Refractories and Industrial Ceramics最新文献

This paper presents the results of studies on silicon carbide production by self-propagating high-temperature synthesis. To provide the necessary energy for the process, the synthesis was performed using magnesium-thermal reduction of silicon dioxide in an argon atmosphere. This study was characterized by the use of carbon fibers as a carbon source. It was determined that during magnesium-thermal synthesis, hexagonal particles with a size of 1 – 2 μm and a thickness of approximately 0.2 – 0.3 μm were mainly formed. X-ray phase analysis showed the predominant formation of a cubic syngony of silicon carbide.

Microstructure defects arising in the manufacture of oxide ceramics based on aluminum oxide were studied. Several common problems arising in the manufacture of ceramic materials from fine-grained starting powders with high sintering activity as well as differences in the optimal properties of materials intended for use at high and moderate temperatures were considered. Samples of ceramic materials of the mullite–corundum system modified with zirconium dioxide were obtained by co-deposition of the initial powders followed by their grinding, pressing, and sintering. The fracture surfaces of samples were examined on a scanning electron microscope to study defects in the microstructure of powder ceramics. Characteristic defects in the microstructure were identified. The reasons for their appearance were explained. Possible ways to solve the problems of degradation of the properties of oxide ceramic materials were proposed based on technical literature data and the experimental results.

The manufacturing processes and mechanical properties of ceramics based on fused corundum and an organic aluminum(hafnium binder were studied. Samples of ceramics with the composition Al₂O₃/HfO₂ were prepared. The features of the sintering process of the ceramic materials and their heat-treatment modes were studied. The quality of the front layer was assessed. The tensile strength in bending of the manufactured ceramic samples was tested. The microstructure of the ceramics consisted of grains of fused corundum, the surface of which was uniformly covered with a film of Al₂O₃–HfO₂ binder. The tensile strength in bending of the ceramic samples with an Al–Hf binder ranged from 1.1 to 5.5 MPa, which meets the requirements for industrial ceramic casting molds.

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.