determination of equilibrium phases through testing of reversibility via in-situ X-ray diffraction, and (c) molar volume measurements as a function of temperature for equilibrium phases. From these, an experimental HfO₂–Ta₂O₅-temperature phase diagram has been constructed which is consistent with the Gibbs Phase Rule.     

To the Question of Assessing the Sensitivity of Ultrasonic Testing of Welded Joints of Energy Industry Objects

Russian Journal of Nondestructive Testing - The standards of evaluating welded joints based on the results of nondestructive ultrasonic testing are described. The results of calculating the optimum...     

Comparative Physical-Chemical Properties of Binary and Multicomponent Semiconductors in CdS–ZnSe and CdS–ZnS Systems

Solid substitution solutions in CdS–ZnSe and CdS–ZnS systems have been fabricated and certified. Bulk (crystal chemistry, structural, and optical) and surface (acid–base) properties of these solutions have been examined as compared to each other and their binary components. Regularities of changes in the investigated properties upon changes in the systems’ compositions and in a series of analogs have been established: these regularities have predominantly exhibited an extremal nature. Interrelations between the established regularities have been validated, which allows predicting, based only on bulk properties, the surface activity of advanced materials (fabricated solid solutions) toward gases of varied electronic nature—components of natural and technological media. Practical guidelines on application of these materials to produce appropriate sensors have been provided.     

Peculiarities of Magnetic Behavior of CuO Nanoparticles Produced by Plasma-Arc Synthesis in a Wide Temperature Range

Copper oxide nanoparticles, produced by direct plasmochemical synthesis in a low-pressure arc discharge plasma, show a wide variety of magnetic properties depending on the strength of the external magnetic field and the temperature. At low strength of the field and throughout the studied temperature range, the ferromagnetic state dominates. This state is caused by disordering of the spins on the surface of the nanoparticles. At high strength of the field and under temperatures of less than 200 K, nanoparticles exhibit a paramagnetic state due to the spin-glass behavior of copper atoms. At high strength of the field (more than 3 kOe) and under temperatures of above 300 K, the diamagnetic state of nanoparticles is observed, due to local eddy currents caused by oxygen vacancies. The temperature of antiferromagnetic ordering under study is significantly lowered (down to ～ 100 K).     

Temperature induced phase transition in nanocomposites based on low-density polyethylene matrix

The temperature dependence of the complex dielectric permittivity of composites based on a low-density polyethylene matrix containing dispersed nanoparticles of copper and zinc oxides has been studied. It is established that a phase transition takes place in the volume of a composite at a temperature of about 60°C. Exposure of the composite samples to a flux of 10-keV electrons leads to changes in the temperature dependence of the permittivity. Mechanisms are proposed that can explain the observed behavior.     

Computer analysis of the aerodynamics and heat exchange of a cylinder in a viscous oscillating flow

The paper considers the results of analyzing the aerodynamics and heat exchange of a fixed cylinder under nonstationary airflow with average-velocity alternating pulsations numerically. It is shown that the pulsations significantly affect the vortex separation frequency, the Karman vortex street behind the cylinder, the pulsation frequency of the aerodynamic and heat exchange coefficients, and their average and amplitude values. The authors determined the engineering applications.     

Study of the structure and mechanical properties of submicrocrystalline and nanocrystalline copper produced by high-rate pressing

Evolution of the structure of pure copper (99.8 %) in the course of severe plastic deformation performed by the new method of dynamic channel-angular pressing (DCAP) and the mechanical properties of the arising mixed SMC+NC structures have been studied. The rate of deformation of the material during DCAP is ∼10⁵ s⁻¹, the duration of the process of deformation is 500 μs, the pressure does not exceed 2 GPa. It has been established that in the course of twofold-fourfold pressing the grains and subgrains of copper become refined by three orders of magnitude. It has been found that a decrease in the inner radius of the profile of the zone of intersection of the channels in the die (R) from 7 mm to 0 leads to the formation in the bulk samples of an SMC+NC structure consisting of grains and subgrains with a size from 50 to 350 nm. It is shown that the high-rate deformation with the use of the DCAP method increases the copper hardness by a factor of 2–2.2; the strength grows by a factor of 1.4; and the plasticity remains high. The estimation of the variation of the value of shear along the cross section of the samples upon DCAP showed that in the scheme with R = 7 mm the relative shear is γ ≤ 1.65; in the scheme with R = 0, γ = 1.8-2.0. In the case of a scheme with R = 0, the DCAP leads to a considerable (in comparison with the initial state) increase in the strength without loss of plasticity even upon single-pass pressing.