Ti3SiC2-Cu composites by mechanical milling and spark plasma sintering: Possible microstructure formation scenarios

We present several possible microstructure development scenarios in Ti₃SiC₂-Cu composites during mechanical milling and Spark Plasma Sintering (SPS). We have studied the effect of in situ consolidation during milling of Ti₃SiC₂ and Cu powders and melting of the Cu matrix during the SPS on the hardness and electrical conductivity of the sintered materials. Under low-energy milling, (3–5) vol.%Ti₃SiC₂-Cu composite particles of platelet morphology formed, which could be easily SPS-ed to 92–95% relative density. Under high-energy milling, millimeter-scale (3–5) vol.%Ti₃SiC₂-Cu granules formed as a result of in situ consolidation and presented a challenge to be sintered into a bulk fully dense sample; the corresponding SPS-ed compacts demonstrated a finer-grained Cu matrix and more significant levels of hardening compared to composites of the same composition processed by low-energy milling. The 3 vol.% Ti₃SiC₂-Cu in situ consolidated and Spark Plasma Sintered granules showed an extremely high hardness of 227 HV. High electrical conductivity of the Ti₃SiC₂-Cu composites sintered from the granules was an indication of efficient sintering of the granules to each other. Partial melting of the Cu matrix, if induced during the SPS, compromised the phase stability and uniformity of the microstructure of the Ti₃SiC₂-Cu composites and thus it is not to be suggested as a pathway to enhanced densification in this system.     

Novel Phase-Transition Behavior in an Aqueous Electrolyte Solution

We have investigated the near-critical behavior of the susceptibility of a ternary liquid mixture of 3-methylpyridine, water, and sodium bromide as a function of the salt concentration. The susceptibility was determined from light-scattering measurements performed at a scattering angle of 90° in the one-phase region near the locus of lower consolute points. A sharp crossover from asymptotic Ising behavior to mean-field behavior has been observed at concentrations ranging from 8 to 16.5 mass% NaBr. The range of asymptotic Ising behavior shrinks with increasing salt concentration and vanishes at a NaBr concentration of about 17 mass%, where complete mean-field-like behavior of the susceptibility is observed. A simultaneous pronounced increase in the background scattering at concentrations above 15 mass%, as well as a dip in the critical locus at 17 mass% NaBr, suggests that this phenomenon can be interpreted as mean-field tricritical behavior associated with the formation of a microheterogeneous phase due to clustering of the molecules and ions. An analogy with tricritical behavior observed in polymer solutions as well as the possibility of a charge-density-wave phase is also discussed. In addition, we, have observed a third soap-like phase on the liquid–liquid interface in several binary and ternary liquid mixtures.     

Thermodynamics of Liquid–Liquid Criticality in Supercooled Water in a Mean-Field Approximation

In a recent publication, it has been shown how a non-analytic scaling theory of critical phenomena can describe the available experimental information for the thermodynamic properties of supercooled water, when it is assumed to exhibit a liquid–liquid critical point. In this article, we present a mean-field equation of state which also represents the experimental data for supercooled water. Compared to the scaling theory, the mean-field equation has the advantage of simplicity for practical calculations of the properties of supercooled water. The insensitivity to a particular form of a critical equation of state is due to a lack of experimental data asymptotically close to the liquid–liquid critical point. Hence, while the assumed existence of a liquid–liquid critical point in water can account for the observed thermodynamic behavior of supercooled water, the actual location of such a liquid–liquid critical point cannot be determined accurately from the available experimental thermodynamic property data.     

An Iterative Method of the Structural-Parametric Design of Robust Systems with State Controllers

An iterative method for designing a robust control system with state controllers is proposed that includes a transformation of the plant structure to improve its controllability by correcting the singular values of the controllability Gramian and the subsequent synthesis of the basic controller for the corrected plant using modal control. This approach allows us to design systems satisfying the robust stability condition for the given intervals of variation of the plant parameters.     

Use of Classical Decision-Making Criteria to Choose Measures to Decrease Economic Losses Due to Nuclear and Radiation Accidents

Classical decision-making criteria are used to choose measures to decrease the economic losses due to possible nuclear and radiation accidents occurring when spent nuclear fuel is removed from nuclear-powered submarines and stored during submarine salvaging operations. The economic losses are chosen as the optimization index. As an illustration of the proposed approach, three scenarios of possible accidents and a limited number of measures to lessen their consequences are examined. Analysis of classical criteria is used as a basis for choosing an optimal strategy for decreasing the economic losses.     

Effect of Geological and Geophysical Characteristics of Complex-Structure Ferruginous Quartzite Ore Bodies on Blasting and Processing Performance

In terms of the complex-structure ferruginous quartzite ore body mining in the Kursk Magnetic Anomaly, the authors validate the requirement to account for anisotropy of rocks with a view to improving performance of preparatory and blasting operations, stabilizing grain size composition, reducing production of oversizes, saving energy input of milling, enhancing useful component extraction into concentrate and decreasing losses with regard to the sound subsoil management conditions. The effect of the first to third scale anisotropy on the quality of blasting fragmentation of ferruginous quartzite is analyzed. The theoretical formulas to calculate radius of controlled fragmentation zone as function of geological and geophysical characteristics of rock mass are presented, and the practical results of blasting at open pit mines in the Kursk Magnetic Anomaly area are described.     

Monitoring Potentially Hazardous Areas at Korobkovo Deposit of the Kursk Magnetic Anomaly

The article reports the results obtained in the trial of elements of the monitoring system for potentially hazardous areas at Korobkovo deposit of the Kursk Magnetic Anomaly. The system is based on the seismic and deformation measurements aimed to estimate and control shear stiffness of potentially hazardous faults. The fault shear stiffness is estimated through the analysis of parameters of seismic waves in the vicinity of a fault. The sources of seismic signals in the trial were explosions carried out at the neighbor surface and underground mines.