Vol 57, No 5 (2017)

The possibility is demonstrated of preparing porous ceramic based on zirconium dioxide micro- and nanopowder using crystallization of carbamide in a suspension. Different suspension cooling regimes are studied for oxide powders (in air, in a freezing chamber, in snow). It is shown that sintered ceramic porosity and pore size depend directly on suspension composition and cooling method. As a result of this ceramic is prepared with porosity of 30 – 60% with pore diameter of 0.2 – 200 μm.

Modification of pitch matrix carbon nanomaterials improves sintering properties and strength of structural graphites based upon it. An effect is revealed for the method of adding nanomaterials and additive concentration on pitch and graphite properties.

Research results from the preparation of zirconium nitride powders from the elements via combustion in a laboratory reactor are presented. The optimal synthetic conditions for zirconium nitride with respect to charge composition and initial N₂ pressure are determined. Test samples of zirconium nitride of purity up to 99.5% are prepared.

Results are provided for a study of the effect of planar grinding regimes with diamond wheels on Al₂O₃–TiC-ceramic surface condition. A correlation is established for grinding depth, and longitudinal and transverse feed with roughness, waviness, and morphology of a machined surface. The correlations revealed are planned for application in creating methodology for standardizing the precision of ceramic components and its production provision.

Combined synthesis from powders of elements B, C, and Si at 1400, 1500, and 1650°C is used to prepare heterophase powders in the system SiC–B₄C containing 80, 57, and 30 (mol.%) boron carbide. Powders containing only SiC and B₄C phases are prepared at 1550°C from a mixture with 5% excess silicon given vibration grinding for 60 h. The powder has a unimodal particle size distribution and d₅₀ = 3.5 μm with a volume concentration of 12% submicron particles.

Technology is developed for preparing periclase-chromite composition refractories based on fused grains of increased thermal-shock resistance. Technology is created for preparing periclase composition refractories based on fused grains exhibiting a high service temperature (up to 1900°C) and improved thermal shock resistance. Refractory material SHS-technology is developed on whose basis fused refractory objects, brickwork mortars, and torcrete mixes for hot torcreting are created. Refractory materials are turned out on an industrial scale in OAO Kombinat Magnezit. They are used for the most worn parts of linings such as the tuyere zone in horizontal converters, the slag belt of ore-roasting furnaces (ORF), in the reaction zone of a Waelz kiln, ORF outlet assemblies, Kivcet unit arches, and Vanyukov furnaces. Lining life is increased by a factor of 1.5 – 2.5.

As a result of conducting numerical experiments a complex effect is revealed for titanium carbide coating thickness on the change in stressed state of a Si₃N₄–TiC–Y₂O₃-ceramic surface layer under action of a distributed force. It is established that an increase in TiC-coating thickness leads to an increase in σ_i inhomogeneity and an ambiguous change in σ₁₁, σ₂₂, and σ₁₂ inhomogeneity within a nitride ceramic surface layer.

The lining of furnaces is an extremely important element of the construction of furnaces, serving to separate the work space of the furnace from the outside and reducing irreversible losses of heat. What is known as a solid – gas lining, or system of alternating layers of solid material and gas spaces, makes it possible to decrease the cost of the brickwork and reduce heat losses through the brickwork. A condition of ideal contact between the layers must be realized in a multi-layer, cast-in-place lining. The presence of pores and gas spaces complicates the process of heat transfer within the lining, which, in turn, tends to produce losses of heat from the work space of the furnace.

Results are provided for a study of porous ceramic materials prepared in the course of chemical and exothermic reactions based on a system containing secondary resources (chamotte scrap, mullite-containing waste, aluminum smelting slag), aluminium phosphate binder, aluminum refractory clay, and various additives. Temperature dependences are established for heat capacity and thermal conductivity in the range 30 – 1000°C for the material obtained. It is shown that the optimum overall aluminum and slag content in a mixture for preparing porous materials is 10 – 20%. It is established that addition of magnesite and chrome-magnesite, and also ammonium dihydrophosphate, makes it possible to control density and strength of the materials obtained.

A method of reducing dust emission and the power consumption of a ventilation system by improving the management of forced delivery of recirculated air to the charging trough is proposed. A portion of the ventilated air is fed to the charging trough, which tends to reduce the volumes of ejected air entrained by the stream of free-flowing material. The influence of the geometric parameters and the flow rate of the recirculated jet on the volume of discharged air are investigated by means of computer modeling.

Aprocedure is presented for studying flake graphite used in OOO Gruppa Magnezit for quality evaluation and possible application in carbon-containing material manufacture. Results are provided for studying graphite from various deposits within Russia, China, Brazil, India, Norway, and Africa. The significance of entirely new graphite quality indices and their interpretation is demonstrated in accordance with the procedure proposed.

A description of different constructions of tubular belt conveyors with spherically shaped rollers is given. Through use of the functional relationships between the tribotechnical assemblies of the conveyors, the energy losses caused by friction and wear of the service elements are determined, their contribution to rolling and sliding friction established, and the significance of each technical and economic criterion of the relative competitive advantage of alternative variants of tubular belt conveyors determined.

Results of a study of the precision characteristics of contact and contactless methods of measuring the temperature of the surface of a material are presented.

Results are provided for a study of the effect of carbon component on physicochemical and production properties of corundum-silicon carbide-carbon concrete. It is shown that carbon with a more perfect structure provides better concrete mix rheological properties, greater object density and strength, and also better oxidation resistance.

Mechanisms are considered for local (pitting) wear formation of the working layer of periclase-carbon steelpouring ladle lining in converter production. The most frequent reasons for formation of this type of wear are established.