Refractories and Industrial Ceramics最新文献

Optimal material and charge compositions of technical ceramics for grinding media were developed. The samples with an alumina content of 55.25 – 64.93 and 65.79 – 74.21 wt.% for obtaining mullite and mullite-corundum ceramics, respectively, exhibited the highest material composition and technological properties. The possibilities of using kaolins of various grades for the development of new compositions of low-temperature sintered grinding media are shown.

Ceramic composites (1 – x)ZrSiO₄–xZrO₂ with low thermal conductivity were obtained by sintering nanosized powders in the range 1000 – 1300°C in air. The fracture surface of ceramic samples was studied using electron microscopy after sintering at 1300°C; their thermal behavior, by dilatometry. The chemical resistance of the composites was evaluated by leaching in distilled water. In the future, such ceramic composites can be used as matrices for long-term environmentally safe storage and subsequent final isolation from the environment of individual isotopes of the actinide(rare-earth fraction of high-level waste (HLW).

Basics of technology for producing alumina-zirconia ceramics reinforced with strontium hexa-aluminate using ultrafine components and a precursor of strontium zirconate are described. It is shown, that grinding initial oxides and charges to an ultrafine state in a bead mill and creating a reinforcing network within a composite structure by introducing a precursor before wet grinding and subsequent two-stage sintering provides high ceramic density (not less than 99.5% of theoretical) and strength properties (static bending strength of at least 1200 MPa, crack resistance of at least 6.9 MPa·m^1/2).

This work presents the properties of the glass phase of fusion-cast refractories with 28 – 94% ZrO₂. The effect of glass phase composition on the main performance properties of refractories, namely, corrosion resistance and tendency to release defects, is discussed. It is revealed that a decrease in the amount of glass phase in fusion-cast baddeleyite-corundum refractories with a simultaneous increase in the amount of ZrO₂ results in an increase in corrosion resistance and complication of the annealing conditions of the products. The glass phase properties that determine the tendency of refractories to release defects depend mainly on the SiO₂ to Na₂O ratio, the purity of raw materials, and the method of charge melting. Oxidative melting with treatment of the melt with an oxygen–gas mixture is a prerequisite for the formation of a refractory glass phase in refractories and manufacturing products with a low tendency to the formation of defects.

The dependence of the resistance of basic refractories to high-temperature plastic deformation under load on the amount of zirconium dioxide modifying additive is reported. Creep curves are presented and analyzed. ZrO₂ nanoparticles (average particle size 100 nm) were added to the composition in the range 0.25 – 0.75 wt %. The resistance to high-temperature plastic deformation was significantly improved and was due to the interaction of the ZrO₂ additive with CaO contained in the synthetic periclase obtained by precipitation. Increasing the amount of ZrO₂ additive above 0.5 wt % was found not to have a significant effect.

In order to evaluate the effect of impact of the nature of solid fuel on performance indicators of a shaft melting furnace of the cupola type with an internal diameter of 2200 mm and a layer height of 4.5 m, and conditions for its oxidation, the real range of change in the properties of industrial coke batches of various manufacturers is determined (8 varieties) under conditions of non-oxidation heating of coke samples in an argon atmosphere at the rate of 5 deg/min to a temperature of 1000°C and isothermal exposure in an air atmosphere. Operating conditions of the mine unit on these cokes are evaluated with respect to values of specific coke consumption, mineral melt yield, thermal efficiency and changes in conditions for development of heat transfer from gases to materials based upon the ratio of heat capacities of their flows obtained from industrial tests. It is shown that an increase in the complete coke oxidation interval from 7 to 12.5 – 13.0 min will provide a decrease in specific coke consumption from 265 to 225 kg/ton of melt, i.e., by 15.9%, an increase in yield of mineral melt from 25.3 to 30.02%, i.e., by 18.66%, with a decrease in cupola total thermal efficiency from 61.7 to 60.2%, i.e., by 1,5%. For this it is advisable to use coke with maximum heat of combustion. Use of coke mineral raw material during melting, which has a rate of change of sample weight from 5.0 up to 8.0 – 8.5%/min (more active coke), provides a coke minimum specific consumption at the level of 224 kg/ton of melt with a maximum yield of molten smelting product of at least 29.8% of the weight of the initial components with unit thermal efficiency at 61.7%. For this it is necessary to use more active coke with respect to blast oxygen. Heat transfer process conditions from gases to materials during smelting are characterized by low intensity with the lowest ratio of heat capacities of material and gas flows not lower than 0.827 in the range of complete coke oxidation 12.5 – 13.0 min and an average rate of change in sample weight of about 6.0%/min.

The influence of the composition of compacted powders based on CT 3000 LS SG alumina, as well as the process parameters of quasi-isostatic pressing and firing, on the structural and mechanical characteristics of grinding balls with a diameter of 40 mm is shown. The revealed patterns are used to optimize the production process of high-density corundum balls. The results of integrated tests of their physical and mechanical properties are presented. The particle size of the raw material component was shown to have a determining effect on the hardness, density, and operational characteristics of the resultant grinding bodies.

Depleted gold-bearing sulfide mineral materials can be employed in cement production, construction industry, road construction, and other sectors of the national economy. This will enable metallurgical enterprises to switch to low-waste or nonwaste technologies. Research on and practice of ore beneficiation with a high degree of sulfidity reveal that gold recovery is directly dependent on the degree of ore sulfidity and the content of the main ore sulfide minerals. To increase the efficiency of gold recovery, a device for the enrichment of gold-bearing sulfide materials using centrifugal flotation is developed.

Structural changes in cerium dioxide on heating in a vacuum in the range 25 – 1600°C, in air in the range of 25 – 1500 °C, and during successive annealing in the range of 1600 – 2100°C in air, followed by water quenching, are studied. In the CeO_2–x crystal lattice the F ⟶ F¹ phase transformation in a vacuum proceeds in the range of 1100 – 1600°C; in addition, at 1200°C, X-ray lines of the C-type Ce₂O₃ phase appear. The thermal expansion coefficient of phases of the fluorite type F and F¹ in the range of 25 – 1500°C in air, as well as phases of the fluorite type F, F¹ and type C Ce₂O₃ in the range of 25 – 1600°C are determined in a vacuum and their dependence on the change in oxygen content in the CeO_2–x crystal lattice is found. Kinetic conditions for reduction of cerium dioxide in a vacuum and oxidation in air are different. The cubic structure of the fluorite type F CeO_2–x, when specimens are heated in air, is preserved up to 1800°C with the content of anionic vacancies, and at 1900°C the transformation F ⟶ F¹ occurs. Formation of loops, edge and screw dislocations within the structure of cerium dioxide grains after specimen annealing in the range of 1900 – 2100°C in air are discovered for the first time. Decomposition of the structure F¹ into cerium oxide phases of types F and C proceeds at 2100°C along the height and boundaries of screw dislocations. It is found that fragments of the C-type phase of cerium oxide are located in loops over the height of screw dislocations, which indicates movement and evaporation of these fragments. During specimen oxidation at 1600°C in air, a black-colored type C Ce₂O_3–x phase in a gradient of different concentrations moves along certain trajectories to opposite grain boundaries, abuts against dislocation loops, bends them, and is oxidized to phases F¹ and F. Within the structure of polycrystalline cerium dioxide, during heating in a vacuum and in air, certain concentrations of defects control phase transformations.

Based on the hypothesis about the dominant effect of the concentration, median diameter, dispersion, temperature, and humidity of dust particles at the outlet of the shaft furnace on the environmental efficiency of drying materials in shaft furnaces, a device for thermal aeration dust separation is proposed. Analysis of mathematical simulation of aerothermodynamic processes in a two-phase asbestos dust-gas flow medium confirmed the conclusions of industrial research on the effect of aerothermodynamic parameters of direct flow on the temperature and humidity of asbestos dust in a shaft furnace. Based on the principle of classification additivity, a mathematical model of aeration separation of dust particles directly in a shaft furnace depending on the parameters of the heat carrier and the proposed device has been constructed.