Том 59, № 3 (2018)

Results are provided for a laboratory study of the applicability of refractories in the Al₂O₃–Cr₂O₃ system in bubble-agitated double-chamber laboratory furnaces during processing of a broad spectrum of iron-containing materials, including technogenic waste. Laboratory tests are conducted for refractory life in a medium of molten iron. Conditions are modeled for exploitation of a refractory in melting and reducing zones of a bubble-agitated type furnace. Optical microscopy is used to study zones and the overall depth of crucible reaction with melt at the melt – refractory crucible interface.

We consider the process of motion of steel flows and the refractory equipment of the “tundish ladle (TL) – open jet (OJ) –mold” system of a continuous billet-casting machine (CBCM). We indicate the specific features of control over the metal flows in the analyzed system and analyze the specific features of the design of elements of the CBCM guaranteeing the possibility of rational transportation of the cast metal in the TL – OJ – mold system. The improvement of the design guarantees the rational motion of the flows of liquid metal in the mold and creates conditions for the improvement of the quality of billets.

The phase composition of synthesized TiC and TiN materials and also the properties of mullite–TiC–TiN specimens with a different ratio of TiC and TiN, sintered by a spark plasma method in the range 1200 – 1600°C with a compaction load of 75 MPa are studied. Specimens with a different ratio of TiC and TiN are characterized by intense mullitization in the range from 1200 to 1600°C. an increase in TiC concentration, and correspondingly a reduction in TiN concentration in sintered powder mixtures facilitates formation at 1500°C of a densely sintered crystallized structure consisting of numerous mullite crystals, TiC and partly TiN, formed from melts. In the range 1400 – 1600°C the relative density and linear shrinkage of specimens gradually increases with a reduction in open porosity, but specimen elasticity modulus, Vickers hardness, and ultimate strength in compression increase.

Results are provided for development of porous ceramic materials based on cordierite. The pore forming agents used are wood waste and carbamide in crystalline form. Analysis of the pore structure shows that all specimens have a complex pore space structure with a considerable number of elongated connected pores. The best porosity parameters are achieved using an organic crystalline pore former. It is shown that nano-dispersed aluminum metal has a strengthening effect during porous ceramic sintering. An organic clay suspension improves cordierite powder sintering capacity and leads to formation of additional nano- and micro-pores.

Penetration of sodium into carbon-graphite material (CGM) specimens previously modified with lithium is studied. Sodium diffusion coefficients are calculated after treating CGM with lithium vapor and values are determined for activation energy of diffusion under different conditions. The kinetic dependences obtained make it possible to determine the sodium diffusion mechanism in modified CGM. The efficiency is demonstrated of preliminary treatment with lithium vapor that makes it possible to prevent aluminum electrolyzer cathode lining surface layer breakdown during operation. The tests on CGM specimens performed make it possible to create prerequisites for developing technology for hearth surface protection from sodium penetration during electrolysis in molten cryolite-alumina.

Sintering peculiarities of ceramics prepared by semidry pressing were investigated. The fillers were Y₂O₃ and fused corundum α-Al₂O₃ . The binders were pure or Y- or Mg-modified alumoxane. The mechanism of sintering processes in the studied ceramic at various temperatures and its influence on the properties of the resulting ceramic were analyzed. The phase composition and thermomechanical properties of test ceramics prepared at 1500°C were studied. Prepared test ceramic crucibles had improved heat resistance and were robust to thermal cycling. The possibility of using the developed ceramic crucibles for melting and casting of chemically active and highly heat-resistant metals and alloys was discussed.

The influence of synthesis conditions on the development, thermal behavior, and sintering characteristics was investigated for nano- and macro-crystalline Bi₅FeTi₃O₁₅-based ceramic materials with a perovskite-like four-layered Aurivillius phase structure. It was shown that the start of grains sintering corresponds with the start of surface phase melting, given that the surface phase composition can be controlled by changing the chemical composition of the initial mixture. The temperatures of crystallization, phase transition, decomposition, sintering activation of the produced materials were determined along with the thermal coefficient of their linear expansion.

A solution of sodium silicate (liquid glass) was prepared and used as an inorganic binder for cold-hardening mixtures of refractory molds for metal casting. Wastes from rice production, i.e., rice hulls, were the source of silicon oxide. Several methods for synthesizing liquid glass were examined and characterized.

Features are revealed for the effect of surface relief and thermal load at temperature and stress intensity of the main silicon nitride structural components located in a surface layer. It is proposed to use these relationships for forming a structural and technological basis of planning data and manufacturing ceramic components and tools.

The results of a physical and chemical investigation of pyrophyllite from the Kul’-Yurt-Tau deposit in the Republic of Bashkortostan (Russia) are presented. The features of the strengthening process, the structure, and the hardening kinetics were determined for the refractory composite based on quartz-pyrophyllite raw material.

The effect of heat treatment duration of the properties of specimens prepared on the basis of composite composition HCBS in the Al₂O₃–SiO₂–SiC system is studied. With a content of 10 and 30% SiC in specimens its fineness varies within the limits 3 – 200 μm. Amethod is proposed for evaluating the degree of SiC oxidation within composite material. Depending on specimen composition this index is within the limit 50 – 100%. Maximum values of σ_ben and σ_co for SiC-containing specimens reach 80 and 390 MPa respectively.

For the improvement of the efficiency of systems of local exhaust ventilation, it is necessary to localize the emission of pollutants with minimum losses of the electric power. The application of rotating exhaust cylinder in a shelter may lead both to a decrease in the dust losses into the aspiration system and to lowering the costs of transportation of dusty aerosols in air ducts. We study the velocities of distribution of the airflows near the rotating exhaust cylinder depending on the frequency of rotation and the discharge of exhaust air. The accumulated results can be used in designing closed local exhaust hoods (aspiration shelters equipped with a dust-collecting chamber).