Vol 59, No 1 (2018)

The significance of the question of corrosion and erosion resistance for refractory materials in direct heating electric furnaces for vitrification of highly active waste (HAW) is substantiated. Algorithms are provided for evaluating their resistance to action of phosphate melts under electric furnace operating conditions. Comparative corrosion tests are performed for refractory materials surpassing Bk-33 objects with respect to quality in melts of aluminophosphate glass with simulation of HAW. Tests results are valuable for selecting lining material in planning ÉP-500 type vitrification electric furnaces with a prolonged service life, and also the next generation of moveable and small-scale melting units.

We consider the refractory equipment of section continuous billet-casting machines (CBCM) of the following system: tundish ladle (TL)–submerged nozzle (SN)–crystallizer, and analyze the processes of control over the metal flows in this system. We indicate the specific features of the structure of elements of section CBCM responsible for the rational transportation of the poured metal in the TL–SN–crystallizer system and the efficient formation of steel flows in the crystallizer and creating conditions for the enhancement of the quality of metal.

Results are provided for a study of the chemical composition and microstructure of fuzed periclase grains. A method is proposed for modifying periclase skin grains with coal tar pitch that reduces grain porosity and improves the adhesion of a carbon binder to its surface during carbon-containing refractory manufacture.

This article studies the influence of raw material, sintering temperature, particle size, and Al₂O₃ content on densification of mullite ceramics. Thermal cycle treatments were conducted to evaluate thermal shock resistance of samples. Microstructures of samples were also investigated to reveal effects of various parameters and thermal test. Flexural strength retention rises while density decreases, resulting from increasing extra space for stress release. Tridymite precipitation is found to be harmful in improving thermal shock resistance.

The problem of hardening (increasing the stability) of the carbon graphite hearth lining for protection against diffusion of sodium and cryolite-alumina melt (CAM) is discussed. Analytical evaluation showed that the main protection against various kinds of electrolyte effects on the carbon graphite lining is the application of various coatings that have not found wide industrial application due to their failure. It was demonstrated that the addition of lithium to the cryolite-alumina melts has a positive effect on the properties of the carbon graphite hearth lining. It was established that lithium has an active influence on the change in the physical and operational properties of the lining as a result of the intercalation process. The improvement in the properties of the carbon graphite electrolysis cell lining was confirmed by a series of experimental studies carried out with lithium electrolytes.

We present the results of investigations by the nondestructive acoustic methods of the physicomechanical properties of zinc-oxide ceramic varistors produced by the leading foreign firms, such as ABB and Epcos, and the St.-Petersburg Plant of Energy-Protective Devices. We describe and discuss the results of application of this method for the determination of the properties of disk-shaped varistors with various diameter-to-height ratios. Note the range of particle dimensions of the powders used for the formation of varistors affects their physicomechanical properties.

FactSage^TM software is used successfully in the Gruppa Magnezit engineering section making it possible to calculate thermodynamic equilibria in multicomponent systems, to construct phase diagrams, and to calculate viscosity in molten slags and glasses, etc. Use of specialized software makes it possible to both analyze premature wear of linings, and also the preliminary selection of refractory compositions, slag modifiers or directly for slag regimes optimum from the point of view of fulfilling metallurgical tasks and reducing refractory specific consumption. Modeling results are provided for processes occurring within ferrous and nonferrous metallurgy units.

In order to provide a good resistance for refractory structures towards high-temperature deformation during manufacture of engineering ceramic during firing at 1650°C a corundum refractory material is developed with a weight faction of more than 95 wt.% Al₂O₃. The ceramic binder used is high-temperature calcium hexa-aluminate formed during firing molded objects from a thixotropic mixture consisting of refractory filler of electromelted corundum and components for forming a binder, i.e., high-alumina cement (HAC) and finely ground alumina.

Impregnation of a two-dimensional reinforced carbon-carbon composite material (CCCM) is studied. The aim of the work is to study impregnation of CCCM pore space with such compounds as MoSi₂ and TaSi₂. For this purpose liquid-phase impregnation is used by placing plates of Si and Mo on a CCCM surface and holding at 1500°C. The structure of the specimens obtained is studied and it is possible to establish the depth of impregnated layer, and phase and elemental analysis make it possible to establish element distribution over the impregnated layer thickness.

Results are provided for a study of the efficiency of using schungite rocks as a binder in refractory materials. It is demonstrated that refractory compositions with schungite binder have the better physicochemical indices than compositions with a traditional graphite binder.

An innovative universal structure of the thermal insulation of the melting tanks of glass-melting furnaces, designed for melting tinted glass of various chemical compositions, is proposed. A separation of the portions of continuous insulation with air gaps provides reduction in the resulting heat flux into the ambient air from the bottom and walls of the tank by 30 and 14%, respectively.

Sintering of aluminum-oxynitride powders prepared by self-propagating high-temperature synthesis in a nitrogen-containing gel was researched. Use of the powders without extensive mechanical grinding was problematical because of their low specific surface areas. Equipment fitted with grinding containers lined with high-density plates and grinding balls made of the same material, 9Al₂O₃·5AlN, were required to solve this problem.