Vol 59, No 5 (2019)

We describe the operating parameters of high-production-capacity container-glass melting furnaces and specify the service conditions of the melting-tank lining at a specific glass-melt production rate of 2.5 – 3.0 t/(m²·d) and a specific glass production per furnace run of 7000 – 8000 metric tons/m². We recommend that melt-molded baddeleyite-corundum and vibration-cast sintered chromium-aluminum-zirconium refractories be used in tank structures.

Experience of using refractory materials based on chrome-oxide in electric glass-melting furnaces for fiberglass production is described. Prospects are noted for using chromium oxide refractories from the point of view of both the service reliability and the furnace campaign duration.

Production aspects are considered for preparing porous ceramic based on α-Al₂O₃ using the effect of zonal compaction during powder workpiece sintering of very fine combustion products in air of flaky aluminum powder PAP-2 particles. It is shown that formation of a porous structure in sintered material proceeds by a local breakage mechanism through boundaries of aggregates with formation of pores between agglomerates, and also due to occurrence of a closed intergranular pore system. Properties of the ceramic obtained are: density 2.45 g/cm3, total porosity 39%, open porosity 30%, closed porosity 9%, the and ultimate strength in bending 50 – 60 MPa.

Hybrid aluminum matrix composites (HAMCs) reinforced with different amounts of ceramic particulates consisting of silicon carbide (SiC) and graphite (Gr) were developed. The amount of ceramic powder was 5 – 15 mass%. Parameters of the hybrid composites such as microstructure, density, and porosity and mechanical properties such as hardness and tensile strength were analyzed. Scanning-electron-microscope photomicrographs showed a uniform distribution of (SiC + Gr) particles in the Al matrix. The density and porosity of the hybrid composite increased from 2.69 to 2.72 g/cm³ and from 0.37 to 1.20%, respectively; Vickers hardness and tensile strength, from 49.5 to 85 VHN and from 161.5 to 187 MPa, respectively. The relative elongation decreased from 8.6 for 5.3 as the content of ceramic particulates (SiC + Gr) increased from 0 to 15 mass%.

Results are provided for a study of the effect of adding cenospheres (coal combustion waste) on hydration of alumina cement and exothermic reaction parameters. It is established that an increase in addition of cenospheres retards cement hydration, and reduces specimen density after firing at 1200°C up to 40%, strength up to 60% and shrinkage up to 95% compared with control specimens. With respect to parameters for the relationship of strength and density an amount of 5 – 10% of cenospheres is the optimum.

Properties are determined for electrocorundum grinding grits and powders of different grain size from various producers. Powder particle size distribution and also rheological properties are determined by a static method; bulk and tapping densities, time for emergence from a funnel, natural repose angle, flow criteria, compactability and degree of tapping (indices of powder mobility and compactability), and some dynamic properties using a Revolution instrument. Scanning electron microscopy is used to study features of powder morphology. Results are used for comparative analysis of powders and conclusions are drawn.

A procedure for modeling phase formation in the multicomponent CaO–MgO–Al₂O₃–SiO₂–FeO–Fe₂O₃ oxide system has been proposed. This procedure can be used to predict the equilibrium phase composition of both the refractory and refractory-slag systems in order to modify the chemical composition of smelter slags, improve the service life of the lining of the metallurgical units, and deliberately provide them with the properties of mineral binders.

High-density (with a relative density of up to 98.8%) ultra-high-temperature ceramic materials (UHTCs) based on the ZrB₂–TaC–SiC system were obtained by hot pressing for 15 min at 2000°C 30 MPa of pressure in an argon atmosphere. Phase composition, lattice parameters, microstructure, flexural strength, Vickers hardness and crack resistance were studied. The maximum values of strength, hardness and crack resistance were 440 MPa, 20.3 GPa and 5.3 MPa·m^1/2, respectively. The effect of the ZrB₂/TaC ratio on the lattice constants and the mechanical properties of the material is established.

The heterogeneous CaB₆–TiB₂ powder mixtures were synthesized by reducing the mixture of TiO₂ and CaCO₃ with boron carbide in vacuum at 1400 – 1650°C. Reaction hot pressing was conducted according to the following regime: 1500°C (synthesis in vacuum) – 1900°C (pressing in Ar). As a result of synthesizing CaB₆–TiB₂ at mass ratio of 1:1 and 1600°C followed by isothermal soaking for 1 hour, a heterogeneous mixture was obtained containing crystalline phases of CaB₆ and TiB₂ with the residual B₄C impurity (0.5 wt. %). The powder particles represent grains measuring 1 – 3 μm in diameter and containing two phases CaB₆ and TiB₂ in the form of crystallites measuring 0.1 – 1.0 μm in diameter uniformly distributed throughout the particle volume.

It is shown that the pyrocatechin (1, 2-dihydrohybezene) in an amount of 0.005 – 0.010 wt.% solid components has a pronounced plasticizing effect on mixtures of polyfraction corundum filler and colloidal SiO₂-solution binder, stabilized with ammonia ions, intended for preparing cement-free refractory concrete. Self-consolidating refractory compositions are prepared with minimum water content.

Refractory heat-insulating materials produced in Russia are characterized. The thermal stability of high-alumina heat-insulating materials filament-reinforced based on mullite-silica glass fiber is investigated. Thermal stability data of products with crystallized and non-crystallized matrixes is presented.

We show the applicability of the method of designing ceramic tools based on the analysis of their stress-strain state in the choice of ceramics used for the creation of ceramic end milling cutters. We present the relationship between the properties of Al₂O₃ and Si₃N₄ ceramics and temperature, displacements, and stresses formed in the cutting edge of the ceramics cutter under the conditions of nonstationary thermoelasticity.

Rheological properties are described both for the initial (basic) bauxite composite HCBS and the same HCBS with 15% SiC, as well as with the addition of 1 and 2% of Si. The effect of adding metallic silicon is investigated, which decreases the sintering temperature and promotes formation of closed porosity. It is established that in materials containing added Si in the firing temperature range of 1300 – 1400 °C with a reduction in open porosity from 2.7 to 1.6% oxidation of SiC or Si slows down or is inhibited. Dilatometric analysis shows that during non-isothermal heating of the samples containing 10 – 30% of SiC there is a certain degree of SiC oxidation and material mullitization is retarded.

We study the method of catching of pollutants with the use of a local suction unit placed over an impermeable plane and in the closed domain of an aspiration hood. The suction unit is screened by a circular swirling jet. The results of investigations of the behavior of dust particles in the air flow near the suction unit are presented.